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Publisher: Elsevier   (Total: 3051 journals)

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Showing 1 - 200 of 3048 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 7)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 24, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 22, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 86, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 30, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 358, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 1)
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 226, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 10, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 24, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 4, SJR: 0.383, h-index: 19)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 4)
Acute Pain     Full-text available via subscription   (Followers: 13)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 6)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 21)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 133, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 26, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 22, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 25, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 4)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 27, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 9, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 29, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Dermatology     Full-text available via subscription   (Followers: 12)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 6)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 42, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 50, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 22, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.497, h-index: 31)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 8, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 13)
Advances in Pharmacology     Full-text available via subscription   (Followers: 15, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 17)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 62)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 2, SJR: 0.1, h-index: 2)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 5)
Advances in Space Research     Full-text available via subscription   (Followers: 362, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 7, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 16)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 326, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 8, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 411, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 16, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 40, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 54, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 5, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 11, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 8)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access   (Followers: 1)
Algal Research     Partially Free   (Followers: 8, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 4, SJR: 0.776, h-index: 35)
Alpha Omegan     Full-text available via subscription   (SJR: 0.121, h-index: 9)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 9, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 46, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 49, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 47, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 40, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 9, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 26, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 200, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 59, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 6)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 26, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 24, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 35, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 58, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 12)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 4, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 37, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 165, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 8, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 12)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 1)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 168, SJR: 1.907, h-index: 126)

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Journal Cover Acta Materialia
  [SJR: 3.683]   [H-I: 202]   [226 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-6454
   Published by Elsevier Homepage  [3051 journals]
  • Simultaneous X-ray diffraction, crystallography and fluorescence mapping
           using the Maia detector
    • Authors: Henry J. Kirkwood; Martin D. de Jonge; Ondrej Muránsky; Felix Hofmann; Daryl L. Howard; Chris G. Ryan; Grant van Riessen; Matthew R. Rowles; Anna M. Paradowska; Brian Abbey
      Pages: 1 - 10
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Henry J. Kirkwood, Martin D. de Jonge, Ondrej Muránsky, Felix Hofmann, Daryl L. Howard, Chris G. Ryan, Grant van Riessen, Matthew R. Rowles, Anna M. Paradowska, Brian Abbey
      Interactions between neighboring grains influence the macroscale behavior of polycrystalline materials, particularly their deformation behavior, damage initiation and propagation mechanisms. However, mapping all of the critical material properties normally requires that several independent measurements are performed. Here we report the first grain mapping of a polycrystalline foil using a pixelated energy-dispersive X-ray area detector, simultaneously measuring X-ray fluorescence and diffraction with the Maia detector in order to determine grain orientation and estimate lattice strain. These results demonstrate the potential of the next generation of X-ray area detectors for materials characterization. By scanning the incident X-ray energy we investigate these detectors as a complete solution for simultaneously mapping the crystallographic and chemical properties of the sample. The extension of these techniques to broadband X-ray sources is also discussed.
      Graphical abstract image

      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.025
      Issue No: Vol. 144 (2017)
       
  • Anomalous hardening in magnesium driven by a size-dependent transition in
           deformation modes
    • Authors: Gi-Dong Sim; Gyuseok Kim; Steven Lavenstein; Mohamed H. Hamza; Haidong Fan; Jaafar A. El-Awady
      Pages: 11 - 20
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Gi-Dong Sim, Gyuseok Kim, Steven Lavenstein, Mohamed H. Hamza, Haidong Fan, Jaafar A. El-Awady
      Here, we report a comprehensive study that combines in situ scanning electron microscopy experiments and atomistic simulations to quantify the effect of crystal size on the transformation in deformation modes in a-axis oriented Mg single crystals at room temperature. The experimental results indicate that the deformation is dominated by the nucleation and propagation of tensile twins. The stress required for twin propagation was found to increase with decreasing sample size, showing a typical “smaller is stronger” behavior. Furthermore, an anomalous increase in strain hardening is first reported for microcrystals having diameters larger than ∼18 μm, which is induced by twin-twin and dislocation-twin interactions. The hardening rate gradually decreases toward the bulk response as the microcrystal size increases. Below 18 μm, deformation is dominated by the nucleation and propagation of a single tensile twin followed by basal slip activity in the twinned crystal, leading to no apparent hardening. In addition, molecular dynamics simulations indicate a transition from twinning mediated plasticity to dislocation mediated plasticity for crystal sizes below a few hundred nanometers in size. A deformation mechanism map for twin oriented Mg single crystals, ranging from the nano-scale to bulk scale is proposed based on the current simulations and experiments. The current predicted size-affected deformation mechanism of twin oriented Mg single crystals can lead to better understanding of the competition between dislocations plasticity and twinning plasticity.
      Graphical abstract image

      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.033
      Issue No: Vol. 144 (2017)
       
  • Solubility in Zr-Nb alloys from first-principles
    • Authors: Maeva Cottura; Emmanuel Clouet
      Pages: 21 - 30
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Maeva Cottura, Emmanuel Clouet
      The thermodynamic properties of the Zr-Nb alloy are investigated at temperatures below 890 K with ab initio calculations. The solution energies of the bcc Nb-rich and hcp Zr-rich solid solutions obtained within the framework of density functional theory are in good agreement with experimental data, although insufficient for a quantitative description of the miscibility gap, for which non configurational entropy has to be accounted for. Whereas electronic free energies can be neglected, we show, using the harmonic approximation and the density functional perturbation theory, that both solution free energies are strongly modified by the contribution related to atomic vibrations. Considering this vibrational free energy leads to a good description of the phase diagram.
      Graphical abstract image

      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.035
      Issue No: Vol. 144 (2017)
       
  • Synergistic effect of ultrasonic melt treatment and fast cooling on the
           refinement of primary Si in a hypereutectic Al–Si alloy
    • Authors: Jae-Gil Jung; Tae-Young Ahn; Young-Hee Cho; Su-Hyeon Kim; Jung-Moo Lee
      Pages: 31 - 40
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Jae-Gil Jung, Tae-Young Ahn, Young-Hee Cho, Su-Hyeon Kim, Jung-Moo Lee
      A mechanism describing the synergistic effect of ultrasonic melt treatment (UST) and subsequent fast cooling on the refinement of primary Si particles in a hypereutectic Al−Si alloy was investigated by examining inoculant particles via high-resolution transmission electron microscopy, serial sectioning, and melt filtration. The application of UST activated non-wetting MgAl2O4 particles with diameters of ∼0.5 μm to nucleate the primary Si phase. The cavitation-enhanced wetting of MgAl2O4 particles caused the formation of the AlP phase at the MgAl2O4 interface, further improving the nucleation potential. The cavitation-enhanced wetting and dispersion of inclusions (such as MgAl2O4) also resulted in the refinement and de-agglomeration of AlP particles. The UST-induced changes to the inoculant particles ultimately increased their number density, and the observed effects became more pronounced after increasing the degree of undercooling up to 20 K, leading to enhanced refinement of primary Si particles at higher cooling rates (up to 102 K s−1).
      Graphical abstract image

