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  Subjects -> COMPUTER SCIENCE (Total: 1991 journals)
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COMPUTER SCIENCE (1157 journals)                  1 2 3 4 5 6 | Last

Showing 1 - 200 of 872 Journals sorted alphabetically
3D Printing and Additive Manufacturing     Full-text available via subscription   (Followers: 13)
Abakós     Open Access   (Followers: 4)
ACM Computing Surveys     Hybrid Journal   (Followers: 23)
ACM Journal on Computing and Cultural Heritage     Hybrid Journal   (Followers: 9)
ACM Journal on Emerging Technologies in Computing Systems     Hybrid Journal   (Followers: 13)
ACM Transactions on Accessible Computing (TACCESS)     Hybrid Journal   (Followers: 3)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Applied Perception (TAP)     Hybrid Journal   (Followers: 6)
ACM Transactions on Architecture and Code Optimization (TACO)     Hybrid Journal   (Followers: 9)
ACM Transactions on Autonomous and Adaptive Systems (TAAS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Computation Theory (TOCT)     Hybrid Journal   (Followers: 12)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Computer Systems (TOCS)     Hybrid Journal   (Followers: 18)
ACM Transactions on Computer-Human Interaction     Hybrid Journal   (Followers: 14)
ACM Transactions on Computing Education (TOCE)     Hybrid Journal   (Followers: 5)
ACM Transactions on Design Automation of Electronic Systems (TODAES)     Hybrid Journal   (Followers: 1)
ACM Transactions on Economics and Computation     Hybrid Journal  
ACM Transactions on Embedded Computing Systems (TECS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Information Systems (TOIS)     Hybrid Journal   (Followers: 21)
ACM Transactions on Intelligent Systems and Technology (TIST)     Hybrid Journal   (Followers: 8)
ACM Transactions on Interactive Intelligent Systems (TiiS)     Hybrid Journal   (Followers: 3)
ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP)     Hybrid Journal   (Followers: 10)
ACM Transactions on Reconfigurable Technology and Systems (TRETS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Sensor Networks (TOSN)     Hybrid Journal   (Followers: 9)
ACM Transactions on Speech and Language Processing (TSLP)     Hybrid Journal   (Followers: 11)
ACM Transactions on Storage     Hybrid Journal  
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 25)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Ad Hoc Networks     Hybrid Journal   (Followers: 11)
Adaptive Behavior     Hybrid Journal   (Followers: 11)
Advanced Engineering Materials     Hybrid Journal   (Followers: 26)
Advanced Science Letters     Full-text available via subscription   (Followers: 8)
Advances in Adaptive Data Analysis     Hybrid Journal   (Followers: 8)
Advances in Artificial Intelligence     Open Access   (Followers: 16)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Computer Science : an International Journal     Open Access   (Followers: 14)
Advances in Computing     Open Access   (Followers: 2)
Advances in Data Analysis and Classification     Hybrid Journal   (Followers: 51)
Advances in Engineering Software     Hybrid Journal   (Followers: 26)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 10)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Human-Computer Interaction     Open Access   (Followers: 20)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Remote Sensing     Open Access   (Followers: 38)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Advances in Technology Innovation     Open Access   (Followers: 2)
AEU - International Journal of Electronics and Communications     Hybrid Journal   (Followers: 8)
African Journal of Information and Communication     Open Access   (Followers: 8)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Air, Soil & Water Research     Open Access   (Followers: 9)
AIS Transactions on Human-Computer Interaction     Open Access   (Followers: 6)
Algebras and Representation Theory     Hybrid Journal   (Followers: 1)
Algorithms     Open Access   (Followers: 11)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 4)
American Journal of Computational Mathematics     Open Access   (Followers: 4)
American Journal of Information Systems     Open Access   (Followers: 7)
American Journal of Sensor Technology     Open Access   (Followers: 4)
Anais da Academia Brasileira de Ciências     Open Access   (Followers: 2)
Analog Integrated Circuits and Signal Processing     Hybrid Journal   (Followers: 7)
Analysis in Theory and Applications     Hybrid Journal   (Followers: 1)
Animation Practice, Process & Production     Hybrid Journal   (Followers: 5)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 11)
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 7)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of Software Engineering     Hybrid Journal   (Followers: 13)
Annual Reviews in Control     Hybrid Journal   (Followers: 6)
Anuario Americanista Europeo     Open Access  
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applied and Computational Harmonic Analysis     Full-text available via subscription   (Followers: 2)
Applied Artificial Intelligence: An International Journal     Hybrid Journal   (Followers: 14)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Clinical Informatics     Hybrid Journal   (Followers: 2)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Computer Systems     Open Access   (Followers: 1)
Applied Informatics     Open Access  
Applied Mathematics and Computation     Hybrid Journal   (Followers: 33)
Applied Medical Informatics     Open Access   (Followers: 11)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Soft Computing     Hybrid Journal   (Followers: 16)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Architectural Theory Review     Hybrid Journal   (Followers: 3)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 5)
Archive of Numerical Software     Open Access  
Archives and Museum Informatics     Hybrid Journal   (Followers: 133)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Artifact     Hybrid Journal   (Followers: 2)
Artificial Life     Hybrid Journal   (Followers: 6)
Asia Pacific Journal on Computational Engineering     Open Access  
Asia-Pacific Journal of Information Technology and Multimedia     Open Access   (Followers: 1)
Asian Journal of Computer Science and Information Technology     Open Access  
Asian Journal of Control     Hybrid Journal  
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
Australian Educational Computing     Open Access   (Followers: 1)
Automatic Control and Computer Sciences     Hybrid Journal   (Followers: 4)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Automatica     Hybrid Journal   (Followers: 11)
Automation in Construction     Hybrid Journal   (Followers: 6)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 8)
Basin Research     Hybrid Journal   (Followers: 5)
Behaviour & Information Technology     Hybrid Journal   (Followers: 52)
Bioinformatics     Hybrid Journal   (Followers: 311)
Biomedical Engineering     Hybrid Journal   (Followers: 16)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 17)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 32)
Briefings in Bioinformatics     Hybrid Journal   (Followers: 44)
British Journal of Educational Technology     Hybrid Journal   (Followers: 129)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 10)
c't Magazin fuer Computertechnik     Full-text available via subscription   (Followers: 2)
CALCOLO     Hybrid Journal  
Calphad     Hybrid Journal  
Canadian Journal of Electrical and Computer Engineering     Full-text available via subscription   (Followers: 14)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal  
Cell Communication and Signaling     Open Access   (Followers: 1)
Central European Journal of Computer Science     Hybrid Journal   (Followers: 5)
CERN IdeaSquare Journal of Experimental Innovation     Open Access  
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
ChemSusChem     Hybrid Journal   (Followers: 7)
China Communications     Full-text available via subscription   (Followers: 7)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
CIN Computers Informatics Nursing     Full-text available via subscription   (Followers: 12)
Circuits and Systems     Open Access   (Followers: 16)
Clean Air Journal     Full-text available via subscription   (Followers: 2)
CLEI Electronic Journal     Open Access  
Clin-Alert     Hybrid Journal   (Followers: 1)
Cluster Computing     Hybrid Journal   (Followers: 1)
Cognitive Computation     Hybrid Journal   (Followers: 4)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Communication Methods and Measures     Hybrid Journal   (Followers: 12)
Communication Theory     Hybrid Journal   (Followers: 20)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Algebra     Hybrid Journal   (Followers: 3)
Communications in Partial Differential Equations     Hybrid Journal   (Followers: 3)
Communications of the ACM     Full-text available via subscription   (Followers: 53)
Communications of the Association for Information Systems     Open Access   (Followers: 18)
COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering     Hybrid Journal   (Followers: 3)
Complex & Intelligent Systems     Open Access  
Complex Adaptive Systems Modeling     Open Access  
Complex Analysis and Operator Theory     Hybrid Journal   (Followers: 2)
Complexity     Hybrid Journal   (Followers: 6)
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Computación y Sistemas     Open Access  
Computation     Open Access  
Computational and Applied Mathematics     Hybrid Journal   (Followers: 2)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational and Structural Biotechnology Journal     Open Access   (Followers: 2)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Astrophysics and Cosmology     Open Access   (Followers: 1)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computational Cognitive Science     Open Access   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Condensed Matter     Open Access  
Computational Ecology and Software     Open Access   (Followers: 9)
Computational Economics     Hybrid Journal   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 14)
Computational Linguistics     Open Access   (Followers: 23)
Computational Management Science     Hybrid Journal  
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Molecular Bioscience     Open Access   (Followers: 2)
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computational Particle Mechanics     Hybrid Journal   (Followers: 1)
Computational Research     Open Access   (Followers: 1)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computational Science and Techniques     Open Access  
Computational Statistics     Hybrid Journal   (Followers: 13)
Computational Statistics & Data Analysis     Hybrid Journal   (Followers: 31)
Computer     Full-text available via subscription   (Followers: 87)
Computer Aided Surgery     Hybrid Journal   (Followers: 3)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 7)
Computer Communications     Hybrid Journal   (Followers: 10)
Computer Engineering and Applications Journal     Open Access   (Followers: 5)
Computer Journal     Hybrid Journal   (Followers: 8)
Computer Methods in Applied Mechanics and Engineering     Hybrid Journal   (Followers: 21)
Computer Methods in Biomechanics and Biomedical Engineering     Hybrid Journal   (Followers: 10)
Computer Methods in the Geosciences     Full-text available via subscription   (Followers: 1)
Computer Music Journal     Hybrid Journal   (Followers: 16)
Computer Physics Communications     Hybrid Journal   (Followers: 6)
Computer Science - Research and Development     Hybrid Journal   (Followers: 7)
Computer Science and Engineering     Open Access   (Followers: 17)
Computer Science and Information Technology     Open Access   (Followers: 12)
Computer Science Education     Hybrid Journal   (Followers: 13)
Computer Science Journal     Open Access   (Followers: 20)
Computer Science Master Research     Open Access   (Followers: 10)
Computer Science Review     Hybrid Journal   (Followers: 10)

        1 2 3 4 5 6 | Last

Journal Cover Advanced Engineering Materials
  [SJR: 0.81]   [H-I: 81]   [26 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1438-1656 - ISSN (Online) 1527-2648
   Published by John Wiley and Sons Homepage  [1580 journals]
  • Front Cover: Advanced Engineering Materials 11∕2017
    • Abstract: Cellular structures fabricated via extrusionbased 3D-printing of inks containing NiO particles (left) are heat-treated in a hydrogen atmosphere to remove the polymer binder and residual solvents, reduce the NiO to metallic Ni, and sinter the particles. The resulting metallic Ni micro-trusses (right) have nearly fully dense struts with excellent surface quality and they exhibit high strengths and high ductilities. More details can be found in the article 1600365 by David C. Dunand and co-workers.
      PubDate: 2017-11-20T05:49:39.94461-05:0
      DOI: 10.1002/adem.201770037
  • Back Cover: Advanced Engineering Materials 11∕2017
    • Abstract: A novel microfluidic component, an accumulator, has been developed for the storage and release of healing fluids in a regenerative coating system. This image shows the deformation of the accumulator when pressurized with overlaid contours of the deformation from 3D digital image correlation. Further information can be found in the article 1700319 by Scott R. White and and co-workers.
      PubDate: 2017-11-20T05:49:36.653137-05:
      DOI: 10.1002/adem.201770040
  • Editorial: Metallic Foams Special Section
    • Authors: Miguel Angel Rodríguez-Pérez; Eusebio Solórzano
      PubDate: 2017-11-20T05:49:34.256137-05:
      DOI: 10.1002/adem.201700545
  • Microstructural Evolution and Properties of a Hot Extruded and
           HPT-Processed Resorbable Magnesium WE43 Alloy
    • Authors: Dexue X. Liu; Xin Pang, Denglu L. Li, Chenggong G. Guo, Jittraporn Wongsa-Ngam, Terence G. Langdon, Marc A. Meyers
      PubDate: 2017-11-20T05:49:32.992604-05:
      DOI: 10.1002/adem.201700723
  • Masthead: Adv. Eng. Mater. 11∕2017
    • PubDate: 2017-11-20T05:49:31.220301-05:
      DOI: 10.1002/adem.201770038
  • Contents: Adv. Eng. Mater. 11∕2017
    • PubDate: 2017-11-20T05:49:29.377273-05:
      DOI: 10.1002/adem.201770039
  • Optimization of Strength-Electrical Conductivity Properties in Al–2Fe
           Alloy by Severe Plastic Deformation and Heat Treatment
    • Authors: Andrey E Medvedev; Maxim Y Murashkin, Nariman A Enikeev, Ruslan Z Valiev, Peter D Hodgson, Rimma Lapovok
      Abstract: High-pressure torsion at room temperature followed by two processing routes, either 1) annealing at 200 °C for 8 h or 2) elevated temperature (200 °C) high-pressure torsion, are employed to obtain simultaneous increase in mechanical strength and electrical conductivity of Al–2 wt%Fe. The comparative study of microstructure, particle distribution, mechanical properties, and electrical conductivity for both processing routes gives the optimal combination of high mechanical strength and high electrical conductivity in Al–2Fe alloy. It is shown that while the mechanical strength is approximately the same for both processing routes (>320 MPa), high-pressure torsion at elevated temperature results in higher conductivity (≥52% IACS) due to reduction of Fe solute atom concentration in Al matrix compared to annealing treatment. High-pressure torsion at 200 °C has been demonstrated as a new and effective way for obtaining combination of high mechanical strength and electrical conductivity in Al–Fe alloys.The dynamic aging of UFG Al–Fe alloy (HPT at 200 °C) has been used to enhance the electrical conductivity. Comparison of observed results with static aging (annealing at 200 °C for 8 h), also performed in present work, shows superiority of dynamically aged alloy over statically aged. The increase of electrical conductivity by ≈3% IACS is accompanied by substantial decrease of heat treatment time from 8 h for static annealing to 5 min for high temperature deformation.
      PubDate: 2017-11-20T02:50:28.962728-05:
      DOI: 10.1002/adem.201700867
  • Microstructure and Texture Development in Al–3%Brass Composite
           Produced through ARB
    • Authors: Ehsan Tolouei; Mohammad Reza Toroghinejad, Hamed Asgari, Hossein Monajati Zadeh, Fakhreddin Ashrafizadeh, Jerzy A. Szpunar, Philippe Bocher
      Abstract: In the present work, aluminum-3% brass composite sheets are produced by accumulative roll bonding (ARB) process up to nine passes at ambient temperature. Evolution of rolling texture is studied by texture measurement using X-ray diffraction method. The results show that ARB process leads to the formation of copper ({112} ) and Dillamore ({4 4 11} ) as the major texture components. The intensity of copper and Dillamore components enhances to values as high as 19 times that of random with increasing number of passes to 9. It is observed that the 5th pass is a transition in development of the texture components, after which the intensities undergo a drop. The textures are comparable to ARB process of high purity aluminum, indicating that the addition of 3% brass particles do not cause any significant change in the deformation behavior. Electron backscatter diffraction (EBSD) technique is used to examine the microstructure; the results reveal formation of ultrafine grains (UFG), starting in the 3rd pass and covers the entire structure after the 5th pass. The major mechanisms involved are identified as rotation of the sub-grains, as well as grain boundary migration.Aluminum–brass composite is produced by ARB process up to nine passes. Recrystallization and formation of new grains start from the 3rd pass and continues to the 7th pass. Intensity of the textures decreases after recrystallization; Dillamore and Copper components are the main textures of the composite.
      PubDate: 2017-11-17T02:31:33.642186-05:
      DOI: 10.1002/adem.201700463
  • An Evaporative Initiated Chemical Vapor Deposition Coater for Nanoglue
    • Authors: Greg C. Randall; Luis Gonzalez, Ron Petzoldt, Fred Elsner
      Abstract: The authors present an evaporative initiated chemical vapor deposition (iCVD) coater and use it to establish a submicron bonding process for millimeter-scale foils with potentially rough surface features. The coater uses a simple benchtop design suited to research labs, with pre-heated metal pins instead of hot filaments, and direct evaporation of reactants within the chamber. Coatings of poly(glycidyl methacrylate) (pGMA) with thickness 100–800 nm are achieved at rates of 10–40 nm min−1 on substrates common in high energy laser compression experiments. Coating uniformities of 10–30 nm mm−1 are demonstrated in a ≈60 × 10 mm zone under the heated pins. As an aside, the authors further show the ability to coat intentionally non-uniform layers in a monomer vapor diffusion gradient. Coatings are formed on both plastics and solids ranging from smooth, non-burred silicon or lithium fluoride to rough and burred metals (aluminum and copper). These coated substrates are then chemically bonded under mild heat and pressure. Detailed surface, thickness, and cross-sectional characterization is performed to confirm a submicron bond gap and to troubleshoot the common clearance issues from burrs, roughness, and surface curvature. Peeling and dropping bond strength tests confirm the bonds are robust, when coated and assembled under conditions to mitigate clearance issues.A simplified evaporative initiated chemical vapor deposition (iCVD) coater is developed for submicron bond gaps in materials with potentially imperfect surfaces. A robust bonding process is designed to overcome the most common irregular surface features (curvature, roughness, and burrs) followed from contact elasticity analysis. Bond gaps of 0.2–1.5 µm are achieved in combinations of common plastics, metals, and ceramic-like foils.
      PubDate: 2017-11-16T10:00:30.304446-05:
      DOI: 10.1002/adem.201700839
  • Nanometer-Thick Ionic Liquids as Boundary Lubricants
    • Authors: Xiao Gong; Lei Li
      Abstract: Ionic liquids (ILs) are fascinating materials with unique combination of solid and liquid properties. Due to high thermal stability and promising tribological properties, there have been increasing research interests in applying ILs as boundary lubricants. In this review, the authors will discuss the recent progress on this topic with the emphasis on the relationship between the molecular arrangement of ILs confined to a solid and the tribological properties. First, the fundamentals on boundary lubrication and the state-of-the-art lubricants will be reviewed briefly. Second, the progress on the molecular structure of ILs confined to a solid surface will be discussed. Afterward, the experimental and computational efforts on the ILs as boundary lubricants will be discussed in details with emphasis on the effect of IL structure, solid substrates, and IL-soild interaction. Finally, the future research directions will be discussed.Ionic liquids (ILs) are fascinating materials with unique combination of solid and liquid properties. In this review, we discuss the recent progress on their potential application as boundary lubricants with the emphasis on the relationship between the molecular arrangement of ILs confined to a solid and the tribological properties.
