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Artificial Intelligence and Robotics Research
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  • Metals, Vol. 11, Pages 1883: Selective Laser Melting of High Relative
           Density and High Strength Parts Made of Minor Surface Oxidation Treated
           Pure Copper Powder

    • Authors: Peng Yang, Xingye Guo, Dingyong He, Zhen Tan, Wei Shao, Hanguang Fu
      First page: 1883
      Abstract: Pure Copper (Cu) is very difficult to prepare using selective laser melting (SLM) technology. This work successfully prepared the pure Cu with high relative density and high strength by the SLM technology using a surface oxidation treatment. The gas-atomized pure Cu powder was used as the feedstock in this work. Before the SLM process, the pure Cu powder was initially handled using the surface oxidation treatment to coat the powder with an extremely thin layer of Cu2O. The SLMed highly dense specimens contain α-Cu and nano-Cu2O phases. A relationship between the processing parameters (laser power (LP), scanning speed (SS), and hatch space (HS)) and density of Cu alloy in SLM was also investigated. The microstructure of SLMed Cu consists of fine grains with grain sizes ranging from 0.5 to ~30 μm. Tensile testing and detailed microstructural characterization were performed on specimens in the as-SLMed and pure copper state specimens. The mechanical property experiments showed that the specimens prepared by SLM technology containing nano-oxide phases had higher yield strength and tensile strength than that of other SLM-built pure copper. However, the elongation was remarkably decreased compared to other SLM-built pure copper, due to the fine grains and the nano-oxides.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121883
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1884: Dynamic Simulations of Manufacturing
           Processes: Hybrid-Evolving Technique

    • Authors: Amir M. Horr, Johannes Kronsteiner
      First page: 1884
      Abstract: Hybrid physical-data-driven modeling techniques have steadily been developed to address the multi-scale and multi-physical aspects of dynamic process simulations. The analytical and computational features of a new hybrid-evolving technique for these processes are elaborated herein and its industrial applications are highlighted. The authentication of this multi-physical and multi-scale framework is carried out by developing an integrated simulation environment where multiple solver technologies are employed to create a reliable industrial-oriented simulation framework. The goal of this integrated simulation framework is to increase the predictive power of material and process simulations at the industrial scale.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121884
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1885: Multi-Level Resistive Switching of
           Pt/HfO2/TaN Memory Device

    • Authors: Hojeong Ryu, Hoeje Jung, Kisong Lee, Sungjun Kim
      First page: 1885
      Abstract: This work characterizes resistive switching and neuromorphic simulation of Pt/HfO2/TaN stack as an artificial synaptic device. A stable bipolar resistive switching operation is performed by repetitive DC sweep cycles. Furthermore, endurance (DC 100 cycles) and retention (5000 s) are demonstrated for reliable resistive operation. Low-resistance and high-resistance states follow the Ohmic conduction and Poole–Frenkel emission, respectively, which is verified through the fitting process. For practical operation, the set and reset processes are performed through pulses. Further, potentiation and depression are demonstrated for neuromorphic application. Finally, neuromorphic system simulation is performed through a neural network for pattern recognition accuracy of the Fashion Modified National Institute of Standards and Technology dataset.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121885
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1886: Comparison of the Flow Field in a Slab
           Continuous Casting Mold between the Thicknesses of 180 mm and 250 mm by
           High Temperature Quantitative Measurement and Numerical Simulation

    • Authors: Yibo Liu, Jian Yang, Fuxiang Huang, Keran Zhu, Fenggang Liu, Jian Gong
      First page: 1886
      Abstract: In the present work, the flow field in a slab continuous casting mold with thicknesses of 180 and 250 mm are compared using high temperature quantitative measurement and numerical simulation. The results of the numerical simulation are in agreement with those of the high temperature quantitative measurement, which verifies the accuracy and reliability of the numerical simulation. Under the same working conditions, the velocities near the mold surface with the thickness of 180 mm were slightly higher than those of the mold with the thickness of 250 mm. The flow pattern in the 180 mm thick mold maintains DRF more easily than that in 250 mm thick mold. The kinetic energy of the jet dissipates faster in the 250 mm thick mold than in the 180 mm mold. For double-roll flow (DRF), as the argon gas bubbles can be flushed into the deeper region under the influence of strong jets on both sides, the argon bubbles distribute widely in the mold. For single-roll flow (SRF), as the argon bubbles float up quickly after leaving the side holes, the bubble distribution is more concentrated in the width direction, which may cause violent interface fluctuation and slag entrainment. The fluctuation at the steel-slag interface in the mold with 180 mm thickness is greater than that in the mold with 250 mm thickness but less than 5 mm. The increase of mold thickness may lead to a decrease of the symmetry of the flow field in the thickness direction and uniformity of mold powder layer thickness. In summary, the steel throughput should be increased in the 250 mm thick mold compared with that in the 180 mm thick mold.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121886
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1887: Phase Transitions in the
           Co–Al–Nb–Mo System

    • Authors: Denis Davydov, Nataliya Kazantseva, Nikolai Popov, Nina Vinogradova, Igor Ezhov
      First page: 1887
      Abstract: Phase transitions in the Co-rich part of the Co–Al–Nb–Mo phase diagram are studied by energy dispersive spectroscopy (EDS), X-ray analysis, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) measurements. The obtained results were compared with the results for alloys of the binary Co–Al and ternary Co–Al–Nb, and Co–Al–Mo systems. Formation of the intermetallic phase with the L12 structure was found in a range of alloys with 10 at.% Al, 2–9 at.% Nb, and 3–7 at.% Mo. Intermetallic compound Co2Nb, Laves phase with the different chemical composition and crystal structure (C14 and C36) was detected in the Co–Al–Nb and Co–Al–Nb–Mo samples after vacuum solution treating at 1250 °C for 30 h.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121887
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1888: Tailoring the Austenite Fraction of a Cu and
           Ni Containing Medium-Mn Steel via Warm Rolling

    • Authors: Zigan Xu, Jiyao Li, Xiao Shen, Tarek Allam, Silvia Richter, Wenwen Song, Wolfgang Bleck
      First page: 1888
      Abstract: Developing medium-Mn steels (MMnS) demands a better understanding of the microstructure evolution during thermo-mechanical treatments (TMTs). This study demonstrates the relationship among processing, microstructure, and mechanical properties of a warm-rolled medium-Mn steel (MMnS) containing 1.5 wt. % Cu and 1.5 wt. % Ni. After short-time warm rolling (WR) in an intercritical temperature range, a significant quantity (40.6 vol.%) of austenite was reverted and retained after air cooling. The microstructure and tensile properties of the WR specimens were compared with two typical process routes, namely hot rolling+ cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT). The WR specimen exhibited comparable tensile properties with the CRAT specimens (967 MPa yield strength, 1155 MPa tensile strength, 23% total elongation), with a remarkably shortened process route, which was derived from the dislocation accumulation and austenite reversion during rolling. The WR route stands out among the traditional CRAT and the extended WRAT routes for its excellent tensile properties and compact processing route.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121888
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1889: In Situ Evaluation of the Influence of
           Interstitial Oxygen on the Elastic Modulus of La2NiO4

    • Authors: Yuta Kimura, Takashi Nakamura, Koji Amezawa, Keiji Yashiro, Tatsuya Kawada
      First page: 1889
      Abstract: Lattice defects significantly affect the mechanical properties of crystalline metal oxides. The materials for the components of solid oxide fuel cells (SOFCs) are no exception, and hence understanding of the interplay between lattice defects and the mechanical properties of components is important to ensure the mechanical stability of SOFCs. Herein, we performed an in situ evaluation of the temperature and P(O2) dependence of the elastic moduli of La2NiO4 (LN214), a candidate for the cathode material of SOFCs, using the resonance method to understand the influence of interstitial oxygen on its elastic properties. Above 873 K, both the Young’s and shear moduli of LN214 slightly decreased with increasing P(O2), suggesting that these elastic moduli are correlated with interstitial oxygen concentration and decreased with increasing interstitial oxygen. We analyzed the influence of interstitial oxygen on the Young’s modulus of LN214, based on numerically obtained lattice energy. The P(O2) dependence of the Young’s modulus of LN214 was found to be essentially explained by variation in the c-lattice constant, which was triggered by variation in interstitial oxygen concentration. These findings may contribute to a better understanding of the relationship between lattice defects and mechanical properties, and to the improvement of the mechanical stability of SOFCs.
      Citation: Metals
      PubDate: 2021-11-24
      DOI: 10.3390/met11121889
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1890: The Effect of Subsequent Stress-Induced
           Martensite Aging on the Viscoelastic Properties of Aged NiTiHf
           Polycrystals

    • Authors: Anton I. Tagiltsev, Elena Y. Panchenko, Ekaterina E. Timofeeva, Yuriy I. Chumlyakov, Ekaterina S. Marchenko, Ibrahim Karaman
      First page: 1890
      Abstract: This study investigated the effect of stress-induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H-phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress-induced martensite aging at 428 K for 12 h results in the appearance of a two-way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress-induced martensite aging is associated with the oriented growth of thermal-induced martensite. After stress-induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress-induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121890
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1891: Advanced Trends in Metallurgy and Weldability
           of High-Strength Cold-Resistant and Cryogenic Steels

    • Authors: Andrei I. Rudskoi, Sergey G. Parshin
      First page: 1891
      Abstract: Thermomechanical Controlled Processing (TMCP), the initial microstructure and mechanical properties of rolled products made of high-strength steels, have a significant influence on the properties and reliability of welded structures for low temperature and cryogenic service. This paper systematizes advanced research trends in the field of metallurgy and weldability of high-strength cold-resistant and cryogenic steels. The classification and properties of high-strength steels are given and TMCP diagrams and phase transformations are considered. Modern methods of improving the viscoplasticity of rolled steel and welded joints are analyzed. The problems of the weldability of high-strength steels are reduction of impact toughness at low temperatures, hydrogen embrittlement, anisotropy, and softening of welded joints in the heat-affected zone. The authors propose a systemic concept and methods for improving the metallurgy and weldability of high-strength steels for low temperature and cryogenic service.
      Citation: Metals
      PubDate: 2021-11-23
      DOI: 10.3390/met11121891
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1892: Phase Equilibria in the System
           CaO-SiO2-La2O3-Nb2O5 at 1400 °C

    • Authors: Chengjun Liu, Jiyu Qiu, Zhengyue Liu
      First page: 1892
      Abstract: CaO-SiO2-La2O3-Nb2O5 system is of great significance for the pyrometallurgical utilization of Bayan Obo tailing resources. In the present work, the phase equilibrium of this quaternary system at 1400 °C was determined by a thermodynamic equilibrium experiment. On the basis of the recently determined CaO-La2O3-Nb2O5 phase diagram, some boundary surfaces of primary phase fields of CaO-SiO2-La2O3-Nb2O5 phase diagram were modified; then, the 1400 °C isothermal surface in the primary phase fields of SiO2, CaNb2O6, Ca2Nb2O7, and LaNbO4 was constructed, respectively. On this basis, CaO-SiO2-Nb2O5 pseudo-ternary phase diagrams with w(La2O3) = 5%, 10%, 15%, and 20% were determined, respectively. Considering the importance of equilibrium crystallization reaction type, we proposed a new rule named Tangent Line Rule to judge the univariant reaction type in the quaternary phase diagram. By applying Tangent Line Rule and Tangent Plane Rule previously proposed, some univariant and bivariant crystallization reaction types in the CaO-SiO2-La2O3- Nb2O5 phase diagram were determined, respectively. The current work can provide original data for the establishment of a thermodynamic database of Nb-bearing and REE-bearing slag system; the proposed Tangent Line Rule will promote the application of a spatial quaternary phase diagram.
      Citation: Metals
      PubDate: 2021-11-24
      DOI: 10.3390/met11121892
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1893: High-Temperature Surface Oxide Growth
           Kinetics of Al–Si–Zr Bulk Alloys and Ribbons

    • Authors: Denitsa Kiradzhiyska, Gueorgui Vassilev, Rositsa Mancheva, Svetlana Yaneva, Nikolina Milcheva
      First page: 1893
      Abstract: A typical modification technique of the functional properties of Al–Si based alloys is the addition of some third element in trace level. In the present work, ternary Al–Si–Zr bulk and ribbon alloys have been prepared. The kinetics of high-temperature surface oxidation has been studied by thermogravimetric method. It was found that at the start of the experiment the chemical reaction velocity is rate-controlling while for longer times the (oxygen) diffusion is the rate-controlling process. Activation energy of the two stages of oxidation has been obtained. Additional studies such as thermochemical analysis, optical and electron microscopy, and microhardness tests have been done.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121893
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1894: Preparation of a Nickel Layer with
           Bell-Mouthed Macropores via the Dual-Template Method

    • Authors: Ruishan Yang, Weiguo Yao, Guangguang Qian, Yanli Dou
      First page: 1894
      Abstract: A relatively static and unique bubble template is successfully realized on a microporous substrate by controlling the surface tensions of the electrodeposit solution, and a nickel layer containing macropores is prepared using this bubble template. When the surface tension of the solution is 50.2 mN/m, the desired bubble template can be formed, there are fewer bubbles attached to other areas on the substrate, and a good nickel layer is obtained. In the analysis of the macropore formation process, it is found that the size of the bell-mouthed macropores can be tailored by changing the solution stirring speed or the current density to adjust the growth rate of the bubble template. The size change of a macropore is measured by the profile angle of the longitudinal macropore, section. As the solution stirring speed increases from 160 to 480 r/min, the angle range of the bell-mouthed macropores cross-sectional profile is increased from 21.0° to 44.3°. In addition, the angle range of the bell-mouthed macropore cross-sectional profile is increased from 39.3° to 46.3° with the current density increasing from 1 to 2.5 A/dm2. Different from the dynamic hydrogen bubble template, the bubble template implemented in this paper stays attached on the deposition and grows slowly, which is novel and interesting, and the nickel layer containing macropores prepared using this bubble template is applied in completely different fields.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121894
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1895: Permeability Measurements of 3D
           Microstructures Generated by Phase Field Simulation of the Solidification
           of an Al-Si Alloy during Chill Casting

    • Authors: Ralf Berger, Markus Apel, Gottfried Laschet, Wilhelm Jessen, Wolfgang Schröder, Jens Wipperfürth, Johannes Austermann, Christian Hopmann
      First page: 1895
      Abstract: The permeability of the semi-solid state is important for the compensation of volume shrinkage during solidification, since insufficient melt feeding can cause casting defects such as hot cracks or pores. Direct measurement of permeability during the dynamical evolution of solidification structures is almost impossible, and numerical simulations are the best way to obtain quantitative values. Equiaxed solidification of the Al-Si-Mg alloy A356 was simulated on the microscopic scale using the phase field method. Simulated 3D solidification structures for different stages along the solidification path were digitally processed and scaled up to generate 3D models by additive manufacturing via fused filament fabrication (FFF). The Darcy permeability of these models was determined by measuring the flow rate and the pressure drop using glycerol as a model fluid. The main focus of this work is a comparison of the measured permeability to results from computational fluid flow simulations in the phase field framework. In particular, the effect of the geometrical constraint due to isolated domain walls in a unit cell with a periodic microstructure is discussed. A novel method to minimize this effect is presented. For permeability values varying by more than two orders of magnitude, the largest deviation between measured and simulated permeabilities is less than a factor of two.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121895
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1896: Characterization and Analysis of
           Nanocrystalline Soft Magnetic Alloys: Fe Based

    • Authors: Jason Daza, Wael Ben Mbarek, Lluisa Escoda, Joan-Josep Suñol
      First page: 1896
      Abstract: Soft magnetic nanocrystalline alloys have been widely analysed and studied during the past years. However, optimisation of specific chemical compositions is still being developed. The applicability of these soft nanocrystalline alloys depends mainly on the presence of the desired nanocrystalline phases within the alloy. In this study, the analysed alloys are manufactured by mechanical alloying. The analyses performed on the samples include a microstructural analysis, a thermal analysis, and a complementary functional analysis in the form of the thermomagnetic response of some samples. Regarding Fe-based alloys, thermal stability for samples containing B was higher than those containing P (crystal growth peaks in the range between 895–905 K and 775–800 K respectively). The higher magnetization of saturation, Ms, was found in Fe–Mn alloys, whereas the addition of boron provoked a decrease of Ms and the nanocrystals size.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121896
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1897: Creep Behavior of Compact
           γ′-γ″ Coprecipitation Strengthened IN718-Variant
           Superalloy