      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.039
      Issue No: Vol. 144 (2017)
       
  • Twinning mechanism at three-grain tri-junction during directional
           solidification of multi-crystalline silicon
    • Authors: T. Jain; H.K. Lin; C.W. Lan
      Pages: 41 - 50
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): T. Jain, H.K. Lin, C.W. Lan
      We propose a model to explain the formation mechanism of twin grains at the three-grain tri-junction (3GTJ) on the growth interface during directional solidification of multi-crystalline silicon. We also attempt to confirm its validity by comparing with the experimental results. This model is an extension of the previous model for the two-dimensional (2D) nucleation at the grain boundaries (GBs). It is found that the energy barriers for faceting and twinning nucleus at the 3GTJ are much smaller than that at GBs. As a result, a higher twinning probability can be obtained at a much lower undercooling. Two types of tri-junctions are considered according to the experiments and the dominant factors which decide the twinning probability on each facet at the 3GTJ are further discussed.
      Graphical abstract image

      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.042
      Issue No: Vol. 144 (2017)
       
  • Strain accumulation during microstructurally small fatigue crack
           propagation in bcc Fe-Cr ferritic stainless steel
    • Authors: E. Malitckii; H. Remes; P. Lehto; Y. Yagodzinskyy; S. Bossuyt; H. Hänninen
      Pages: 51 - 59
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): E. Malitckii, H. Remes, P. Lehto, Y. Yagodzinskyy, S. Bossuyt, H. Hänninen
      Strain accumulation was studied by digital image correlation technique (DIC) during microstructurally small fatigue crack propagation in polycrystalline 18%Cr ferritic stainless steel. Load-controlled fatigue testing was performed with R-ratio of 0.1 and frequency 10 Hz. The maximum applied stress was well below the yield stress of the studied material. The effect of the observed strain field on crack growth rate variation is discussed. Fracture surfaces were studied by scanning electron microscopy (SEM) evidencing the connection between the mechanism of the fatigue crack growth, accumulated strain and crack growth rate. Detailed study of fracture surface morphology was carried out by atomic force microscopy (AFM). Results indicate two processes of material damage accumulation and failure during cyclic loading: 1) local shear strain zones form successively ahead of the crack tip, and 2) fatigue crack growth occurs by both single- and multiple-slip mechanisms. The place and intensity of shear strain localization zones vary during the crack growth that is related closely to the local variation of crack growth rate.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.038
      Issue No: Vol. 144 (2017)
       
  • Similar local order in disordered fluorite and aperiodic pyrochlore
           structures
    • Authors: Jacob Shamblin; Cameron L. Tracy; Raul I. Palomares; Eric C. O'Quinn; Rodney C. Ewing; Joerg Neuefeind; Mikhail Feygenson; Jason Behrens; Christina Trautmann; Maik Lang
      Pages: 60 - 67
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Jacob Shamblin, Cameron L. Tracy, Raul I. Palomares, Eric C. O'Quinn, Rodney C. Ewing, Joerg Neuefeind, Mikhail Feygenson, Jason Behrens, Christina Trautmann, Maik Lang
      A major challenge to understanding the response of materials to extreme environments (e.g., nuclear fuels/waste forms and fusion materials) is to unravel the processes by which a material can incorporate atomic-scale disorder, and at the same time, remain crystalline. While it has long been known that all condensed matter, even liquids and glasses, possess short-range order, the relation between fully-ordered, disordered, and aperiodic structures over multiple length scales is not well understood. For example, when defects are introduced (via pressure or irradiation) into materials adopting the pyrochlore structure, these complex oxides either disorder over specific crystallographic sites, remaining crystalline, or become aperiodic. Here we present neutron total scattering results characterizing the irradiation response of two pyrochlores, one that is known to disorder (Er2Sn2O7) and the other to amorphize (Dy2Sn2O7) under ion irradiation. The results demonstrate that in both cases, the local pyrochlore structure is transformed into similar short range configurations that are best fit by the orthorhombic weberite structure, even though the two compositions have distinctly different structures, aperiodic vs. disordered-crystalline, at longer length scales. Thus, a material's resistance to amorphization may not depend primarily on local defect formation energies, but rather on the structure's compatibility with meso-scale modulations of the local order in a way that maintains long-range periodicity.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.044
      Issue No: Vol. 144 (2017)
       
  • Dislocation interactions at reduced strain rates in atomistic simulations
           of nanocrystalline Al
    • Authors: Maxime Dupraz; Zhen Sun; C. Brandl; Helena Van Swygenhoven
      Pages: 68 - 79
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Maxime Dupraz, Zhen Sun, C. Brandl, Helena Van Swygenhoven
      Molecular dynamics simulations of transient stress drops have been carried out in different regimes on a nanocrystalline Aluminum sample with average grain size of 12 nm. Besides confirming the interpretation of experimental results obtained during in situ X-ray diffraction, the creep simulations performed at 2 or 3 orders of magnitude lower strain rates than usual reveal deformation mechanisms that have not been observed previously. First of all, it is evidenced that the misfit dislocations available at the GB assist the propagation of a lattice dislocation on a plane with low resolved shear stress. Furthermore, it is shown that the interaction of two dislocations gliding on parallel slip planes can result in the emission of a vacancy in the grain interior. Finally, the importance of the Schmid factor in the activation of slip in nanocrystalline structures is discussed.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.043
      Issue No: Vol. 144 (2017)
       
  • Microstructure and mechanical properties of a precipitation-strengthened
           Al-Zr-Sc-Er-Si alloy with a very small Sc content
    • Authors: Anthony De Luca; David C. Dunand; David N. Seidman
      Pages: 80 - 91
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Anthony De Luca, David C. Dunand, David N. Seidman
      The precipitation hardening behavior of an Al-0.08Zr-0.014Sc-0.008Er-0.10Si (at.%) alloy was investigated utilizing microhardness, electrical conductivity, atom-probe tomography (APT), and compressive creep-measurements. This new composition, with a Sc:Zr atomic ratio of less than 1:5 represents a significant reduction of the alloy's cost when compared to the more usual Al-0.06Sc-0.02Zr based alloys with typical Sc:Zr atomic ratios of 3:1. To study the precipitation behavior of this low-Sc alloy, isothermal aging experiments between 350 and 425 °C for a duration of up to 6 months were performed. The low concentration of Sc, compensated by the high Zr concentration, permits the alloy to achieve a higher peak microhardness than the corresponding Sc-richer, Zr-leaner alloys. The low-Sc alloy also shows better over aging resistance, as anticipated from the smaller diffusivity of Zr when compared to Sc, leading to slower coarsening kinetics. Atom-probe tomography demonstrates that the high microhardness is due to the formation of a high number density of nano-precipitates, ∼1023 m−3 for peak aging conditions, with a mean radius of 1.9 nm, thus yielding a high volume fraction (0.35%) of nano-precipitates. Like alloys with much higher Sc and Er concentrations, the (Al,Si)3(Sc,Zr,Er) nano-precipitates still exhibit a core-shell structure with a concentration of Zr in the shell of up to 25 at.%, and a Sc- and Er-enriched core. Compressive creep experiments at 300 °C demonstrate that the new alloy, with only 0.014 at% Sc, is as creep resistant as a binary Al-0.08Sc at.% alloy, displaying a threshold stress of 17.5 ± 0.6 MPa at peak aged condition.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.040
      Issue No: Vol. 144 (2017)
       