      PubDate: 2017-11-15T11:58:30.954432-05:
      DOI: 10.1002/adem.201700617
  • Diversity in Addressing Reaction Mechanisms of Nano-Thermite Composites
           with a Layer by Layer Structure
    • Authors: Hongtao Sui; Lauren LeSergent, John Z. Wen
      Abstract: The reaction mechanisms and microstructures of various layered nano-thermite composites are investigated through characterization of their energetic properties. Migration of reactive components across the reaction zone is analyzed, which plays an important role in determining the process initiation, reaction propagation, and chemical stability at low temperatures. Distinct types of nanoparticles are deposited onto filter paper in a sequence, using the vacuum filtration method, which promotes intimate contact between neighboring reactive layers. Scanning Electron Microscopy (SEM) images demonstrate a well-defined contact region between the two layers in the Al/CuO or Al/NiO composites. Differential Scanning Calorimetry (DSC) data shows that the thermite reaction occurs below the melting temperature of Al, resulting in rapid heat release, and improves reaction initiation. Elemental mapping results reveal the migration of Al, Ni/Cu, and oxygen before and after the thermite reaction, which is arranged during thermogravimetric analysis (TGA). This analysis indicates the dominant pathway of the thermite reaction in each composite, through either decomposition of the CuO nanoparticles in the Al/CuO composite or through direct migration of reactive components across the conducting surface within the Al/NiO composite.Layer-by-layer structured Al–CuO and Al–NiO nanoparticles are investigated via characterization of their microstructures and elemental mapping. Experimental data indicates for Al–CuO the reaction involves decomposition of CuO into oxygen, while for Al–NiO migration of reactive species across the conducting surface is critical.
      PubDate: 2017-11-15T11:57:02.787975-05:
      DOI: 10.1002/adem.201700822
  • 3D Printing of Diamond Tools for Dental Ceramics Processing
    • Authors: Zhibo Yang; Junchen Hu, Kaiqiang Li, Aiju Liu, Shian Liu
      Abstract: This paper is focused on preparing diamond tools with orderly arranged abrasive particles for dental ceramics processing via 3D printing. This allows one to overcome such drawbacks of the existing methods of dental ceramics processing as weak bonding strength, short service life, and irregular diamond distribution in diamond tools. Firstly, the CAD model of the dental diamond tool is constructed using 3D cartographic software, with level-scan-path geometry information generated via hierarchcal slicing. Then, using Ni–Cr alloy powder and diamond as raw materials, the dental ceramics processing diamond tool with orderly arranged diamond particles is prepared via a 3D printer. Next, an X-ray diffractometer, energy dispersive spectrometer, and scanning electron microscope are used to analyze the microstructure of the Ni–Cr alloy and diamond particle interfaces, resulting in the identification of their bonding mechanism. Finally, the diamond grinding wheel produced by 3D printing is subjected to dental zirconia ceramics grinding performance tests. The results obtained confirm that diamond particles experience normal wear, while no abrasive falling off occurs on the 3D printed diamond tool surface.In this paper, diamond tools for dental ceramics processing are manufactured using the 3D printing technology. Laser fast scanning is utilized to make the 3D distribution of diamond particles more regular, thus, significantly improving the manufacturing performance of grinding wheels.
      PubDate: 2017-11-15T11:56:27.324339-05:
      DOI: 10.1002/adem.201700747
  • Smart Energetics: Sensitization of the Aluminum-Fluoropolymer Reactive
    • Authors: Sara L. Row; Lori J. Groven
      Abstract: The development of smart energetics is at the forefront of the research community. The desire is to have energetics that could have ON/OFF capability, tunable performance, and/or targeted energy delivery. Therefore, efforts have been focused on designing systems that respond to stimuli in a controlled manner. In this paper, nanoscale aluminum (nAl)/fluoropolymer reactive systems are studied and the piezoelectric nature of the fluoropolymers is used as a means to sensitize the system. Using a capacitor type setup, and drawing on our previous efforts, three fluoropolymer/nAl systems are studied and their sensitivities upon application of a DC voltage are quantified using BAM drop weight as the indicator. It is found, upon application of 1.0 kV, that for all three fluoropolymer/Al systems the sensitivity is greatly increased. For example, for the THV221/nAl system the impact energy required for ignition is reduced from 63 to 10 J. Further increasing the applied voltage is shown to further increase the sensitivity for all systems studied. The role of electroactive phase content and sensitization time is also discussed.Aluminum/fluoropolymer reactives are formulated and demonstrate switchable behavior upon application of a DC voltage. The drop weight sensitivity is on par with powdered RDX and PETN. This demonstrates that piezoelectric fluoropolymer bound reactives could be developed into smart energetics.
      PubDate: 2017-11-14T12:50:22.264431-05:
      DOI: 10.1002/adem.201700409
  • Impact of Cement Hydration on Durability of Cellulosic Fiber-Reinforced
           Cementitious Composites in the Presence of Metakaolin
    • Authors: Jianqiang Wei
      Abstract: Degradation of cellulosic fiber in the alkaline environment of concrete generated in the process of cement hydration is the primary reason for the low durability of such composites. However, the impact of cement hydration on cellulosic fiber's degradation in cementitious systems has not been thoroughly understood. This paper presents the dependence of deterioration behavior of cellulosic fiber-cement systems on cement hydration in the presence of metakaolin. Experimental investigations, such as isothermal calorimetry, thermogravimetric analysis and energy dispersive X-ray spectroscopy, and thermodynamic simulations are carried out to investigate cement hydration kinetics and hydration products. Durability of cellulosic fiber-reinforced cement composite is assessed based on the degradation in flexural properties. The results indicate that, in the presence of metakaolin, the hydration of cement is enhanced accompanied by consumption of calcium hydroxide, low release of hydration heat, decreased Ca/Al and Ca/Si ratios of C–S–H phase, and reduced OH- and Ca2+ amounts in pore solution. A cement substitution by 30 wt% metakaolin results in an improvement of flexural toughness and durability of cellulosic fiber-reinforced cement composites by 42 and 269%, respectively. The correlations between composite durability and hydration of Portland cement are established.Hydration of cement is identified as a crucial factor in understanding the deterioration behavior of cellulosic fibers-reinforced cementitious composites. Effect of metakaolin, on durability of cellulosic fiber-reinforced cement composites are evaluated by means of degradation in flexural properties. Based on the experimental and simulation observations, correlations between durability of cellulosic fiber-cement system and cement chemistry are established.
      PubDate: 2017-11-14T02:27:19.086803-05:
      DOI: 10.1002/adem.201700642
  • Production and Anisotropic Tensile Behavior of Resin-Metal
           Interpenetrating Phase Composites
    • Authors: Bibo Yao; Zhaoyao Zhou, Liuyang Duan, Jie Qin
      Abstract: Metal-polymer composites can be used to synthesize material properties. A variety of interpenetrating phase composites have been produced by spontaneously infiltrating porous short-fiber preforms with unsaturated polyester resin under vacuum conditions. Porous preforms are fabricated by compacting and sintering short 304 stainless steel fibers from cutting stainless steel fiber ropes. Tensile experiments are conducted, and fractographs are examined via scanning electron microscopy. The results reveal that the tensile strength, elongation at maximum stress, and elasticity modulus of the IPCs increase with the increasing fiber fractions and exhibit anisotropy in different directions. The tensile strength and elongation at maximum stress are significantly improved compared with the consistent preforms. A nonlinear elastic behavior and sawtooth-like fluctuation during yield deformation are noted. Compared with the through-thickness direction, a higher tensile strength and larger elongation at maximum stress are observed in the in-plane direction. Finer-diameter fibers can improve the strength and increase the elongation at maximum stress. The tensile fracture surfaces show a mixture of brittle and plastic fracture characteristics.Metal-resin IPCs are produced by vacuum-infiltration of unsaturated polyester resin into the stainless steel preforms and their tensile properties are analyzed. The tensile strength and elongation at maximum stress increase with the increasing fiber fractions and exhibit anisotropy. Finer diameter fibers can improve the strength and increase the elongation at maximum stress. The tensile fracture surfaces show a mixture of brittle and plastic fracture characterizations.
      PubDate: 2017-11-14T02:25:36.705722-05:
      DOI: 10.1002/adem.201700669
  • Mesoporous Silica Spheres Incorporated Aluminum/Poly (Vinylidene Fluoride)
           for Enhanced Burning Propellants
    • Authors: Haiyang Wang; Jeffery B. DeLisio, Scott Holdren, Tao Wu, Yong Yang, Junkai Hu, Michael R. Zachariah
      Abstract: In this paper, we demonstrate that preparation by electrospray deposition of mesoporous SiO2 particles can be employed as additives to Aluminum/Poly (Vinylidene Fluoride) (Al/PVDF) to enhance reaction velocity. We find that the reaction velocity of Al/PVDF with 5 wt% SiO2 is 3× higher. The presence of meso-SiO2 appears to accelerate the decomposition of PVDF, with a significant increase in HF release, resulting in higher heat release. We believe that hot-spots around meso-SiO2 may serve as multiple ignition points, with the multi-layered structure promoting heat convection to increase the propagation rate.With 5 wt% mesoporous silica, the burning rate of Al/PVDF film was 3× times higher. The meso-SiO2 appears to highly accelerate the decomposition of PVDF, with a significant increase in HF release and higher heat release. Hot-spots around meso-SiO2 may serve as multiple ignition points and the multi-layered structure promote the heat convection thus highly increase the spreading rate.
      PubDate: 2017-11-14T02:25:26.939421-05:
      DOI: 10.1002/adem.201700547
  • Microstructure-Dependent Local Fatigue Cracking Resistance of Bimodal
           Ti–6Al–4V Alloys
    • Authors: Ling-Rong Zeng; Li-Ming Lei, Jia Yang, Xue-Mei Luo, Guang-Ping Zhang
      Abstract: The fatigue crack growth behavior of the bimodal Ti–6Al–4V alloys with two different volume fractions of the primary α phase (αp) of 76 and 36% is investigated by the in situ testing technique. The experimental results show that the crack growth rate of the αp = 36% Ti–6Al–4V alloy is lower than that of the αp = 76% one. The local fatigue crack growth rate is evidently decreased by the various boundaries including αp grain boundaries, boundaries between the αp phase and basketweave microstructure, and α/β lamellar interfaces. A criterion associated with the boundary characteristics is obtained to evaluate the grain boundary resistance to the fatigue crack growth in the engineering alloys.Local crack growth rate and fatigue cracking resistance of the Ti–6Al–4V alloys with different volume fractions of primary α phases are investigated in situ in SEM. Local resistance to fatigue cracking related to the boundary characteristics is evaluated quantitatively by EBSD. A criterion for the grain boundary resistance to the crack growth is proposed.
      PubDate: 2017-11-13T03:15:37.565735-05:
      DOI: 10.1002/adem.201700702
  • Influence of Ingot and Powder Metallurgy Production Route on the Tensile
           Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge
    • Authors: P. M. Kellner; R. Völkl, U. Glatzel
      Abstract: Refractory metals and their alloys show potential for high temperature applications, due to the elevated melting points often paired with very good creep resistance. Spark plasma sintering (SPS) as well as arc-melting is used here to prepare quaternary and quinternary Mo–9Si–8B–xAl–yGe (x is 0 or 2; y is 0 or 2, all numbers in at%) samples. All samples consist of a Mo solid solution (Moss) and two intermetallic phases: Mo3Si (A15) and Mo5SiB2 (T2). Aluminum and germanium reduce the melting point and slightly decrease the density of the material. The specimens are homogenized and coarsened by a subsequent heat-treatment in vacuum at 1850 °C for 24 h. The resulting microstructure is investigated using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. A vacuum creep testing device for small tensile creep specimens is presented. It is heated by graphite radiation heaters usable up to 1500 °C in vacuum of 2 · 10-4 Pa with an oil diffusion pump. Tensile creep tests are performed at 1250 °C and stresses from 50 MPa up to 250 MPa. Specimens produced by ingot metallurgy feature superior creep properties compared to powder metallurgy samples.In this study, tensile creep tests are performed for Mo–Si–B alloys at 1250 °C and stresses from 50 to 250 MPa manufactured by argon arc melting and powder metallurgy. Specimens produced by argon arc melted feature superior creep properties compared to powder metallurgy ones, due to grain size.
      PubDate: 2017-11-13T02:46:55.570691-05:
      DOI: 10.1002/adem.201700751
  • Macroporous SiOC Ceramics with Dense Struts by Positive Sponge Replication
    • Authors: Abhisek Choudhary; Swadesh K. Pratihar, Ashish K. Agrawal, Shantanu K. Behera
      Abstract: Highly porous SiOC ceramics (≥90% open porosity) containing dense struts have been prepared following positive sponge replication technique using silsesquioxane based preceramic polymer. The morphological features including cell size, cell window size, and strut size of the macroporous SiOC ceramics have been analyzed using electron microscopy. Subtle variation in the crosslinking condition of the preceramic polymer infiltrated polyurethane template enables the formation of hollow as well as dense struts, which has a profound influence on compressive strength of the macroporous bodies. Synchrotron radiation micro computed tomography is used to construct the three dimensional images of the macroporous ceramics that indicate isotropy of the pores and excellent interconnectivity.Control of slurry viscosity and crosslinking temperature in the processing of preceramic polymer infiltrated PU sponge affords macroporous SiOC ceramics with 90% open porosity, dense struts, and excellent mechanical strength. Synchrotron X-ray microtomography exhibits excellent interconnectivity, homogeneity, and isotropy of the pores.
      PubDate: 2017-11-09T12:02:36.46478-05:0
      DOI: 10.1002/adem.201700586
  • Key Factors Achieving Large Recovery Strains in Polycrystalline
           Fe–Mn–Si-Based Shape Memory Alloys: A Review
    • Authors: Huabei Peng; Jie Chen, Yongning Wang, Yuhua Wen
      Abstract: Fe–Mn–Si-based shape memory alloys are the most favorable for large-scale applications owing to low cost, good workability, good machinability, and good weldability. However, polycrystalline Fe–Mn–Si-based shape memory alloys have low recovery strains of only 2–3% after solution treatment, although monocrystalline ones reach a large recovery strain of ≈9%. This review gives an overview of the improvement of recovery strains for polycrystalline Fe–Mn–Si-based shape memory alloys. It is proposed that two fundamental aspects, that is, composition design and microstructure design, shall be satisfied for obtaining large recovery strains of above 6%. Alloying compositions determining the ceiling of recovery strains shall follow three guidelines: (i) Si content is 5–6 wt%; (ii) 20 wt% ≤ Mn ≤ 32 wt%; (iii) addition of elements strongly strengthening austenite matrix. Microstructure design includes coarsening austenitic grains and reducing twin boundaries as far as possible together with introducing a high density of stacking faults and second phases of strengthening austenite.Low cost Fe–Mn–Si-based shape memory alloys are suitable for large-scale applications. However, their recovery strains are only 2–3% in solution-treated polycrystalline status. This review summarizes the origin of shape memory effect and the improvement history of recovery strains. It is concluded that two fundamental aspects, that is, composition design and microstructure design, shall be followed to achieve a large recovery strain of above 6%.
      PubDate: 2017-11-09T11:56:27.165908-05:
      DOI: 10.1002/adem.201700741
  • Mechanical Properties and Interlaminar Fracture Toughness of
           Glass-Fiber-Reinforced Epoxy Composites Embedded with Shape Memory Alloy
    • Authors: Li-Dan Xu; Ming-Fang Shi, Xiao-Yu Sun, Zhen-Qing Wang, Bin Yang
      Abstract: The effects of the content and position of shape memory alloy (SMA) wires on the mechanical properties and interlaminar fracture toughness of glass-fiber-reinforced epoxy (GF/epoxy) composite laminates are investigated. For this purpose, varying numbers of SMA wires are embedded in GF/epoxy composite laminates in different stacking sequences. The specimens are prepared by vacuum-assisted resin infusion (VARI) processing and are subjected to static tensile and three-point-bending tests. The results show that specimens with two SMA wires in the stacking sequence of [GF2/SMA/GF1/SMA/GF2] and four SMA wires in the stacking sequence of [GF4/SMA/GF2/SMA/GF4] exhibit optimal performance. The flexural strength of the optimal four-SMA-wire composite is lower than that of the pure GF/epoxy composite by 5.76% on average, and the flexural modulus is improved by 5.19%. Mode-I and II interlaminar fracture toughness tests using the SMA/GF/epoxy composite laminates in the stacking sequence of [GF4/SMA/GF2/SMA/GF4] are conducted to evaluate the mechanism responsible for decreasing the mechanical properties. Scanning electron microscopy (SEM) observations reveal that the main damage modes are matrix delamination, interfacial debonding, and fiber pullout.The effects of the content and position of shape memory alloy (SMA) wires on the mechanical properties and interlaminar fracture toughness of glass-fiber-reinforced epoxy (GF/epoxy) composite laminates are investigated. The main damage modes are studied by Scanning electron microscopy (SEM).
      PubDate: 2017-11-09T11:55:52.804025-05:
      DOI: 10.1002/adem.201700646
  • Stress Reduction of 3D Printed Compliance-Tailored Multilayers
    • Authors: Shanmugam Kumar; Brian L. Wardle, Muhamad F. Arif, Jabir Ubaid
      Abstract: Multilayered multi-material interfaces are encountered in an array of fields. Here, enhanced mechanical performance of such multi-material interfaces is demonstrated, focusing on strength and stiffness, by employing bondlayers with spatially-tuned elastic properties realized via 3D printing. Compliance of the bondlayer is varied along the bondlength with increased compliance at the ends to relieve stress concentrations. Experimental testing to failure of a tri-layered assembly in a single-lap joint configuration, including optical strain mapping, reveals that the stress and strain redistribution of the compliance-tailored bondlayer increases strength by 100% and toughness by 60%, compared to a constant modulus bondlayer, while maintaining the stiffness of the joint with the homogeneous stiff bondlayer. Analyses show that the stress concentrations for both peel and shear stress in the bondlayer have a global minimum when the compliant bond at the lap end comprises ≈10% of the bondlength, and further that increased multilayer performance also holds for long (relative to critical shear transfer length) bondlengths. Damage and failure resistance of multi-material interfaces can be improved substantially via the compliance-tailoring demonstrated here, with immediate relevance in additive manufacturing joining applications, and shows promise for generalized joining applications including adhesive bonding.By crafting a spatially compliance-tailored bondlayer utilizing additive manufacturing, mechanical performance can be increased significantly compared to the homogeneous stiff or compliant bondlayer, imparting greater strength, strain to break, and toughness, while maintaining stiffness of the homogeneous stiff bondlayer.
      PubDate: 2017-11-08T08:15:47.562197-05:
      DOI: 10.1002/adem.201700883
  • Effect of Laser Shock Peening on the Microstructures and Properties of
           Oxide-Dispersion-Strengthened Austenitic Steels
    • Authors: Xueliang Yan; Fei Wang, Leimin Deng, Chenfei Zhang, Yongfeng Lu, Michael Nastasi, Marquis A. Kirk, Meimei Li, Bai Cui
      Abstract: Oxide-dispersion-strengthened (ODS) austenitic steels are promising materials for next-generation fossil and nuclear energy systems. In this study, laser shock peening (LSP) has been applied to ODS 304 austenitic steels, during which a high density of dislocations, stacking faults, and deformation twins are generated in the near surface of the material due to the interaction of laser-driven shock waves and the austenitic steel matrix. The dispersion particles impede the propagation of dislocations. The compressive residual stress generated by LSP increases with successive LSP scans and decreases along the depth, with a maximum value of −369 MPa. The hardness on the surface can be improved by 12% using LSP. In situ transmission electron microscopy (TEM) irradiation studies reveal that dislocations and incoherent twin boundaries induced by LSP serve as effective sinks to annihilate irradiation defects. These findings suggest that LSP can improve the mechanical properties and irradiation resistance of ODS austenitic steels in nuclear reactor environments.Laser shock peening (LSP) has been applied to oxide-dispersion-strengthened (ODS) austenitic steels in order to improve the mechanical properties and irradiation resistance. Significant plastic deformation and compressive residual stress are generated by LSP in the near surface, improving the hardness. Dislocations and incoherent twin boundaries induced by LSP can serve as effective sinks to annihilate irradiation defects.