    • Authors: Semanti Mukhopadhyay, Hariharan Sriram, Christopher H. Zenk, Richard DiDomizio, Andrew J. Detor, Robert W. Hayes, Gopal B. Viswanathan, Yunzhi Wang, Michael J. Mills
      First page: 1897
      Abstract: The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121897
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1898: Pressure Dependence of Structural and
           Mechanical Properties of Single-Crystal Tungsten: A Molecular Dynamics
           Study

    • Authors: Xuepeng Liu, Kezhong Xu, Hua Zhai
      First page: 1898
      Abstract: In the current study, molecular dynamics (MD) simulations were performed to study the pressure dependence of the structural and mechanical properties of single-crystal tungsten. The results show that single-crystal tungsten possesses noteworthy high-pressure stability and exhibits linear lattice contraction with increasing external pressure. Consistent with the results of the performed experiments, the predicted elastic moduli, including Young’s modulus, shear modulus, and bulk modulus, as well as Poisson’s ratio and Pugh’s modulus ratio, show a clear increasing trend with the increase in pressure. Under uniaxial tensile loading, the single-crystal tungsten at high pressures experiences a phase transition from BCC to FCC and other disordered structures, which results in a stripe-like morphology in the tungsten crystal. These results are expected to deepen our understanding of the high-pressure structural and mechanical behaviors of tungsten materials.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121898
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1899: Fatigue and Fracture Behavior of Cryogenic
           Materials Applied to LNG Fuel Storage Tanks for Coastal Ships

    • Authors: Tae-Yeob Kim, Sung-Won Yoon, Ji-Hoon Kim, Myung-Hyun Kim
      First page: 1899
      Abstract: The aim of this study is to investigate the applicability of automatic plasma arc welding (PAW) to cryogenic materials used in liquefied natural gas (LNG) fuel storage tanks based on experimental data. The mechanical properties of the materials were tested at room and cryogenic temperatures to investigate the fatigue and fracture performances of weld joints made by PAW. In addition, the influence of welding parameters on the welded joints such as material types and temperature were considered in this experimental study. Based on the results obtained by this experimental study, it was observed that the experimental results of all materials at room and cryogenic temperatures satisfied all the requirements of each mechanical test. Finally, we propose the experimental results of PAW that can be used in the structural design of LNG fuel storage tank applications.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121899
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1900: Enhancement of the Mechanical and
           Tribological Properties of Aluminum-Based Alloys Fabricated by SPS and
           Alloyed with Mo and Cr

    • Authors: Sergey N. Grigoriev, Alexander Mironov, Ekaterina Kuznetsova, Yuri Pristinskiy, Pavel Podrabinnik, Nestor Washington Solís Pinargote, Iosif Gershman, Pavel Peretyagin, Anton Smirnov
      First page: 1900
      Abstract: Multicomponent aluminum-based alloys doped with chromium (Cr) and molybdenum (Mo), fabricated by spark plasma sintering (SPS), derived from a powder mixture prepared by mechanical alloying, were studied in this work. The morphology of the pristine and worn surfaces was analyzed using a scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system. The obtained alloys exhibited higher hardness (73 and 72) for the Al–Mo and Al–Cr alloys, respectively, compared to reference bronze. Besides improved hardness, SPS-sintered alloys also showed a lower value of the weight and linear wear and the highest score-resistance compared to bronze. The enhanced tribological behavior is related to the formation of secondary structures on the friction surfaces of rubbing pairs, which in turn reduce wear. For the first time, the present research has demonstrated the effectiveness of the addition of Mo and Cr for the fabrication of sintered multicomponent Al-based alloys with a tailored microstructure that induces the formation of secondary structures on the tribosurfaces due to the self-organization processes during friction.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121900
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1901: Microstructure, Mechanical Properties, and
           Thermal Stability of Carbon-Free High Speed Tool Steel Strengthened by
           Intermetallics Compared to Vanadis 60 Steel Strengthened by Carbides

    • Authors: Alena Michalcová, Vojtěch Pečinka, Zdeněk Kačenka, Jan Šerák, Jiří Kubásek, Pavel Novák, Dalibor Vojtěch
      First page: 1901
      Abstract: High speed tool steels are materials that exhibit superior mechanical properties (e.g., high hardness). They should also be resistant to thermal exposure to maintain high hardness during the machining process. In this paper, a C-free tool steel formed of Fe matrix and a Mo6Co7 intermetallic phase was studied. This steel was compared to the well-known Vanadis 60 steel containing Fe matrix and carbides. Microstructures were investigated by scanning (SEM) and transmission (TEM) electron microscopy, and the mechanical properties and thermal stability of both materials were compared. It was proven that the strengthening in the Vanadis 60 steel was mainly caused by the carbides, while the C-free steel was strengthened by the Mo6Co7 phase. The hardness values of both materials were comparable in the utilization state (approx. 950 HV). The hardness of Vanadis 60 steel decreased after several minutes of annealing at 650 °C under the value that enables material utilization. The hardness value of the steel strengthened by the intermetallics also decreased but significantly slower. Based on these results, the main finding of this study is that the C-free steel exhibited much better thermal stability and may be utilized at higher temperatures for longer periods of time than Vanadis 60.
      Citation: Metals
      PubDate: 2021-11-25
      DOI: 10.3390/met11121901
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1902: Influence of Preheating Temperature on
           Changes in Properties in the HAZ during Multipass MIG Welding of Alloy AW
           6061 and Possibilities of Their Restoration

    • Authors: Iva Novakova, Jaromir Moravec, Jan Novak, Pavel Solfronk
      First page: 1902
      Abstract: Fusion welding of heat-treatable aluminum alloys is generally accompanied by a significant decrease in mechanical properties in the HAZ caused by the dissolution of the hardening phase. The intensity of this decrease in mechanical properties can be reduced by limiting the heat input value. However, this approach is in direct conflict with the principles for welding aluminum and its alloys. Due to the very high thermal conductivity of aluminum alloys, it is necessary to use preheating for thicknesses larger than 5 mm to eliminate non-penetration and cold joints. This paper aims to show the influence of multiple temperature cycles, performed at different preheating temperatures, on changes in the microstructure and mechanical properties. At the same time, the extent to which the original properties of the material can be restored by natural and artificial aging at 160, 175 and 190 °C is also investigated.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121902
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1903: Tailings Settlement Velocity Identification
           Based on Unsupervised Learning

    • Authors: Jincheng Xie, Dengpan Qiao, Runsheng Han, Jun Wang
      First page: 1903
      Abstract: In order to reasonably and accurately acquire the settlement interface and velocity of tailings, an identification model of tailing settlement velocity, based on gray images of the settlement process and unsupervised learning, is constructed. Unsupervised learning is used to classify stabilized tailing mortar, and the gray value range of overflow water is determined. Through the identification of overflow water in the settlement process, the interface can be determined, and the settlement velocity of tailings can be calculated. Taking the tailings from a copper mine as an example, the identification of tailings settling velocity was determined. The results show that the identification model of tailing settlement speed based on unsupervised learning can identify the settlement interface, which cannot be manually determined in the initial stage of settlement, effectively avoiding the subjectivity and randomness of manual identification, and provide a more scientific and accurate judgment. For interfaces that can be manually recognized, the model has high recognition accuracy, has a rapid and efficient recognition process, and the relative error can be controlled within 3%. It can be used as a new technology for measuring the settling velocity of tailings.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121903
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1904: Selective Leaching of Molybdenum from Bulk
           Concentrate by Electro-Oxidation

    • Authors: Kyeong Woo Chung, Ho-Sung Yoon, Chul-Joo Kim, Ho-Seok Jeon
      First page: 1904
      Abstract: This paper proposes selective leaching of molybdenum from Mo/Cu complex bulk concentrates in a 5 M NaCl solution using the electro-oxidation method. Here, the effects of several factors such as pH, pulp density, current density, and temperatures were investigated. A higher leaching yield of Mo increased with increasing pH from 5 to 9 and decreased with increasing pulp density from 1 to 10%. A rise in current density did not help enhance Mo, and the elevating temperature did not always result in a higher leaching yield. Application of ultrasonic led to higher leaching yield of Mo. Ninety-two percent of leaching yield was obtained upon leaching of Mo in 5 M NaCl at 25 °C, pulp density of 5%, and the current density of 0.292 A/g under ultrasonic irradiation with a power of 27 kW. The resultant residue mainly consisted of chalcopyrite.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121904
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1905: Upscaling Severe Torrefaction of Agricultural
           Residues to Produce Sustainable Reducing Agents for Non-Ferrous Metallurgy
           

    • Authors: Hary Demey, Elvira Rodriguez-Alonso, Elie Lacombe, Maguelone Grateau, Nicolas Jaricot, André Chatroux, Sebastien Thiery, Muriel Marchand, Thierry Melkior
      First page: 1905
      Abstract: Torrefaction of almond shells and olive stones, which are typically considered agricultural waste in the southern regions of the European Union, was investigated in this work for application as reducing agents in the metallurgical industry. Four different temperatures were tested: 250, 280, 300 and 350 °C. The evolution of the solid yields with the temperature was determined with TGA measurements. This showed that the duration of torrefaction should not exceed 45 min. The kinetic profiles were successfully fitted using the pseudo-first-order rate equation (PFORE). Then, torrefaction for 45 min was systematically carried out at every temperature and for each resource in a laboratory-scale batch device. The raw and torrefied biomasses were characterized using proximate, ultimate and calorific analyses. The carbon/oxygen ratio and the heating values were increased as a result of the torrefaction severity (from 20 MJ/kg for both raw biomasses to 30 MJ/kg at 350 °C). The highest mass losses were obtained at the highest temperature (67.35 and 65.04 %w for almond shells and olive stones, respectively, at 350 °C). The fixed carbon value also increased, being higher than 67 %w for torrefaction at 350 °C. The large-scale torrefaction at 350 °C (45 min) of these biomasses was carried out in a continuous pilot plant. The solids were characterized as well, and their properties were close to those of the biomasses torrefied in the laboratory-scale batch reactor under the same conditions. This thermal treatment provided biochars with all the required properties to be used as reducing materials in metallurgy.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121905
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1906: Response of Floc Networks in Cemented Paste
           Backfill to a Pumping Agent

    • Authors: Jiaqi Zhu, Shunchuan Wu, Haiyong Cheng, Xiaojie Geng, Jin Liu
      First page: 1906
      Abstract: Cemented paste backfill is critical for the development of green mines, the safe exploitation of mineral resources deep underground, and the efficient disposal of solid wastes produced by mining. In this paper, the mechanism underpinning how the pumping agent works was studied. The number, area, and fractal dimension of pores in the microstructure of fresh paste were quantitatively analyzed using scanning electron microscopy (SEM), image processing, and fractal theory, and the response of flocs was investigated. The results show that floc networks disintegrated and the liquid network became the dominant structure under the action of the pumping agent, which enhanced the lubrication and promotion of multi-scale particles. In addition, the force chains became fragile and scattered, diminishing the yield stress of the paste. The pores had a more homogenized dimension and the porosity was 15.52% higher. The increase in the fractal dimension of the pores indicated that there was a higher self-similarity, in terms of microstructure, with a strengthened liquid network. The migration of floc structures contributed to the enhancement of the fluidity and rheology of the paste. This study provides insights into the effects of floc and liquid networks on the performance of paste, and it is of engineering significance in terms of realizing safe and efficient CPB operations.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121906
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1907: Effects of La on Thermal Stability, Phase
           Formation and Magnetic Properties of
           Fe–Co–Ni–Si–B–La High Entropy Alloys

    • Authors: Jiaming Li, Jianliang Zuo, Hongya Yu
      First page: 1907
      Abstract: The microstructure, phase formation, thermal stability and soft magnetic properties of melt-spun high entropy alloys (HEAs) Fe27Co27Ni27Si10−xB9Lax with various La substitutions for Si (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) were investigated in this work. The Fe27Co27Ni27Si10−xB9La0.6 alloy shows superior soft magnetic properties with low coercivity Hc of ~7.1 A/m and high saturation magnetization Bs of 1.07 T. The content of La has an important effect on the primary crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2) of the alloys. After annealing at relatively low temperature, the saturation magnetization of the alloy increases and the microstructure with a small amount of body-centered cubic (BCC) phase embedded in amorphous matrix is observed. Increasing the annealing temperature reduces the magnetization due to the transformation of BCC phase into face-centered cubic (FCC) phase.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121907
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1908: Influence of Batch Mass on Formation of NiTi
           Shape Memory Alloy Produced by High-Energy Ball Milling

    • Authors: Tomasz Goryczka, Piotr Salwa
      First page: 1908
      Abstract: A high-energy ball milling technique was used for production of the equiatomic NiTi alloy. The grinding batch was prepared in two quantities of 10 and 20 g. The alloy was produced using various grinding times. Scanning electron microscopy, X-ray diffraction, hardness measurement and differential scanning calorimetry were used for materials characterization at various milling stages. The produced alloy was studied by means of microstructure, chemical and phase composition, average grain and crystallite size, crystal lattice parameters and microstrains. Increasing the batch mass to 20 g and extending the grinding time to 140 h caused the increase in the average size of the agglomerates to 700 µm while the average crystallites size was reduced to a few nanometers. Microstrains were also reduced following elongation of milling time. Moreover, when the grinding time is extended, the amount of the monoclinic phase increases at the expense of the body-centered cubic one—precursors of crystalline, the B2 parent phase and the B19′ martensite. Crystallization takes place as a multistage process, however, at temperatures below 600 °C. After crystallization, the reversible martensitic transformation occurred with the highest enthalpy value—4 or 5 J/g after 120 and 140 h milling, respectively.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121908
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1909: Solid Solution Strengthening of Mo, Re, Ta
           and W in Ni during High-Temperature Creep

    • Authors: Lukas Haußmann, Hamad ur ur Rehman, Dorothea Matschkal, Mathias Göken, Steffen Neumeier
      First page: 1909
      Abstract: Solid solution strengthening of the unordered γ matrix phase by alloying elements is of great importance during creep of Ni-based superalloys, particularly at high temperatures above 1000 °C. To study the role of different potent solutes, we have conducted creep experiments on binary Ni-2X alloys (X = Mo, Re, Ta, W) at 1000 °C, 1050 °C, and 1100 °C at a constant stress of 20 MPa. Compared to mechanical tests below 800 °C, where the size of the elements mostly determines the solid solution hardening contribution, the strengthening contribution of the different alloying elements above 1000 °C directly correlates with their diffusivity. Therefore, elements such as Ta that lead to strong solid solution hardening at low temperatures become less effective at higher temperatures and are exceeded by slower diffusing elements, such as Re.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121909
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1910: Innovations in Monitoring, Control and Design
           of Laser and Laser-Arc Hybrid Welding Processes

    • Authors: Zheng-Xiong Ma, Pei-Xin Cheng, Jie Ning, Lin-Jie Zhang, Suck-Joo Na
      First page: 1910
      Abstract: With the rapid development of high power laser, laser welding has been widely used in many fields including manufacturing, metallurgy, automobile, biomedicine, electronics, aerospace etc. Because of its outstanding advantages, such as high energy density, small weld size, easy automation. Combining the two heat sources of laser and arc for welding can achieve excellent results due to the synergistic effect. Laser welding is a complicated physical and chemical metallurgical process, involving the laser beam and molten pool, keyholes and materials melting, evaporation and multiple physical process. Process monitoring and quality control are important content of research and development in the field of laser welding, which is the premise to obtain fine weld with high quality. Numerical simulation technology can describe many complex physical phenomena in welding process, which is very important to predict weld forming and quality and clarify the underline mechanism. In this paper, the research progress of process monitoring, quality control and autonomous intelligent design of laser and laser-arc hybrid welding based on numerical simulation were reviewed, and the research hotspots and development trends of laser welding in the future are predicted.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121910
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1911: Plasmonic Gold Nanorod Size-Controlled:
           Optical, Morphological, and Electrical Properties of Efficiency Improved
           Tin Disulfide Vacuum-Free Hybrid Solar Cells