  • Determining the strengths of HCP slip systems using harmonic analyses of
           lattice strain distributions
    • Authors: Paul R. Dawson; Donald E. Boyce; Jun-Sang Park; Euan Wielewski; Matthew P. Miller
      Pages: 92 - 106
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Paul R. Dawson, Donald E. Boyce, Jun-Sang Park, Euan Wielewski, Matthew P. Miller
      A robust methodology is presented to extract slip system strengths from lattice strain distributions for polycrystalline samples obtained from high-energy x-ray diffraction (HEXD) experiments with in situ loading. The methodology consists of matching the evolution of coefficients of a harmonic expansion of the distributions from simulation to the coefficients derived from measurements. Simulation results are generated via finite element simulations of virtual polycrystals that are subjected to the loading history applied in the HEXD experiments. Advantages of the methodology include: (1) its ability to utilize extensive data sets generated by HEXD experiments; (2) its ability to capture trends in distributions that may be noisy (both measured and simulated); and (3) its sensitivity to the ratios of the family strengths. The approach is used to evaluate the slip system strengths of Ti-6Al-4V using samples having relatively equiaxed grains. These strength estimates are compared to values in the literature.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.032
      Issue No: Vol. 144 (2017)
       
  • Transmission electron microscopy characterization of dislocation structure
           in a face-centered cubic high-entropy alloy Al0.1CoCrFeNi
    • Authors: X.D. Xu; P. Liu; Z. Tang; A. Hirata; S.X. Song; T.G. Nieh; P.K. Liaw; C.T. Liu; M.W. Chen
      Pages: 107 - 115
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): X.D. Xu, P. Liu, Z. Tang, A. Hirata, S.X. Song, T.G. Nieh, P.K. Liaw, C.T. Liu, M.W. Chen
      Structural characterization of dislocations and dislocation reactions in a face-centered cubic high entropy alloy was conducted using the state-of-the-art spherical aberration corrected transmission electron microscopy. We experimentally measured the stacking fault energy of the high entropy alloy from the atomic images and diffraction contrast of dislocation cores. The low stacking fault energy results in widely dissociated dislocations and extensive dislocation reactions, which leads to the formation of immobile Lomer and Lomer-Cottrell dislocation locks. These dislocation locks act as both dislocation barriers and sources and are responsible for the significant work hardening with a large hardening rate in the alloy. Based on the atomic-scale characterization and classical dislocation theory, a simple equation was derived to describe the work hardening behavior of the high entropy alloy in the early-stage of plastic deformation.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.050
      Issue No: Vol. 144 (2017)
       
  • Unveiling the mechanisms of cold sintering of ZnO at 250 °C by varying
           applied stress and characterizing grain boundaries by Kelvin Probe Force
           Microscopy
    • Authors: J. Gonzalez-Julian; K. Neuhaus; M. Bernemann; J. Pereira da Silva; A. Laptev; M. Bram; O. Guillon
      Pages: 116 - 128
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): J. Gonzalez-Julian, K. Neuhaus, M. Bernemann, J. Pereira da Silva, A. Laptev, M. Bram, O. Guillon
      The sintering behavior of nanocrystalline ZnO was investigated at only 250 °C. Densification was achieved by the combined effect of uniaxial pressure and the addition of water both in a Field Assisted Sintering Technology/Spark Plasma Sintering apparatus and a hand press with a heater holder. The final pure ZnO materials present high densities (>90% theoretical density) with nano-grain sizes. By measuring the shrinkage rate as a function of applied stress it was possible to identify the stress exponent related to the densification process. A value larger than one points to non-linear relationship going beyond single solid-state diffusion or liquid phase sintering. Only a low amount of water (1.7 wt%) was needed since the process is dictated by the adsorption on the surface of the ZnO particles. Part of the adsorbed water dissociates into H+ and OH− ions, which diffuse into the ZnO crystal structure, generating grain boundaries/interfaces with high defect chemistry. As characterized by Kelvin Probe Force Microscopy, and supported by impedance spectroscopy, this highly defective grain boundary area presents much higher surface energy than the bulk. This highly defective grain boundary area with high potential reduces the activation energy of the atomic diffusion, leading to sinter the compound at low temperature.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.055
      Issue No: Vol. 144 (2017)
       
  • Composition design of high entropy alloys using the valence electron
           concentration to balance strength and ductility
    • Authors: Ruirun Chen; Gang Qin; Huiting Zheng; Liang Wang; Yanqing Su; YuLung Chiu; Hongsheng Ding; Jingjie Guo; Hengzhi Fu
      Pages: 129 - 137
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Ruirun Chen, Gang Qin, Huiting Zheng, Liang Wang, Yanqing Su, YuLung Chiu, Hongsheng Ding, Jingjie Guo, Hengzhi Fu
      The valence electron concentration (VEC) is an important physical factor for phase formation. A high VEC is conducive to forming an FCC phase and improving an alloy's ductility, while a low VEC is beneficial in forming a BCC phase that improves an alloy's strength. This is demonstrated for two HEAs, CoCrCuFeNi (FCC) and AlCoCrFeNi (BCC), that were designed as matrix alloys, where Ni and Mo are alloyed. The microstructure, phase evolution, and the mechanical properties for (AlCoCrFeNi)100-x Ni x and (CoCrCuFeNi)100-x Mo x were systematically investigated. As the phase structure for the (AlCoCrFeNi)100-x Ni x high entropy alloy (HEA) transformed from a BCC to an FCC crystal structure as the Ni content increased from 0 at.% to 16 at.%, the FCC volume fraction increased from 0% to 85%, its compressive fracture strain increased from 25% to 40%, its VEC increased from 7.2 to 7.6. As the phase structure for the (CoCrCuFeNi)100-x Mo x HEA transformed from FCC to BCC as the Mo content increased from 0 at.% to 16 at.%, the BCC volume fraction increased from 0% to 65%, its compressive yield strength increased from 260 MPa to 928 MPa, its VEC decreased from 8.8 to 8.3. Selecting an element based upon an alloy's VEC is a practical method for designing compositions for HEAs that balance strength and ductility. According to the needs of practical applications, balancing both strength and plasticity requires the following criteria for selecting an element for incorporation into an HEA system: matrix strength is improved by selecting an element with a VEC lower than the average VEC of the matrix, while ductility is improved by selecting another element with a VEC higher than the average VEC for the matrix.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.058
      Issue No: Vol. 144 (2017)
       