      PubDate: 2017-11-07T11:46:29.396414-05:
      DOI: 10.1002/adem.201700641
  • Effect of High-Energy Ball Milling on Mechanical Properties of the Mg–Nb
           Composites Fabricated through Powder Metallurgy Process
    • Authors: Alireza Vahid; Peter Hodgson, Yuncang Li
      Abstract: New biocompatible and biodegradable Mg–Nb composites used as bone implant materials are fabricated through powder metallurgy process. Mg–Nb mixture powders are prepared through mechanical milling and manual mixing. Then, the Mg–Nb composites are fabricated through cold press and sintering processes. The effect of mechanical milling and Nb particles as reinforcements on the microstructures and mechanical properties of Mg–Nb composites are investigated. The mechanical milling process is found to be effective in reducing the size of Mg and Nb particles, distributing the Nb particles uniformly in the Mg matrix and obtaining Mg–Nb composite particles. The Mg–Nb composite particles can be bound together firmly during the sintering process, result in Mg–Nb composite structures with no intermetallic formation, lower porosity, and higher mechanical properties compared to composites prepared through manual mixing. Interestingly, the mechanical properties of manually mixed Mg–Nb composites appear to be even lower than that of pure Mg.New biodegradable Mg–Nb composites are fabricated through powder metallurgy process. The effect of mechanical milling and Nb particles as reinforcements on the microstructures and mechanical properties of the composites are investigated. The mechanical milling reduces the size of Mg and Nb particles and distributes the Nb particles uniformly in the Mg matrix, produces composites with low porosity and high mechanical properties.
      PubDate: 2017-11-06T04:27:47.527067-05:
      DOI: 10.1002/adem.201700759
  • Vibration Damping of Carbon Nanotube Assembly Materials
    • Authors: Jingna Zhao; Fulin Wang, Xin Zhang, Linjie Liang, Xueqin Yang, Qingwen Li, Xiaohua Zhang
      Abstract: Vibration reduction is of great importance in various engineering applications, and a material that exhibits good vibration damping along with high strength and modulus has become more and more vital. Owing to the superior mechanical property of carbon nanotube (CNT), new types of vibration damping material can be developed. This paper presents recent advancements, including our progresses, in the development of high-damping macroscopic CNT assembly materials, such as forests, gels, films, and fibers. In these assemblies, structural deformation of CNTs, zipping and unzipping at CNT connection nodes, strengthening and welding of the nodes, and sliding between CNTs or CNT bundles are playing important roles in determining the viscoelasticity, and elasticity as well. Toward the damping enhancement, strategies for micro-structure and interface design are also discussed.Carbon nanotube (CNT) assembly materials are superior vibration damping materials, with performance better than conventional metal and polymer materials. The interface engineering between CNTs and at CNT connection nodes is the key to tune the damping performance. This review addresses the recent progresses on the vibrational properties of CNT forests, gels, films, and fibers.
      PubDate: 2017-11-06T04:26:51.449241-05:
      DOI: 10.1002/adem.201700647
  • Microstructure and Tribological Behavior of Stripe Patterned TiN Film
           Prepared with Filtered Cathodic Vacuum Arc Deposition (FCVAD)
    • Authors: Ping Chen; Yingqian La
      Abstract: This paper describes an experimental investigation into the influence of the stripe interspace and applied load on the tribological behavior of stripe patterned TiN films. The stripe patterned TiN films are deposited on an H13 steel surface by masked deposition with the filtered cathodic vacuum arc discharge (FCVAD) technique. The surface micro morphology, chemical composition, crystal structure, and mechanical properties of the films is characterized using 3D white light interferometry, scanning electron microscopy (SEM), X-ray diffractometry (XRD), and a nano-indentation tester, respectively. The tribological performance of patterned TiN is measured using a UMT-5 tribometer, and the friction and wear mechanisms are analyzed, compared with that of the full TiN film and H13 steel substrate. The results show that the stripe patterned TiN films has better tribological properties than the full TiN film. These results are attributed to the synergistic effect between the surface pattern and the TiN film. The stripe interspace and the applied load has a more significant effect on the wear rate of the stripe patterned TiN films than the coefficient of friction of their friction pairs. A further study, however, is needed to analyze the relationship between the applied load and the wear rates of the stripe patterned TiN films.This paper describes an experimental investigation into the influence of the stripe interspace and applied load on the tribological behavior of stripe patterned TiN films. The stripe patterned TiN films are prepared by masked deposition using filtered cathodic vacuum arc discharge technique.
      PubDate: 2017-11-02T08:51:05.514755-05:
      DOI: 10.1002/adem.201700700
  • Compositional and Tribo-Mechanical Characterization of Ti-Ta Coatings
           Prepared by Confocal Dual Magnetron Co-Sputtering
    • Authors: Amin Bahrami; Jonatán Pérez Álvarez, Osmary Depablos-Rivera, Roberto Mirabal-Rojas, Agustin Ruíz-Ramírez, Stephen Muhl, Sandra E. Rodil
      Abstract: Titanium-Tantalum coatings are deposited by magnetron co-sputtering technique, using independently driven titanium and tantalum targets. The effect of the Ta content on the structure, mechanical, and wear properties of Ti films is investigated. It is found that the percentage of the added Ta varies linearly from 3.7 to 31.3 at% by increasing the power applied to the Ta target from 10 to 100 W. The XRD results show that the coatings are crystalline, and there is no evidence of the formation of intermetallic phases, instead formation of metastable phases of α″ and β depending on Ta content are observed, though the samples are deposited at low temperature (150 °C). It is shown that the elastic strain to failure (H/Er; hardness to reduced elastic moduli ratio) can be increased by 40% through the formation of crystalline phases with a lower E, while the hardness remains constant. The tribological study shows that increasing the Ta content up to 14.9 at% causes a significant improvement in adhesion of the coating to a soft metallic substrate.The production of nanostructured, hard, and tough metallic coatings using vapor deposition method is of increasing interests in the coating of metallic substrates. The results in this study show that addition of Ta to the Ti coatings improves the toughness and adhesion of coatings to the substrate, although it has not significant effect on the hardness of coatings.
      PubDate: 2017-11-02T04:05:58.465537-05:
      DOI: 10.1002/adem.201700687
  • Directly Verifiable Neutron Diffraction Technique to Determine Retained
           Austenite in Steel
    • Authors: Tatiana Lychagina; Alexander Zisman, Ekaterina Yashina, Dmitry Nikolayev
      Abstract: Conventional procedures for quantitative analysis of retained austenite in steels by neutron diffraction ignore the effect of crystallographic texture and rely on a-priori parameters rather than a direct calibration with appropriate etalons. As the main drawback, this method is not directly verified by independent data. In order to get over the verification problem, that is, to calibrate the method, reference sandwich-like samples with predefined amounts of austenite have been prepared. Neutron diffraction allows to measure large samples from one hand and to get rid of the texture influence from the other. Application of the proposed method was illustrated by volume fractions of retained austenite determination in medium-carbon martensitic steel tempered at various temperatures. Main result of our work is the developed method based on complete orientation averaging by means of neutron diffraction and usage of the calibration samples. It allowed to refine the austenite detectability limit to about 0.1% (vol.). Based on the method calibration, low fractions of retained austenite (0.13–2.9%) have been determined in the medium-carbon martensitic steel tempered at various temperatures.The new method of the quantitative analysis for retained austenite in steels by neutron diffraction is proposed. This approach is based on the calibration with reference samples in order to reliably evaluate low fractions of retained austenite in textured steels with detectability limit refined to 0.1%. The suggested method implies direct verification of the results.
      PubDate: 2017-10-30T07:41:46.467493-05:
      DOI: 10.1002/adem.201700559
  • Ultra-Smooth, Chemically Functional Silica Surfaces for Surface
           Interaction Measurements and Optical/Interferometry-Based Techniques
    • Authors: Howard A. Dobbs; Yair Kaufman, Jeff Scott, Kai Kristiansen, Alex M. Schrader, Szu-Ying Chen, Peter Duda, Jacob N. Israelachvili
      Abstract: The study of interfacial phenomena is central to a range of chemical, physical, optical, and electromagnetic systems such as surface imaging, polymer interactions, friction/wear, and ion-transport in batteries. Studying intermolecular forces and processes of interfaces at the sub-nano scale has proven difficult due to limitations in surface preparation methods. Here, we describe a method for fabricating reflective, deformable composite layers that expose an ultra-smooth silica (SiO2) surface (RMS roughness
      PubDate: 2017-10-30T06:25:58.062495-05:
      DOI: 10.1002/adem.201700630
  • Experimental Study on the Effect of Cooling Rate on the Secondary Phase in
           As-Cast Mg–Gd–Y–Zr Alloy
    • Authors: Keyan Wu; Xuyang Wang, Lv Xiao, Zhongquan Li, Zhiqiang Han
      Abstract: The effect of cooling rate on the composition, morphology, size, and volume fraction of the secondary phase in as-cast Mg–Gd–Y–Zr alloy is investigated. In the study, a casting containing five steps with thickness of 10–50 mm is produced, in which cooling rate ranging from 2.6 to 11.0 K s−1 is created. The secondary phase is characterized using optical microscope (OM), scanning electron microscope (SEM), and electron probe micro-analyzer (EPMA). The volume fraction of the secondary phase is determined using OM and quantitative metallographic analysis, and Vickers hardness test is conducted to verify the analysis results. The effect of the cooling rate on the volume fraction of the secondary phase is discussed in detail. The result shows that with the increase of the cooling rate, the size of the secondary phase decreases. The effect of the cooling rate on the volume fraction of the secondary phase is complicated somewhat. A comprehensive analysis on the experimental data shows that a critical cooling rate may exist, over which the volume fraction of the secondary phase decreases with the increase of the cooling rate, however under which the volume fraction increases with the increase of the cooling rate.The effect of cooling rate on the composition, morphology, size, and volume fraction of the secondary phase in as-cast Mg–Gd–Y–Zr alloy is investigated. The mechanisms governing the variation of the volume fraction of the secondary phase with cooling rates are revealed.
      PubDate: 2017-10-30T01:41:32.854279-05:
      DOI: 10.1002/adem.201700717
  • Friction Reduction Induced by Elliptical Surface Patterns under Lubricated
    • Authors: Andreas Rosenkranz; Adam Szurdak, Philipp G. Grützmacher, Gerhard Hirt, Frank Mücklich
      Abstract: Recording Stribeck-like curves is an efficient way to evaluate the frictional performance and efficiency of patterned surfaces. Elliptical patterns with varying area density and structural depth are fabricated by micro-coining on steel substrates (AISI 304). A ball-on-disc tribometer is used to perform unidirectional sliding experiments for the polished reference and the elliptical patterns dependent on the sliding velocity. In this study, a clear connection between structural parameters such as length of long and short axis, aspect ratio, and pitch with the frictional behavior can be found. Comparing patterns with comparable depth and area density underlines that elliptical patterns having larger individual features (increased length of both axes) separated by a larger pitch reduce the COF more significantly. The number of tribologically active individual elliptical structures, recirculation effects of the lubricant, as well as the pattern geometry that may lead to undesired edge effects and stress concentrations need to be taken into consideration to explain those findings. The sample with the smallest structural depth, the smallest area density, and the lowest aspect ratio (A1) leads to the maximum friction reduction (4-fold) for all velocities which underlines the enormous potential of elliptical structures in terms of friction reduction.The frictional performance of elliptical surface patterns fabricated by hot micro-coining is investigated by recording Stribeck-like curves. The sample with the smallest structural depth, the smallest area density, and the lowest aspect ratio lead to the maximum friction reduction by a factor of 4, which underlines the enormous potential of elliptical structures in terms of friction reduction.
      PubDate: 2017-10-25T09:55:36.549437-05:
      DOI: 10.1002/adem.201700731
  • Fabrication and Optical Properties of Periodic Ag Nano-Pore and
           Nano-Particle Arrays with Controlled Shape and Size over Macroscopic
           Length Scales
    • Authors: Colm T. Mallon; Kiang W. Kho, Houda Gartite, Robert J. Foster, Tia E. Keyes
      Abstract: A facile and economical route to preparation of highly ordered sliver pore or particle arrays with controlled pore-shape and size extended over cm2 areas is described. The substrates are prepared at planar and curved surfaces via sphere-imprinted polymer (PDMS) templating using polystyrene spheres with diameters of 820, 600, or 430 nm. Nano-pore arrays are created by sputtering 80 nm of Ag directly onto the templates and nano-particle arrays are prepared by electrode-less deposition of Ag from Tollen's reagent. The shape of the nano-pore or particles in the array conformed to that of the imprint of the sphere on the template. Stretching the flexible template enable creation of cuboid shaped nano-voids and nano-particles following Ag deposition. Diffuse reflectance from the spherical Ag nano-cavity arrays showed absorbance maxima at wavelengths comparable similar to the diameter of the templating sphere, whereas reflectance from the cuboid arrays, showed little correlation with the sphere diameter. The cuboid nano-particle arrays showed the most intense visible absorption which is red-shifted compared to the spherical arrays. White light diffraction from the arrays, observed by rotating 1 cm2 substrates relative to a fixed light source, reflected exactly the symmetry axes of the periodic nano-features in the arrays demonstrating the remarkable macroscopic order of the periodic structures. Raman spectra of 1-benzenethiol adsorbed at the arrays indicated SERS enhancements from the substrates are attributed mainly to surface nano-roughness with only moderate contributions from the periodically corrugated structures. Despite excitation at the major resonance dip in the reflectance spectrum, a weak, localized rim dipole mode is found to elicit a small increase in the SERS enhancement factor for the 430 nm diameter spherical arrays. FDTD studies of nano-void arrays provided insights into various factors affecting the SERS experiment and confirmed the array's plasmonic spectra are dominated by propagating plasmon modes under microscope excitation/collection angles.In this paper, a facile and economical route to preparation of highly ordered silver nano-pore arrays via sphere imprinted PDMS templating is described. We demonstrated that a series of various pore-shapes, ranging from spherical and cuboid, can be obtained by stretching the polymer template. FDTD simulation is also carried out to provide insights into the plasmonic origin of the observed SERS enhancements.
      PubDate: 2017-10-24T11:53:03.324955-05:
      DOI: 10.1002/adem.201700532
  • The Influence of Hydrogen on the Low Cycle Fatigue Behavior of Medium
           Strength 3.5NiCrMoV Steel Studied Using Notched Specimens
    • Authors: Qian Liu; Andrej Atrens
      Abstract: The influence of hydrogen on low cycle fatigue (LCF) of 3.5NiCrMoV steel electrochemically hydrogen charged in the acidified pH 2 0.1 M Na2SO4 solution is studied. In the presence of hydrogen, the fatigue life decreases significantly by ≈70 to ≈80% by: (i) the crack initiation period is decreased; and (ii) the crack growth rate is accelerated. SEM observation indicates that in the presence of hydrogen, the fracture surface shows flat transgranular fracture with vague striations and some intergranular fracture at lower stresses. The fatigue crack growth rate increases with increasing cyclic stress amplitude and with hydrogen fugacity. Once the fatigue crack reaches a critical length, the specimen becomes mechanical unstable and fracture due to ductile overload occurs. The hydrogen contribution to the final fracture process is not significant.The influence of hydrogen on low cycle fatigue of 3.5NiCrMoV steel electrochemically hydrogen charged is studied. In the presence of hydrogen, the fatigue life decreases significantly by ≈70–80% (as illustrated in the figure) by: (i) the crack initiation period is decreased; and (ii) the crack growth rate is accelerated.
      PubDate: 2017-10-23T08:05:45.765029-05:
      DOI: 10.1002/adem.201700680
  • Challenges of Diffusion Bonding of Different Classes of Stainless Steels
    • Authors: Thomas Gietzelt; Volker Toth, Andreas Huell
      Abstract: Solid state diffusion bonding is used to produce monolithic parts exhibiting mechanical properties comparable to those of the bulk material. This requires diffusion of atoms across mating surfaces at high temperatures, accompanied by grain growth. In case of steel, polymorphy helps to limit the grain size, since the microstructure is transformed twice. The diffusion coefficient differs extremely for ferritic and austenitic phases. Alloying elements may shift or suppress phase transformation until the melting range. In this paper, diffusion bonding experiments are reported for austenitic, ferritic, and martensitic stainless steels possessing varying alloying elements and contents. Passivation layers of different compositions are formed, thus affecting the local diffusion coefficient and impeding diffusion across faying surfaces. As a consequence, different bonding temperatures are needed to obtain good bonding results, making it difficult to control the deformation of parts, since strong nonlinearities exist between temperature, bonding time, and bearing pressure. For martensitic stainless steel, it is shown that it is very easy to obtain good bonding results at low deformation, whereas ferritic and austenitic stainless steels require much more extreme bonding parameters.Diffusion bonding is employed for full cross-sectional joining of complex geometries. The graphical abstract shows a part for ITER (International Thermonuclear Experimental Reactor) made of austenitic stainless steel, containing 3D cooling structures. Thermally stable passivation layers make it difficult to form a monolithic part. Employing a self-stabilizing design, the bonding area is increased with process time, allowing to control deformation.
      PubDate: 2017-10-23T00:20:58.312674-05:
      DOI: 10.1002/adem.201700367
  • Fragmentation of α Grains Accelerated by the Growth of β Phase in
           Ti–5Al–2Sn–2Zr–4Mo–4Cr during Hot Deformation
    • Authors: Jin-Zhao Sun; Miao-Quan Li, Hong Li
      Abstract: The fragmentation of elongated α grains accelerated by the growth of β phase in Ti–5Al–2Sn–2Zr–4Mo–4Cr during hot deformation was examined using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It was determined that boundary splitting resulted in the fragmentation of αE. The kinked sharp α grains, which were formed with help of “civilian” growth of β phase, are necessary structures for the fragmentation of elongated α grains. In addition, the texture results showed an initial deviation from Burgers orientation relationship (OR) in α/β interphase boundaries, indicating that the “civilian” growth of the β phase based on the pre-existing β grain boundaries implied a constant loss of coherency in α/β interphase boundaries, which also accelerated the fragmentation of elongated α grains.The “civilian” growth of the β phase preferentially occurs in the location surrounded by DT, which promotes the formation of groove that plays an important role in the fragmentation of αE. The “ civilian” growth of the β phase based on the pre-existing β grain boundaries, suggesting a constant deviation from Burgers OR in α/β interphase boundaries, also accelerates the fragmentation of αE.