    • Authors: Minsu Kim, Nguyen Tam Nguyen Truong, Nguyen Hoang Lam, Nam Le, Asiya M. Tamboli, Mohaseen S. Tamboli, Jae Hak Jung
      First page: 1911
      Abstract: The different size of plasmonic gold nanorods (NRs) were synthesized by the overgrown seeds method and applied to vacuum-free hybrid solar cells (VFHSCs). Tin disulfide (SnS2) quantum dots were synthesized and used as an n-type material of the device. The synthesized materials were characterized by different techniques such as transmission electron microscopy (TEM), UV-Vis spectroscopy, and atomic force microscopy (AFM). The Au (NRs) had a different of size of NR1 (Width: 4 nm; Length: 12 nm), NR2 (Width: 5 nm; Length: 16 nm), NR3 (Width: 6 nm; Length: 22 nm) which were measured using a TEM technique. The Au NR particles were incorporated into the PEDOT:PSS as a hole transport layer (HTL) of solar cells device. The effects of Au NRs size on the device performance were investigated. A thin film of Zin oxide (ZnO) was used as a buffer layer of the device. The influence of buffer layer thickness on the device’s active layer surface morphology was also studied. At the optimized condition, the highest power conversion efficiency was obtained at about ~3.7%.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121911
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1912: A Novel Classification Method for Pores in
           Laser Powder Bed Fusion

    • Authors: Natan Nudelis, Peter Mayr
      First page: 1912
      Abstract: Nowadays, additive manufacturing (AM) using laser powder bed fusion (LPBF) is acknowledged for its ability to generate near-net-shape components for various industries such as aerospace, automotive, and health industries. However, internal defects seem to be the inevitable concomitant in the current state of laser powder bed fusion of Al alloys. Hence, knowledge of the formation, different types, and morphologies of pores and their suppression is an essential element for successful future AM applications. The purpose of this research is to qualify a new approach of defect classification using X-ray tomography. In this framework, this research examined the influence of size, shape, and location of pores on crack initiation for AlSi10Mg parts produced by LPBF. For this reason, a total number of 39,228 pores detected in a cylindrical sample were categorised. Additionally, 26 selected pores of different morphology from the X-ray scan were analysed by means of finite element analysis (FEA). Moreover, fracture mechanics determinations were carried out to examine the correlations between pore characteristics and degree of stress concentration. The result is an evaluated novel pore classification method that can be used for process adjustments, quality assurance, as well as further research.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121912
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1913: Interface Strengthening of
           α-Mg/C14–Mg2Ca Eutectic Alloy

    • Authors: Satoshi Araki, Koji Oishi, Yoshihiro Terada
      First page: 1913
      Abstract: This study investigates the effect of the α/C14 interface on the creep strength of α-Mg/C14–Mg2Ca eutectic alloy at 473 K under a stress of 40 MPa. The α/C14 interface is composed of terraces and steps, with terraces parallel to the (1101)α pyramidal plane of the α-Mg lamellae and to the (1120)C14 columnar plane of the C14–Mg2Ca lamellae. The creep curves of the alloy exhibit three stages: a normal transient creep stage, a minimum creep rate stage, and an accelerating stage. The minimum creep rate is proportional to the lamellar spacing, indicating that the α/C14 lamellar interface plays a creep-strengthening role. In the high-resolution transmission electron microscopy image captured of the specimen after the creep test, <a> dislocations can be mainly seen within the soft α-Mg lamellae, and they are randomly distributed at the α/C14 interface. In contrast, dislocations are rarely introduced in the hard C14–Mg2Ca lamellae. It is deduced that the α/C14 interface presents a barrier to dislocation gliding within the α-Mg lamellae and does not help rearrange the dislocations.
      Citation: Metals
      PubDate: 2021-11-26
      DOI: 10.3390/met11121913
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1914: The Effect of Silica Sand Proportion in Laser
           Scabbling Process on Cement Mortar

    • Authors: Tam-Van Huynh, Youngjin Seo, Dongkyoung Lee
      First page: 1914
      Abstract: Cement mortar composite has a wide range of applications on construction sites, including masonry, plastering and concrete repair. In construction sites, scabbling process is a method to remove from a few millimeters to several centimeters of defect concrete surfaces. As a result, it is essential to investigate the scabbling characteristics for cement mortar with different silica sand proportion in laser scabbling process. In this study, 5 types of cement mortar with different silica sand proportions in mixing were fabricated and scabbled by using a high-density power laser beam. The effects of silica sand proportion in color changing and penetration depth of the samples after laser scabbling process were studied. Furthermore, the generation of micro-cracks and pores were observed by using scanning electron microscopy (SEM). In addition, chemical composition changes between processed zone and non-processed zone were also evaluated by Energy Dispersive X-ray (EDX) analysis. The results of this study are expected to provide valuable knowledge in understanding of the laser scabbling process for cement-based materials.
      Citation: Metals
      PubDate: 2021-11-27
      DOI: 10.3390/met11121914
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1915: Evaluation of Fatigue Characteristics of
           Aluminum Alloys and Mechanical Components Using Extreme Value Statistics
           and C-Specimens

    • Authors: Jungsub Lee, Sang-Youn Park, Byoung-Ho Choi
      First page: 1915
      Abstract: In this study, the fatigue characteristics of aluminum alloys and mechanical components were investigated. To evaluate the effect of forging, fatigue specimens with the same chemical compositions were prepared from billets and forged mechanical components. To evaluate the cleanliness of the aluminum alloys, the cross-sectional area of specimens was observed, and the maximum inclusion sizes were obtained using extreme value statistics. Rotary bending fatigue tests were performed, and the fracture surfaces of the specimens were analyzed. The results show that the forging process not only elevated the fatigue strength but also reduced the scatter of the fatigue life of aluminum alloys. The fatigue characteristics of C-specimens were obtained to develop finite-element method (FEM) models. With the intrinsic fatigue properties and strain–life approach, the FEM analysis results agreed well with the test results.
      Citation: Metals
      PubDate: 2021-11-27
      DOI: 10.3390/met11121915
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1916: High-Pressure Cooling in Finishing Turning of
           Haynes 282 Using Carbide Tools: Haynes 282 and Inconel 718 Comparison

    • Authors: Antonio Díaz-Álvarez, José Díaz-Álvarez, José Luis Cantero, Mª Henar Miguélez
      First page: 1916
      Abstract: Despite the interest of industry in nickel-based superalloys and its main features (high temperatures resistance, hardness, low thermal conductivity, among others), even today they are still materials that are difficult to cut. Cutting tools withstand both high pressures and temperatures highly localized at the cutting area because of the elevated work hardening of the alloy and the problems for the cutting fluid to access the region, with the consequent strong tool wear. The use of cutting fluids at high pressures improves coolant access and heat removal. This paper analyzed the machining of Haynes 282 alloy by means of coated carbide tools under high-pressure cutting fluids at finishing conditions. Tests were developed at different cutting speeds and feeds quantifying the machining forces, surface roughness, tool wear, and tool life. Values of 45.9 min and Ra between 2 µm and 1 µm were obtained in this study for tool life and roughness, respectively, for the combination of cutting speed 50 m/min and feed 0.1 mm/rev. Likewise, a comparative analysis is included with the results obtained in previous works developed by the authors relating to the finishing turning of Haynes 282 and Inconel 718 under conventional pressure cooling. The comparative analysis with Inconel 718 is included in the study due to its importance within the nickel base superalloys being widely used in industry and widely analyzed in scientific literature.
      Citation: Metals
      PubDate: 2021-11-27
      DOI: 10.3390/met11121916
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1917: Critical Assessment of the Electric Effect in
           Electric Arc Welding

    • Authors: Rongshan Qin
      First page: 1917
      Abstract: This work provides a critical assessment of electric effects on the microstructure evolution at the heat-affected zone in electric arc welding. Electric effects are the interactions between electromagnetic fields and materials’ microstructures. They differ from the arc effect and the Joule heating effect by providing an alternative contribution to nucleation, grain growth, recrystallisation and tempering. The influence of the electric effect on grain size, defects, anisotropic properties, precipitates and residual stress has been examined kinetically and thermodynamically. The use of adaptable electric current densities, pulse durations, pulse frequencies and electrode movements is suggested to achieve desirable microstructures and mechanical properties for the weldments.
      Citation: Metals
      PubDate: 2021-11-27
      DOI: 10.3390/met11121917
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1918: Conductance Quantization Behavior in
           Pt/SiN/TaN RRAM Device for Multilevel Cell

    • Authors: Jongmin Park, Seungwook Lee, Kisong Lee, Sungjun Kim
      First page: 1918
      Abstract: In this work, we fabricated a Pt/SiN/TaN memristor device and characterized its resistive switching by controlling the compliance current and switching polarity. The chemical and material properties of SiN and TaN were investigated by X-ray photoelectron spectroscopy. Compared with the case of a high compliance current (5 mA), the resistive switching was more gradual in the set and reset processes when a low compliance current (1 mA) was applied by DC sweep and pulse train. In particular, low-power resistive switching was demonstrated in the first reset process, and was achieved by employing the negative differential resistance effect. Furthermore, conductance quantization was observed in the reset process upon decreasing the DC sweep speed. These results have the potential for multilevel cell (MLC) operation. Additionally, the conduction mechanism of the memristor device was investigated by I-V fitting.
      Citation: Metals
      PubDate: 2021-11-27
      DOI: 10.3390/met11121918
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1919: Recent Progress in Hybrid Aluminum Composite:
           Manufacturing and Application

    • Authors: Elvira Wahyu Arum Fanani, Eko Surojo, Aditya Rio Prabowo, Hammar Ilham Akbar
      First page: 1919
      Abstract: Due to their excellent properties, the requirement for materials with higher characteristics has transformed primary alloy into composite materials. Composites are particularly essential for various applications in numerous engineering purposes because of their superior mechanical, physical, and machining qualities. Compared to traditional materials, aluminum composite has various advantages and superior characteristics. To reduce production costs and obtain the desired properties, the researchers developed a hybrid aluminum matrix composite (HAMC), an AMC with two or more types of reinforcement. Further studies were conducted to improve the qualities and manufacturing processes of composites to improve their properties. Various methods are available to HAMC manufacturing, and different manufacturing methods result in different characteristics of HAMC composites, viewed from physical properties, mechanical properties, and production cost. In addition, differences in the type, size, and amount of reinforcement produce various hybrid composite properties, especially in the physical properties, mechanical properties, and tribological behavior of HAMC. This work presents a comprehensive review of recent progress in HAMC study with various reinforcement particles, manufacturing techniques, physical, mechanical, and tribological properties of HAMC. On the other side, this work provides discussion for application, challenges, and future work conducted for HAMC development.
      Citation: Metals
      PubDate: 2021-11-28
      DOI: 10.3390/met11121919
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1920: Analysis of Dynamic Response Behavior of
           Crack under Impact Stress Wave

    • Authors: Yan Peng, Yang Liu, Wei Zhang
      First page: 1920
      Abstract: The structural parts of construction machinery mostly fail due to impact load, but current research on the failure behavior of the impact load has not established a complete theoretical system. Based on wave theory and fracture mechanics, this paper analyzed the wave behavior of shock stress waves and established a model of shock stress wave propagation. Given the dynamic response behavior of the stress and strain field at the crack tip, dynamic fracture mechanics theory was used to solve the dynamic fracture strength stress factor and evaluate the dynamic fracture performance of the structure with crack damage under shock waves. Through dynamic response analysis and numerical calculation of the typical SHPB (split Hopkinson pressure bar) test standard compact tension (CT) specimens under the short-term strong shock stress wave, the stress and strain evolution law of the material under the shock wave was analyzed, and the correlation of the shock stress wave was verified. This research work can meet the requirements of engineering design and has practical engineering significance, playing an important role in material safety design.
      Citation: Metals
      PubDate: 2021-11-28
      DOI: 10.3390/met11121920
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1921: Dissolution of the Primary γ′
           Precipitates and Grain Growth during Solution Treatment of Three Nickel
           Base Superalloys

    • Authors: Karen Alvarado, Ilusca Janeiro, Sebastian Florez, Baptiste Flipon, Jean-Michel Franchet, Didier Locq, Christian Dumont, Nathalie Bozzolo, Marc Bernacki
      First page: 1921
      Abstract: Second phase particles (SPP) play an essential role in controlling grain size and properties of polycrystalline nickel base superalloys. The understanding of the behavior of these precipitates is of prime importance in predicting microstructure evolutions. The dissolution kinetics of the primary γ′ precipitates during subsolvus solution treatments were investigated for three nickel base superalloys (René 65, AD730 and N19). A temperature-time codependency equation was established to describe the evolution of primary γ′ precipitates of each material using experimental data, the Thermo-Calc software and the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The dissolution kinetics of precipitates was also simulated using the level-set (LS) method and the former phenomenological model. The precipitates are represented using an additional LS function and a numerical treatment around grain boundaries in the vicinity of the precipitates is applied to reproduce their pinning pressure correctly. Thus, considering the actual precipitate dissolution, these simulations aim to predict grain size evolution in the transient and stable states. Furthermore, it is illustrated how a population of Prior Particle Boundaries (PPB) particles can be considered in the numerical framework in order to reproduce the grain size evolution in the powder metallurgy N19 superalloy. The proposed full-field strategy is validated and the obtained results are in good agreement with experimental data regarding the precipitates and grain size.
      Citation: Metals
      PubDate: 2021-11-28
      DOI: 10.3390/met11121921
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1922: Enhanced Leaching of Zinc from
           Zinc-Containing Metallurgical Residues via Microwave Calcium Activation
           Pretreatment

    • Authors: Aiyuan Ma, Xuemei Zheng, Lei Gao, Kangqiang Li, Mamdouh Omran, Guo Chen
      First page: 1922
      Abstract: Given the shortage of zinc resource, the low utilisation efficiency of secondary zinc resource, and the crucial problem that the synchronous dissolution of zinc from different mineral phases, an activation pretreatment method merged with calcium activation and microwave heating approach was proposed to enhance the zinc leaching from complex encapsulated zinc-containing metallurgical residues (ZMR). Results indicated that under the optimal pretreatment conditions, including microwave activation temperature of 400 °C, CaO addition of 25% and activation time of 20 min, the zinc leaching rate reached 91.67%, which was 3.9% higher than that by conventional roasting pretreatment. Meanwhile, microwave heating presents excellent treatment effects, manifested by the zinc leaching rates, all exceeding that of conventional roasting under the same conditions, while the process temperature is decreased by 200 °C. In addition, XRD and SEM-EDS analysis denoted that microwave calcification pretreatment can effectively promote the transformation of the refractory zinc minerals like Zn2SiO4 and ZnFe2O4 into the easily leachable zinc oxides. The distinctive selective heating characteristics of microwave heating strengthened the dissociation of mineral inclusion, and the generated cracks increased the interfacial reaction area and further enhancing the leaching reaction of zinc from ZMR.
      Citation: Metals
      PubDate: 2021-11-28
      DOI: 10.3390/met11121922
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1923: Production and Characterization of a 316L
           Stainless Steel/β-TCP Biocomposite Using the Functionally Graded
           Materials (FGMs) Technique for Dental and Orthopedic Applications