  • Microstructural deformation in fatigued nanotwinned copper alloys
    • Authors: Nathan M. Heckman; Matthew F. Berwind; Christoph Eberl; Andrea M. Hodge
      Pages: 138 - 144
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Nathan M. Heckman, Matthew F. Berwind, Christoph Eberl, Andrea M. Hodge
      In this study, the uniaxial tension-tension fatigue behavior of fully nanotwinned magnetron sputtered Cu-6wt%Al, Cu-2wt%Al, and Cu-10 wt%Ni is presented. These alloys have average twin thicknesses ranging from 4 to 8 nm, average grain widths from 90 to 180 nm, and tensile strengths from 1 to 1.5 GPa. In the high cycle regime (103 to 107 cycles), the nanotwinned alloys exhibit fatigue strengths ranging from 210 to 370 MPa, which is higher than previously observed in nanotwinned Cu (fatigue strengths between 80 and 200 MPa). Fatigue strengths are normalized by tensile strength for Cu alloys with different microstructures to study the correlation between tensile and fatigue properties. Post-mortem analysis of the materials reveals a newly observed deformation mechanism, where localized detwinning leads to intergranular fracture between columnar grains. Overall, materials displaying detwinning as a deformation mechanism show lower normalized fatigue strengths in comparison to materials that deform with slip band like behavior.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.057
      Issue No: Vol. 144 (2017)
       
  • Strain-engineered allotrope-like bismuth nanowires for enhanced
           thermoelectric performance
    • Authors: Jeongmin Kim; Min-Wook Oh; Gwansik Kim; Je-Hyeong Bahk; Jae Yong Song; Seong Gi Jeon; Dong Won Chun; Jee-Hwan Bae; Wooyoung Shim; Wooyoung Lee
      Pages: 145 - 153
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Jeongmin Kim, Min-Wook Oh, Gwansik Kim, Je-Hyeong Bahk, Jae Yong Song, Seong Gi Jeon, Dong Won Chun, Jee-Hwan Bae, Wooyoung Shim, Wooyoung Lee
      Allotropy is a fundamental concept that has been frequently studied since the mid-1800s. Although the bulk allotropy of elemental solids is fairly well understood, it remains challenging to reliably produce an allotrope at the nanoscale that has a different crystal structure and accompanies a change in physical properties for specific applications. Here, we demonstrate a "heterostructure" approach to produce allotrope-like bismuth nanowires, where it utilizes the lattice constant difference between bismuth and tellurium in core/shell structure. We find that the resultant strain of [100]-grown Bi nanowires increases the atomic linear density along the c-axis that has been predicted from theoretical considerations, enabling us to establish a design rule for strain-induced allotropic transformation. With our >400-nm-diameter nanowires, we measure a thermoelectric figure of merit ZT of 0.5 at room temperature with reduced thermal conductivity and enhanced Seebeck coefficient, which are primarily a result of the rough interface and the reduced band overlap according to our density-functional calculations.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.062
      Issue No: Vol. 144 (2017)
       
  • High frequency in situ fatigue response of Ni-base superalloy René-N5
           microcrystals
    • Authors: Steven Lavenstein; Bryan Crawford; Gi-Dong Sim; Paul A. Shade; Christopher Woodward; Jaafar A. El-Awady
      Pages: 154 - 163
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Steven Lavenstein, Bryan Crawford, Gi-Dong Sim, Paul A. Shade, Christopher Woodward, Jaafar A. El-Awady
      A novel in situ scanning electron microscope (SEM), high frequency fatigue testing methodology is developed using a combination of laser milling, focused ion beam fabrication and nanoindentation. This methodology is used to investigate crack initiation, propagation, fracture, fatigue life, and the mechanical response of microcantilever samples of a Ni-based superalloy (René-N5) under different cyclic strain amplitudes. The crack initiation and propagation in the microcantilever is monitored by observing changes in the beam's dynamic stiffness and continuous SEM imaging. The dynamic stiffness response of the micro-beams exhibits a transition from softening to hardening at a critical strain amplitude of 7 × 10 − 3 . Theoretical analysis indicates that this transition corresponds to the stress required to shear γ ′ precipitates. SEM imaging reveals the evolution of significant extrusions, intrusions, and slip traces during cyclic loading above this critical strain amplitude. Below this strain amplitude, very little surface roughening is observed. In addition, the measured dynamic stiffness is observed to exhibit two regimes of decrease after crack initiation. These two regimes correspond to short and large crack propagation. Finally, an overall increase in fatigue life is observed when comparing to bulk scale experiments on nickel-base superalloys. It is proposed that this is an inherent size effect in the small-volume, single crystal specimens tested.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.049
      Issue No: Vol. 144 (2017)
       
  • Hydrogen-modified dislocation structures in a cyclically deformed
           ferritic-pearlitic low carbon steel
    • Authors: Shuai Wang; Akihide Nagao; Petros Sofronis; Ian M. Robertson
      Pages: 164 - 176
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Shuai Wang, Akihide Nagao, Petros Sofronis, Ian M. Robertson
      The fatigue-crack growth rate of a ferritic-pearlitic low carbon steel was faster when the tests were conducted in high-pressure H2 gas environments than in air. The predominant fracture feature changed from ductile fatigue striations with some “quasi-cleavage-like” regions when the test was conducted in air to mixed “quasi-cleavage” and “flat” facets when tested in a H2 gas environment. The microstructure beneath the fracture surfaces produced in air was sub-grains, and over a distance of 15 μm from the fracture surface, the dimensions of the sub-grains increased. With hydrogen, dense dislocation bands and refined dislocation cells existed beneath the “quasi-cleavage” and “flat” fracture surfaces. The cell size increased with distance from the fracture surface. The decrease in the dimensions of the key microstructural features as the fracture surface is approached is attributed to the propagation of the crack through an already deformed matrix. The differences in evolved dislocation structure are explained in terms of the hydrogen-enhanced localized plasticity mechanism, and the hydrogen-modified dislocation structure establishes the local conditions that promote the fracture mode transition from ductile fatigue striations to a mixture of “quasi-cleavage” and “flat” features, which directly leads to enhanced fatigue-crack growth.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.034
      Issue No: Vol. 144 (2017)
       
  • Alternative misfit dislocations pattern in semi-coherent FCC {100}
           interfaces
    • Authors: Shuai Shao; Firas Akasheh; Jian Wang; Yue Liu
      Pages: 177 - 186
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Shuai Shao, Firas Akasheh, Jian Wang, Yue Liu
      The character of interface misfit dislocations is determined according to interface crystallography and minimization of interface energy, which includes coherent interface energy and dislocation line energy. The core energy of dislocations is generally ignored in such analysis. In this work, we demonstrate that the core energy of misfit dislocations is dependent on the mechanical and thermal loading condition, and ultimately determines the nature of interface misfit dislocation patterns (MDP). Employing atomistic simulations with empirical interatomic potentials, we show the transformation of conventional MDP consisting of a/2<110> dislocation into an alternative MDP consisting of mixed a<100> and a/2<110> dislocations under elevated temperatures and/or normal-to-interface tensile stresses. Although a<100> type dislocations typically have greater line energy in bulk, molecular statics/dynamics calculations show that a<100> type misfit dislocations are preferred over a/2<110> type under elevated temperatures and/or normal-to-interface tensile stresses due to their reduced core energy. In addition, we found that the a<100> dislocations possess significantly reduced vacancy formation energies compared to the a/2<110> dislocations. The potential application of this unique property of the alternative dislocation pattern for nanoscale multilayered composite as a functional material is discussed.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.052
      Issue No: Vol. 144 (2017)
       