      PubDate: 2017-10-20T03:15:42.869267-05:
      DOI: 10.1002/adem.201700200
  • High-Entropy Alloys: Potential Candidates for High-Temperature
           Applications – An Overview
    • Authors: Sathiyamoorthi Praveen; Hyoung Seop Kim
      Abstract: Multi-principal elemental alloys, commonly referred to as high-entropy alloys (HEAs), are a new class of emerging advanced materials with novel alloy design concept. Unlike the design of conventional alloys, which is based on one or at most two principal elements, the design of HEA is based on multi-principal elements in equal or near-equal atomic ratio. The advent of HEA has revived the alloy design perception and paved the way to produce an ample number of compositions with different combinations of promising properties for a variety of structural applications. Among the properties possessed by HEAs, sluggish diffusion and strength retention at elevated temperature have caught wide attention. The need to develop new materials for high-temperature applications with superior high-temperature properties over superalloys has been one of the prime concerns of the high-temperature materials research community. The current article shows that HEAs have the potential to replace Ni-base superalloys as the next generation high-temperature materials. This review focuses on the phase stability, microstructural stability, and high-temperature mechanical properties of HEAs. This article will be highly beneficial for materials engineering and science community whose interest is in the development and understanding of HEAs for high-temperature applications.In recent years, high entropy alloys (HEAs) receive wide attention due to its unique alloy design concept and outstanding properties. This review presents a general overview of HEAs as a potential candidate for high-temperature applications. The need for the profound research on the high-temperature properties of HEAs is highlighted.
      PubDate: 2017-10-18T06:35:39.302184-05:
      DOI: 10.1002/adem.201700645
  • Study of Fatigue Behavior of Epoxy-Carbon Composites under Mixed Mode I/II
    • Authors: Clara Rocandio; Jaime Viña, Antonio Argüelles, Silvia Rubiera
      Abstract: This paper presents an experimental assessment of the initiation and propagation of interlaminar cracks under mixed mode I/II dynamic fracture loading of a composite material with an MTM45-1 epoxy matrix and unidirectional IM7 carbon-fiber reinforcement. The aims of the experimental program developed for this purpose are to determine, on the one hand, the initiation curves of the fatigue delamination process, understood as the number of load cycles needed to generate a fatigue crack, and on the other, the crack growth rate (delamination rate) for different percentages of static Gc, in both cases for two mode mixities (0.2 and 0.4) and for a tensile ratio R = 0.1. All this with the goal of quantifying the influence of the degree of mode mixity on the overall behavior of the laminate under fatigue loading. The results show that the energy release rate increases with increasing loading levels for both degrees of mode mixity and that the fatigue limit is located around the same percentages. However, crack growth rate behavior differs from one degree of mode mixity to the other. This difference in the behavior of the material may be due to the varying influence of mode I loading on the delamination process.The initiation curves of the fatigue delamination process of a composite materials with an MTM45-1 epoxy matrix and unidirectional IM7 carbon-fiber reinforcements have been obtained for two mode mixities and for a tensile ratio. Crack growth rate behavior differs from one degree of mode mixity to the other, being the cause the varying of mode I loading on the delamination process.
      PubDate: 2017-10-18T06:30:40.214583-05:
      DOI: 10.1002/adem.201700569
  • Reactive Structural Materials: Preparation and Characterization
    • Authors: Daniel L. Hastings; Edward L. Dreizin
      Abstract: Reactive structural materials, which can serve both as structural elements as well as a source of chemical energy released upon initiation have emerged as an important class of metal-based composites for use in various energetic systems. Such materials rely on a variety of exothermic reactions, from oxidation to formation of metal-metalloid and intermetallic phases. The rates of these reactions are as important as the energy that may be released, in order for them to occur at the time scales compatible with the requirements of applications. Therefore, chemical composition, scale at which reactive components are mixed, and the structure and morphology of materials are important and can be controlled by the method of preparation and compaction of the composite materials. Methods of preparation of the composite structures are briefly reviewed as well as methods of characterization of their mechanical and energetic properties. In addition to common thermo-analytical and static mechanical property measurements, dynamic tests of mechanical properties as well as ignition and combustion experiments are necessary to understand the fragmentation, initiation, and heat release expected for these materials when they are stimulated by an impact, shock, or rapid heating. Reaction mechanisms are studied presently for the thin layers and small samples of reactive materials initiated in carefully designed experiments. In other experiments, impact and explosive initiation are characterized for larger material compacts in the conditions imitating practical scenarios. Examples of results describing thermal, impact, and explosive initiation of some of the reactive materials are presented.Reactive structural materials serve both as structural elements and a source of chemical energy released upon initiation. Chemical composition, scale at which reactive components are mixed, and the structure of materials are controlled by the method of preparation and compaction of the composites. Material types, their synthesis and methods of characterization of their mechanical and energetic properties are reviewed.
      PubDate: 2017-10-17T07:46:53.032036-05:
      DOI: 10.1002/adem.201700631
  • Liquid PMMA: A High Resolution Polymethylmethacrylate Negative Photoresist
           as Enabling Material for Direct Printing of Microfluidic Chips
    • Authors: Frederik Kotz; Karl Arnold, Stefan Wagner, Werner Bauer, Nico Keller, Tobias M. Nargang, Dorothea Helmer, Bastian E. Rapp
      Abstract: Polymethymethacrylate (PMMA) is one of the most important thermoplasts and a commonly used material in microsystem fabrication, for example, microfluidics owning mainly to its optical transparency, biocompatibility, low autofluorescence, and low cost. However, being a thermoplastic material PMMA is typically structured using industrial replication techniques making PMMA unsuitable for rapid prototyping. The fact that neither material nor processing technique can be directly transferred from laboratory to industrial state makes the research-to-business conversion often extremely difficult in microfluidics since material properties have a major impact on the final system behavior. This paper presents “Liquid PMMA,” a fast curing viscous PMMA prepolymer which can be used as a negative photoresist and directly structured using ultraviolet or visible light with tens of micron resolution and smooth surfaces. Using this technique microfluidic chips in PMMA can be fabricated within minutes. The cured Liquid PMMA parts show the same high optical transparency, low autofluorescence, and surface properties like commercial PMMA. In this way, microfluidic chips can be rapidly developed and optimized on the laboratory scale in the same material which is later on used on the industrial scale.Polymethylmethacrylate (PMMA) is an important industrial material for microfluidics owing mainly to its optical transparency, biocompatibility, and low cost. We present “Liquid PMMA,” a fast curing PMMA prepolymer which can be used as a negative photoresist and directly structured by light. PMMA microchips can be structured within minutes.
      PubDate: 2017-10-17T07:45:40.963088-05:
      DOI: 10.1002/adem.201700699
  • Using Post-Deformation Annealing to Optimize the Properties of a ZK60
           Magnesium Alloy Processed by High-Pressure Torsion
    • Authors: Seyed A. Torbati-Sarraf; Shima Sabbaghianrad, Terence G. Langdon
      Abstract: A ZK60 magnesium alloy with an initial grain size of ≈10 µm is processed by high-pressure torsion (HPT) through 5 revolutions under a constant compressive pressure of 2.0 GPa with a rotation speed of 1 rpm. An average grain size of ≈700 nm is achieved after HPT with a high fraction of high-angle grain boundaries. Tensile experiments at room temperature show poor ductility. However, a combination of reasonable ductility and good strength is achieved with post-HPT annealing by subjecting samples to high temperatures in the range of 473–548 K for 10 or 20 min. The grain size and texture changes are also examined by electron back scattered diffraction (EBSD) and the results compared to long-term annealing for 2500 min at 450 K. The results of this study suggest that a post-HPT annealing for a short period of time may be effective in achieving a reasonable combination of strength and ductility.The production of ultrafine grained structure through the severe plastic deformation processes is of increasing interests in lightweight materials. Magnesium alloys show poor ductility at room temperature after severe plastic deformation. The results of this study suggest that a post-HPT annealing for a short period of time can be effective in achieving a reasonable combination of strength and ductility.
      PubDate: 2017-10-16T01:46:40.061658-05:
      DOI: 10.1002/adem.201700703
  • Nature-Inspired Lightweight Cellular Co-Continuous Composites with
           Architected Periodic Gyroidal Structures
    • Authors: Oraib Al-Ketan; Ahmad Soliman, Ayesha M. AlQubaisi, Rashid K. Abu Al-Rub
      Abstract: Shell-core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three-dimensional (3D), periodic, co-continuous, and complex composite materials made of a hard-shell and soft-core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell-core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell-core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.The figure shows designed and 3D printed architected co-continuous composites with rigid shell and soft core configuration. The proposed co-continuous composite employs a topology-property relationship that allows controlling the mechanical and physical properties by tuning its architecture.
      PubDate: 2017-10-16T01:05:42.596707-05:
      DOI: 10.1002/adem.201700549
  • Novel 3D-Printed Hybrid Auxetic Mechanical Metamaterial with
           Chirality-Induced Sequential Cell Opening Mechanisms
    • Authors: Yunyao Jiang; Yaning Li
      Abstract: New hybrid auxetic chiral mechanical metamaterial are designed and fabricated via multi-material 3D printing. Due to the chirality-induced rotation, the material have unique sequential cell-opening mechanisms. Mechanical experiments on the 3D printed prototypes and systematic FE simulations show that the effective stiffness, the Poisson's ratio and the cell-opening mechanisms of the new design can be tuned in a very wide range by tailoring two non-dimensional parameters: the cell size ratio and stiffness ratio of component materials. As example applications, sequential particle release mechanisms and color changing mechanisms of the new designs are also systematically explored. The present new design concepts can be used to develop new multi-functional smart composites, sensors and/or actuators which are responsive to external load and/or environmental conditions for applications in drug delivery and color changing for camouflage.Novel hybrid auxetic chiral mechanical metamaterial are designed and fabricated via multi-material 3D printing. Due to chirality-induced rotation, the new auxetic mechanical metamaterials have unique sequential cell-opening mechanisms under uni-axial tension. As demos, the present new design concepts are used to develop multi-functional smart materials for sequential particle release and color changing for camouflage.
      PubDate: 2017-10-11T08:10:42.053775-05:
      DOI: 10.1002/adem.201700744
  • Mechanical and Electromagnetic Interference Shielding Behavior of C/SiC
           Composite Containing Ti3SiC2
    • Authors: Xiaomeng Fan; Xiaowei Yin, Yanzhi Cai, Litong Zhang, Laifei Cheng
      Abstract: In order to obtain the composites with the integration of structural and functional properties, Ti3SiC2 is introduced into C/SiC due to its excellent damage tolerance and electromagnetic interference (EMI) shielding properties. C/SiC–Ti3SiC2 has the lower tensile strength, while the higher compressive strength than C/SiC. The penetration energy of C/SiC–Ti3SiC2 in the impact experiment is improved at least three times than that of C/SiC, resulting from the improved damage tolerance. With the introduction of Ti3SiC2, the EMI shielding effectiveness increases from 31 to 41 dB in X-band (8.2 to 12.8 GHz) due to the increase of electrical conductivity. C/SiC–Ti3SiC2 reveals the great potential as structural and functional materials based on the multi-functional properties.With the introduction of Ti3SiC2 by liquid silicon infiltration, the dense inter-bundle matrix with high damage-tolerance and electrical-conductivity can be obtained for C/SiC–Ti3SiC2, resulting in the better compressive strength, impact resistance, and electromagnetic interference shielding properties than those of C/SiC, which reveals the great potential as structural and functional materials.
      PubDate: 2017-10-11T08:01:15.82601-05:0
      DOI: 10.1002/adem.201700590
  • Influences of Friction Stir Welding and Post-Weld Heat Treatment on
           Al–Cu–Li Alloy
    • Authors: Yi Lin; Change Lu, Chengyang Wei, Ziqiao Zheng
      Abstract: In this paper, the influences of friction stir welding (FSW) and post-weld heat treatment (PWHT) on the microstructures and tensile properties of Al–Cu–Li alloy are investigated. After FSW, strengthen loss occurred in the welding area. Remarkable softening occurs in the thermo-mechanically affected zone (TMAZ) resulting from dissolution of Al3Li (δ′) phases. Recrystallization and precipitation of ultra-fine δ′ phases take place in the nugget zone (NZ) that lightens the softening degree of this zone. A noteworthy enhancement in the hardness and tensile strength of the joint is achieved after T8 re­aging treatment (3% − pre-deformation, 30 h at 152 °C). However, re-solution treatment coupled with re-aging treatment leads to ductility deterioration in the joint because coplanar slip of coarse Al3Li phases induces severe stress concentration during plastic deformation.The paper investigates the microstructure and mechanical properties evolution of Al–Cu–Li alloy during FSW and PHWTs. The results show that dissolution of strengthening phases induces the strength loss after FSW, and the T8 re-aging treatment can effectively enhances the strength of joint without the ductility being excessively deteriorated.
      PubDate: 2017-10-10T06:21:18.021152-05:
      DOI: 10.1002/adem.201700652
  • 3-D Printing and Development of Fluoropolymer Based Reactive Inks
    • Authors: Fidel D. Ruz-Nuglo; Lori J. Groven
      Abstract: Engineering reactive materials is an ever present goal in the energetics community. The desire is to have energetics configured in such a manner that performance is tailored and energy delivery can be targeted. Additive manufacturing (3-D printing) is one area that could significantly improve our capabilities in this area, if adequate formulations are developed. In this paper, fluoropolymer based reactive inks are developed with micron (mAl) and nanoscale aluminum (nAl) serving, as the fuel at high solids loading (up to 67 wt%) and their viscosity required for 3-D printing is detailed. For the pen-type technique and valves used in this work, it is required to have viscosities on the order of 104–105 cP. For printed traces with apparent diameters under
      PubDate: 2017-10-09T07:10:53.772388-05:
      DOI: 10.1002/adem.201700390
  • Galvanic Corrosion and Mechanical Behavior of Fiber Metal Laminates of
           Metallic Glass and Carbon Fiber Composites
    • Authors: Lee Hamill; Douglas C. Hofmann, Steven Nutt
      Abstract: The possibility of galvanic corrosion typically prohibits the pairing of carbon fiber and aluminum in a fiber metal laminate (FML). In this study, the authors describe a new type of FML comprised of alternating layers of bulk metallic glass (BMG) and carbon fiber reinforced polymer (CFRP) composite. The authors compare the galvanic coupling and mechanical behavior of an Al-based FML and a BMG-CFRP FML. Results show that when paired with CFRPs, BMG exhibits far less galvanic corrosion than aluminum paired with CFRP. In fact, the corrosion between BMG and CFRP is similar in magnitude to the corrosion between aluminum and glass fiber, the two constituent materials of GLARE, the most widely used FML. While interlaminar shear strength and flexural strength are similar for both FML types, the tensile strength and modulus of BMG-based FMLs are greater than those of Al-based FMLs.The galvanic corrosion resistance and mechanical performance of two fiber metal laminates are compared. Results show negligible galvanic corrosion and increased tensile strength and modulus in BMG-CFRP laminates when compared to AL-CFRP counterparts. To date, very few galvanic corrosion resistant options exist for CFRP-based FMLs, and the results of this study expand those options.
      PubDate: 2017-10-09T02:25:49.736964-05:
      DOI: 10.1002/adem.201700711
  • Optimization of Composite Foam Concept for Protective Helmets to Mitigate
           Rotational Acceleration of the Head in Oblique Impacts: A Parametric Study
    • Authors: Yasmine Mosleh; Leonard Pastrav, Aart Willem van Vuure, Bart Depreitere, Jos Vander Sloten, Jan Ivens
      Abstract: Rotational acceleration of the head is known to be the cause of traumatic brain injuries. It was hypothesized that by introducing anisotropy in a foam liner in head protection applications, for example, protective helmets, rotational acceleration transmitted to the head can be further mitigated. Therefore, composite foam with a cylinder/matrix configuration with anisotropy at “macro level” is proposed as a smart structural solution to replace single layer foam headliners of the same weight and thickness. In this paper, a parametric study on the cylinder/matrix configuration is performed and the results are compared with these of single layer expanded polystyrene foam. The structure is subsequently optimized for the best performance in mitigation of rotational acceleration and velocity. Oblique impact results show that the parameters such as the number of cylinders in a given structure, and the compliance of the matrix foam significantly affect the extent of rotational acceleration and velocity mitigation. Optimized composite foam configurations are subsequently proposed and they demonstrate a mitigation of rotational acceleration and velocity up to 44 and 19%, respectively. Moreover, relevant global head injury criteria such as HIC (Head Injury Criterion), RIC (Rotational Injury Criterion), HIPmax (Head Impact Power), GAMBIT (Generalised Acceleration Model for Brain Injury Threshold), and BrIC (Brain Injury Criterion) demonstrated reduction up to 27, 67, 31, 26, and 19%, respectively.In this paper, a parametric study on composite foam with cylinder/matrix configuration is performed to optimize the structure for mitigation of head rotational acceleration during oblique impact. The results show that parameters such as the number of cylinders in the structure, and the compliance of the matrix foam significantly affect the extent of mitigation of head rotational acceleration.
      PubDate: 2017-10-09T02:25:37.747543-05:
      DOI: 10.1002/adem.201700443
  • The Fabrication and Characterization of Bimodal Nanoporous Si with
           Retained Mg through Dealloying
    • Authors: Tyler L. Maxwell; T. John Balk
      Abstract: The fabrication and characterization of bimodal nanoporous silicon films with retained magnesium, achieved through a novel approach utilizing free corrosion dealloying of precursor Si–Mg films in distilled water, is studied. Investigation of film structure and chemical composition using various techniques reveals important characteristics potentially relevant to lithium-ion battery applications. Dealloying of precursor films results in a hierarchal structure, where larger ligaments have an average width of 83 nm and smaller ligaments an average width of 19 nm. A thin, porous surface layer is present on most dealloyed films and is largely composed of magnesium and silicon oxides, as verified by XPS surface analysis. TEM studies reveal that as-dealloyed films are amorphous, but nanocrystalline silicon grains form after vacuum annealing at 500 °C. EDS mapping and XPS reveal three distinct chemical composition regions through the film thickness, where residual magnesium generally increases as a function of film thickness, with the highest amount of retained magnesium at the surface. The ligament size, composition, and structure, combined with the simple, non-hazardous nature of the dealloying method, make this an attractive material and processing technique for efficient and scalable production of lithium-ion battery anode material.This paper presents a facile approach to create bimodal nanoporous silicon films with residual magnesium, by dealloying sputter-deposited silicon-magnesium precursors in distilled water. The microstructure of films before and after annealing is characterized with SEM and TEM, while chemical composition is analyzed with EDS and XPS surface analysis. This material's characteristics make it a promising candidate for lithium–ion battery applications.