    • Authors: Bruna Horta Bastos Kuffner, Patricia Capellato, Larissa Mayra Silva Ribeiro, Daniela Sachs, Gilbert Silva
      First page: 1923
      Abstract: Metallic biomaterials are widely used for implants and dental and orthopedic applications due to their good mechanical properties. Among all these materials, 316L stainless steel has gained special attention, because of its good characteristics as an implantable biomaterial. However, the Young’s modulus of this metal is much higher than that of human bone (~193 GPa compared to 5–30 GPa). Thus, a stress shielding effect can occur, leading the implant to fail. In addition, due to this difference, the bond between implant and surrounding tissue is weak. Already, calcium phosphate ceramics, such as beta-tricalcium phosphate, have shown excellent osteoconductive and osteoinductive properties. However, they present low mechanical strength. For this reason, this study aimed to combine 316L stainless steel with the beta-tricalcium phosphate ceramic (β-TCP), with the objective of improving the steel’s biological performance and the ceramic’s mechanical strength. The 316L stainless steel/β-TCP biocomposites were produced using powder metallurgy and functionally graded materials (FGMs) techniques. Initially, β-TCP was obtained by solid-state reaction using powders of calcium carbonate and calcium phosphate. The forerunner materials were analyzed microstructurally. Pure 316L stainless steel and β-TCP were individually submitted to temperature tests (1000 and 1100 °C) to determine the best condition. Blended compositions used to obtain the FGMs were defined as 20% to 20%. They were homogenized in a high-energy ball mill, uniaxially pressed, sintered and analyzed microstructurally and mechanically. The results indicated that 1100 °C/2 h was the best sintering condition, for both 316L stainless steel and β-TCP. For all individual compositions and the FGM composite, the parameters used for pressing and sintering were appropriate to produce samples with good microstructural and mechanical properties. Wettability and hemocompatibility were also achieved efficiently, with no presence of contaminants. All results indicated that the production of 316L stainless steel/β-TCP FGMs through PM is viable for dental and orthopedic purposes.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121923
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1924: How Austenitic Is a Martensitic Steel
           Produced by Laser Powder Bed Fusion' A Cautionary Tale

    • Authors: Fan Zhang, Mark R. Stoudt, Souzan Hammadi, Carelyn E. Campbell, Eric A. Lass, Maureen E. Williams
      First page: 1924
      Abstract: Accurate phase fraction analysis is an essential element of the microstructural characterization of alloys and often serves as a basis to quantify effects such as heat treatment or mechanical deformation. Additive manufacturing (AM) of metals, due to the intrinsic nonequilibrium solidification and spatial variability, creates additional challenges for the proper quantification of phase fraction. Such challenges are exacerbated when the alloy itself is prone to deformation-induced phase transformation. Using commonly available in-house X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) and less commonly used synchrotron-based high-energy X-ray diffraction, we characterized nitrogen-atomized 17-4 precipitation-hardening martensitic stainless steel, a class of AM alloy that has received broad attention within the AM research community. On the same build, our measurements recovered the entire range of reported values on the austenite phase fractions of as-built AM 17-4 in literature, from ≈100% martensite to ≈100% austenite. Aided by Calphad simulation, our experimental findings established that our as-built AM 17-4 is almost fully austenitic and that in-house XRD and EBSD measurements are subject to significant uncertainties created by the specimen’s surface finish. Hence, measurements made using these techniques must be understood in their correct context. Our results carry significant implications, not only to AM 17-4 but also to AM alloys that are susceptible to deformation-induced structure transformation and suggest that characterizations with less accessible but bulk sensitive techniques such as synchrotron-based high energy X-ray diffraction or neutron diffraction may be required for proper understanding of these materials.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121924
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1925: Development of Ultrafine Grain IF Steel via
           Differential Speed Rolling Technique

    • Authors: Young Gun Ko, Kotiba Hamad
      First page: 1925
      Abstract: The aim of this paper was to investigate the microstructural development and properties of interstitial free (IF) steel fabricated using the DSR (differential speed rolling) process. Severe plastic deformation of the DSR passes was imposed on the sample for up to four passes, leading to ~1.7 total strain with a speed ratio of 1:4 between the two rolls. Microstructural observation revealed that the equiaxed grain size of ~0.7 µm, including the formation of grain boundaries with a high angle of misorientation, was reached after four operations of DSR, which was attributed to the grain subdivision of severely elongated ferrite grain. Since the deformation mode of the DSR operation was dominated by severe shear deformation, the main shear texture of the bcc components appeared in all DSR operations in which the α-fiber of the {110} slip became a main component in accommodating the severe plastic deformation of the DSR process. The intensity of the shear texture, the {110} and {112} slip, increased by increasing the number of passes. Moreover, the γ-fiber of the <112>-type planes was activated as a result of the alternation of the shear direction during sample rotation. The microhardness and room temperature tensile tests revealed that the strength of the IF steel improved as the amount of strain increased, and this was attributed to the grain refinement and texture characteristics of the samples after the DSR processing.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121925
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1926: Development of Rapidly-Quenched Al-Ge-Si
           Filler Alloys for the Joining of Stainless Steel AISI 304 and Aluminum
           Alloy AA6082

    • Authors: Alexander Ivannikov, Vasilii Fedorov, Anton Abramov, Milena Penyaz, Diana Bachurina, Thomas Uhlig, Alexey Suchkov, Guntram Wagner, Pavel Morokhov, Oleg Sevryukov
      First page: 1926
      Abstract: Aluminum alloys based on the Al-Ge-Si system with a germanium content of up to 40 wt.%, promising for the brazing of aluminum alloy AA6082 with the stainless steel AISI 304, were studied. The temperature characteristics and microstructural and mechanical properties of the filler alloys were systematically investigated. Differential scanning calorimetry showed that with an increase in the germanium content from 28.0 to 40.0 wt.%, the liquidus temperature of the filler alloys decreased from 514.8 to 474.3 °C. X-ray diffraction analysis and electron microscopy data showed that the foil of the filler alloys reveals a homogeneous structure. The ingots of the alloys contain two eutectics, the first of which consists of a solid solution of (Al, Ge) with a solid solution of (Ge, Si), and the second consists of a solid solution of (Al, Ge) with a solid solution based on (Ge). When the content of germanium increases from 28.0 to 40.0 wt.%, a separation of the faceted solid solution particles (Ge, Si) and an increase in their number could be observed. Nanohardness measurements showed that the (Ge, Si) and (Ge) solid solutions had similar nanohardness, with values of 11.6 and 10.2 GPa, respectively. Simultaneously, the Al solid solution and the intermetallic Al7Ge2Fe phase exhibited significantly lower nanohardness values of 0.7 and 6.7 GPa, respectively. Brinell hardness measurements showed that the ingots of the filler alloys were sufficiently ductile and had a hardness comparable to that of AA6082, which is used for brazing with AISI 304 stainless steel. The obtained results for the studied ingots and the rapidly quenched foils can be used to predict the forming structure of the seam after brazing and adjusted for diffusion processes occurring between the brazed materials and the studied filler alloys.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121926
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1927: Recent Progress in Understanding the
           Nano/Micro-Mechanical Behavior of Austenite in Advanced High Strength
           Steels

    • Authors: Qingwen Guan, Wenjun Lu, Binbin He
      First page: 1927
      Abstract: Advanced high strength steels (AHSS) are developed to reduce vehicle weight without sacrificing passenger safety. The newly developed AHSS frequently incorporates the austenite as the intrinsic component with large amount and good stability, which is realized by carefully designed alloying elements and thermo-mechanical processing. To explore the great potential of austenite in enhancing the strain hardening behavior of AHSS, detailed information on the mechanical behavior of single austenite grain is a prerequisite, which can be collected by a small-scale test. The present work reviews the recent progress in understanding the nano/micro-mechanical behavior of austenite in varied AHSS. Three different plasticity modes including dislocation plasticity, martensitic transformation, and deformation twinning can be observed in the austenite grains during small-scale tests, given proper stacking fault energy and crystal orientation. The remaining issues concerned with the nano/micro-mechanical behavior of austenite are discussed. The present review advances the general understanding of the nano/micro-mechanical behavior of austenite grains in AHSS, which may shed light on the precise austenite engineering with the development of new AHSS, realizing the dream of high-performance steels at low cost.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121927
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1928: Quasi-Static, Dynamic Compressive Properties
           and Deformation Mechanisms of Ti-6Al-4V Alloy with Gradient Structure

    • Authors: Lei Lei, Yongqing Zhao, Qinyang Zhao, Shewei Xin, Cong Wu, Weiju Jia, Weidong Zeng
      First page: 1928
      Abstract: Gradient structure metals have good comprehensive properties of strength and toughness and are expected to improve the dynamic mechanical properties of materials. However, there are few studies on the dynamic mechanical properties of gradient structured materials, especially titanium alloys. Therefore, in this study, ultrasonic surface rolling is used to prepare a gradient structure layer on the surface of Ti-6Al-4V, and the quasi-static and dynamic compressive properties of coarse-grained Ti-6Al-4V (CG Ti64) and gradient-structured Ti-6Al-4V (GS Ti64) are investigated. The results show that a GS with a thickness of 293 µm is formed. The quasi-static compressive strength of GS Ti64 is higher than that of CG Ti64. Both CG Ti64 and GS Ti64 exhibit weak strain hardening effects and strain rate insensitivity during dynamic compression, and the compressive strength is not significantly improved. The lateral expansion of CG Ti64 is more obvious, while the lateral side of GS Ti64 is relatively straight, indicating that uniform deformation occurs in GS Ti64. The α phase in the GS produces dislocation cells and local deformation bands, and the lamellar structure is transformed into ultrafine crystals after dynamic compression. Both of them produce an adiabatic shear band under 2700 s−1, a large crack forms in CG Ti64, while GS Ti64 forms a small crack, indicating that GS Ti64 has better resistance to damage. The synergistic deformation of GS and CG promotes Ti-6Al-4V to obtain good dynamic mechanical properties.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121928
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1929: About the Memory of Transformation-Induced
           Plasticity in 35NCD16 Carbon Steel Subjected to Various Thermomechanical
           Histories

    • Authors: Jose Jimenez, Lakhdar Taleb
      First page: 1929
      Abstract: This study deals with Transformation-Induced Plasticity (TRIP) observed in the martensitic transformation of 35NCD16 ferritic steel. In this study, TRIP tests were carried out for two different cases: First, after only free dilatometric (FD) tests, which is used as the reference test for the considered applied stress; second, with TRIP tests being performed similarly to the first case (same thermal cycle, same applied stress) but with pre-thermomechanical loading histories applied. Such histories may be FD tests, TRIP tests, elastoplastic history, etc. The comparison between the results of TRIP test (a) and TRIP test (b) indicates if TRIP holds the memory of the applied loading histories. The current obtained results tell us that TRIP does not hold any significant memory. During the martensite → austenite transformation, the material may present recovery from strain hardening. Waiting for more details about the physical phenomena responsible for the absence of TRIP memory, one can point out the importance of this result as it enables one to use the same specimen for several TRIP tests. However, this result must be validated using other combinations of loading histories (such as multiaxial and cyclic, among others).
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121929
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1930: The Effect of a Slow Strain Rate on the
           Stress Corrosion Resistance of Austenitic Stainless Steel Produced by the
           Wire Laser Additive Manufacturing Process

    • Authors: Maxim Bassis, Abram Kotliar, Rony Koltiar, Tomer Ron, Avi Leon, Amnon Shirizly, Eli Aghion
      First page: 1930
      Abstract: The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121930
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1931: Performance Assessment and Chip Morphology
           Evaluation of Austenitic Stainless Steel under Sustainable Machining
           Conditions

    • Authors: Anshuman Das, Smita Padhan, Sudhansu Ranjan Das, Mohammad S. Alsoufi, Ahmed Mohamed Mahmoud Ibrahim, Ammar Elsheikh
      First page: 1931
      Abstract: Sustainable manufacturing has received great attention in the last few decades for obtaining high quality products with minimal costs and minimal negative impacts on environment. Sustainable machining is one of the main sustainable manufacturing branches, which is concerned with improving environmental conditions, reducing power consumption, and minimizing machining costs. In the current study, the performance of three sustainable machining techniques, namely dry, compressed air cooling, and minimum quantity lubrication, is compared with conventional flood machining during the turning of austenitic stainless steel (Nitronic 60). This alloy is widely used in aerospace engine components, medical applications, gas power industries, and nuclear power systems due to its superior mechanical and thermal properties. Machining was performed using SiAlON ceramic tool with four different cutting speeds, feeds and a constant depth of cut. Consequently, various chip characteristics such as chip morphology, chip thickness, saw tooth distance and chip segmentation frequency were analyzed with both optical and scanning electron microscopes. Performance assessment was performed under the investigated cutting conditions. Our results show that the tool life under MQL machining are 138%, 72%, and 11% greater than dry, compressed air, and flooded conditions, respectively. The use of SiAlON ceramic tool results is more economically viable under the MQL environment as the overall machining cost per component is lower ($0.27) as compared to dry ($0.36), compressed air ($0.31), and flooded ($0.29) machining conditions. The minimum quantity lubrication technique outperformed the other investigated techniques in terms of eco-friendly aspects, economic feasibility, and technical viability to improve sustainability.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121931
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1932: Research on Hydraulic Push-Pull Bending
           Process of Ultra-Thin-Walled Tubes

    • Authors: Xin Zhang, Changcai Zhao, Bing Du, Duan Chen, Yang Li, Zhaojian Han
      First page: 1932
      Abstract: Due to their high strength, high performance, and lightweight characteristics, bent tubes are widely used in many high-end industries, such as aviation, aerospace, shipbuilding, automobile, and petrochemical industries. Ultra-thin-walled (thickness-to-diameter ratio t/D < 0.01) bent tubes are more prone to wrinkling, fracture, and cross-section distortion than ordinary bent tubes, which are difficult to form integrally by traditional bending processes. In this paper, a new bending process with combined loading of hydraulic pressure, push, and pull was proposed to provide a new method for the bending of ultra-thin-walled tube. This process is characterized by the ability to optimize the combination of push, pull, and internal pressure according to the actual bending process in order to minimize the wrinkling of ultra-thin-walled tube during bending. Based on ABAQUS finite element (FE) software, the FE model of the hydraulic push-pull bending process for ultra-thin-walled tube was established. The influence of internal pressure, die clearance, and friction coefficient on the forming quality of bent tubes was discussed, and the optimum process parameters were obtained. Bent tubes with an initial thickness of 0.3 mm, diameter of 60 mm, and bending radius of 165 mm were manufactured in experiments. Through the comparative analysis of experiment and simulation, the accuracy of the FE simulation was verified.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121932
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1933: Review of the Recent Development in Metallic
           Glass and Its Composites

    • Authors: Adit Sharma, Vladislav Zadorozhnyy
      First page: 1933
      Abstract: Metallic glasses are known for their mechanical properties but lack plasticity. This could be prevented by combining them with other materials or by inducing a second phase to form a composite. These composites have enhanced thermo-physical properties. The review paper aims to outline a summary of the current research done on metallic glass and its composites. A background in the history, properties, and their applications is discussed. Recent developments in biocompatible metallic glass composites, fiber-reinforced metallic glass, ex situ and in situ, are discussed.
      Citation: Metals
      PubDate: 2021-11-29
      DOI: 10.3390/met11121933
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1934: Gold Compounds Inhibit the Ca2+-ATPase
           Activity of Brain PMCA and Human Neuroblastoma SH-SY5Y Cells and Decrease
           Cell Viability