  • Surface termination analysis of stoichiometric metal hexaborides: Insights
           from first-principles and XPS measurements
    • Authors: K.M. Schmidt; O. Jaime; J.T. Cahill; D. Edwards; S.T. Misture; O.A. Graeve; V.R. Vasquez
      Pages: 187 - 201
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): K.M. Schmidt, O. Jaime, J.T. Cahill, D. Edwards, S.T. Misture, O.A. Graeve, V.R. Vasquez
      We present a modeling framework and discuss the energetics and structural features of the surface terminations of Ca, Ba, Sr and La hexaborides using density functional theory analysis in combination with X-ray photoelectron spectroscopy. There is significant uncertainty in the literature about the nature of the surface terminations in metal hexaborides in terms of metal versus boron terminations. We show from electronic structure calculations that segregated regions of metal and boron-terminations produce the lowest energies for di-cations of CaB6, SrB6 and BaB6, while trivalent LaB6 minimizes the surface energy by arranging the metal ions in parallel rows on the surface. XPS measurements show that CaB6 and SrB6 have surfaces that are close to stoichiometric for the compound, while BaB6 has surfaces that are Ba-rich. Energetic barriers are calculated for transitions between each of the surface geometries considered. There is a substantial increase in the activation energy for the lanthanum migrations compared to the divalent cations. We also find that the boron octahedra units in these materials tend to contract or expand from their bulk values depending on the proximity to regions of high metal concentrations. These materials have many attractive features, such as low work functions, high hardness, low thermal expansion coefficients, and high melting points, among many other properties of interest for industrial applications. Promising uses of these materials also include catalytic applications for chemical dissociation reactions of various molecules such as hydrogen, water and carbon monoxide, for example, thus, the interest in determining relevant surface properties.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.045
      Issue No: Vol. 144 (2017)
       
  • Strong and tough metal/ceramic micro-laminates
    • Authors: Claudio Ferraro; Sylvain Meille; Julien Réthoré; Na Ni; Jerome Chevalier; Eduardo Saiz
      Pages: 202 - 215
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Claudio Ferraro, Sylvain Meille, Julien Réthoré, Na Ni, Jerome Chevalier, Eduardo Saiz
      There is a growing interest in the development of composites with complex structures designed to generate enhanced mechanical properties. The challenge is how to implement these structures in practical materials with the required degree of control. Here we show how freeze casting of ceramic preforms combined with metal infiltration can be used to fabricate Al2O3/Al-4wt% Mg micro-laminated composites. By manipulating the solid content of the suspension and the morphology of the ceramic particles (from platelets to round particles) it is possible to access a range of structures with layer thickness varying between 1 and 30 μm and metallic contents between 66 and 86 vol%. The mechanical response of the materials is characterized by combining bending tests with observation of crack propagation in two and three dimensions using different imaging techniques. These composites are able to combine high strength and toughness. They exhibit a rising R-curve behaviour although different structures generate different toughening mechanisms. Composites fabricated with Al2O3 particles exhibit the highest fracture resistance approaching 60 MPa m1/2, while laminates prepared from Al2O3 platelets exhibit higher strengths (above 700 MPa) while retaining fracture resistance up to ∼40 MPa m1/2. The results provide new insights on the effect of structure on the mechanical properties in metal-ceramic composites as well as on the design of appropriate testing procedures.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.059
      Issue No: Vol. 144 (2017)
       
  • Tailoring the mechanical properties of sputter deposited nanotwinned
           nickel-molybdenum-tungsten films
    • Authors: Gi-Dong Sim; Jessica A. Krogstad; Kelvin Y. Xie; Suman Dasgupta; Gianna M. Valentino; Timothy P. Weihs; Kevin J. Hemker
      Pages: 216 - 225
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Gi-Dong Sim, Jessica A. Krogstad, Kelvin Y. Xie, Suman Dasgupta, Gianna M. Valentino, Timothy P. Weihs, Kevin J. Hemker
      Advanced metallic alloys are attractive in microelectromechanical systems (MEMS) applications that require high density, electrical and thermal conductivity, strength, and dimensional stability. Here we report the mechanical behavior of direct current (DC) magnetron sputter deposited Nickel (Ni)-Molybdenum (Mo)-Tungsten (W) films annealed at various temperatures. The films deposit as single-phase nanotwinned solid solutions and possess ultra-high tensile strengths of approximately 3 GPa, but negligible ductility. Subsequent heat treatments resulted in grain growth and nucleation of Mo-rich precipitates. While films annealed at 600 °C or 800 °C for 1 h still showed brittle behavior, films annealed at 1,000 °C for 1 h were found to exhibit strength greater than 1.2 GPa and near 10% tensile ductility. In addition to the excellent mechanical properties, alloy films further exhibit remarkably improved dimensional stability – a lower coefficient of thermal expansion and greater microstructural stability. An excellent balance between mechanical properties and dimensional stability make sputter deposited Ni-Mo-W alloys promising structural materials for MEMS applications.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.065
      Issue No: Vol. 144 (2017)
       
  • Texture-directed twin formation propensity in Al with high stacking fault
           energy
    • Authors: S. Xue; W. Kuo; Q. Li; Z. Fan; J. Ding; R. Su; H. Wang; X. Zhang
      Pages: 226 - 234
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): S. Xue, W. Kuo, Q. Li, Z. Fan, J. Ding, R. Su, H. Wang, X. Zhang
      Twin boundaries can enhance the strength and preserve the ductility of a variety of metallic materials with face centered cubic structures. However, twin boundaries are rare in aluminum due to its high stacking fault energy. There are limited successes for the formation of nanotwins in Al. Here, we show that twin morphology and twin density in Al can be altered by tailoring the textures of films. Transmission Kikuchi diffraction and transmission electron microscopy studies on (111), (110) and (112) textured Al films indicate that Al (112) film has the highest twin density. Two design criteria are identified for the introduction of a high density of growth twins into Al.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.053
      Issue No: Vol. 144 (2017)
       
  • Spatially resolved localization and characterization of trapped hydrogen
           in zero to three dimensional defects inside ferritic steel
    • Authors: Waldemar Krieger; Sergiy V. Merzlikin; Asif Bashir; Agnieszka Szczepaniak; Hauke Springer; Michael Rohwerder
      Pages: 235 - 244
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Waldemar Krieger, Sergiy V. Merzlikin, Asif Bashir, Agnieszka Szczepaniak, Hauke Springer, Michael Rohwerder
      In this work, localized hydrogen (H) detection measurements were conducted on a model ferritic (Fe 5 wt.-% Ni) steel which enables a systematic study of 0- (vacancies), 1- (dislocations), 2- (grain boundaries) and 3- (inclusions) dimensional defects, induced by varying mechanical and thermal treatments, without changing the chemical composition of the material. Spatially resolved detection with Scanning Kelvin Probe Force Microscopy (SKPFM) as an electrochemical technique with a resolution on a nanometric scale in combination with Thermal Desorption Spectroscopy (TDS) and microstructure characterization using electron microscopy indicated a domination of at least two trapping sites. Step by step the dominating H trapping sites were identified as dislocations and vacancies with estimated desorption energies of 29 ± 5 and 38 ± 5 kJ mol−1. Furthermore, voids, inclusions and their interface to the matrix where found to be trapping sites binding low amounts of H, invisible for TDS measurements but detectible with SKPFM. Unexpectedly, no H was detected inside high angle grain boundaries. This study shows that dislocation and vacancies are the main trapping sites whereas vacancies getting increasingly important after cold rolling of steel rich of inclusions. Furthermore, the importance of using several techniques to understand the trapping behaviour of H even in simplified model alloys is underlined.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.066
      Issue No: Vol. 144 (2017)
       