      PubDate: 2017-10-09T01:25:42.579217-05:
      DOI: 10.1002/adem.201700519
  • Rationally Designed Silicon Nanostructures as Anode Material for
           Lithium-Ion Batteries
    • Authors: Tong Shen; Zhujun Yao, Xinhui Xia, Xiuli Wang, Changdong Gu, Jiangping Tu
      Abstract: Silicon (Si) is promising for high capacity anodes in lithium-ion batteries due to its high theoretical capacity, low working potential, and natural abundance. However, there are two main drawbacks that impede its further practical applications. One is the huge volume expansion generating during lithiation and delithiation progresses, which leads to severe structural pulverization and subsequently rapid capacity fading of the electrode. The other is the relatively low intrinsic electronic conductivity, therefore, seriously impacting the rate performance. In the past decades, numerous efforts have been devoted for improving the cycling stability and rate capability by rational designs of different nanostructures of Si materials and incorporations with some conductive agents. In this review, the authors summarize the exciting recent research works and focus on not only the synthesis techniques, but also the composition strategies of silicon nanostructures. The advantages and disadvantages of the nanostructures as well as the perspective of this research field are also discussed. We aim to give some reference for engineering application on Si anodes in lithium ion batteries.The authors summarize the strategies that developed lately for improving the electrochemical performance of Si materials. Special focus in this review is the recent progresses in the rational fabrication of Si nanostructures with multiple morphologies, including nanoparticles, nanowires, thin films, and porous structures. Moreover, further improvement tactics, such as collaborating with carbonaceous materials, conductive polymers, and alloy materials are also discussed.
      PubDate: 2017-10-05T08:32:53.56802-05:0
      DOI: 10.1002/adem.201700591
  • Combined Microwave and Laser Heating for Glazing of 8Y–ZrO2 and
    • Authors: Sebastian Lehmann; Jens Böckler, Monika Willert-Porada, Andreas Rosin, Christian Richter
      Abstract: Sintered porous yttria-stabilized zirconia and zirconia composite ceramics with zirconium silicate are surface glazed by Laser-Assisted Microwave Plasma Processing (LAMPP). Suitable process parameters for surface glazing are determined for those ceramics. The plasma process is monitored by means of pyrometry and optical emission spectroscopy. In order to prove the quality of the surface glazing and to characterize hot corrosion resistance, tests with molten vanadium pentoxide are performed. After 4 h of exposure, the penetration depth of the molten salt is investigated as a function of ceramic composition and pre-treatment by glazing. Upon hot corrosion testing of glazed and non-glazed ceramics, the molten vanadium pentoxide reacts selectively with yttrium oxide, forming yttrium vanadate, and causes crack formation in the zirconia ceramics due to transition to monoclinic zirconia. The results for LAMPP-glazed ceramics show, that a surficial melting phase is achieved because process temperatures exceed 3000 °C. Hence, a dense, crack-free and hardness-enhanced surface layer achieves a better resistance to hot corrosion as compared to non-glazed ceramics. Due to LAMPP-glazing, the vanadium ingress is reduced from 33 to 7 μm for yttria-stabilized zirconia and from 104 to 17 μm for zirconia composite ceramic. Reactions and microstructural changes taking place upon LAMP-Processing are discussed.Suitable process parameters for surface glazing by Laser-Assisted Microwave Plasma Processing of sintered porous zirconia-based ceramics are determined. The plasma process is monitored by means of pyrometry and optical emission spectroscopy. Microstructural investigation and phase analysis is performed before and after hot corrosion test with molten vanadium pentoxide. The dense, crack-free surface layer provides a better resistance to hot corrosion.
      PubDate: 2017-10-04T02:56:26.085561-05:
      DOI: 10.1002/adem.201700615
  • Synthesis of Composite Nanosheets of Graphene and Boron Nitride and Their
           Lubrication Application in Oil
    • Authors: Yuchen Liu; Srikanth Mateti, Chao Li, Xuequan Liu, Alexey M. Glushenkov, Dan Liu, Lu Hua Li, Daniel Fabijanic, Ying Chen
      Abstract: Composite nanosheets of graphene and boron nitride have been produced in large quantities for the first time using high-energy ball milling in ammonia gas as an exfoliation agent. The anti-wear properties of the composite nanosheets as a lubricant additive are investigated via a four-ball method. The results show that the composite nanosheets are exfoliated from the commercial graphite and h-BN powders and combined into graphene/BN composite nanosheets during the ball milling process. The composite nanosheets formed have diameters larger than 200 nm and consist of heterostructures of approximately 10 monolayers of graphene and BN. The composite nanosheets exhibit better wear resistance and friction reduction properties than the homogeneous nanosheets because of the stronger interaction between graphene and BN nanosheets, which can effectively improve the anti-wear properties of mineral base oil as a lubricant additive.The graphene/BN composite nanosheets produced by gas-assisted ball milling process form a protection film on the testing material surface leading to a lower friction coefficient and improved anti-wear properties.
      PubDate: 2017-09-29T10:41:35.337143-05:
      DOI: 10.1002/adem.201700488
  • Understanding Wear Interface Evolution to Overcome Friction and Restrain
           Wear of TiAl–10 wt%Ag Composite
    • Authors: Kang Yang; Hongru Ma, Xiyao Liu, Qiang He
      Abstract: The main objective of this paper is to study wear interface evolution for analyzing the of friction and wear property of TiAl–10 wt%Ag composite. The results show that the friction coefficient and wear rate of TiAl–10 wt%Ag rapidly reduce at 0–25 min and rhythmically fluctuate at 25–60 min. TiAl–10 wt%Ag at 60–240 min obtains low friction and less wear. It is concluded that silver with the low shearing strength of about 125 MPa shows the eminent plastic deformation on wear interface. It effectively reduces friction resistance and material loss, cause TiAl–10 wt%Ag to obtain low friction coefficient, and less wear rate at 0–25 min. Increased silver content, reduces oxide content, and varies wear mechanisms cause the repeating variation of friction resistance and material loss, which results in the rhythmical fluctuation of friction coefficient and wear rate at 25–60 min. High silver contents exist on smooth wear interfaces, exhibit the eminent plastic deformation to lower friction and reduce wear. TiAl–10 wt%Ag obtains the low friction and less wear at 60–240 min.At 240 min, small plastic deformation body forms on smooth wear interface. It indicates that the main wear mechanism of TiAl–10 wt%Ag is plastic deformation. The FESEM surface micro-morphology of wear interface in rectangular region is clearly exhibited. Solid lubricant silver is uniformly distributed on wear interface, and exhibits excellent plastic deformation, leading to low friction and less wear.
      PubDate: 2017-09-28T11:27:37.882845-05:
      DOI: 10.1002/adem.201700637
  • Porous Polymer Membranes by Hard Templating – A Review
    • Authors: Mario Stucki; Michael Loepfe, Wendelin J. Stark
      Abstract: Membranes are designed to bridge a precise separation process at the nanoscale with industrial applications running at cubic meters per hour. This review outlines materials applied in membrane production with a particular focus on polymers. Membrane performance and created value are directly linked to controlled pore formation. Their economic relevance has created a number of large companies and associated academic research at top institutions. The authors review, therefore, starts from well-established techniques applied in products and then moves on to evolving concepts from academia. Pore formation through hard templating is a versatile field for separation processes. A more detailed view is given on the two known concepts for nanopore formation, namely colloidal templates and random hard salt templating. A comparison between these two concepts underlines their relevance to combine a process specific separation with large scale manufacturing requirements (i.e., upscale possibility, flexible process control and environmental impact).Membranes bridge nanoscale separation with high volume throughput. The development of membranes has resulted in a large variety of materials used for porous separators. This article introduces the relevant membrane processes and focuses on porous polymer membranes. Its main body explains sacrificial hard templating. Ordered colloidal crystals are compared to random templates with respect to their scalability and application.
      PubDate: 2017-09-28T00:05:53.544922-05:
      DOI: 10.1002/adem.201700611
  • A Combined Electromagnetic Levitation Melting, Counter-Gravity Casting,
           and Mold Preheating Furnace for Producing TiAl Alloy
    • Authors: Jieren Yang; Hu Wang, Yulun Wu, Xuyang Wang, Rui Hu
      Abstract: In this work, the authors describe the development of TiAl castings over a wide range of approaches. To overcome casting defects and cracks that appear in TiAl castings, a novel furnace is designed and constructed. The design combines induction skull melting, counter-gravity casting, and mold heating, which facilitates both filling and microstructure formation via a controllable process. This aim is to improve shaping capabilities and microstructural control for TiAl castings. Melting and casting experiments on TiAl alloys with a nominal composition corresponding to Ti–48Al–2Cr–2Nb (at%) are carried out and discussed. X-ray examinations indicate that the shaping of the TiAl components dose not contain macro casting defects, validating the advantages of this technique. The results are of interest to researchers devoted to technical innovations and modifications for TiAl casting at the industrial scale.The design combines induction skull melting, counter-gravity casting and mold heating a), which facilitates the shaping of the TiAl components b and c), and the decreasing of the defect d) via a controllable process. The results are of interest to researchers devoted to produce high-quality TiAl castings.
      PubDate: 2017-09-25T11:11:37.441471-05:
      DOI: 10.1002/adem.201700526
  • Tensile Strength Evolution and Damage Mechanisms of Al–Si Piston Alloy
           at Different Temperatures
    • Authors: Meng Wang; Jianchao Pang, Yu Qiu, Haiquan Liu, Shouxin Li, Zhefeng Zhang
      Abstract: The Al–Si piston alloys always bear different temperatures because of its peculiar component structure and service condition. Therefore, the tensile strength, elongation to fracture, and corresponding damage mechanisms of Al12SiCuNiMg piston alloys (ASPA) have been investigated with in situ technique at different temperatures. The tensile properties show two-stage tendencies: the former stage (25–280 °C) is determined by easily broken phases with inherent brittleness (such as primary Si), and the fracture behavior presents rapid brittle fracture after reaching the critical stress (about 430 MPa, based on in situ technique and the elastic stress field model). The later one (280–425 °C) is dominated by particles debonding and θphase coarsening. The plastic deformation behavior, dynamic recovery, and flow process become more significant on account of thermal activation. The Considère criterion h = K indicates that the transition of damage behaviors from insufficient local strength to insufficient matrix strength and the corresponding failure model shifts from brittle to ductile fracture. Based on the damage mechanisms, the elastic field model and thermal activation relation model have been established to characterize the strength of the ASPA at different temperature ranges.The tensile properties of Al-Si alloy show two-stage tendencies: the former stage is 25–280 °C and later one is 280–425 °C. Fracture mechanism changes from broken Si (insufficient local strength) at 25 °C to debonding particles (insufficient matrix strength) at 350 °C.The elastic field model and thermally activation relation model have been established to characterize the strength at different temperature ranges.
      PubDate: 2017-09-25T01:52:22.944493-05:
      DOI: 10.1002/adem.201700610
  • High-Entropy Alloy (HEA)-Coated Nanolattice Structures and Their
           Mechanical Properties
    • Authors: Libo Gao; Jian Song, Zengbao Jiao, Weibing Liao, Junhua Luan, James Utama Surjadi, Junyang Li, Hongti Zhang, Dong Sun, Chain Tsuan Liu, Yang Lu
      Abstract: Nanolattice structure fabricated by two-photon lithography (TPL) is a coupling of size-dependent mechanical properties at micro/nano-scale with structural geometry responses in wide applications of scalable micro/nano-manufacturing. In this work, three-dimensional (3D) polymeric nanolattices are initially fabricated using TPL, then conformably coated with an 80 nm thick high-entropy alloy (HEA) thin film (CoCrFeNiAl0.3) via physical vapor deposition (PVD). 3D atomic-probe tomography (APT) reveals the homogeneous element distribution in the synthesized HEA film deposited on the substrate. Mechanical properties of the obtained composite architectures are investigated via in situ scanning electron microscope (SEM) compression test, as well as finite element method (FEM) at the relevant length scales. The presented HEA-coated nanolattice encouragingly not only exhibits superior compressive specific strength of ≈0.032 MPa kg−1 m3 with density well below 1000 kg m−3, but also shows good compression ductility due to its composite nature. This concept of combining HEA with polymer lattice structures demonstrates the potential of fabricating novel architected metamaterials with tunable mechanical properties.High entropy alloy (HEA)-coated nanolattice structures with tunable mechanical properties have been developed, with the characteristics feature sizes spanning from 5 nm to 20 μm.
      PubDate: 2017-09-20T03:11:21.139452-05:
      DOI: 10.1002/adem.201700625
  • Nucleation Crystallography of Ni Grains on CrFeNb Inoculants Investigated
           by Edge-to-Edge Matching Model in an IN718 Superalloy
    • Authors: Wenchao Yang; Pengfei Qu, Lin Liu, Ziqi Jie, Taiwen Huang, Feng Wang, Jun Zhang
      Abstract: In this work, the nucleation crystallography of CrFeNb intermetallic particles as a grain refiner for Ni-based IN718 superalloys is studied using Edge-to-Edge Matching model. Three distinguishable orientation relationships between CrFeNb intermetallic particles and Ni grains are well predicted: [11¯0]Ni∖∖[1¯21¯0]CrFeNb, (111)Ni 1.28° from (0004)CrFeNb, [11¯0]Ni∖∖[1¯21¯0]CrFeNb, (111)Ni 1.32° from (202¯0)CrFeNb, and [11¯0]Ni//[0001]CrFeNb, (111)Ni 0.72° from (202¯0)CrFeNb. The results indicate that CrFeNb intermetallic particles have a strong nucleation potency as an effective grain refiner for Ni-based superalloy and the existence of semi-coherent interfaces between the CrFeNb intermetallic particles and Ni grains. Furthermore, the IN718 superalloy is used to experimentally validate the grain refinement effect of CrFeNb intermetallic particles, showing that its grain size is obviously refined from 8.60 to 1.23 mm. And, the corresponding heterogeneous nucleation mechanism of grain refinement at the atomic level is further identified.The nucleation crystallography of CrFeNb particle on Ni grain is studied using Edge-to-Edge Matching model. Three orientation relationships are predicted to indicate a semi-coherent interface. A relaxation of some atoms may be necessary to minimize the nucleation interface energy. IN718 superalloy is used to validate the grain refinement effect.
      PubDate: 2017-09-20T02:45:26.937527-05:
      DOI: 10.1002/adem.201700568
  • Mechanical Properties of a Novel Zero Poisson's Ratio Honeycomb
    • Authors: Yu Chen; Ming-Hui Fu
      Abstract: In this paper, a novel honeycomb is proposed by embedding a rib into every cell of the existing zero Poisson's ratio (ZPR) configuration, semi re-entrant honeycomb (SRH). Analytical model is developed to investigate the in-plane mechanical properties of the new honeycomb, and the resulting theoretical expressions are compared with the experimental tests and numerical results obtained from two different finite element (FE) models (3D beam model and 3D solid model), leading to a good correlation. FE analysis, analytical modeling, and experimental tests of the new honeycomb show that it can achieve ZPR effect in two principal directions. For further studies, parameters analyses are carried out to explore the dependence of the in-plane mechanical properties versus the geometric parameters. The results show that bending is the dominated deformation model when the new honeycomb is compressed along the x- direction, while stretch controlled in the y- directional compression. It is remarkable that the new proposed honeycomb features superior specific stiffness and more flexible in mechanical properties tailoring compared to the other ZPR honeycombs in the literature. Given these benefits, the new honeycomb may be promising in some practical applications.Honeycombs with zero Poisson's ratio (ZPR) are increasingly used in many important fields because of their unusual properties. A novel ZPR honeycomb is proposed by embedding a rib into every cell of the existing ZPR configuration, semi re-entrant honeycomb (SRH). The new proposed ZPR honeycomb exhibits superior specific stiffness and shows flexible in mechanical properties tailoring. Given these benefits, it may be promising in some applications.
      PubDate: 2017-09-19T01:20:37.058205-05:
      DOI: 10.1002/adem.201700452
  • ZnO Coated Anodic 1D TiO2 Nanotube Layers: Efficient Photo-Electrochemical
           and Gas Sensing Heterojunction
    • Authors: Siowwoon Ng; Petr Kuberský, Milos Krbal, Jan Prikryl, Viera Gärtnerová, Daniela Moravcová, Hanna Sopha, Raul Zazpe, Fong Kwong Yam, Aleš Jäger, Luděk Hromádko, Ludvík Beneš, Aleš Hamáček, Jan M. Macak
      Abstract: The authors demonstrate, in this work, a fascinating synergism of a high surface area heterojunction between TiO2 in the form of ordered 1D anodic nanotube layers of a high aspect ratio and ZnO coatings of different thicknesses, produced by atomic layer deposition. The ZnO coatings effectively passivate the defects within the TiO2 nanotube walls and significantly improve their charge carrier separation. Upon the ultraviolet and visible light irradiation, with an increase of the ZnO coating thickness from 0.19 to 19 nm and an increase of the external potential from 0.4–2 V, yields up to 8-fold enhancement of the photocurrent density. This enhancement translates into extremely high incident photon to current conversion efficiency of ≈95%, which is among the highest values reported in the literature for TiO2 based nanostructures. In addition, the photoactive region is expanded to a broader range close to the visible spectral region, compared to the uncoated nanotube layers. Synergistic effect arising from ZnO coated TiO2 nanotube layers also yields an improved ethanol sensing response, almost 11-fold compared to the uncoated nanotube layers. The design of the high-area 1D heterojunction, presented here, opens pathways for the light- and gas-assisted applications in photocatalysis, water splitting, sensors, and so on.Ultrathin and homogeneous ZnO coatings within high aspect ratio TiO2 nanotubular structure are demonstrated. ALD ZnO coatings within high surface area TiO2 nanotubes layer form a heterojunction with excellent photoelectrochemical activity and good ethanol sensing response. These enhancements are contributed by the passivated surface traps on tube wall, increased light absorption, close match of coating thickness, and Debye length.
      PubDate: 2017-09-19T01:20:26.109066-05:
      DOI: 10.1002/adem.201700589
  • Strategies for Drug Encapsulation and Controlled Delivery Based on
           Vapor-Phase Deposited Thin Films
    • Authors: Alberto Perrotta; Oliver Werzer, Anna Maria Coclite
      Abstract: Vapor-phase deposition methods allow the synthesis and engineering of organic and inorganic thin films, with high control on the chemical composition, physical properties, and conformality. In this review, the recent applications of vapor-phase deposition methods such as initiated chemical vapor deposition (iCVD), plasma enhanced chemical vapor deposition (PE-CVD), and atomic layer deposition (ALD), for the encapsulation of active pharmaceutical drugs are reported. The strategies and emergent routes for the application of vapor-deposited thin films on the drug controlled release and for the engineering of advanced release nanostructured devices are presented.Vapor-phase deposition methods allow the synthesis of (in)organic thin films, with high control on the chemical-physical properties and conformality. In this review, the encapsulation strategies of active drug molecules by means of vapor phase deposition processes are reported. The effects of (pre-) treatment and thin film deposition on controlled drug release and morphology are also reviewed, together with future perspectives and ‘smart’ device applications.