    • Authors: Maria Berrocal, Juan J. Cordoba-Granados, Sónia A. C. Carabineiro, Carlos Gutierrez-Merino, Manuel Aureliano, Ana M. Mata
      First page: 1934
      Abstract: Plasma membrane calcium ATPases (PMCA) are key proteins in the maintenance of calcium (Ca2+) homeostasis. Dysregulation of PMCA function is associated with several human pathologies, including neurodegenerative diseases, and, therefore, these proteins are potential drug targets to counteract those diseases. Gold compounds, namely of Au(I), are well-known for their therapeutic use in rheumatoid arthritis and other diseases for centuries. Herein, we report the ability of dichloro(2-pyridinecarboxylate)gold(III) (1), chlorotrimethylphosphinegold(I) (2), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (3), and chlorotriphenylphosphinegold(I) (4) compounds to interfere with the Ca2+-ATPase activity of pig brain purified PMCA and with membranes from SH-SY5Y neuroblastoma cell cultures. The Au(III) compound (1) inhibits PMCA activity with the IC50 value of 4.9 µM, while Au(I) compounds (2, 3, and 4) inhibit the protein activity with IC50 values of 2.8, 21, and 0.9 µM, respectively. Regarding the native substrate MgATP, gold compounds 1 and 4 showed a non-competitive type of inhibition, whereas compounds 2 and 3 showed a mixed type of inhibition. All gold complexes showed cytotoxic effects on human neuroblastoma SH-SY5Y cells, although compounds 1 and 3 were more cytotoxic than compounds 2 and 4. In summary, this work shows that both Au (I and III) compounds are high-affinity inhibitors of the Ca2+-ATPase activity in purified PMCA fractions and in membranes from SH-SY5Y human neuroblastoma cells. Additionally, they exert strong cytotoxic effects.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121934
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1935: A Comparison of Methods for the
           Characterisation of Waste-Printed Circuit Boards

    • Authors: Jonovan Van Yken, Ka Yu Cheng, Naomi J. Boxall, Chris Sheedy, Aleksandar N. Nikoloski, Navid R. Moheimani, Anna H. Kaksonen
      First page: 1935
      Abstract: Electronic waste is a growing waste stream globally. With 54.6 million tons generated in 2019 worldwide and with an estimated value of USD 57 billion, it is often referred to as an urban mine. Printed circuit boards (PCBs) are a major component of electronic waste and are increasingly considered as a secondary resource for value recovery due to their high precious and base metals content. PCBs are highly heterogeneous and can vary significantly in composition depending on the original function. Currently, there are no standard methods for the characterisation of PCBs that could provide information relevant to value recovery operations. In this study, two pre-treatments, smelting and ashing of PCB samples, were investigated to determine the effect on PCB characterisation. In addition, to determine the effect of particle size and element-specific effects on the characterisation of PCBs, samples were processed using four different analytical methods. These included multi-acid digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, nitric acid digestion followed by X-ray fluorescence (XRF) analysis, multi-acid digestion followed by fusion digestion and analysis using ICP-OES, and microwave-assisted multi-acid digestion followed by ICP-OES analysis. In addition, a mixed-metal standard was created to serve as a reference material to determine the accuracy of the various analytical methods. Smelting and ashing were examined as potential pre-treatments before analytical characterisation. Smelting was found to reduce the accuracy of further analysis due to the volatilisation of some metal species at high temperatures. Ashing was found to be a viable pre-treatment. Of the four analytical methods, microwave-assisted multi-acid digestion offered the most precision and accuracy. It was found that the selection of analytical methods can significantly affect the accuracy of the observed metal content of PCBs, highlighting the need for a standardised method and the use of certified reference material.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121935
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1936: Mechanical and Microstructural
           Characterization of Ultrasonic Welded NiTiCu Shape Memory Alloy Wires to
           Silver-Coated Copper Ferrules

    • Authors: Toni Sprigode, Andreas Gester, Guntram Wagner, Thomas Mäder, Björn Senf, Welf-Guntram Drossel
      First page: 1936
      Abstract: The aim of this study was to investigate the mechanical behavior, and the microstructure of NiTiCu shape memory alloy wires joined with silver-coated copper ferrules via ultrasonic spot welding. Therefore, the electrical resistance was measured during tensile testing, and the joints were analyzed by scanning electron microscopy. Energy-dispersive X-ray spectroscopy has determined the compounds of the developed welding zones. Furthermore, the influence of the ultrasonic welding on the transition temperatures of the NiTiCu wires was examined via differential scanning calorimetry. Tensile tests have shown that the ultimate tensile strengths of the joints reached almost 100% of that of the base material. An additional heat treatment rebuilt the typical shape memory alloy behavior after the ultrasonic welding process detwinned the martensitic wires. In addition, the B19′ structure of the welding zone and the ultrasonic spot-welding process did not affect the transition temperatures of the shape memory alloy.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121936
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1937: Numerical Investigation of Flow
           Characteristics of Molten Steel in the Tundish with Channel Induction
           Heating

    • Authors: Bin Yang, Hong Lei, Yingshi Xu, Kun Liu, Peng Han
      First page: 1937
      Abstract: In the continuous process, fluid flow is an important physical phenomena in the tundish, as it affects the process of heat transfer, bubble motion and inclusion collision-coalescence and grow up. This paper undertakes a detailed numerical investigation of fluid flow characteristics in the tundish with and without induction heating. The individual unit method and the volume subtraction model are applied to analyze the flow characteristics. A quantitative evaluation method of flow characteristics is proposed to investigate the flow characteristics. In the tundish with and without induction heating, firstly, the main flow behavior of molten steel is mixed flow in the receiving chamber; secondly, the main flow behavior of molten steel is plug flow in the channel; lastly, the main flow pattern is mixed flow, and the minor flow pattern is plug flow in the discharging chamber. The method of the volume subtraction model is an effective way to analyze the flow characteristics in the tundish with channel induction heating.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121937
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1938: Numerical and Non-Destructive Analysis of an
           Aluminum-CFRP Hybrid 3D Structure

    • Authors: Leandro Soares Silva, Henrique Fernandes, Michael Schwarz, Hans-Georg Herrmann, Aldemir Cavalini
      First page: 1938
      Abstract: Advanced materials are widely used in many industries. They play an important role especially in the aeronautic and automotive sectors where weight reduction is required in order to reduce fuel consumption. Composite materials have a high strength to weight ratio and are applied in airplane construction. Nevertheless, sometimes it is not viable to replace all metal parts by composite ones due to the cost factor. In this sense, hybrid structures are highly welcome. In order to ensure the safety of these hybrid components during their entire life cycle, non-destructive testing evaluation (NDT&E) methods are used and sometimes they are the only option. In this study, we use infrared thermography (IRT) to inspect an aluminum-composite hybrid structure with a 3D shape. The sample has a composite part with a small metal inlay (EN AW-6082) overmolded with a thermoplastic layer. The inlay is bended to reach the desired 3D geometry. This sample was design to be used for the connection between an A- or B-pillar and a car roof made of carbon fiber reinforced polymer (CFRP). A dual-band infrared camera is used in order to capture images in two different spectral ranges. In addition, two data processing techniques for infrared images are applied to enhance the images: principal component thermography (PCT) and partial least squares thermography (PLST). Then, a signal-to-noise ratio analysis is performed with three randomly chosen previous known defects to assess the quality of the images and detected defects. Results showed that principal component thermography has a slight advantage over partial least squares thermography in our specific experiments. Specifically, for the long-wave infrared band, PCT presented, among the defects analyzed, PCT presented a mean value 12.5% higher while the standard deviation was almost three times lower than PLST. In parallel to the non-detructive analysis, a numerical finite element model was formulated in ANSYS® to analyze the total deformations to which the metal-composite-hybrid structure is subjected during a possible use. Results obtained with the numerical model indicate that the interface region between composite and metal parts is where the highest degree of deformation occur, which indicates possible regions where defects and failures may occur in real use cases.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121938
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1939: Hot-Deformation Behavior and Processing Maps
           of a Low-Carbon Fe-2 wt% Nb Steel

    • Authors: Wentao Luo, Pengzhan Cai, Ziyong Hou, Yuhui Wang, Ling Zhang, Guilin Wu
      First page: 1939
      Abstract: In the present work, the deformation behavior and processing maps of a low-carbon Fe-2 wt% Nb steel were studied by means of hot-compression tests at temperatures of 800–1150 °C and strain rates of 0.01–10 s−1. The hot-processing maps at different strains and corresponding microstructural evolution were constructed and discussed. The hot-deformation behaviors of two different phase regions, i.e., austenite + NbC dual-phase and ferrite + NbC dual-phase, were predicted by determining the constitutive equations using Arrhenius-type and Zener–Hollomon models. The results suggest that the hot-deformed microstructures of the material present a strong correlation with the processing parameters in the hot-processing maps. In addition, the optimum parameters based on the processing maps were obtained, and the instable and the safe domains during the hot deformation in the hot-processing maps provide solid theoretical guidance for industrial production.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121939
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1940: Effect of Cryogenic Treatment on
           Microstructure, Mechanical Properties and Distortion of Carburized Gear
           Steels

    • Authors: Yongming Yan, Ke Liu, Zixiang Luo, Maoqiu Wang, Xinming Wang
      First page: 1940
      Abstract: The effects of cryogenic treatment and low temperature tempering on the microstructure, mechanical properties and distortion of the 20Cr2Ni4A and 17Cr2Ni2MoVNb carburized gear steels were investigated. The results showed that the case hardness of the experimental steels was increased after the cryogenic treatment, due to the decrease of the retained austenite content and the precipitation of the tiny carbides. The wear resistance of the two steels after cryogenic treatment was improved, although the wear mechanisms were different for 17Cr2Ni2MoVNb and 20Cr2Ni4A steels. The distortion of the Navy C-ring specimens underwent shrinkage before expansion during the cryogenic process, and the distortion of 17Cr2Ni2MoVNb steel was smaller than that of 20Cr2Ni4A steel.
      Citation: Metals
      PubDate: 2021-11-30
      DOI: 10.3390/met11121940
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1941: Emerging Interconnection Technology and
           Pb-Free Solder Materials for Advanced Microelectronic Packaging

    • Authors: Byungmin Ahn
      First page: 1941
      Abstract: In the field of electronics packaging, Pb-bearing solder alloys are mostly used as robust interconnecting materials [...]
      Citation: Metals
      PubDate: 2021-12-01
      DOI: 10.3390/met11121941
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1942: Study of the Effect of a Plug with Torsion
           Channels on the Mixing Time in a Continuous Casting Ladle Water Model

    • Authors: Gerardo Aguilar, Gildardo Solorio-Diaz, Alicia Aguilar-Corona, José Angel Ramos-Banderas, Constantin A. Hernández, Fernando Saldaña
      First page: 1942
      Abstract: The use of porous plugs in injecting gas through the bottom of a ladle forms vertical plumes in a very similar way to a truncated cone. The gas plume when exiting the plug has a smaller diameter compared to that formed in the upper zone of the ladle because inertial forces predominate over buoyancy forces in this zone. In addition, the magnitude of the plume velocity is concentrated in an upward direction, which increases the likelihood of low velocity zones forming near the bottom of the ladle, especially in lower corners. In this work, a plug with spiral-shaped channels with different torsion angles is proposed, with the objective that the gas, when passing through them, has a tangential velocity gain or that the velocity magnitude is distributed in the three axes and does not just focus on the upward direction, helping to decrease low velocity zones near the bottom of the ladle for better mixing times. For the experimentation, we worked in a continuous casting ladle water model with two configuration injections, which in previous works were reported as the most efficient in mixing the steel in this ladle. The results obtained using the PIV technique (particle image velocimetry) and conductimetry technique indicate that the plugs with the torsion channels at angles of 60° and 120° improve the mixing times for the two injection configurations.
      Citation: Metals
      PubDate: 2021-12-01
      DOI: 10.3390/met11121942
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1943: Effect of Mold Width on the Flow Field in a
           Slab Continuous-Casting Mold with High-Temperature Velocity Measurement
           and Numerical Simulation

    • Authors: Jian-Qiu Liu, Jian Yang, Chao Ma, Yi Guo, Wen-Yuan He, Chang-Liang Zhao, Ren-Bo Jiang, Yin-Tao Guo
      First page: 1943
      Abstract: In this paper, the effects of the width of the mold on the surface velocity, flow field pattern, turbulent kinetic energy distribution, and surface-level fluctuation in the mold were studied with measurement of the flow velocity near the surface of the mold at high temperature with the rod deflection method and numerical calculation with the standard k-ε model coupled with the discrete-phase model (DPM) model for automobile exposed panel production. Under the conditions of low fixed steel throughput of 2.2 ton/min, a nozzle immersion depth of 140 mm, and an argon gas flow rate of 4 L/min, as the width of the mold increases from 880 mm to 1050 mm and 1300 mm, the flow velocity near the surface of the mold decreases. The flow direction changes from the positive velocity with the mold widths of 880 mm and 1050 mm to the unstable velocity with the mold width of 1300 mm. The calculated results are in good agreement with the measured results. The turbulent kinetic energy near the submerged entry nozzle (SEN) gradually increases, and the risk of slag entrainment increases. Under the conditions of high fixed steel throughput of 3.5 ton/min, the SEN immersion depth of 160 mm, and the argon gas flow rate of 10 L/min, as the width of the mold increases from 1600 mm to 1800 mm and 2000 mm, the velocity near the mold surface decreases. The flow velocity at 1/4 of the surface of the mold is positive with the mold width of 1600 mm, while the velocities are negative with the widths of 1800 mm and 2000 mm. The calculated results are basically consistent with the measured results. The high turbulent kinetic energy area near the nozzle expands to a narrow wall, and the risk of slag entrainment is significantly increased. In both cases of low and high fixed steel throughput, the change rules of the flow field in the mold with the width are basically the same. The argon gas flow rate and the immersion depth of SEN should be adjusted reasonably to optimize the flow field in the mold with different widths under the same fixed steel throughput in the practical production.
      Citation: Metals
      PubDate: 2021-12-01
      DOI: 10.3390/met11121943
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1944: Microstructure and Phase Formation of Novel
           Al80Mg5Sn5Zn5X5 Light-Weight Complex Concentrated Aluminum Alloys

    • Authors: Jon Mikel Sanchez, Alejandro Pascual, Iban Vicario, Joseba Albizuri, Teresa Guraya, Haize Galarraga
      First page: 1944
      Abstract: In this work, three novel complex concentrated aluminum alloys were developed. To investigate the unexplored region of the multicomponent phase diagrams, thermo-physical parameters and the CALPHAD method were used to understand the phase formation of the Al80Mg5Sn5Zn5Ni5, Al80Mg5Sn5Zn5Mn5, and Al80Mg5Sn5Zn5Ti5 alloys. The ingots of the alloys were manufactured by a gravity permanent mold casting process, avoiding the use of expensive, dangerous, or scarce alloying elements. The microstructural evolution as a function of the variable element (Ni, Mn, or Ti) was studied by means of different microstructural characterization techniques. The hardness and compressive strength of the as-cast alloys at room temperature were studied and correlated with the previously characterized microstructures. All the alloys showed multiphase microstructures with major α-Al dendritic matrix reinforced with secondary phases. In terms of mechanical properties, the developed alloys exhibited a high compression yield strength up to 420 MPa, high compression fracture strength up to 563 MPa, and elongation greater than 12%.
      Citation: Metals
      PubDate: 2021-12-01
      DOI: 10.3390/met11121944
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1945: Titanium and Its Alloys for Biomedical
           Applications

    • Authors: Hyun-Do Jung
      First page: 1945
      Abstract: In the past decades, metals have been considered as promising materials in the fields of regenerative medicine and tissue engineering [...]
      Citation: Metals
      PubDate: 2021-12-02
      DOI: 10.3390/met11121945
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1946: Complex Structure Modification and
           Improvement of Properties of Aluminium Casting Alloys with Various Silicon
           Content