  • Towards the prediction of hydrothermal ageing of 3Y-TZP bioceramics from
           processing parameters
    • Authors: Chong Wei; Laurent Gremillard
      Pages: 245 - 256
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Chong Wei, Laurent Gremillard
      Hydrothermal ageing of yttria-stabilized tetragonal zirconia ceramics can have a strong influence on the lifetime of zirconia devices. Ageing kinetics are often described by the Mehl–Avrami–Johnson equation, most often used as a phenomenological description. This work seeks to relate the parameters of MAJ equations (Vmax, n, b0 and Q) to microstructural characteristics of the zirconia material: grain sizes, Y2O3 partitioning, monoclinic, tetragonal and cubic phases ratio. Samples with identical nominal composition of 3Y-TZP were prepared with grain sizes ranging from 190 nm to 773 nm. From their microstructural parameters, a relationship between microstructural parameters and sintering cycles was first proposed, followed by a relationship between ageing parameters and microstructural parameters. These results provide a convenient framework to better develop the sintering cycle of zirconia biomaterial in order to maximize their resistance to hydrothermal ageing.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.061
      Issue No: Vol. 144 (2017)
       
  • In situ micromechanical testing in environmental scanning electron
           microscope: A new insight into hydrogen-assisted cracking
    • Authors: Bjørn Rune Sørås Rogne; Nousha Kheradmand; Yun Deng; Afrooz Barnoush
      Pages: 257 - 268
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Bjørn Rune Sørås Rogne, Nousha Kheradmand, Yun Deng, Afrooz Barnoush
      The susceptibility of Fe–26Al–0.5Cr (at.%) intermetallic alloy to hydrogen assisted cracking was evaluated by micromechanical fracture mechanics specimens. The notched micro-beams were loaded in situ in an environmental scanning electron microscope under two conditions: one with low pressure to avoid any hydrogen effect and the other with water vapour to promote hydrogen uptake and hydrogen assisted cracking. Fractographic and electron backscatter diffraction analysis carried out on the fracture surfaces of the ruptured beams revealed the mechanisms of the crack propagation. Under both conditions, the failure was cleavage-like, accommodated with plastic deformation. The results show the influence of hydrogen-induced embrittlement on the initiation of the fracture and the plasticity of the crack tip during the propagation of the crack, where the latter becomes localised and uniform over the fracture surface. From the observations, a three stage crack propagation process is proposed. Also, the fracture toughness of the samples was evaluated by linear elastic fracture mechanics and the validity of the results are discussed.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.037
      Issue No: Vol. 144 (2017)
       
  • Microstructure evolution during austenite reversion in Fe-Ni martensitic
           alloys
    • Authors: H. Shirazi; G. Miyamoto; S. Hossein Nedjad; T. Chiba; M. Nili Ahmadabadi; T. Furuhara
      Pages: 269 - 280
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): H. Shirazi, G. Miyamoto, S. Hossein Nedjad, T. Chiba, M. Nili Ahmadabadi, T. Furuhara
      The change of microstructure during reverse transformation by continuous heating and isothermal holding above Af temperature were studied in Fe-11, 18 and 23 Ni (mass %) alloys. In-situ observation by using confocal laser scanning microscopy (CLSM) and in-situ/ex-situ electron backscatter diffraction (EBSD) analysis were used for direct observation of reverse transformation. It was found that the start temperatures (As) for austenite reversion decrease with increasing of Ni content while they are higher than T0 temperatures. Reverse transformation in the Fe-23 Ni alloy is accompanied with a sharp surface relief indicating that reverse transformation occurs martensitically in this alloy. EBSD measurements show that reversed austenite grains in this alloy are formed with nearly identical crystallographic orientations to the prior one, which means orientations and boundaries of prior austenite grains are preserved due to the austenite memory effect. By further holding above Af temperature spontaneous recrystallization of reverted austenite proceeds. The Fe-18 Ni alloy also shows similar microstructure change during reversion. Near Kurdjamov-Sachs (K-S) orientation relationship is found between reversed austenite and initial martensite during reversion of the Fe-18 and 23 Ni alloys. However, when the Ni content is decreased to 11%, no specific orientation relationship is found between reversed austenite and initial martensite, indicating that the reversion mechanism is changed from martensitic to partitionless diffusional (massive) mechanism.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.068
      Issue No: Vol. 144 (2017)
       
  • Unraveling the origin of twin related domains and grain boundary evolution
           during grain boundary engineering
    • Authors: Christopher M. Barr; Asher C. Leff; Ryan W. Demott; Roger D. Doherty; Mitra L. Taheri
      Pages: 281 - 291
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Christopher M. Barr, Asher C. Leff, Ryan W. Demott, Roger D. Doherty, Mitra L. Taheri
      Grain boundary engineering of Fe-based austenitic stainless steels and other materials has been successful in producing a large increase in twin and twin related grain boundaries from a wide range of thermomechanical treatments. However, the exact mechanisms and effective grain boundary network descriptors to create the heavily twinned microstructures are yet to be fully understood. In this study, we provide insight into the grain boundary engineering process by examining sequential progression of the same spatial location of a twin related microstructure through thermomechanical processing. The results show that clusters of twin related grain boundaries called twin related domains form during primary recrystallization. The size of the twin related domains increases as the level of strain falls toward the critical strain for recrystallization. Growth of twin related domains during recrystallization results in the formation of twin boundaries behind the migrating grain boundary front. Formation of higher order twin boundaries occurs when two separate grain boundary fronts of the same twin related domain impinge upon each other. We also present relevant microstructural descriptors with emphasis on twin related domain statistics to recrystallization phenomena in grain boundary engineering materials.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.007
      Issue No: Vol. 144 (2017)
       