      PubDate: 2017-09-19T00:16:03.700173-05:
      DOI: 10.1002/adem.201700639
  • Sub-Micron Anisotropic InP-based III–V Semiconductor Material Deep
           Etching for On-Chip Laser Photonics Devices
    • Authors: Doris Keh-Ting Ng; Chee Wei Lee, Vivek Krishnamurthy, Qian Wang
      Abstract: Two InP-based III–V semiconductor etching recipes are presented for fabrication of on-chip laser photonic devices. Using inductively coupled plasma system with a methane free gas chemistry of chlorine and nitrogen at a high substrate temperature of 250 °C, high aspect ratio, anisotropic InP-based nano-structures are etched. Scanning electron microscopy images show vertical sidewall profile of 90° ± 3°, with aspect ratio as high as 10. Atomic Force microscopy measures a smooth sidewall roughness root-mean-square of 2.60 nm over a 3 × 3 μm scan area. The smallest feature size etched in this work is a nano-ring with inner diameter of 240 nm. The etching recipe and critical factors such as chamber pressure and the carrier plate effect are discussed. The second recipe is of low temperature (−10 °C) using Cl2 and BCl3 chemistry. This recipe is useful for etching large areas of III–V to reveal the underlying substrate. The availability of these two recipes has created a flexible III–V etching platform for fabrication of on-chip laser photonic devices. As an application example, anisotropic InP-based waveguides of 3 μm width are fabricated using the Cl2 and N2 etch recipe and waveguide loss of 4.5 dB mm−1 is obtained.Two InP-based III-V semiconductor etching recipes are presented for fabrication of on-chip laser photonic devices using inductively coupled plasma system with a methane free gas chemistry. The smallest feature size etched in this work is a nano-ring with inner diameter of 240 nm. InP-based waveguides of 3 μm width fabricated give a waveguide loss of 4.5 dB mm–1.
      PubDate: 2017-09-18T08:06:10.535529-05:
      DOI: 10.1002/adem.201700465
  • Multi-Stable Mechanical Structural Materials
    • Authors: Lingling Wu; Xiaoqing Xi, Bo Li, Ji Zhou
      Abstract: Energy absorbing is an important and desirable property in mechanical and civil engineering. Here, a proof-of-concept method is presented as a new approach to achieve artificial mechanical materials with tunable compressive behavior for energy absorbing constructed from unit cells with a snap fit structure. The artificial structure undergoes a series of stable configurations derived from the sequential insertion of the plug into the groove of the snap fit. Both, experimental and simulation results manifest the multi-stable and tunable mechanical properties of the structure. The mechanical energy dissipated by the proposed structure is demonstrated to be dependent on the lead-in angle of the snap fit and the deflection ratio of the groove, as well as on the coefficient of friction between the plug and the groove of the snap fit. The system designed, herein, exhibits mechanical properties that can be tuned not only by adjusting the geometric parameters, but also by tuning the coefficient of friction between the plug and the groove, allowing the mechanical properties to be tailored post-fabrication. Furthermore, the proposed model can be extended to the macro-, micro-, or nanoscales. These findings provide a simple method to obtain artificial materials with tunable energy absorbing properties, which can be applied in areas such as the design of automobile bumpers and foldable devices that facilitate their transportation.In this paper, the authors proposed a new class of mechanical structural material with multi-stable mechanical properties for energy absorbing and demonstrated its fabrication using Sylgard® 184 silicone. The proposed model is constructed from unit cells having a snap fit structure, which has two stable configurations derived from the insertion of the plug into the groove of the snap fit. During the deformation, the tilting beams store a portion of energy, while the remaining energy is dissipated by the mechanical friction effect between the plug and groove of the snap fit. Besides, the energy absorbed (E_in) and the energy required to break the second equilibrium state (E_out) can be tuned independently. The relationships between the mechanical performance and the geometric parameters of the snap fit are investigated via both simulations and experiments. Adjustable energy absorption properties are obtained by changing the width ratio, the lead-in angle, and the coefficient of friction of the snap fit, which permits a more practicable method to tune the mechanical properties of the structural material. The mechanism proposed, herein, is theoretically scale-independent, that is, the manipulation of the mechanical properties can be extended to the micro- or nanoscale, if appropriate fabrication processes are available. This approach proves to be a low-cost, easily accessible, and reusable method that has a broad application potential in industry, such as in the design of automobile bumper beams, vibration isolation materials, and foldable instruments.
      PubDate: 2017-09-18T08:05:45.553865-05:
      DOI: 10.1002/adem.201700599
  • Antibacterial Efficacy of Sacrifical Anode Thin Films Combining Silver
           with Platinum Group Elements within a Bacteria-Containing Human Plasma
    • Authors: Adham Abuayyash; Nadine Ziegler, Jan Gessmann, Christina Sengstock, Thomas A. Schildhauer, Alfred Ludwig, Manfred Köller
      Abstract: Silver (Ag) dots arrays (64 and 400 dots per mm2) are fabricated on a continuous platinum (Pt), palladium (Pd), or iridium (Ir) thin film (sacrifical anode systems for Ag) and for comparison on titanium (Ti) film (non-sacrifical anode system for Ag) by sputter deposition and photolithographic patterning. The samples are embedded within a tissue-like plasma clot matrix containing Staphylococcus aureus (S. aureus), cultivated for 24 h. Bacterial growth is analyzed by fluorescence microscopy. Among platinum group sacrifical anode elements and a dense Ag sample, only the high Ag ion releasing Ag–Ir system is able to inhibit the bacterial growth within the adjacent plasma clot matrix. This study demonstrates that the antibacterial efficiency of Ag coatings is reduced under tissue-like conditions. However, the new sacrificial anode based Ag–Ir system can overcome this limitation.Sacrificial anode silver dot arrays, fabricated on continuous platinum, palladium, or iridium thin films by sputter deposition and photolithographic patterning are embedded within a tissue-like plasma clot matrix containing growing Staphylococcus aureus. Among these samples or a dense Ag film, only the Ag–Ir dot array is able to inhibit the bacterial growth within the plasma clot matrix.
      PubDate: 2017-09-18T08:00:22.123943-05:
      DOI: 10.1002/adem.201700493
  • Effect of Thermal Oxidation on Microstructure and Corrosion Behavior of
           the PVD Hf-Coated Mg Alloy
    • Authors: Dongfang Zhang; Zhengbing Qi, Binbin Wei, Zhoucheng Wang
      Abstract: Hafnium coatings are fabricated on magnesium alloys by magnetron sputtering and are further submitted to the thermal oxidation treatment at temperature of 200, 300, and 400 °C. The thin hafnium oxide film and new grain boundaries are observed on the hafnium coatings during the appropriate treatment temperature (300 °C). These changes in microstructure result in surface densification, oxidation, and low porosity of the treated coating that significantly decrease its susceptibility to corrosion. Consequently, the thermal oxidation treatment hafnium coating exhibits a more positive corrosion potential, lower corrosion current density, and higher polarization resistance than that of the as-deposited coating using an electrochemical system. Moreover, the enhanced adhesion of the treated coating produced by applying an appropriate treatment temperature facilitates an efficient long-term protection of magnesium alloy.Thermal oxidation as an effective yet feasible post-treatment is conducting on the PVD Hf coated Mg alloy. Surface densification, thin oxide film, and enhanced adhesion are obtained on the post treated coating. As a result, the treated coating exhibits more efficient barrier to corrosive media with positive corrosion potential, low corrosion current density, and high polarization resistance.
      PubDate: 2017-09-18T01:00:38.093829-05:
      DOI: 10.1002/adem.201700556
  • MWCNTs as Conductive Network for Monodispersed Fe3O4 Nanoparticles to
           Enhance the Wave Absorption Performances
    • Authors: Kaili Yu; Min Zeng, Yichao Yin, Xiaojun Zeng, Jue Liu, Ya Li, Wukui Tang, Yu Wang, Jing An, Jun He, Ronghai Yu
      Abstract: Magnetic oxides are widely used as electromagnetic (EM) wave absorbers. To promote the absorption efficiency, tremendous efforts have been contributed to adjusting the composite, structure, and size of magnetic loss materials. Employing carbon materials (CNTs, CF, graphene, PANI) is an efficient way to improve the dielectric loss of the matrix. Anchoring the tiny-monodispersed Fe3O4 nanoparticles (NPs) onto the lightweight multi − walled carbon nanotubes (MWCNTs) leads to improve dielectric loss and impedance matching characteristic. Magnetic Fe3O4 NPs along the one-dimensional nanotubes direction play a good synergetic role with MWCNTs due to the interfacial strong chemical and structure bonding. The as-synthesized Fe3O4/MWCNTs nanocomposites exhibit efficient EM wave absorption characteristics (RL av−10 dB) with a maximum reflection loss of −63.64 dB at 12.08 GHz and a diminutive thickness of only 1.6 mm. The magnetic Fe3O4 NPs show strong chemical and structure bonding with the one-dimensional MWCNTs. This work may show a way to broaden the application of such kinds of lightweight high-performance absorbing materials frameworks.Anchoring the tiny and monodispersed Fe3O4 NPs onto the lightweight MWCNTs results in a strong bonding in Fe3O4/MWCNTs nanocomposites, which exhibit excellent EM wave absorption properties. The MWCNTs can act as the conductive network to enhance the dielectric loss and balance the magnetic loss for good impedance matching.
      PubDate: 2017-09-18T01:00:29.878778-05:
      DOI: 10.1002/adem.201700543
  • Graphene Oxide/Polymer-Based Biomaterials
    • Authors: Duygu Ege; Ali Reza Kamali, Aldo R. Boccaccini
      Abstract: Since its discovery in 2004, derivatives of graphene have been developed and heavily investigated in the field of tissue engineering. Among the most extensively studied forms of graphene, graphene oxide (GO), and GO/polymer-based nanocomposites have attracted great attention in various forms such as films, 3D porous scaffolds, electrospun mats, hydrogels, and nacre-like structures. In this review, the most actively investigated GO/polymer nanocomposites are presented and discussed, these nanocomposites are based on chitosan, cellulose, starch, alginate, gellan gum, poly(vinyl alcohol) (PVA), poly(acrylamide), poly(ϵ-caprolactone) (PCL), poly(lactic acid) (PLLA), poly(lactide-co-glycolide) (PLGA), gelatin, collagen, and silk fibroin (SF). The biological and mechanical performance of such nanocomposites are comprehensively scrutinized and ongoing research questions are addressed. The analysis of the literature reveals overall the great potential of GO/polymer nanocomposites in tissue engineering strategies and indicates also a series of challenges requiring further research efforts.In this review paper, the mechanical and biological performance of graphene oxide/polymeric nanocomposites are analyzed in detail and discussed. Additionally, useful graphics are provided which lead researchers to compare the mechanical properties of films, electrospun mats, fibers, nacre-like structures, and hydrogels of graphene oxide/polymeric nanocomposites at first glance. Finally, the potential of these nanocomposites in tissue engineering are reported with suggestions for future research.
      PubDate: 2017-09-14T07:41:13.801311-05:
      DOI: 10.1002/adem.201700627
  • Preparation of Ni-Encapsulated ZTA Particles as Precursors to Reinforce
           Iron-Based Composites
    • Authors: Juanjian Ru; Yehua Jiang, Rong Zhou, Jing Feng, Yixin Hua, Qionglian Yang
      Abstract: Ni-encapsulated ZTA (ZTA@Ni) particles as precursors to reinforce high chromium cast iron (HCCI) matrix composites are synthesized by electroless deposition using a choline chloride-ethylene glycol (ChCl-EG) ionic liquid additive. The effects of NiSO4 concentration, ChCl-EG concentration, reaction temperature, and ZTA loading capacity on the surface morphology, coating thickness, and elemental distribution of the ZTA@Ni particles are investigated. The deposition sequence of the Ni coating layer is analyzed according to changes in the morphology of samples obtained at different reaction stages. A schematic illustration of the deposition process with the ChCl-EG additive is established. It is demonstrated that ChCl-EG plays the important role of hindering the fast nucleation and crystal growth of Ni nuclei. In addition, the abrasive wear resistance of the ZTA@Ni-reinforced HCCI composite is higher than that of the matrix and the ZTA-reinforced composite. Close contact between the ZTA@Ni particles and the matrix benefits load transfer from the matrix to the reinforcement. The diffusion of metallic Ni leads to the formation of numerous nuclei to refine the particle size of carbides adjacent to the interface and reinforce the interfacial bonding strength.Ni-encapsulated ZTA particles as precursors to reinforce iron matrix composites are prepared by electroless deposition using a choline chloride-ethylene glycol (ChCl-EG) ionic liquid additive. The position sequence of the Ni coating layer is analyzed, and a schematic illustration is proposed. ChCl-EG plays the role of hindering the fast nucleation and crystal growth of Ni nuclei.
      PubDate: 2017-07-10T04:16:10.330658-05:
      DOI: 10.1002/adem.201700268
  • Carbon Coated Alumina Nanofiber Membranes for Selective Ion Transport
    • Authors: Vera S. Solodovnichenko; Denis V. Lebedev, Victoria V. Bykanova, Alexey V. Shiverskiy, Mikhail M. Simunin, Vladimir A. Parfenov, Ilya I. Ryzhkov
      Abstract: The authors propose a novel type of ion-selective membranes, which combine the advantages of ceramic nanofibrous media with good electrical conductivity. The membranes are produced from Nafen alumina nanofibers (diameter around 10 nm) by filtration of nanofiber suspension through a porous support followed by drying and sintering. Electrical conductivity is achieved by depositing a thin carbon layer on the nanofibers by chemical vapor deposition (CVD). Raman and FTIR spectroscopy, X-ray fluorescence analysis, and TEM are used to confirm the carbon structure formation. The deposition of carbon leads to decreasing porosity (from 75 to 62%) and specific surface area (from 146 to 107 m2 g−1) of membranes, while the pore size distribution maximum shifts from 28 to 16 nm. Measurements of membrane potential in an electrochemical cell show that the carbon coated membranes acquire high ionic selectivity (transference numbers 0.94 for anion and 0.06 for cation in aqueous KCl). Fitting the membrane potential data by the Teorell–Meyer–Sievers model shows that the fixed membrane charge increases proportionally with increasing electrolyte concentration. The carbon coated membranes are ideally polarizable for applied voltages from −0.5 to +0.8 V. The potential applications of produced membranes include nano- and ultrafiltration, separation of charged species, and switchable ion-transport selectivity.A novel type of ion-selective membranes based on alumina nanofibers with the diameter of ≈10 nm is proposed. A carbon layer deposited on the nanofibers by the CVD method provides electrical conductivity and ionic selectivity to the membranes. The potential applications of membranes include nano- and ultrafiltration of charged species. The nanofibrous structure with conductive carbon layer is perspective for realizing switchable ion-transport selectivity.
      PubDate: 2017-07-10T01:18:46.422282-05:
      DOI: 10.1002/adem.201700244
  • Tailoring the Microstructure and Mechanical Property of AZ80 Alloys by
           Multiple Twinning and Aging Precipitation
    • Authors: Chunpeng Wang; Renlong Xin, Dongrong Li, Bo Song, Zhe Liu, Qing Liu
      Abstract: AZ80 alloy is a relatively inexpensive age-hardenable Mg alloy. To improve its precipitation strengthening effect, the discontinuous precipitates generally nucleating from grain boundaries should be reduced. In this study, the authors applied strain-path change compression on a wrought AZ80 alloy to generate multiple {10-12} twins and then the pre-deformed alloy is subjected to aging at 180 °C for different period. The effects of the pre-generated twins on precipitation behavior and hence the mechanical properties are investigated. It is found that multiple {10-12} twins are formed in the AZ80 alloy after two paths of compressions along the transverse and rolling directions. Consequently, continuous precipitation is largely promoted during the subsequent aging process. Moreover, the continuous precipitates preferred to form inside the {10-12} twin lamellae. Discontinuous precipitation is almost inhibited during aging at 180 °C for 4–96 h in the sample containing many multiple twins. Compare to the directly peak-aged sample, the pre-twinned and subsequently peak-aged alloys generally exhibit greatly superior mechanical properties. The yield strength, ultimate strength, and elongation for tension along RD are 242 MPa, 476 MPa, and 19.4%, respectively. These excellent properties are attributed to the combined effects of grain refinement, texture weakening, and enhanced precipitate strengthening.Strain-path change compression is applied on a wrought AZ80 alloy to generate multiple {10-12} twins. During the subsequent aging process, continuous precipitation is largely promoted. Compare to the directly peak-aged sample, the pre-twinned and subsequently peak-aged alloys exhibit greatly superior mechanical properties. These excellent properties are attributed to the combined effects of grain refinement, texture weakening, and enhanced precipitate strengthening.
      PubDate: 2017-07-06T06:21:14.149532-05:
      DOI: 10.1002/adem.201700332
  • Enhanced Bipolar Strain Response in Lithium/Niobium Co-Doped
           Sodium–Barium Bismuth Titanate Lead-Free Ceramics
    • Authors: Shang Gao; Zhaojun Yao, Li Ning, Guangzhi Dong, Huiqing Fan, Qiang Li
      Abstract: The (Na0.484Bi0.456Ba0.06)Ti0.97Nb0.03O3 − xLi+ (x = 0, 0.005, 0.01, 0.015) lead-free piezoelectric ceramics are prepared by conventional solid-state reaction technique. X-ray diffraction and surface scanning electron microscope images confirm the pure perovskite structure of sintered ceramics. Electric field and composition-dependent strain behavior are investigated. The highest bipolar strain of 0.47% is achieved at x = 0.01 with the applied electric-field of 70 kV cm−1, and the corresponding normalized strain (d33*) reaches up to 671 pm V−1. Moreover, the giant strain exhibits excellent thermal stability and fatigue-resistance (within 105 switching cycles) properties. The origin of the strain can be attributed to transition between ferroelectric and relaxor ferroelectric induced by the applied electric field, and introduction of Li cations further enhances the strain behavior. AC impedance analysis indicate the appearance of grain boundary effect with increasing Li+ addition, which is also reflected on the dielectric and dielectric loss curves. It is believed that the environmental friendly binary system can be a promising candidate for piezoactuators.In this work, Li/Nb co-doped Na0.484Bi0.456Ba0.06TiO3 ceramics are prepared using conventional solid-state reaction method. The giant electric-field-induced strain of 0.47% (E = 70 kV cm–1) is achieved, meanwhile, the strain exhibits excellent fatigue resistance and temperature stability properties. The Li/Nb modified lead-free polycrystalline ceramics can be a promising candidate for actuator applications.