    • Authors: Anastasiya D. Shlyaptseva, Igor A. Petrov, Alexandr P. Ryakhovsky, Elena V. Medvedeva, Victor V. Tcherdyntsev
      First page: 1946
      Abstract: The possibility of using complex structure modification for aluminium casting alloys’ mechanical properties improvement was studied. The fluxes widely used in the industry are mainly intended for the modification of a single structural component of Al–Si alloys, which does not allow unifying of the modification process in a production environment. Thus, a new modifying flux that has a complex effect on the structure of Al–Si alloys has been developed. It consists of the following components: TiO2, containing a primary α-Al grain size modifier; BaF2 containing a eutectic silicon modifier; KF used to transform titanium and barium into the melt. The effect of the complex titanium dioxide-based modifier on the macro-, microstructure and the mechanical properties of industrial aluminium–silicon casting alloys containing 5%, 6%, 9%, 11% and 17% Si by weight was studied. It was found that the tensile strength (σB) of Al–Si alloys exceeds the similar characteristics for the alloys modified using the standard sodium-containing flux to 32%, and the relative elongation (δ) increases to 54%. The alloys’ mechanical properties improvement was shown to be the result of the flux component’s complex effect on the macro- and microstructure. The effect includes the simultaneous reduction in secondary dendritic arm spacing due to titanium, the refinement and decreasing size of silicon particles in the eutectic with barium and potassium, and the modifying of the primary silicon. The reliability of the studies was confirmed using up-to-date test systems, a significant amount of experimental data and the repeatability of the results for a large number of samples in the identical initial state.
      Citation: Metals
      PubDate: 2021-12-01
      DOI: 10.3390/met11121946
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1947: Effect of Autoclaving Cycles on the Cyclic
           Fatigue Resistance of Race and Race Evo Nickel-Titanium Endodontic Rotary
           Files: An In Vitro Study

    • Authors: Rahaf A. Almohareb, Reem Barakat, Aroob Albakri, Manal Altamimi
      First page: 1947
      Abstract: Objective: The aim of this study was to evaluate the influence of autoclave sterilization on the resistance to cyclic fatigue of two nickel-titanium (NiTi) endodontic files of identical design and taper, but with different NiTi alloy treatments: the newly introduced heat-treated Race Evo and the electropolished Race files. Materials and methods: Fifteen Race (25/0.06) files and fifteen Race Evo (25/0.06) files (n = 30 in total) were randomly assigned to five sub-groups each consisting of three files of the same NiTi alloy treatment. One group served as a control with files unautoclaved. The four remaining groups were sterilized in a steam sterilizer for 1, 3, 5, and 10 autoclave cycles, respectively. Files then underwent cyclic fatigue testing in a simulated metal canal block. A scanning electron microscope was used to inspect the surface of the fractured instruments. Statistical analysis was conducted using independent t-test and multi-factorial analysis of variance with significance set at a p value of ≤0.05. Results: Both Race Evo and Race files showed no significant difference between the different autoclaving cycles in terms of the number of cycles to fracture (p = 0.232 and p = 0.359). Despite rotating at a higher speed, the number of cycles to fracture of heat-treated Race Evo files was significantly higher than that of Race files (p ≤ 0.0001). Conclusion: Autoclave sterilization has no significant effect on the resistance to cyclic fatigue of heat-treated Race Evo or electropolished Race files. However, Race Evo files showed superior resistance to cyclic fatigue irrespective of autoclaving cycles.
      Citation: Metals
      PubDate: 2021-12-02
      DOI: 10.3390/met11121947
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1948: WAAM-Fabricated Laminated Metal Composites

    • Authors: Niclas Spalek, Jakob Brunow, Moritz Braun, Marcus Rutner
      First page: 1948
      Abstract: Laminated metal composites are a promising design since the hybrid design enables superior and tailorable material properties compared with bulk material. The article introduces for the first time, laminated metal composites consisting of multiple bilayers of alternating layers of ductile and high-strength steel processed by wire arc additive manufacturing (WAAM). The layup of the laminated metal composites is built up by alternating deposits made of ductile steel and high-strength steel type wires. Governing parameters in the fabrication process affecting the material properties, such as dilution, are discussed. Enhanced material properties of the laminated metal composites fabricated by WAAM are investigated under static tensile, impact and tension-tension high-cycle-fatigue loading and compared to the relating homogenous weld metal. Potential reasons for the retardation of crack propagation in laminated metal composites fabricated by WAAM compared to findings in roll-bonded laminated metal composites are discussed. WAAM is conducted by a collaborative robot providing a high level of flexibility in respect to geometry and scalability. Tailorability of material properties through WAAM-fabricated laminated metal composites adds an important layer of flexibility which has not been explored yet.
      Citation: Metals
      PubDate: 2021-12-02
      DOI: 10.3390/met11121948
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1949: Tool Downscaling Effects on the Friction Stir
           Spot Welding Process and Properties of Current-Carrying Welded
           Aluminum–Copper Joints for E-Mobility Applications

    • Authors: Aristide Tchouaha Tankoua, Tobias Köhler, Jean Pierre Bergmann, Michael Grätzel, Philip Betz, Dirk Lindenau
      First page: 1949
      Abstract: According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.
      Citation: Metals
      PubDate: 2021-12-03
      DOI: 10.3390/met11121949
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1950: Microstructure and Mechanical Properties of
           Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment
           Conditions

    • Authors: Byungsue Shin, Kwangyuk Kim, Sung Yi, Sanggyu Choi, Soongkeun Hyun
      First page: 1950
      Abstract: In this study, the changes in the microstructure and mechanical properties during isothermal heat treatment of cast steel before and after hot deformation were investigated using medium-carbon steel with low alloy content. The microstructural characteristics of the cast and hot-rolled medium-carbon steel under isothermal heat-treatment conditions were examined using optical microscopy and scanning electron microscopy in conjunction with electron backscatter diffraction. The variation in the mechanical properties was evaluated using Rockwell hardness and tensile tests. After maintaining an austenitizing condition at 1200 °C for 30 min, an isothermal heat treatment was performed in the range 350–500 °C, followed by rapid cooling with water. Both the cast steel and hot-rolled steel did not completely transform into bainitic ferrite during isothermal heat treatment. The partially untransformed microstructure was a mixture of martensite and acicular ferrite. At 500 °C, the prior austenite phase changed to Widmanstätten ferrite and pearlite. At 450 °C, bainitic ferrite and cementite were coarsened by the coalescence of ferrite and subsequent diffusive growth. The mechanical properties increased as the isothermal heat-treatment temperature decreased, and the hardness of the cast steel was generally higher than that of the hot-rolled steel. Hardness and strength showed similar trends, and overall mechanical properties tend to decrease as the isothermal heat-treatment temperature increases, but there are slight differences depending on complex factors such as various phase fractions and grain size.
      Citation: Metals
      PubDate: 2021-12-03
      DOI: 10.3390/met11121950
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1951: Correlation between Laser-Ultrasound and
           Microstructural Properties of Laser Melting Deposited Ti6Al4V/B4C
           Composites

    • Authors: Wanwei Xu, Xue Bai, Zhonggang Sun, Xin Meng, Zhongming Guo
      First page: 1951
      Abstract: The presence of large microtextured clusters (MTC) composed of small α-phase crystallites with preferred crystallographic orientations in 3D printed near-α titanium alloys leads to poor mechanical and fatigue properties. It is therefore crucial to characterize the size of MTCs nondestructively. Ti6Al4V/B4C composite materials are manufactured using Laser Melting Deposition (LMD) technology by adding an amount of nano-sized B4C particles to the original Ti6Al4V powder. TiB and TiC reinforcements precipitating at grain boundaries stimulate the elongated α crystallites and coarse columnar MTCs to equiaxed transition, and microstructures composed of approximately equiaxed MTCs with different mean sizes of 11–50 μm are obtained. Theoretical models for scattering-induced attenuation and centroid frequency downshift of ultrasonic waves propagating in such a polycrystalline medium are presented. It is indicated that, the studied composite material has an extremely narrow crystallographic orientation distribution width, i.e., a strong degree of anisotropy in MTCs. Therefore, MTCs make a dominant contribution to the total scattering-induced attenuation and spectral centroid frequency downshift, while the contribution of fine α-phase crystallites is insignificant. Laser ultrasonic inspection is performed, and the correlation between laser-generated ultrasonic wave properties and microstructural properties of the Ti6Al4V/B4C composites is analyzed. Results have shown that the deviation between the experimentally measured ultrasonic velocity and the theoretical result determined by the Voigt-averaged velocity in each crystallite is no more than 2.23%, which is in good agreement with the degree of macroscopically anisotropy in the composite specimens. The ultrasonic velocity seems to be insensitive to the size of MTCs, while the spectral centroid frequency downshift is approximately linear to the mean size of MTCs with a goodness-of-fit (R2) up to 0.99. Actually, for a macroscopically untextured near-α titanium alloy with a relatively narrow crystallographic orientation distribution, the ultrasonic velocity is not correlated with the properties of MTCs, by contrast, the central frequency downshift is dominated by the size and morphology of MTCs, showing great potentials in grain size evaluation.
      Citation: Metals
      PubDate: 2021-12-03
      DOI: 10.3390/met11121951
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1952: Distortion-Induced Fatigue Reassessment of a
           Welded Bridge Detail Based on Structural Stress Methods

    • Authors: Vencislau Quissanga, Guilherme Alencar, Abílio de Jesus, Rui Calçada, José da Silva
      First page: 1952
      Abstract: Typically, bridge structural systems are affected by random loads that can cause significant damage. One challenging problem in this field is the high-stress amplitude associated with distortion-induced fatigue. In this study, the hot-spot method and the master S-N curve method were validated for the evaluation of fatigue resistance induced by distortion in welded joints of steel bridges. Validation of the master S-N curve method in this research was a necessary prior step for application of the method in real case studies of road bridges, which will be subject to loads of variable amplitudes in the near future, ensuring the basis for the application. The method of validation was based on an important available full-scale fatigue test database, which was generated decades ago to serve as the foundation for the assessment of distortion-induced fatigue. Modelling was carried out based on the finite element method with the aid of ANSYS software, considering the shell and solid elements and equivalent structural stresses. The experimental results were compared with the numerical ones obtained with the two methodologies, and the difference, in terms of global and local tension, was less than 1%.
      Citation: Metals
      PubDate: 2021-12-03
      DOI: 10.3390/met11121952
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1953: Adaptation of the Rist Operating Diagram as a
           Graphical Tool for the Direct Reduction Shaft

    • Authors: Thibault Quatravaux, Jose Barros, Pascal Gardin, Gabriel Lucena
      First page: 1953
      Abstract: The blast-furnace operating diagram proposed by Rist was revised to direct reduction and was specifically applied to the Midrex NGTM process. The use of this graphical tool in the study of an industrial process highlighted the staggered nature of the reduction in the shaft furnace with, in particular, the existence of a prereduction zone in the upper part where metallization is thermodynamically impossible. A sensitivity study also showed the impact of the in situ reforming rate on the ability of the gas to completely reduce iron oxides. Finally, we graphically defined the minimum quality required for the top gas to produce direct-reduced iron.
      Citation: Metals
      PubDate: 2021-12-04
      DOI: 10.3390/met11121953
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1954: Assessment of the Heat Input Effect on the
           Distribution of Temperature Cycles in the HAZ of S460MC Welds in MAG
           Welding

    • Authors: Jaromír Moravec, Martin Švec, Šárka Bukovská, Jiří Sobotka
      First page: 1954
      Abstract: Temperature cycles generated during welding have a significant effect on the changes in the HAZ of welds, regardless of whether these are changes in structure or mechanical properties; however, it is problematic to obtain temperature cycles with sufficient accuracy across the entire HAZ so that they can be generally taken and used in welding simulations and for real experiments of processes occurring in HAZ. In particular, for a study in a specific location, it is important to know the maximum temperature of the cycle and the cooling rate defined mainly by the parameter t8/5. No studies in which anybody tries to find a mathematical description defining the basic parameters of temperature cycles in the HAZ could be found in the performed research. Therefore, the study presented in this paper results in a mathematical description defining the dependence of achieved maximum temperature on the distance from the fusion line in the HAZ of S460MC welds and with heat input values in the interval from 8 to 14 kJ·cm−1. Moreover, this paper presents the influence of heat input value on the weld pool geometry, including the effect of heat input value on grain coarsening in the highly heated HAZ.
      Citation: Metals
      PubDate: 2021-12-05
      DOI: 10.3390/met11121954
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1955: Modification of the Structural,
           Microstructural, and Elastoplastic Properties of Aluminum Wires after
           Operation

    • Authors: Aleksandr A. Levin, Maria V. Narykova, Alexey I. Lihachev, Boris K. Kardashev, Andrej G. Kadomtsev, Pavel N. Brunkov, Andrei G. Panfilov, Nikita D. Prasolov, Makhsud M. Sultanov, Vasily N. Kuryanov, Vladimir N. Tyshkevich
      First page: 1955
      Abstract: The health of the components that make up the cables of power lines, and hence their service life, is governed at the micro level by changes in their structure and microstructure. In this paper, the structure and microstructure of aluminum wires of overhead power transmission lines (without a steel core) of different service life from 0 to 62 years have been investigated by quantitative techniques of X-ray diffraction, diffraction of back-scattered electrons, and the densitometric method. Elastoplastic properties of the wires have been tested by the acoustic-resonance method. A decrease in the Al material density Δρ/ρ∼−0.165% was found in the near-surface layer of ∼36 μm depth and in the bulk of the wires with an increase in the service life from 0 to 18 years. The density decrease is associated with the accumulation of microcracks. The following density increase (Δρ/ρ∼−0.06%) in wires with a service life of 62 years is attributed to the formation of ∼0.7 vol.% of crystalline Al oxides in the near-surface layers of the wires. The nature of the change in the elastic modulus, microplastic flow stress, and decrement indicates complex structural changes correlating with the results obtained by diffraction methods.
      Citation: Metals
      PubDate: 2021-12-05
      DOI: 10.3390/met11121955
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1956: Finite-Elements Modeling and Simulation of
           Electrically-Assisted Rotary-Draw Bending Process for 6063 Aluminum Alloy
           Micro-Tube

    • Authors: Xinwei Wang, Jie Xu, Minghan Ding, Yanhu Zhang, Zhenlong Wang, Bin Guo, Debin Shan
      First page: 1956
      Abstract: Bent micro-tubes have been frequently applied in electronics, medical devices and aerospace for heat transfer due to the increasing heat flux in high-density electric packages. Rotary-draw bending (RDB) is a commonly used process in forming tubes due to its versatility. However, the control of forming defects is the key problem in micro-tube bending in terms of wall thinning, cross-sectional deformation and wrinkling. In this paper, a three-dimensional (3D) finite-elements (FE) modeling of electrically-assisted (EA) RDB of 6063 aluminum alloy micro-tubes is developed with the implicit method in ABAQUS. The multi-field coupled behavior was simulated and analyzed during the EA RDB of micro-tubes. Several process parameters such as micro-tube diameter, bending radius, current density and electrical load path were selected to study their effects on the bending defects of the Al6063 micro-tubes. The simulated results showed that the cross-sectional distortion could be improved when electrical current mainly pass through the vicinity of the tangent point in the micro-tube RDB, and the cross-sectional distortion tended to decrease with the increases of current density and tube diameter, and the decreases of bending speed and radius. A trade-off should be made between the benefit and side effect due to electrical current since the risk of wall thinning and wrinkling may increase.
      Citation: Metals
      PubDate: 2021-12-05
      DOI: 10.3390/met11121956
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1957: Fracture Mechanics and Fatigue Design in
           Metallic Materials

    • Authors: Dariusz Rozumek
      First page: 1957
      Abstract: Devices, working structures and their elements are subjected to the influence of various loads [...]
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121957
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1958: Microstructure–Mechanical Properties
           and Application of Magnesium Alloys

    • Authors: Talal Al-Samman, Dietmar Letzig, Sangbong Yi
      First page: 1958
      Abstract: Transport is a major contributor to CO2 emissions and is considered the most urgent global climate problem [...]
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121958
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1959: The Corrosion and Wear Behaviors of a
           Medium-Carbon Bainitic Steel Treated by Boro-Austempering Process