  • Defect-mediated multiple-enhancement of phonon scattering and decrement of
           thermal conductivity in (YxYb1-x)2SiO5 solid solution
    • Authors: Zhilin Tian; Chunfu Lin; Liya Zheng; Luchao Sun; Jialin Li; Jingyang Wang
      Pages: 292 - 304
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Zhilin Tian, Chunfu Lin, Liya Zheng, Luchao Sun, Jialin Li, Jingyang Wang
      Rare earth (RE) silicates are promising candidates for environmental and thermal barrier coating (ETBC) materials. Low thermal conductivity is one of the main concerned thermal properties in ETBC design. We herein adopted multiple phonon scattering mechanisms to lower thermal conductivity of (YxYb1-x)2SiO5 solid solutions. Bulk samples were prepared by hot pressing method and RE atomic occupations, Raman spectra, thermal conductivities were measured as well as Debye temperature was obtained from temperature dependent Young's modulus. It is interesting to note that huge mass and size misfits between Yb and Y ions dominate the decrement of thermal conductivity. Furthermore, Yb2+ increases the concentration of oxygen vacancy, and it further decreases heat conduction. This work highlights the possible defect engineering in RE silicates for their advances in ETBC applications.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.064
      Issue No: Vol. 144 (2017)
       
  • Strong converse magnetoelectric effect in (Ba,Ca)(Zr,Ti)O3 - NiFe2O4
           multiferroics: A relationship between phase-connectivity and interface
           coupling
    • Authors: M. Naveed-Ul-Haq; Vladimir V. Shvartsman; Harsh Trivedi; Soma Salamon; Samira Webers; Heiko Wende; Ulrich Hagemann; Jörg Schröder; Doru C. Lupascu
      Pages: 305 - 313
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): M. Naveed-Ul-Haq, Vladimir V. Shvartsman, Harsh Trivedi, Soma Salamon, Samira Webers, Heiko Wende, Ulrich Hagemann, Jörg Schröder, Doru C. Lupascu
      Studying multiferroic magnetoelectrics has been a focus field for the last decade and a half, and the exploration of new materials is one of the several aspects of this quest. Here we report on the synthesis and characterization of NiFe2O4-based multiferroic composites which employ (Ba,Ca)(Zr,Ti)O3 as the ferroelectric/piezoelectric component and NiFe2O4 as the magnetostrictive phase. We find that these composites show excellent magnetoelectric properties. Especially the composite with 30 vol% of NiFe2O4 has a converse ME coefficient approximately two times larger than the previously reported one for BaTiO3-CoFe2O4 composites. A relationship between the phase connectivity within these composites and the ME properties was explored by the time of flight secondary ion mass microscopy. We believe that our investigation will be helpful for the design of magnetoelectric materials as components of sensors and memory devices.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.048
      Issue No: Vol. 144 (2017)
       
  • Twin-interface interactions in nanostructured Cu/Ag: Molecular dynamics
           study
    • Authors: R. Béjaud; J. Durinck; S. Brochard
      Pages: 314 - 324
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): R. Béjaud, J. Durinck, S. Brochard
      The interaction of deformation twins with interfaces in nanostructured Cu/Ag is studied using molecular dynamics simulations. The influence of the interface structure on twin nucleation, propagation and thickening is analysed, and the role of the misfit interfacial dislocations mesh is detailed. In particular, we show that the interface can induce, directly or indirectly via Lomer dislocations, the nucleation of twinning dislocations. A thorough description of the involved mechanisms is given. Through this atomic scale approach, our study offers some useful understanding of the mechanical twinning process in nanolamellar composites, where twinning appears to be a common plasticity mechanism.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.036
      Issue No: Vol. 144 (2017)
       
  • Temperature-dependence of mode I fracture toughness of a bulk metallic
           glass
    • Authors: Devaraj Raut; R.L. Narayan; Parag Tandaiya; Upadrasta Ramamurty
      Pages: 325 - 336
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Devaraj Raut, R.L. Narayan, Parag Tandaiya, Upadrasta Ramamurty
      Within the temperature range over which the shear band (SB)-mediated plastic deformation is dominant, metallic glasses exhibit an intermediate temperature ductility minimum (ITDM), which occurs at about 65% of the glass transition temperature, T g . This ITDM is associated with a small number of SBs, with each band carrying large amount of plastic strain, which in turn leads to their easy transition to shear cracks, eventually leading to fracture. Some MGs are known to exhibit high room temperature (RT) fracture toughness, which has been associated with SB-mediated crack-tip plasticity. Hence, it is expected that ITDM would also correspond to a minimum in toughness. In order to ascertain this, temperature-dependence of mode I fracture toughness, J c , of a bulk metallic glass (BMG), Vitreloy 105, was investigated by recourse to 4-point bend testing of single edge notched specimens within 298–475 K range, which corresponds to ∼0.44 and 0.7T g of the tested BMG. Complementary finite element analyses were utilized to convert the critical load for fracture into J c . Results confirm a minimum in J c at ∼0.67T g , which is in agreement with the results of unnotched 3-point bend experiments on unnotched bars that show ITDM at 0.65T g . These observations are rationalized with the aid of notch plastic deformation and post mortem fractographic characterizations and in terms of the influence of temperature on factors such as the number of shear bands, the barrier for their conversion into shear cracks, and hydrostatic stress gradients ahead of the notch tip. This study highlights the sensitive nature of BMGs' fracture toughness, even when they are nominally ductile, to temperature.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.063
      Issue No: Vol. 144 (2017)
       
  • The α→ω and β→ω phase transformations in Ti–Fe alloys under
           high-pressure torsion
    • Authors: A.R. Kilmametov; Yu. Ivanisenko; A.A. Mazilkin; B.B. Straumal; A.S. Gornakova; O.B. Fabrichnaya; M.J. Kriegel; D. Rafaja; H. Hahn
      Pages: 337 - 351
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): A.R. Kilmametov, Yu. Ivanisenko, A.A. Mazilkin, B.B. Straumal, A.S. Gornakova, O.B. Fabrichnaya, M.J. Kriegel, D. Rafaja, H. Hahn
      The formation of ω-phase under high-pressure torsion (HPT) has been studied in Ti–Fe alloys. Seven alloys with Fe concentration from 0 to 10 wt % have been annealed between 600 and 950 °C, quenched and HPT-treated at 7 GPa, 1 rpm, 5 and 0.1 anvil rotations (equivalent strain e eq = 156 and = 3.1, respectively). The strain after 0.1 rot. corresponds to the transient state of HPT, and that after 5 rot. corresponds to the HPT steady-state and to the dynamic equilibrium between formation and annihilation of microstructure defects. A defect-rich high-pressure ω-phase forms after HPT and persists in the samples also after the pressure release. The amount of retained ω-phase after HPT depends on the iron concentration. It increases from 40% in pure titanium, reaches maximum of 95% at 4 wt % Fe and then decreases again to 10% at 10 wt % Fe. It is because the addition of iron influences the lattice parameters in β and ω-phases in a different manner. The minimal lattice mismatch between β- and ω-phases is reached at 4 wt % Fe. A good conformity between the lattices of the β- and ω-phases enhances the probability of the martensitic (diffusionless) β→ω transformation. Based on the XRD and TEM observations, the crystallography and mechanisms of α→ω and β→ω phase transformations (which can be diffusionless as well as controlled by mass transfer) under the influence of pure shear by HPT are discussed.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.051
      Issue No: Vol. 144 (2017)
       