      PubDate: 2017-07-06T06:20:28.580674-05:
      DOI: 10.1002/adem.201700125
  • Surface Functionalization of Micro/Nanostructured Titanium with Bioactive
           Ions to Regulate the Behaviors of Murine Osteoblasts
    • Authors: Guisen Wang; Yi Wan, Bing Ren, Teng Wang, Zhanqiang Liu
      Abstract: Surface topography and chemical composition are centrally important in current implants for enhancing cellular responses. To investigate the synergistic effect of micro/nanostructure and bioactive ions on the spreading, proliferation, and differentiation of murine osteoblasts, the micro/nanostructured titanium surface containing bioactive ions (Zn2+ and Sr2+) was fabricated via sandblasting, acid etching, alkali-heat treatment, and ion exchange. Compared to polished titanium substrates, micro/nanostructured titanium substrates displayed the enhanced roughness and hydrophilicity. And surface functionalization of micro/nanostructured using Zn2+/Sr2+ ions exhibited the sustained release for a period of time. Meanwhile, cell experiments indicated that the Zn/Sr loaded micro/nanostructured titanium surfaces had a great potential to promote cell spreading, proliferation, and differentiation. This study provides a more promising method to design the surface of titanium implants for enhancing osseointegration.The hierarchical micro/nanostructure containing bioactive ions (Zn2+ and Sr2+) were fabricated on the surface of titanium by combined use of sandblasting, acid etching, alkali-heat treatment and ion exchange. The treated titanium substrates presented sustained ion release behavior. Surface functionalization of micro/nanostructured titanium with bioactive ions provided a favorable interfacial environment for the spreading, proliferation, and differentiation of osteoblasts.
      PubDate: 2017-07-03T08:01:11.345968-05:
      DOI: 10.1002/adem.201700299
  • Application of X-Ray Microtomography to Evaluate Complex Microstructure
           and Predict the Lower Bound Fatigue Potential of Cast
           Al–7(0.7)Si–4Cu–3Ni–Mg Alloys
    • Authors: Thomas O. Mbuya; Ian Sinclair, Katherine A. Soady, Philippa A. S. Reed
      Abstract: The 3D architecture of intermetallics and porosity in two multicomponent cast Al–7(0.7)Si–4Cu–3Ni–Mg alloys is characterized using conventional microscopy and X-ray microtomography. The two alloys are found to contain intermetallic phases such as Al3Ni, Al3(NiCu)2, Al9FeNi, and Al5Cu2Mg8Si6 that have complex networked morphology in 3D. The results also show that HIPping does not significantly affect the volume fraction, size, and shape distribution of the intermetallic phases in both alloys. A novel technique similar to serial sectioning that circumvents quantification difficulties associated with interconnected particles is used to quantify the intermetallics. The largest particle size distribution is then correlated to fatigue performance using extreme value analysis to predict the maximum particle size in a sample of S-N fatigue specimens and subsequently, the lower bound fatigue life. The predictions are found to correlate well with fatigue data. The effect of HIPping on porosity characteristics is also characterized. Large pore clusters with complex morphology are observed in the unHIPped versions of both alloys, but more significant in the low Si (Al–0.7Si–4Cu–3Ni–Mg) alloy. However, these are significantly reduced after HIPping. The differences between 2D and 3D pore morphology and size distribution is discussed in terms of the appropriate pore size parameter for fatigue life prediction.Two cast Al–7(0.7)Si–4Cu–3Ni–Mg alloys contain a complex 3D network of intermetallics and large complex-shaped pores. HIPping reduces the volume fraction (Vf), size and shape complexity of pores, but no effect is observed for intermetallics except a slight reduction in the Vf of 0.7 wt% Si alloy. A novel technique akin to serial sectioning is used to quantify intermetallics. The upper tail of particle sizes correlates well with fatigue crack initiating particles.
      PubDate: 2017-07-03T01:26:19.534505-05:
      DOI: 10.1002/adem.201700218
  • 3D Printing of Free-Standing Stretchable Electrodes with Tunable Structure
           and Stretchability
    • Authors: Hong Wei; Kai Li, Wen Guang Liu, Hong Meng, Pei Xin Zhang, Chao Yi Yan
      Abstract: Free-standing stretchable electrodes with high stretchability and resistance stability are desired for future wearable electronic applications. However, it is very difficult to achieve high stretchability (typically restricted by the substrate) and meanwhile maintain low resistance change upon stretching. Innovative designs and fabrication strategies need to be developed to meet the required characteristics. We report the successful fabrication of free-standing wavy elastic electrodes achieving very high stretchability (>300% for PDMS) and outstanding resistance stability (only 5% relative resistance change at 100% strain), simultaneously. We systematically studied designs with different joining angles and shapes to optimize the electrode performances. The 3D free-standing electrodes with outstanding stretchability and electrical stability has great potential for further optimizations and applications in future stretchable and wearable electronic devices.We demonstrate the successful 3D printing of wavy elastic electrodes with high stretchability and excellent resistance stability. Stretchable electrodes with different shapes and designs were systematically studied. Serpentine shaped design with 45° joining angle exhibited the best performances, which is in contrary to conventional 2D electrodes. Our fabrication strategy paves the way for further 3D printing of more complex stretchable electronic devices.
      PubDate: 2017-07-03T01:25:27.849675-05:
      DOI: 10.1002/adem.201700341
  • Gradient Structures in Thin-Walled Metallic Tubes Produced by Continuous
           High Pressure Tube Shearing Process
    • Authors: Rimma Lapovok; Yuanshen Qi, Hoi P. Ng, Laszlo S. Toth, Yuri Estrin
      Abstract: A new severe plastic deformation process, the authors refer to as High Pressure Tube Shearing (HPTS), is proposed. This type of deformation processing enhances the strength of the walls of metallic tubes by producing gradient microstructures with ultrafine grained layers in near-surface regions. The thickness of the layers associated with a gradient in microstructure can be controlled by tuning the rotational and translational speeds of the process. The paper describes several examples of steel and titanium tubes processed by different variants of HPTS. The possibility of producing gradient microstructures with ultrafine grained layers at inner or outer surface of a tube, or at both surfaces is demonstrated by in-depth theoretical analysis, finite element simulations, and experimental investigation of the microstructure and texture of tube walls.A new continuous severe plastic deformation process, named High Pressure Tube Shearing, is proposed, Figure 1. This deformation technique enhances the strength of the walls of metallic tubes by producing gradient microstructures with ultrafine grained layers in near-surface regions. The thickness of the layers associated with a gradient in microstructure can be controlled by tuning the rotational and translational speeds.
      PubDate: 2017-07-03T01:21:52.402208-05:
      DOI: 10.1002/adem.201700345
  • Microstructure Evolution and Ablation Mechanism of C/C and C/C-SiC
           Composites Under a Hypersonic Flowing Propane Torch
    • Authors: Xiaochao Jin; Xueling Fan, Peng Jiang, Qiang Wang
      Abstract: The high-velocity oxygen fuel thermal spray system can provide a hypersonic flowing environment in which the temperature, pressure, and speed are all sufficiently high to represent a more realistic environment of hypersonic vehicles than that produced by traditional oxyacetylene flame. In this work, the ablation resistance of C/C and C/C-SiC composites under hypersonic flowing propane flame is investigated, and the microstructure evolution during the ablation process is examined. It is found that different ablation regions are formed depending on the size, and the distributions of temperature and pressure on the front surface of the samples. With the increase of ablation time, a dense and continuous oxide layer forms, which acts as a barrier to prevent the interaction of oxidizing gases and composites, and can also block the conducted heat and resist high temperature scouring of hypersonic flowing flame. In addition, a numerical analysis is performed using ANSYS Fluent software to investigate the fields of velocity, pressure, and temperature on the front surface and around the carbon fibers of the sample. The simulation results further demonstrate the evolution of microstructures of C/C and C/C-SiC composites.High-velocity oxygen fuel thermal spray system can provide a hypersonic flowing environment in which the temperature, pressure, and speed are all sufficiently high to represent a realistic environment of hypersonic vehicles. In this artical, experimental investigations are performed under hypersonic flowing propane torch to provide a better understanding of the ablation mechanism of ultra-high temperature ceramics modified C/C composites.
      PubDate: 2017-07-03T01:21:05.149151-05:
      DOI: 10.1002/adem.201700239
  • A New Horizon for Barreling Compression Test: Exponential Profile Modeling
    • Authors: Mehdi Fardi; Ralph Abraham, Peter D Hodgson, Shahin Khoddam
      Abstract: Exponential Profile Model (EPM) has been recently proposed to interpret barreling compression test's (BCT) data. A basic solution of EPM enables estimation of friction factor and to calculate distributions of strain rate (and strain) in the sample. These critical pre-requisites allow to identify material's flow behavior and to indirectly measure static, dynamic, and meta-dynamic recrystallization properties of the material based on the behavior. In this work, EPM's basic solution is employed in a fixed friction factor mode, the model is assessed and its potentials are outlined. The assessment includes comparing EPM's sample solutions with two reference solutions. The references are a non-isothermal finite element model of BCT and the commonly used solution of the test; Cylindrical Profile Model (CPM). It is shown that despite variations of strain, strain rate, and temperature in Al1050 and AISI 304 stainless steel BCT samples, EPM's solutions agree reasonably well with the finite element solutions. This is particularly true for effective strains bellow 0.7 and friction factors bellow 0.2. It is concluded that EPM presented a far more reliable solution than CPM.A new analytical model for barreling compression test (Top) is introduced. The model (EPM), proves to be far more reliable than the existing models such as Cylindrical Profile Model. EPM relies on the initial and deformed geometry of the test sample (Top) and a new velocity filed (bottom) to identify the test's friction factor and its strain distribution.
      PubDate: 2017-06-29T07:26:25.153451-05:
      DOI: 10.1002/adem.201700328
  • Highly Conductive Three-Dimensional Printing With Low-Melting Metal Alloy
    • Authors: Kimball Andersen; Yue Dong, Woo Soo Kim
      Abstract: It has been challenging to develop a new functional material with high conductivity for the Fused Filament Fabrication (FFF) based 3D printing technology. The proposed low-melting metal alloy filament provides the key to overcome the challenges including printability and conductivity. For this report, two metal alloys are designed to evaluate their suitability for FFF. In order to achieve material compatibility of the designed filament material with the nozzle materials, different nozzle materials are also investigated using thermal analysis. Then, a custom extrusion nozzle is suggested using thermal modeling to optimize the melt-zone for reliable extrusion. And finally, 3D printed circuit is demonstrated from a 3D printed plastic case to the integrated printed-alloy connections for the light-emitting device.Highly conductive metal 3D printing is demonstrated with low-melting Tin-Bismuth-Silver alloy filaments for the integration of 3D printed electronics. The developed alloy filament demonstrates good extrusion characteristics due to its thixotropic nature. Co-deposition of the alloy into 3D printed PLA structures shows compatible with existing thermoplastic additive manufacturing systems.
      PubDate: 2017-06-28T08:05:56.978033-05:
      DOI: 10.1002/adem.201700301
  • Phase-Control Enabled Superior Mechanical and Electrical Properties of
           Nanocrystalline Tungsten-Molybdenum Thin Films
    • Authors: G. Martinez; C. V. Ramana
      Abstract: The authors report on the design and stabilization of the mechanically hard and electrically resistive β-phase W-Mo nanocrystalline thin films at room-temperature (RT). The W-Mo films are deposited under different deposition temperatures in the range of Ts = RT–30 °C. Structural analyses indicate that, as deposited at RT, the W-Mo films crystallize in the metastable β-phase, while those deposited at higher Ts (100–300 °C) exhibit the thermodynamically stable α-phase. The phase-effect is significant on the mechanical characteristics; superior hardness (H); and modulus of elasticity (Er) are found in β-than in α-phase W-Mo films. At the β-to-α phase transformation, significant reduction occurs in H (40  25 GPa) and Er (275  225 GPa) coupled with a reduction in electrical-resistivity (320  180 µΩ-cm). Their findings and the phase-mechanical-electrical property correlation established may provide further possibilities to design and tailor the performance of W-based thin films for future electronic and electromechanical device applications.The authors report on the superior mechanical properties of nanocrystalline W-Mo thin films. The phase-effect is significant on the hardness and elastic modulus, which are high in β-than in α-phase W-Mo films. These findings and the phase-mechanical-electrical property correlation established may provide further possibilities to design and tailor the performance of W-based films for future electronic and electromechanical device applications.
      PubDate: 2017-06-28T08:05:29.719304-05:
      DOI: 10.1002/adem.201700354
  • Large-Scale Synthesis of Nanostructured Nitride Layer on Ti Plate Using
           Mechanical Shot Peening and Low-Temperature Nitriding
    • Authors: Quantong Yao; Jian Sun, Depeng Shen, Weiping Tong, Liang Zuo
      Abstract: A nanostructured nitride layer is produced on a large titanium plate using mechanical shot peening (MSP) followed by a low-temperature gaseous nitriding method. The combined effect of the MSP and low-temperature nitriding on the microstructural evolution and mechanical properties is investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, as well as hardness, wear resistance, and toughness tests. The results of the characterization are compared to a coarse-grained specimen produced by a standard nitriding process. The results show that a nitride layer with a thickness of 10–15 µm is produced on the MSP-treated Ti plate after nitriding at 550 °C for 5 h. The nitride layer is composed of nanostructured ϵ-TiN and γ-Ti2N phases with a high supersaturation of nitrogen. The nitriding kinetics is significantly enhanced by the nanocrystalline structure. The surface hardness, thickness of the hardened layer, and wear resistance of the nitrided MSP Ti plate are all enhanced relative to the coarse-grained nitrided sample. The toughness of the nanostructured nitrides is greatly improved compared with the conventional nitrided specimen.The authors firstly realize surface nanocrystallization technology in industrialization application. The gaseous nitriding can be performed on Ti plate at low nitriding temperature of 550 °C by nanocrystalline layer assistance. The nitrided layer thickness and toughness are significantly improved comparing with that of the coarse-grained nitrided specimen.
      PubDate: 2017-06-16T07:55:55.708924-05:
      DOI: 10.1002/adem.201700157
  • Dynamic Corrosion and Material Characteristics of Mg–Zn–Zr Mini-Tubes:
           The Influence of Microstructures and Extrusion Parameters
    • Authors: Da-Jun Lin; Fei-Yi Hung, Heng-Jui Liu, Ming-Long Yeh
      Abstract: In this study, magnesium–zinc–zirconium (Mg–Zn–Zr) alloy mini-tubes that fit the diameter of cardiovascular stents are successfully fabricated using an isothermal extrusion method. The influence of extrusion temperature and ram speed on the microstructure are examined. In addition, this research develops a novel dynamic-corrosion apparatus for Mg alloy mini-tube examination, and supplemented with electrochemical, and biocompatibility tests, the optimal criteria for mini-tube extrusion are defined. The optimized specimen not only retains a homogeneous fine-grained structure with a grain size of about 2 µm, but also possesses 300 MPa yielding strength and nearly 15% elongation. Compared with a coarse-grained microstructure, the fine-grained specimens significantly reduces the corrosion and oxidation rates in a dynamic-flow field, resulting in favorable characteristics of degradation, cytocompatibility, and hemocompatibility. The results suggest that precisely controlling the extrusion process can improve the mechanical properties as well as the biocompatibility of Mg alloys for application in cardiovascular implants.The Mg mini-tube is developed for cardiovascular stent application. The extrusion parameter dominates the microstructure, which results in a significant increase in enhanced mechanical properties and corrosion resistance. A new dynamic corrosion test is performed in order to determine the practicability of fine-grained Mg mini-tube.
      PubDate: 2017-06-14T01:56:13.023829-05:
      DOI: 10.1002/adem.201700159
  • Effect of Directional Solidification Variables on the Microstructures of
           Single-Crystal Turbine Blades of Nickel-Based Superalloy
    • Authors: Fu Wang; Zining Wu, Dexin Ma, Andreas Bührig-Polaczek
      Abstract: Single-crystal turbine blades of nickel-based superalloy are directionally solidified at different withdrawal rates of 0.0017 cm s−1–0.01 cm s−1 aiming to investigate the evolution of as-cast microstructures. The results show that the average primary and secondary dendrite arm spacings, λ1¯ and λ2¯, decrease with increasing withdrawal rate, although the complicated geometry of the blades results in local nonhomogeneity of dendrite arm spacings. The experimentally achieved values of λ1¯ can be reasonably predicted by Ma and Sahm's theoretical model, in which the effect of the secondary dendrite on the primary dendrite arm spacing is considered. With increasing withdrawal rate, the shape of the γ/γ′ eutectic varies from a large block-like eutectic island to an interconnected small strip-like morphology. In addition to this, the average size of the γ/γ′ eutectic gradually decreases with increasing withdrawal rate. A reduction in the average sizes of the γ′ precipitates in the dendrite core and interdendritic region is also observed with increasing withdrawal rate. The microsegregation levels of Al, Ti, Ta, Cr, Co, and Mo are alleviated with increasing withdrawal rate.SC blades are directionally solidified at various withdrawal rates (V) to study the evolution of microstructures. The microstructures are refined with increasing V, although the geometry of blades results in local nonhomogeneous microstructures. λ1¯ can be predicted by Ma and Sahm's model. The microsegregation levels of alloying elements are alleviated with increasing V.
      PubDate: 2017-06-09T14:46:06.528927-05:
      DOI: 10.1002/adem.201700297
  • Influence of Torsion Route on the Microstructure and Mechanical Properties
           of Extruded AZ31 Rods
    • Authors: Bo Song; Xiaogang Shu, Hucheng Pan, Guoqiang Li, Ning Guo, Tingting Liu, Linjiang Chai, Renlong Xin
      Abstract: Torsion deformation is an effective and simple technique to tailor the mechanical properties of Mg alloys. In this study, the influences of torsion route on microstructure and mechanical properties of AZ31 rods are investigated. The maximum torsion angle is set as 180° and the two-pass torsion at different torsion routes, twice-successive unidirectional torsion (TA) and reciprocating torsion (TB), is used to process the Mg alloy rods. It is found that the mechanical properties and yield asymmetry are very sensitive to the torsion route. Route TA is more effective for the enhancement of compressive yield strength and the improvement of yield asymmetry, while route TB is more effective for the enhancement of tensile yield strength. It is mainly attributed to the different textural evolutions between the two torsion routes. The relevant mechanisms are addressed and discussed.Torsion deformation is an effective and simple technique to tailor the mechanical properties of Mg alloys. It is found that the mechanical properties and yield asymmetry are very sensitive to the torsion route. Route TA is more effective for the enhancement of compressive yield strength and the improvement of yield asymmetry, while route TB is more effective for the enhancement of tensile yield strength.