    • Authors: Man Liu, Wei Wang, Haijiang Hu, Feng Cai, Sheng Liu, Guang Xu
      First page: 1959
      Abstract: The effects of boro-austempering treatment on growth kinetics of borided layers, microstructure, and properties in a medium-carbon bainitic steel were investigated. The microstructure, distribution in coatings, corrosion, and wear properties of boro-austempered steels were characterized by a microscope, field-emission electron probe micro analyzer, scanning vibrating electrode technique system and wear resistance machine. The results show that the corrosion resistance of steels in different corrosive mediums was significantly enhanced by boro-austempering treatment. In addition, the wear performance of borided layers was improved by more than two times compared to bainitic substrates, proving a better wear property of samples treated through the boro-austempering route. The solubility of carbon and silicon in borides is very little. In addition, the dual-phase coating of FeB and Fe2B was observed, and the internal stress induced during the growth of Fe2B and FeB was almost eliminated. The preferential crystallographic growth directions of Fe2B and FeB are [001] and [010], respectively, which belongs to the (100) plane. Finally, the kinetics equation d2 = 0.125·t of the borided layers at 1223 K was established.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121959
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1960: Practical Approbation of Thermodynamic
           Criteria for the Consolidation of Bimetallic and Functionally Gradient
           Materials

    • Authors: Alexander Khaimovich, Yaroslav Erisov, Anton Agapovichev, Igor Shishkovsky, Vitaliy Smelov, Vasilii Razzhivin
      First page: 1960
      Abstract: This study concerns the key problem of determining the conditions for the consolidation or fracture of bimetallic compounds and high-gradient materials with different coefficients of thermal expansion. The well-known approach to determining the strength is based on the assessment of the critical energy release rates during fracture, depending on the conditions of loading (the portion of shear loading). Unfortunately, most of the experimental results cannot be used directly to select suitable fracture toughness criteria before such a connection is made. This especially applies to the region of interphase interaction, when it is required to estimate the internal energy of destruction accumulated during the preparation of the joint in the adhesion layer within the range of 20–50 μm. Hence, criteria for the adhesive consolidation of bimetallic compound layers were obtained on the basis of the thermodynamics of nonequilibrium processes. The analysis of the quality of the joint using the obtained criteria was carried out on the basis of the calculation of isochoric and isobaric heat capacities and coefficients of thermal expansion of multiphase layers. The applicability of the criteria for the qualitative assessment of the adhesion of layers is demonstrated in the example of bimetallic joints of steel 316L—aluminum alloy AlSi10Mg obtained by the SLM method at various fusion modes.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121960
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1961: Influence of LPBF-Surface Characteristics on
           Fatigue Properties of Scalmalloy®

    • Authors: Jens Musekamp, Thorsten Reiber, Holger Claus Hoche, Matthias Oechsner, Matthias Weigold, Eberhard Abele
      First page: 1961
      Abstract: Laser powder bed fusion (LPBF) has indisputable advantages when designing new components with complex geometries due to toolless manufacturing and the ability to manufacture components with undercuts. However, fatigue properties rely heavily on the surface condition. In this work, in-process surface parameters (three differing contour parameter sets) and post-process surface treatments, namely turning and shot peening, are varied to investigate the influence of each treatment on the resulting fatigue properties of LPBF-manufactured specimens of the aluminium–magnesium–scandium alloy Scalmalloy®. Therefore, metallographic analysis and surface roughness measurements, as well as residual stress measurements, computer tomography measurements, SEM-analyses, tensile and fatigue tests, along with fracture surface analysis, were performed. Despite the fact that newly developed in-process contour parameters are able to reduce the surface roughness significantly, only a minor improvement in fatigue properties could be observed: Crack initiation is caused by sharp, microscopic notches at the surface in combination with high tensile residual stresses at the surface, which are present on all in-process contour parameter specimens. Specimens using contour parameters with high line energy show keyhole pores localized in the subsurface area, which have no effect on crack initiation. Contours with low line energy have a slightly positive effect on fatigue strength because less pores can be found at the surface and subsurface area, which even more greatly promotes an early crack initiation. The post-process parameter sets, turning and shot peening, both improve fatigue behaviour significantly: Turned specimens show lowest surface roughness, while, for shot peened specimens, the tensile residual stresses of the surface radially shifted from the surface towards the centre of the specimens, which counteracts the crack initiation at the surface.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121961
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1962: Laves Phase Formation in High Entropy Alloys

    • Authors: Roman Ryltsev, Vasiliy Gaviko, Svetlana Estemirova, Evgenii Sterkhov, Lubov Cherepanova, Denis Yagodin, Nikolay Chtchelkatchev, Nikolay Dubinin, Sergey Uporov
      First page: 1962
      Abstract: One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x = 12x-VCrMoMnFe, 12x + Sc, 12x + Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x + Be alloy reveals a single-phase C14 structure with a very high concentration of structural defects and ultra-fine dendritic microstructure with an almost homogenous distribution of the constituted elements over the alloy matrix. The analysis of electrical and magnetic properties reveals that the Laves phases are Curie-Weiss paramagnets, which demonstrate metallic conduction; 7x and 12x alloys also reveal a pronounced Kondo-like anomaly. Analysis of experimental data as well as ab initio calculations suggest that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121962
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1963: An Investigation of Atomic Interaction
           between Ag and Ti2AlC under the Processing Temperature of 1080 °C

    • Authors: Guochao Wang, Yafei Li, Weijian Chen, Jianguo Yang, Jie Zhang, Yanming He
      First page: 1963
      Abstract: Ti2AlC is a typical MAX (M: early transition metal, A: main group element, and X: carbon and/or nitrogen) phase with ceramic and metallic properties due to its unique nano-layered structure. In order to investigate the interaction behavior between Ag and Ti2AlC, a sessile drop experiment was conducted at 1080 °C for 5 min. The atomic rearrangement occurred at the Ag–Ti2AlC interface was revealed using high-angle annular dark-field scanning transmission electron microscopy coupled with high-resolution transmission electron microscopy analysis. The results show that Ag nanoclusters generally appeared in most of the Ag–Ti2AlC interaction regions thermally processed at 1080 °C. In addition, Ag can also substitute for Al and Ti atoms in the Ti2AlC, promoting local structural decomposition of the Ti2AlC and producing 4H–Ag with a hexagonal close-packed (hcp) structure. Additionally, Al atoms released from the Ti2AlC lattices can dissolve locally into the liquid Ag, particularly at the grain boundaries. When the loss concentration of Al exceeded the critical level, the Ti2AlC started to decompose and the residual Ti6C octahedrons and Al atoms recombined, giving rise to the production of anti-perovskite Ti3AlC with a cubic structure. Lastly, the discrepancy in substitution behavior of Ag in the Ti2AlC was compared when thermally processed at different temperatures (1030 °C and 1080 °C). This work contributes to the understanding of the intrinsic stability of Ti2AlC MAX ceramics under high-temperature treatment.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121963
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1964: Modelling of the Erosive Dissolution of Metal
           Oxides in a Deep Eutectic Solvent—Choline Chloride/Sulfosalicylic
           Acid—Assisted by Ultrasonic Cavitation

    • Authors: Oleg M. Gradov, Inna V. Zinov’eva, Yulia A. Zakhodyaeva, Andrey A. Voshkin
      First page: 1964
      Abstract: Here we report on the results concerning the influence of ultrasound on the dissolution process of metal oxides CoO, Ni2O3 and Mn2O3 in choline chloride/sulfosalicylic acid as a deep eutectic solvent. The mechanism of dissolution under cavitation conditions with ultrasonic assistance is described. Theoretical research resulted in equations describing the dissolution process kinetics and linking its basic parameters. Optimal conditions for the most effective ultrasound application were found. Experimental data on dissolution kinetics of metal oxides in deep eutectic solvents was also obtained. It was discovered that experimental data correlates well with theoretical calculations, which confirms the correctness of developing a picture about the physicochemical nature of the process under study.
      Citation: Metals
      PubDate: 2021-12-06
      DOI: 10.3390/met11121964
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1965: Design against Fatigue of Super Duplex
           Stainless Steel Structures Fabricated by Wire Arc Additive Manufacturing
           Process

    • Authors: Andrew Sales, Andrei Kotousov, Ling Yin
      First page: 1965
      Abstract: Additive manufacturing (AM) is increasingly used to make complex components for a wide spectrum of applications in engineering, medicine and dentistry. Wire arc additive manufacturing (WAAM), as one of AM processes, utilises electric arc and metal wire to fabricate fully dense and heavy metal parts at relatively low costs and high-energy efficiencies. WAAM was successfully applied in the production of several welding-based metal structures. Recently, there was a growing interest in WAAM processing of super duplex stainless steels (SDSS) due to their high strength and excellent corrosion resistance, which make them the prime choice for load-bearing structures in marine applications. Although a number of studies investigated the microstructural and mechanical properties of WAAM-processed SDSS components, little is known regarding their fatigue performance, which is critical in engineering design. This study reports on the outcomes of fatigue tests and fracture surface fractography of WAAM-processed SDSS. The results obtained indicate a significant anisotropy of fatigue properties and fatigue crack initiations resulting from internal defects rather than surface flaws. Based on these experimental results, we suggest an effective design methodology to improve the fatigue life of the WAAM-fabricated SDSS components. We also indicate that post-manufacturing surface treatments should not be underlined for the enhanced fatigue resistance of WAAM-processed SDSS structures.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121965
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1966: A Novel Required Laser Energy Predicting
           Model for Laser Powder Bed Fusion

    • Authors: Yang Liu, Mingxuan Li, Xiaofeng Lu, Xiaolei Zhu, Peng Li
      First page: 1966
      Abstract: During the process of laser powder bed fusion (LPBF) printing, the energy of heat input have a great influence on the quality of fabricated specimens. In this paper, based on the heat transfer and metallurgical mechanism, a theoretical predicting model of the required laser energy to fabricate high-density LPBF components was established. The theoretical required laser energy density of AlSi10Mg, TC4 and 316L were calculated, which are 51.74 J/mm3, 104.48 J/mm3 and 69.28 J/mm3, respectively. By comparing with the experimental results in the references, it was found that the errors between them are within 10%. In addition, this article discussed the relationship between the VED and the specimen defects, and found that the changing in the VED will alter the types of specimen defects.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121966
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1967: Researching a Moving Target Detection Method
           Based on Magnetic Flux Induction Technology

    • Authors: Chaoqun Xu, Li Yang, Kui Huang, Yang Gao, Shaohua Zhang, Yuting Gao, Lifei Meng, Qi Xiao, Chaobo Liu, Bin Wang, Zhong Yi
      First page: 1967
      Abstract: The ocean is a very important arena in modern warfare where all marine powers deploy their military forces. Due to the complex environment of the ocean, underwater equipment has become a very threatening means of surprise attack in modern warfare. Therefore, the timely and effective detection of underwater moving targets is the key to obtaining warfare advantages and has important strategic significance for national security. In this paper, magnetic flux induction technology was studied with regard to the difficulty of detecting underwater concealed moving targets. Firstly, the characteristics of a magnetic target were analyzed and an equivalent magnetic dipole model was established. Secondly, the structure of the rectangular induction coil was designed according to the model, and the relationship between the target’s magnetism and the detection signal was deduced. The variation curves of the magnetic flux and the electromotive force induced in the coil were calculated by using the numerical simulation method, and the effects of the different motion parameters of the magnetic dipole and the size parameters of the coil on the induced electromotive force were analyzed. Finally, combined with the wavelet threshold filter, a series of field tests were carried out using ships of different materials in shallow water in order to verify the moving target detection method based on magnetic flux induction technology. The results showed that this method has an obvious response to moving targets and can effectively capture target signals, which verifies the feasibility of the magnetic flux induction detection technology.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121967
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1968: Ultrasonic-Assisted Brazing of Titanium
           Joints Using Modified Al-Si-Cu Based Fillers: Brazing at
           Liquid—Semisolid States under Load

    • Authors: Abdulsalam Muhrat, Joaquim Barbosa
      First page: 1968
      Abstract: Brazing joints of Ti/Ti under ultrasonic vibration (USV) and compression load were investigated using optimized and modified filler alloys of Al-Si-Cu-(Ni)-(Sr) group prepared in the lab. Preliminary trails at semisolid to liquid states were conducted using the ready Al-Si-Cu-(Mg) alloy as a filler, then the brazing cycle was redesigned and enhanced according to the microstructural observations of the produced joints. USV assisted brazing at semisolid state of low solid fraction was able to produce joints with round silicon morphology and granular , while at high solid fraction, USV was only able to affect the silicon and intermetallic particles. Applying a compression load after ultrasonic vibration, at a designed solid fraction, was proved to be a successful technique for improving the quality of the joints by reducing the porosity, enhancing the soundness of the joint, and the diffusion at the interface. Based on alloy composition and the improved brazing cycle, joints of thin intermetallic layer and high shear strength (of 93 MPa average value) were achieved. The microstructures and the mechanical behavior were discussed based on the filler compositions and brazing parameters.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121968
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1969: Effect of Temperature on Biobeneficiation of
           Bulk Copper-Nickel Concentrate with Thermoacidophilic Microbial
           Communities

    • Authors: Anna Panyushkina, Natalya Fomchenko, Vladislav Babenko, Maxim Muravyov
      First page: 1969
      Abstract: Bioleaching of the bulk copper–nickel sulfide concentrate was proposed as a method to remove nickel from it and to obtain a concentrate containing copper as chalcopyrite. This approach is based on the different refractoriness of sulfide minerals in ferric sulfate solutions and oxidation by acidophilic microorganisms. The bulk concentrate contained 10.8% copper in the form of chalcopyrite (CuFeS2) and 7.2% nickel that occurred in pentlandite ((Ni,Fe)9S8) and violarite (FeNi2S4). Three microbial communities grown at 35, 40, and 50 °C were used for bioleaching. The microbial community at 40 °C was the most diverse in the genus and species composition. At all temperatures of the process, the key roles in bioleaching belonged to mixotrophic and heterotrophic acidophiles. The highest levels of nickel leaching of 97.2 and 96.3% were observed in the case of communities growing at 40 and 50 °С, respectively. At the same time, the bioleach residue, which could be characterized as a marketable high-grade copper (chalcopyrite) concentrate, was obtained only at 40 °С. This solid contained 15.6% copper and 0.54% nickel. Thus, the biobeneficiation of bulk sulfide concentrates can be a promising field of biohydrometallurgy.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121969
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1970: A New Approach to Low-Cost, Solar
           Salt-Resistant Structural Materials for Concentrating Solar Power (CSP)
           and Thermal Energy Storage (TES)

    • Authors: Fadoua Aarab, Bernd Kuhn, Alexander Bonk, Thomas Bauer
      First page: 1970
      Abstract: “Concentrated solar power” (CSP) and thermal energy storage (TES) are promising renewable energy technologies, which have gained increasing interest and practical application in recent years. CSP and TES systems typically utilize molten salts such as the so-called “solar salt”, a mixture of 60 wt.% NaNO3 and 40 wt.% KNO3, for heat transfer and storage. The overall efficiency of commercially operating CSP and TES systems is currently limited, because of solar salt thermal stability, which prevents process temperatures higher than 600 °C. Even at these temperatures, corrosion of the structural materials applied in salt guiding pipework, tubes and containers is a matter of concern in long-term operation, which necessitates careful material selection. This paper outlines the superior salt corrosion behavior of a novel low-cost, Al2O3-forming, ferritic, Laves phase-strengthened (i.e., structural) steel in NaNO3/KNO3 solar salt at 600 °C. Directions for the further development of the LB2230 trial steel towards improved structural properties are derived in comparison to its predecessor Crofer®22 H.
      Citation: Metals
      PubDate: 2021-12-07
      DOI: 10.3390/met11121970
      Issue No: Vol. 11, No. 12 (2021)
       
  • Metals, Vol. 11, Pages 1871: Early Crack Propagation in Single Tooth
           Bending Fatigue: Combination of Finite Element Analysis and
           Critical-Planes Fatigue Criteria

    • Authors: Franco Concli, Lorenzo Maccioni, Lorenzo Fraccaroli, Luca Bonaiti
      First page: 1871
      Abstract: Mechanical components, such as gears, are usually subjected to variable loads that induce multiaxial non-proportional stress states, which in turn can lead to failure due to fatigue. However, the material properties are usually available in the forms of bending or shear fatigue limits. Multiaxial fatigue criteria can be used to bridge the gap between the available data and the actual loading conditions. However, different criteria could lead to different results. The main goal of this paper is to evaluate the accuracy of different criteria applied to real mechanical components. With respect to this, five different criteria based on the critical plane concept (i.e., Findley, Matake, McDiarmid, Papadopoulos, and Susmel) have been investigated. These criteria were selected because they not only assess the level of damage, but also predict the direction of crack propagation just after nucleation. Therefore, measurements (crack position and direction) on different fractured gear samples tested via Single Tooth Bending Fatigue (STBF) tests on two gear geometries were used as reference. The STBF configuration was numerically simulated via Finite Elements (FE) analyses. The results of FE were elaborated based on the above-mentioned criteria. The numerical results were compared with the experimental ones. The result of the comparison showed that all the fatigue criteria agree in identifying the most critical point. The Findley and Papadopulus criteria proved to be the most accurate in estimating the level of damage. The Susmel criterion turns out to be the most conservative one. With respect to the identification of the direction of early propagation of the crack, the Findley criterion revealed the most appropriate.
      Citation: Metals
      PubDate: 2021-11-21
      DOI: 10.3390/met11111871
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1872: Error Uncertainty Analysis in Planar
           Closed-Loop Structure with Joint Clearances

    • Authors: Yushu Yu, Jinglin Li, Xin Li, Yi Yang
      First page: 1872
      Abstract: For planar closed-loop structures with clearances, the angular and positional error uncertainties are studied. By using the vector translation method and geometric method, the boundaries of the errors are analyzed. The joint clearance is considered as being distributed uniformly in a circle area. A virtual link projection method is proposed to deal with the clearance affected length error probability density function (PDF) for open-loop links. The error relationship between open loop and closed loop is established. The open-loop length PDF and the closed-loop angular error PDF both approach being Gaussian distribution if there are many clearances. The angular propagation error of multi-loop structures is also investigated by using convolution. The positional errors of single and multiple loops are both discussed as joint distribution functions. Monte Carlo simulations are conducted to verify the proposed methods.
      Citation: Metals
      PubDate: 2021-11-21
      DOI: 10.3390/met11111872
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1873: Improvement in the Resistance to Wear of
           Work-Rolls Used in Finishing Stands of the Hot Strip Mills

    • Authors: Alberto Cofiño-Villar, Florentino Alvarez-Antolin, Carlos Hugo Alvarez-Perez
      First page: 1873
      Abstract: Work-rolls manufactured through the Indefinite Chill Double Poured (ICDP) method present an exterior work layer manufactured in a martensitic white cast iron alloyed with 4.5 %Ni, 1.7 %Cr, and 0.7 %Nb (wt.%). In its microstructure, there are abundant carbides of the type M3C and MC, which give high resistance to wear, and graphite particles which improve the service behaviour of the rolls against thermal cycling. The core of the rolls is manufactured in grey cast iron of pearlitic matrix and spheroidal graphite. These work-rolls are used in the finishing stands in Hot Strip Mills for rolling slabs proceeding from continuous casting at 1200 °C. Through the application of a Design of Experiments (DoE), an attempt has been made to identify those manufacturing factors which have a significant effect on resistance to wear of these rolls and to find an optimal combination of levels of these factors which allow for improvement in resistance to wear. To increase resistance to wear, it is recommended to situate, simultaneously, the liquidus temperature and the percentage of Si in the respective ranges of 1250–1255 °C and 1.1–1.15 (wt.%). Higher liquidus temperatures favour the presence of the pro-eutectic constituent rather than the eutectic constituent. The outer zone of the work layer, in contact with the metal sheet, which is being rolled, does not show the graphitising effect of Si (0.8–1.15 wt.%). On the contrary, it confirms the hardening effect of the Si in solid solution of the ferrite. The addition of 0.02% of Mg (wt.%) and the inoculation of 6 kg/T of FeB tend to eliminate the graphitising effect of the Si, thus favouring that the undissolved carbon in the austenite is found to form carbides in contrast to the majority formation of graphite.
      Citation: Metals
      PubDate: 2021-11-21
      DOI: 10.3390/met11111873
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1874: Investigation of the Extrapolation Capability
           of an Artificial Neural Network Algorithm in Combination with Process
           Signals in Resistance Spot Welding of Advanced High-Strength Steels

    • Authors: Bassel El-Sari, Max Biegler, Michael Rethmeier
      First page: 1874
      Abstract: Resistance spot welding is an established joining process for the production of safety-relevant components in the automotive industry. Therefore, consecutive process monitoring is essential to meet the high quality requirements. Artificial neural networks can be used to evaluate the process parameters and signals, to ensure individual spot weld quality. The predictive accuracy of such algorithms depends on the provided training data set, and the prediction of untrained data is challenging. The aim of this paper was to investigate the extrapolation capability of a multi-layer perceptron model. That means, the predictive performance of the model was tested with data that clearly differed from the training data in terms of material and coating composition. Therefore, three multi-layer perceptron regression models were implemented to predict the nugget diameter from process data. The three models were able to predict the training datasets very well. The models, which were provided with features from the dynamic resistance curve predicted the new dataset better than the model with only process parameters. This study shows the beneficial influence of process signals on the predictive accuracy and robustness of artificial neural network algorithms. Especially, when predicting a data set from outside of the training space.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111874
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1875: Understanding the Radiation Resistance
           Mechanisms of Nanocrystalline Metals from Atomistic Simulation

    • Authors: Liang Zhang
      First page: 1875
      Abstract: Metallic materials produce various structural defects in the radiation environment, resulting in serious degradation of material properties. An important way to improve the radiation-resistant ability of materials is to give the microstructure of materials a self-healing ability, to eliminate the structural defects. The research and development of new radiation-resistant materials with excellent self-healing ability, based on defects control, is one of the hot topics in materials science. Compared with conventional coarse-grained materials, nanocrystalline metals with a high density of grain boundary (GB) show a higher ability to resist radiation damage. However, the mechanism of GB’s absorption of structural defects under radiation is still unclear, and how to take advantage of the GB properties to improve the radiation resistance of metallic materials remains to be further investigated. In recent decades, atomistic simulation has been widely used to study the radiation responses of different metals and their underlying mechanisms. This paper briefly reviews the progress in studying radiation resistance mechanisms of nanocrystalline metals by employing computational simulation at the atomic scale.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111875
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1876: Corrosion Resistance of CoCrFeNiMn High
           Entropy Alloy Coating Prepared through Plasma Transfer Arc Claddings

    • Authors: Pei-Hu Gao, Rui-Tao Fu, Bai-Yang Chen, Sheng-Cong Zeng, Bo Zhang, Zhong Yang, Yong-Chun Guo, Min-Xian Liang, Jian-Ping Li, Yong-Qing Lu, Lu Jia, Dan Zhao
      First page: 1876
      Abstract: High entropy alloy attracts great attention for its high thermal stability and corrosion resistance. A CoCrFeNiMn high-entropy alloy coating was deposited on grey cast iron through plasma transfer arc cladding. It formed fine acicular martensite near the grey cast iron, with columnar grains perpendicular to the interface between the grey cast iron substrate and the cladding layer as well as dendrite in the middle part of the coatings. Simple FCC solid solutions present in the coatings which were similar to the powder’s structure. The coating had a microhardness of 300 ± 21.5 HV0.2 when the cladding current was 80 A for the solid solution strengthening. The HEA coating had the highest corrosion potential of −0.253 V when the plasma current was 60 A, which was much higher than the grey cast iron’s corrosion potential of −0.708 V. Meanwhile, the coating had a much lower corrosion current density of 9.075 × 10−7 mA/cm2 than the grey cast iron’s 2.4825 × 10−6 mA/cm2, which reflected that the CoCrFeNiMn HEA coating had much better corrosion resistance and lower corrosion rate than the grey cast iron for single FCC solid solution phase and a relatively higher concentration of Cr in the grain boundaries than in the grains and this could lead to corrosion protection effects.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111876
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1877: Real-Time Defects Analyses Using High-Speed
           Imaging during Aluminum Magnesium Alloy Laser Welding

    • Authors: Sabin Mihai, Diana Chioibasu, Muhammad Arif Mahmood, Liviu Duta, Marc Leparoux, Andrei C. Popescu
      First page: 1877
      Abstract: In this study a continuous wave Ytterbium-doped Yttrium Aluminum Garnet (Yb: YAG) disk laser has been used for welding of AlMg3 casted alloy. A high-speed imaging camera has been employed to record hot vapor plume features during the process. The purpose was to identify a mechanism of pores detection in real-time based on correlations between metallographic analyses and area/intensity of the hot vapor in various locations of the samples. The pores formation and especially the position of these pores had to be kept under control in order to weld thick samples. Based on the characterization of the hot vapor, it has been found that the increase of the vapor area that exceeded a threshold value (18.5 ± 1 mm2) was a sign of pores formation within the weld seam. For identification of the pores’ locations during welding, the monitored element was the hot vapor intensity. The hot vapor core spots having a grayscale level reaching 255 was associated with the formation of a local pore. These findings have been devised based on correlation between pores placement in welds cross-section microscopy images and the hot vapor plume features in those respective positions.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111877
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1878: The Effect of Current Supply Duration during
           Stepwise Electrical Sintering of Silver Nanoparticles

    • Authors: Iksang Lee, Arif Hussain, Hee-Lak Lee, Yoon-Jae Moon, Jun-Young Hwang, Seung-Jae Moon
      First page: 1878
      Abstract: We studied the effect of current supply duration at final-step currents during the stepwise electrical sintering of silver (Ag) nanoparticles (NPs). Ag NPs ink was inkjet-printed onto Eagle-XG glass substrates. Constant final-step currents of 0.4 and 0.5 A with various time intervals were applied to the printed samples. The final-step current of 0.5 A damaged the line at a comparatively shorter time duration. On the other hand, the lower final-step current of 0.4 A prevented the line damage at longer time durations while producing comparatively lower Ag NPs specific resistance. The minimum specific resistances of the printed samples sintered at 0.4 and 0.5 A were 3.59 μΩ∙cm and 3.79 μΩ∙cm, respectively. Furthermore, numerical temperature estimation and scanning electron microscope (SEM) analysis were conducted to elaborate on the results. The numerical temperature estimation results implied that the lower estimated peak temperature at the final-step current of 0.4 A helped prevent Ag NP line damage. The SEM micrographs suggested that a high surface porosity—caused by higher sintering peak temperatures—in the case of the 0.5 A final-step current resulted in a comparatively higher Ag NP line-specific resistance. This contribution is a step forward in the development of Ag NP sintering for printed electronics applications.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111878
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1879: Influence of Quenching and Partitioning
           Parameters on Phase Transformations and Mechanical Properties of Medium
           Manganese Steel for Press-Hardening Application

    • Authors: Charline Blankart, Sebastian Wesselmecking, Ulrich Krupp
      First page: 1879
      Abstract: It has been proven that through targeted quenching and partitioning (Q & P), medium manganese steels can exhibit excellent mechanical properties combining very high strength and ductility. In order to apply the potential of these steels in industrial press hardening and to avoid high scrap rates, it is of utmost importance to determine a robust process window for Q & P. Hence, an intensive study of dilatometry experiments was carried out to identify the influence of quenching temperature (TQ) and partitioning time (tp) on phase transformations, phase stabilities, and the mechanical properties of a lean medium manganese steel. For this purpose, additional scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDX) examinations as well as tensile testing were performed. Based on the dilatometry data, an adjustment of the Koistinen–Marburger (K-M) equation for medium manganese steel was developed. The results show that a retained austenite content of 12–21% in combination with a low-phase fraction of untempered secondary martensite (max. 20%) leads to excellent mechanical properties with a tensile strength higher than 1500 MPa and a total elongation of 18%, whereas an exceeding secondary martensite phase fraction results in brittle failure. The optimum retained austenite content was adjusted for TQ between 130 °C and 150 °C by means of an adapted partitioning.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111879
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1880: Simultaneous Improvement in Mechanical
           Properties and Fatigue Crack Propagation Resistance of Low Carbon Offshore
           Structural Steel EH36 by Cu–Cr Microalloying

    • Authors: Xingdong Peng, Peng Zhang, Ke Hu, Ling Yan, Guanglong Li
      First page: 1880
      Abstract: Improving the mechanical performance of low-carbon offshore steel is of great significance in shipbuilding applications. In this paper, a new Cu-Cr microalloyed offshore structural steel (FH36) was developed based on EH36. The microstructure, mechanical properties, and fatigue crack propagation properties of rolled plates of FH36, EH36, and normalizing rolled EH36 plates (EH36N) manufactured by a thermo-mechanical control process (TMCP) were analyzed and compared (to simplify, the two rolled specimens are signified by FH36T and EH36T, respectively). FH36T showed an obvious advantage in elongation with the value of 29%, 52.2% higher than the EH36T plates. The normalizing process led to a relatively lower yield stress (338 MPa), but substantially increased the elongation (33%) and lessened the yield ratio from 0.77 to 0.67. Electron back-scattered diffraction (EBSD) analysis showed that SFs of the deformation texture of FH36T and EH36N along the transverse direction (TD) and normal direction (ND) were much higher than those of the EH36T plate, which enhanced the lateral movement ability in the width and thickness direction, enhancing the ductility. Moreover, FH36 plates showed a better fatigue crack propagation resistance than rolled EH36 plates. The formation of the jagged shape grain boundaries is believed to induce a decrease of effective stress intensity factor during the fatigue crack propagation process.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111880
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1881: The Grain Boundary Wetting Phenomena in the
           Ti-Containing High-Entropy Alloys: A Review

    • Authors: Boris B. Straumal, Anna Korneva, Alexei Kuzmin, Gabriel A. Lopez, Eugen Rabkin, Alexander B. Straumal, Gregory Gerstein, Alena S. Gornakova
      First page: 1881
      Abstract: In this review, the phenomenon of grain boundary (GB) wetting by melt is analyzed for multicomponent alloys without principal components (also called high-entropy alloys or HEAs) containing titanium. GB wetting can be complete or partial. In the former case, the liquid phase forms the continuous layers between solid grains and completely separates them. In the latter case of partial GB wetting, the melt forms the chain of droplets in GBs, with certain non-zero contact angles. The GB wetting phenomenon can be observed in HEAs produced by all solidification-based technologies. GB leads to the appearance of novel GB tie lines Twmin and Twmax in the multicomponent HEA phase diagrams. The so-called grain-boundary engineering of HEAs permits the use of GB wetting to improve the HEAs’ properties or, alternatively, its exclusion if the GB layers of a second phase are detrimental.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111881
      Issue No: Vol. 11, No. 11 (2021)
       
  • Metals, Vol. 11, Pages 1882: Deformation Behavior of Wrought and EBAM
           Ti-6Al-4V under Scratch Testing

    • Authors: Artur Shugurov, Alexey Panin, Marina Kazachenok, Lyudmila Kazantseva, Sergey Martynov, Alexander Bakulin, Svetlana Kulkova
      First page: 1882
      Abstract: The microstructure, mechanical properties, and deformation behavior of wrought and electron beam additive manufactured (EBAM) Ti-6Al-4V samples under scratching were studied. As-received wrought Ti-6Al-4V was subjected to thermal treatment to obtain the samples with microstructure and mechanical characteristics similar to those of the EBAM samples. As a result, both alloys consisted of colonies of α phase laths within prior β phase grains and were characterized by close values of hardness. At the same time, the Young’s modulus of the EBAM samples determined by nanoindentation was lower compared with the wrought samples. It was found that despite the same hardness, the scratch depth of the EBAM samples under loading was substantially smaller than that of the wrought alloy. A mechanism was proposed, which associated the smaller scratch depth of EBAM Ti-6Al-4V with α′→α″ phase transformations that occurred in the contact area during scratching. Ab initio calculations of the atomic structure of V-doped Ti crystallites containing α or α″ phases of titanium were carried out to support the proposed mechanism.
      Citation: Metals
      PubDate: 2021-11-22
      DOI: 10.3390/met11111882
      Issue No: Vol. 11, No. 11 (2021)
       
 
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