      PubDate: 2017-06-09T07:40:27.919944-05:
      DOI: 10.1002/adem.201700267
  • Novel Heating Elements for Induction Welding of Carbon Fiber/Polyphenylene
           Sulfide Thermoplastic Composites
    • Authors: Rouhollah Dermanaki Farahani; Martine Dubé
      Abstract: Conductive films of carbon nanofibers (CNFs) decorated/coated with metals, either silver (Ag) or nickel (Ni) are fabricated using a solution casting process and used as novel heating elements (HEs) for induction welding of carbon fiber/polyphenylene sulfide (CF/PPS) thermoplastic composites. Prior to making the films, the metal-coated CNFs are prepared by an electroless plating method using Ag or Ni precursors. A solution of the metal-coated CNFs is then casted onto a pure PPS film to give a robust conductive film upon solvent evaporation and annealing in an oven at 200 °C. SEM observation and electrical resistivity measurements reveal that the CNFs are successfully coated with the metals which result in a significant decrease of the films’ electrical resistivity. A third type of HE is also fabricated by solution mixing Ag-coated CNFs and magnetic Fe3O4 nanoparticles. The welding efficiency of the fabricated films is assessed for induction welding of two different types of thermoplastic composites, that is, unidirectional pre-impregnated 16 plies ​​of CF/PPS compression-molded in a quasi-isotropic stacking sequence and 8-ply of satin weave fabric CF/PPS compression-molded in a cross-ply stacking sequence. The mechanical apparent lap shear strength (LSS) of the induction-welded joints is evaluated for the fabricated HEs and compared with the LSS of joints welded using conventional stainless steel mesh susceptors. Under similar testing conditions, Ag-coated CNFs HEs lead to the highest LSS with an average value of ≈31.5 MPa. In general, the new HEs result in superior LSS and higher heating rates when compared to the metallic mesh counterparts. The present work offers a new perspective to push the boundaries toward high quality welding of thermoplastic composites using nanomaterials-based HEs.Novel heating element (HE) types are developed and used for induction welding of thermoplastic composites. The HEs are fabricated using carbon nanofibers (CNFs) that are coated/decorated with metals, either silver or nickel by an electroless plating method. The realization of such HEs leads to the achievement of high quality welding with mechanical apparent lap shear strength values exceeding that obtained for the commonly-used stainless steel mesh susceptors.
      PubDate: 2017-06-07T08:00:14.307129-05:
      DOI: 10.1002/adem.201700294
  • Surface Engineered Nanoparticles: Considerations for Biomedical
    • Authors: Angie S Morris; Aliasger K Salem
      Abstract: The development of reproducible methods for the fabrication of nanoparticles in the 21st century is a major scientific achievement. Currently, there are many well-established methods for the production of nanoparticles of different shapes, sizes, and compositions. Along with these advancements in nanotechnology, nanoparticles have emerged as excellent tools for a diverse range of applications and have become a focus of research globally. With fundamental research being established, efforts are now being directed toward intelligently designed nanoparticles in which the properties of the nanomaterial are finely tuned depending on the application of interest. Usually, this involves the functionalization of the nanoparticle surface with a ligand. In this review, the impact of nanoparticle surface chemistry is discussed as it applies to biological systems.This review summarizes the current approaches for modifying nanoparticle surfaces and the impact on biological systems. Contained in this writing is a wide variety of examples where ligands (such as drugs, polymers, or proteins) are used to tailor the properties of nanoparticles for various biologically-related applications. These applications include targeted drug delivery, biomedical imaging, or the design of safer and more biocompatible nanomaterials.
      PubDate: 2017-06-07T08:00:10.740916-05:
      DOI: 10.1002/adem.201700302
  • Cantilever with High Aspect Ratio Nanopillars on Its Top Surface for
           Moisture Detection in Electronic Products
    • Authors: Nguyen Van Toan; Masaya Toda, Takumi Hokama, Takahito Ono
      Abstract: This work reports the patterning silicon pillars by metal-assisted chemical etching (MACE) process as a post process on a silicon cantilever for a moisture detection. Although the cantilever is very fragile, the patterning of the pillar structures on the cantilever has been successfully demonstrated. The cantilever coated with a material absorbing water (such as polyimide and mesoporous silica) can use as a humidity sensor. Its bending is due to the surface stress change from water molecule absorption. However, the bending of the cantilever is usually at a small value. Here, the silicon cantilever with high aspect ratio pillars on its surface is proposed, which is expected for a larger bending of the cantilever during the water molecule absorption. The moisture detection utilizes the principle that the pillars stack together based upon the condensation behavior of a water vapor on their surfaces.Patterning high aspect ratio nanopillars on the AFM silicon cantilever for the moisture sensing application by metal assisted chemical etching are investigated. The moisture detection utilizes the principle that the pillars stack together based upon the condensation behavior of a water vapor on its surface.
      PubDate: 2017-06-07T08:00:05.077364-05:
      DOI: 10.1002/adem.201700203
  • A Microvascular System for the Autonomous Regeneration of Large Scale
           Damage in Polymeric Coatings 
    • Authors: Ryan C. R. Gergely; Michael N. Rossol, Sharon Tsubaki, Jonathan Wang, Nancy R. Sottos, Scott R. White
      Abstract: Self-healing polymers are capable of self-repair either in response to the damage or through external stimuli, but are limited in their ability to autonomously control the volume of healing agents released, in the length scale of damage they address, and in their ability to respond to multiple damage events. Here, the authors report a novel design for healing agent storage and release for vascular coating systems that allows for complete regeneration of a coating with precise and autonomous control of coating thickness. A variety of healing agent formulations that cure under ambient sunlight are explored and their cure profiles and mechanical properties are reported. In the proposed vascular coating system, the stored healing agent remains stable within the network until large-scale damage (e.g., abrasion) completely removes the protective coating. A precise volume within the network is then released, and cures when exposed to simulated sunlight to reform the protective coating. This coating system facilitates consistent coating thickness and hardness for several cycles of coating removal and regeneration.A new microvascular coating system en-ables fully autonomous regeneration and control of coating thickness. In response to damage, a prescribed amount of healing agent is released through a pressure responsive surface valve to the damaged surface. Exposure to simulated sunlight cures the healing agent to reform the coating.
      PubDate: 2017-06-07T06:54:32.276753-05:
      DOI: 10.1002/adem.201700319
  • Effects of Phase Content and Evolution on the Mechanical Properties of
           Mg95Y2.5Zn2.5 and Mg93.1Y2.5Zn2.5Ti1.6Zr0.3 Alloys Containing LPSO and W
    • Authors: Shouzhong Wu; Zhe Zhang, Jinshan Zhang, Chunxiang Xu, Xiaofeng Niu, Wei Liu
      Abstract: The effects of phase content and evolution on mechanical properties of the alloys are investigated by extruding Mg95Y2.5Zn2.5 and Mg93.1Y2.5Zn2.5Ti1.6Zr0.3 alloys with different original microstructures. The 18R-LPSO phase plays a decisive role in the strength of as-extruded alloys. The spherical W-MgYZn2 phase enhances the deformability and ductility of the alloys. The dynamic recrystallization grains can be observed in all as-extruded alloys. However, the 14H-LPSO clusters and dynamic precipitates only form in the as-cast and T41-treated (solid-solution treatment at 530 °C for 3 h with water cooling) alloys after extrusion. Based on synergistic effects of these phases mentioned above, the T41-treated Mg93.1Y2.5Zn2.5Ti1.6Zr0.3 alloy exhibits good compressive mechanical properties after extrusion.The solid-solution treated Mg93.1Y2.5Zn2.5Ti1.6Zr0.3 alloy exhibits good comprehensive mechanical properties after extrusion, which can be attributed to the synergistic effects of these phases, including 18R-LPSO phase, spherical W-MgYZn2 phase, DRX grains, 14H-LPSO clusters, and dynamic precipitates.
      PubDate: 2017-05-26T00:46:22.974917-05:
      DOI: 10.1002/adem.201700185
  • Activation Energy and High Temperature Oxidation Behavior of
           Multi-Principal Element Alloy
    • Authors: Harpreet Singh Grewal; Ramachandran Murali Sanjiv, Harpreet Singh Arora, Ram Kumar, Aditya Ayyagari, Sundeep Mukherjee, Harpreet Singh
      Abstract: Activation energy and diffusion kinetics are important in modulating the high temperature oxidation behavior of metals. Recently developed multi-principal element alloys, also called high entropy alloys (HEAs), are promising candidate material for high temperature applications. However, the activation energies and diffusion kinetics of HEAs have been limitedly explored. We investigate the diffusional activation energy for oxidation of Al0.1CoCrFeNi HEA. Compared to conventional steels and Ni-based super alloys, the HEA showed a significantly higher diffusion activation energy. This behavior is explained based on low potential energy of the lattice and interstitial sites which effectively trap the atoms, limiting their diffusion. The atomic mean jump frequency for interstitial diffusion of oxygen in the HEA is four-orders of magnitude lower than T22 and T91 steels and seven-orders of magnitude lower compared to pure iron. Al0.1CoCrFeNi HEA showed the lowest oxidation rate compared to conventionally used steels, super-alloys, and coatings.Al0.1CoCrFeNi high entropy alloy shows significantly high activation energy and oxidation resistance. High activation energy lowers the mean jump rate of oxygen atom resulting in sluggish diffusion.
      PubDate: 2017-05-24T06:05:31.354021-05:
      DOI: 10.1002/adem.201700182
  • High-Speed Roll-to-Roll Hot Embossing of Micrometer and Sub Micrometer
           Structures Using Seamless Direct Laser Interference Patterning Treated
    • Authors: Andreas Rank; Valentin Lang, Andrés Fabián Lasagni
      Abstract: In this study, we present a seamless high-speed roll-to-roll hot embossing process using a direct laser interference patterned nickel sleeve as a mold. Line-like patterns with spatial periods of 5.0, 3.9, and 1.5 μm and structure heights of 572, 325, and 141 nm, respectively are used for imprinting PET-foils. The influence of the web speed on the cavity filling and consequently on the structure height and homogeneity of the fabricated patterns is studied. The web speed is varied between 2 and 50 m min−1. For the 5.0 and 3.9 μm periods, a decrease in structure height with the web speed occurs, while for the 1.5 μm period the structure height remains constant in the tested interval. Also a decrease in homogeneity is observed with increasing web speed. Finally, an analytical model, based on the Navier–Stokes equation and Hertzian contact pressure, is used to explain the experimental results. The experimental data are in good agreement with the calculated theoretical values.A seamless high-speed Roll-to-Roll hot embossing process using a direct laser interference patterned Nickel sleeve as a mold is presented. Line-like periodic patterns with spatial periods of 5.0, 3.9, and 1.5 µm are fabricated directly on metallic sleeves using a two-beam configuration interference set-up. The influence of the web speed on the cavity filling and consequently on the structure height of the patterns produced on the PET foils is analyzed, for web speeds between 2 and 50 m min–1. An analytical model, based on the Navier–Stokes equation and Hertzian contact pressure, is used to explain the experimental results.
      PubDate: 2017-05-22T06:00:40.806103-05:
      DOI: 10.1002/adem.201700201
  • Regenerative Polymeric Coatings Enabled by Pressure Responsive Surface
    • Authors: Ryan C. R. Gergely; Nancy R. Sottos, Scott R. White
      Abstract: Protective coatings safeguard the underlying substrate material from environmental attack and are critical for operating in harsh conditions. Self-healing materials have been developed for the autonomous repair of damage in coatings. This work demonstrates a regenerative coating system that is a simplified synthetic analog of skin. A protective UV curable coating reforms with properties identical to the native coating after complete removal. An integrated surface valve prevents premature curing of healing agent contained within a vascular substrate prior to damage-triggered release, facilitating recovery from repeat damage. The protective coating reforms when exposed to simulated sunlight.A protective polymeric coating is regenerated in response to abrasive damage. Abrasion exposes the underlying vasculature, and UV curable epoxy healing agent is delivered to the site of damage via a pressure responsive surface valve. The protective coating is reformed when exposed to simulated sunlight.
      PubDate: 2017-05-18T01:39:04.90776-05:0
      DOI: 10.1002/adem.201700308
  • Microstructural and Mechanical Characterization of Aluminum Matrix
           Composites Produced by Laser Powder Bed Fusion 
    • Authors: Alberta Aversa; Giulio Marchese, Massimo Lorusso, Flaviana Calignano, Sara Biamino, Elisa P. Ambrosio, Diego Manfredi, Paolo Fino, Mariangela Lombardi, Matteo Pavese
      Abstract: Laser powder bed fusion is one of the most widely used additive manufacturing process owing to its ability to produce functional near net shape metal components. This paper focuses on the microstructural and mechanical characterization of four aluminum matrix composites produced by laser powder bed fusion using AlSi10Mg as matrix with four different ceramic particles. On the basis of the building parameters, composites present specific microstructural features able to influence the strengthening mechanisms and, consequently, their mechanical and thermal properties. It is demonstrated that, in order to obtain dense materials, in composite processing, it is indispensable to use energy densities which are higher than that of the matrix. This change in process parameters probably implies a different heat profile in the part during the building process, with a consequent increase in cell size and decrease in yield strength of the MMCs with respect to the pure aluminum.This work investigates the feasibility and the properties of AlSi10Mg matrix composites produced by laser powder bed fusion. It is clarified that high energy densities are required in order to obtain dense composites. The building parameters strongly influence composite microstructures, with evident consequences on their mechanical properties.
      PubDate: 2017-05-17T08:50:36.636005-05:
      DOI: 10.1002/adem.201700180
  • Study on the Compression Properties and Deformation Failure Mechanism of
           Open-Cell Copper Foam 
    • Authors: Jian Chen; Xiongfei Li, Wei Li, Jianjun He, Cong Li, Shuowei Dai, Jianlin Chen, Yanjie Ren
      Abstract: Uniaxial compression experiments on open-cell copper foams are conducted at strain rates of 10−2 s−1, 10−3 s−1, and 10−4 s−1 to obtain the true stress-strain curves. The effects of the strain rate, cell size, and porosity on the mechanical properties is studied. The deformation mechanism of the open-cell copper foams is investigated by experimental research and finite element analysis. The results showed that the compression strength, Young's modulus and yield strength increase with increasing strain rate and decreasing porosity and cell size. A lower strain rate results in higher strain sensitivity. Strain-hardening behavior occurred in the process of high-strain-rate loading. The experimental and simulation results indicate that the failure mechanism of the open-cell copper foam is the layer-by-layer collapse failure mechanism and that stress concentrations form easily at the weak pore struts. The simulation results are consistent with the experimental data at the first and second stages. However, the value of true stress predicted by the simulation at the third stage is slightly higher than that of the experiments.The failure mechanism of open-cell copper foam under compression loading is investigated. The bend of hollow struts in the compression process results in the propagation of cracks. Cracks in the hollow strut extend along the circumferential direction. Besides, the cracks appear at the convex of struts.
      PubDate: 2017-05-12T01:50:29.88125-05:0
      DOI: 10.1002/adem.201600861
  • Nitride, Zirconia, Alumina, and Carbide Coatings on Ti6Al4V Femoral Heads:
           Effect of Deposition Techniques on Mechanical and Tribological
    • Authors: Duygu Ege; İlayda Duru, Ali Reza Kamali, Aldo R. Boccaccini
      Abstract: Ti6Al4V has been extensively studied in orthopedic applications because of its biocompatibility, desirable mechanical strength, and fatigue resistance. A wide range of bioinert ceramics have been investigated to further develop the tribological and mechanical properties of Ti6Al4V for the production of potential femoral heads. However, an analysis of the literature indicates that the performance of the coatings produced has been inconsistent. In this review, for the first-time deposition techniques of the most widely studied bioinert ceramics namely nitrides, carbides, zirconia, and alumina on Ti6Al4V substrates and their relevant mechanical and tribological performance have been analyzed. Finally, graphene has also been suggested for use together with bioinert ceramics due to its excellent mechanical and physical properties for coating Ti6Al4V femoral heads.The materials provided enable the comparison of the relative performance of the various bioinertceramic-based coatings at a glance.
      PubDate: 2017-05-08T01:18:25.841651-05:
      DOI: 10.1002/adem.201700177
  • Bubble Size Distribution in Foaming of Liquid Aluminum and the Role of
           Coarsening and Coalescence 
    • Authors: Shiba Narayan Sahu; Amol Anant Gokhale, Anurag Mehra
      Abstract: Evolution of bubble size distribution in liquid aluminum foam prepared by dissociation of TiH2 particles is studied by rapidly cooling samples during foam expansion and carrying out metallographic analysis of the solidified foam. Further, diameters of bubbles growing directly on TiH2 particles are calculated to arrive at volume expansion and bubble size distribution. The cells in the solidified foam are orders of magnitude coarser and fewer than those predicted by the “pure growth” based model at all stages of foam expansion. If bubble coarsening was accounted for, the calculated bubble sizes are less than, but the same order of magnitude as the experimentally observed cell sizes. The remaining discrepancy of cell size (and population) can be explained based on bubble coalescence, strongly supported by observations on early stages of foaming.The study identifies bubble growth mechanisms operative in “Alporas” type aluminum foams by analyzing cell structures during foam evolution. Bubble growth based on pure diffusion under-predicts the average bubble size, while the classical LSW theory of coarsening predicts kinetics similar to that of later stage of foaming. The initial higher growth rate is attributed to bubble coalescence driven by bubble motion and hydrogen release rate.
      PubDate: 2017-04-07T03:42:12.221816-05:
      DOI: 10.1002/adem.201600745
  • Overview of Composite Metal Foams and Their Properties and Performance
    • Authors: Jacob Marx; Afsaneh Rabiei
      Abstract: This paper reviews the background and evolution of composite metal foam (CMF) from its inception until now. A broad understanding of the processing and basic mechanical, microstructural, and physical properties of different types of composite metal foams is discussed in the first part of the paper. In the second part, some recent studies on high strain rate properties, ballistic performance, radiation attenuation, and thermal properties of composite metal foams are discussed and compared with other bulk and control materials. These properties suggest many potential applications for this novel material in a broad range of engineering structures from ballistic armors to trains', cars', buses', helicopters' crashworthiness systems, and many others such as nuclear casks and thermal insulating units.Composite Metal Foam (CMF) has shown about two order of magnitude higher energy absorption than comparable bulk materials while maintaining a third of their density. High-impact resistance, ballistic and blast energy absorption capabilities highlight some of the unique properties of CMF. Nuclear radiation shielding and thermal insulation are other areas in which composite metal foam excels and outperforms bulk metals. The image shows two types of composite metal foams before and after compression loading without any bulging or shear.
      PubDate: 2017-03-13T01:55:30.990824-05:
      DOI: 10.1002/adem.201600776
  • Open Celled Porous Titanium 
    • Authors: Mohammed Menhal Shbeh; Russell Goodall
      Abstract: Among the porous metals, those made of titanium attract particular attention due to the interesting properties of this element. This review examines the state of research understanding and technological development of these materials, in terms of processing capability, resultant structure and properties, and the most advanced applications under development. The impact of the rise of additive manufacturing techniques on these materials is discussed, along with the likely future directions required for these materials to find practical applications on a large scale.Porous metals cover a wide range of materials, foams, sponges, and lattices, and are of interest for some of the unusual properties and property combinations that they can possess. Here, the processing, properties, and current applications of porous titanium are reviewed, highlighting the state of the art of these materials, and delineating future challenges.
      PubDate: 2017-01-09T01:20:51.488758-05:
      DOI: 10.1002/adem.201600664
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