  • Phase differentiation by electron backscatter diffraction using the
           dictionary indexing approach
    • Authors: Farangis Ram; Marc De Graef
      Pages: 352 - 364
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Farangis Ram, Marc De Graef
      Using the dictionary approach to Electron Backscatter Diffraction (EBSD) analysis, we address: (1) phase differentiation in highly-deformed or fine-grained materials; and (2) phase differentiation between phases with the same Bravais lattice and different lattice parameters. We introduce a phase differentiation confidence index based on the dictionary indexing approach and apply the index to scenarios where the classical EBSD indexing approach has major difficulties in delivering reliable results. We show that dictionary indexing successfully differentiates the phases in these scenarios and report on the confidence of such differentiations. We also show that dictionary indexing is sensitive to hydrostatic strain and can identify the correct amount of hydrostatic strain present in a material.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.069
      Issue No: Vol. 144 (2017)
       
  • On the role of twinning and stacking faults on the crystal plasticity and
           grain refinement in magnesium alloys
    • Authors: S.Q. Zhu; Simon P. Ringer
      Pages: 365 - 375
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): S.Q. Zhu, Simon P. Ringer
      We have investigated the detailed microstructural mechanisms associated with the excellent crystal plasticity and ultra-fine grain refinement observed under high strain-rate deformation of Mg alloys, focusing on ZK60. Firstly, we have identified the clear formation of stacking faults in deformation-induced twinned crystal segments. Specifically, we have found that intrinsic I 1 and I 2 stacking faults bounded by 1 6 < 2 ¯ 023> and 1 3 <10 1 ¯ 0> partial dislocations, respectively, were found to occur in very high number densities within the twins. This was due to the high Schmid factor for stacking fault shearing in twins and the critical role that twin boundaries played in emitting partial dislocations. Secondly, we have clarified the interplay between twinning and stacking faults on the enhanced crystal plasticity. Apart from the strain accommodated by the extensive twinning itself, we propose that the improved plasticity during high strain-rate deformation is mainly due to the nucleation of 1 3 < 11 ¯ 23>{11 2 ¯ 2} dislocation within twins, which provides enough independent slip systems to achieve a homogeneous deformation in the material. Finally, we have demonstrated the interplay between twinning and stacking fault formation on the nucleation of new grains via dynamic recrystallisation. The twin boundaries and stacking faults, especially those of the I 1 type, facilitate the formation of low-angle grain boundaries that can subsequently transition into high-angle grain boundaries, and form ultra-fine dynamically recrystallised grains.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.11.004
      Issue No: Vol. 144 (2017)
       
  • Elastic properties and plastic deformation of TiC- and VC-based
           pseudobinary alloys
    • Authors: D. Edström; D.G. Sangiovanni; L. Hultman; Ivan Petrov; J.E. Greene; V. Chirita
      Pages: 376 - 385
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): D. Edström, D.G. Sangiovanni, L. Hultman, Ivan Petrov, J.E. Greene, V. Chirita
      Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to investigate the possibility of improving ductility by forming pseudobinary cubic M1M2 C alloys, for which M1  = Ti or V and M2  = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 1 1 ¯ 0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material [1]. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.047
      Issue No: Vol. 144 (2017)
       
  • A strategy to predict the fracture toughness of steels with a banded
           ferrite–pearlite structure based on the micromechanics of brittle
           fracture initiation
    • Authors: Kazuki Shibanuma; Yoshiki Nemoto; Takashi Hiraide; Katsuyuki Suzuki; Sunao Sadamatsu; Yoshitaka Adachi; Shuji Aihara
      Pages: 386 - 399
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Kazuki Shibanuma, Yoshiki Nemoto, Takashi Hiraide, Katsuyuki Suzuki, Sunao Sadamatsu, Yoshitaka Adachi, Shuji Aihara
      This paper presents a strategy to predict the fracture toughness of steels with a banded ferrite–pearlite structure using a new model based on the micromechanics of brittle fracture initiation. The model requires only the (1) ferrite grain size and pearlite band thickness distributions, (2) the stress–strain curve, and (3) the specimen geometry and boundary conditions of the fracture toughness test, without the need for any parameter fittings from the experimental results. The model is based on the multiscale model synthesis approach, consisting of three elemental models: (1) the microstructural spatial distribution, (2) a macroscopic finite element analysis, and (3) the microscopic fracture initiation processes, wherein the respective formulations of the fracture criteria of the three stages are proposed, namely, Stage I: micro-crack formation in shear in the pearlite colony; Stage II: the crack entering the adjacent ferrite grain; and Stage III: the propagation of the crack across ferrite grain boundary. The proposed model was validated by comparing it with the experimental results of five kinds of steels with a range of carbon concentrations, ferrite grain sizes, and pearlite band thicknesses. The predicted and experimental results agreed well for all steel samples and temperatures. In addition, the influence of the microstructure on the fracture toughness was discussed using virtual candidate steels containing various carbon concentrations, ferrite grain sizes, and pearlite band thicknesses. The results demonstrate that the proposed model is an effective and powerful tool for quantitatively predicting the fracture toughness of steel with a banded ferrite–pearlite microstructure.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.046
      Issue No: Vol. 144 (2017)
       
  • Hierarchical aging pathways and reversible fragile-to-strong transition
           upon annealing of a metallic glass former
    • Authors: Isabella Gallino; Daniele Cangialosi; Zach Evenson; Lisa Schmitt; Simon Hechler; Moritz Stolpe; Beatrice Ruta
      Pages: 400 - 410
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Isabella Gallino, Daniele Cangialosi, Zach Evenson, Lisa Schmitt, Simon Hechler, Moritz Stolpe, Beatrice Ruta
      The change of physical properties during aging and the associated microscopic dynamics of the Au49Cu26.9Si16.3Ag5.5Pd2.3 bulk metallic glass are investigated using a broad collection of laboratory and synchrotron-based techniques, such as differential- and fast-scanning calorimetry, thermomechanical testing, and x-ray photon correlation spectroscopy. We observe multiple decays in the enthalpy change during aging. This is reflected by a microscopic ordering consisting of distinct stationary dynamical regimes interconnected by abrupt aging processes. The stationary regimes are representative of states of local and transient equilibrium with increasingly higher activation energies. Furthermore, the aging study is conducted with the kinetically fragile frozen-in structure and the underlying fragile-to-strong transition is accessed by the ultra-viscous liquid state during annealing on a long-time scale and corresponds to the last observed enthalpy equilibration decay. The experimental work verifies, for the first time, that in a metallic glass forming system, the fragile-to-strong transition can also occur below the conventional glass transition temperature. Upon reheating, the reverse transformation, i.e. the strong-to-fragile transition, is observed with an entropy change of 0.19 J/(g-atom K), which is 2.4% of the entropy of fusion.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.060
      Issue No: Vol. 144 (2017)
       
  • Relaxation and saturation of electrostriction in 10 mol% Gd-doped
           ceria ceramics
    • Authors: Nimrod Yavo; Ori Yeheskel; Ellen Wachtel; David Ehre; Anatoly I. Frenkel; Igor Lubomirsky
      Pages: 411 - 418
      Abstract: Publication date: 1 February 2018
      Source:Acta Materialia, Volume 144
      Author(s): Nimrod Yavo, Ori Yeheskel, Ellen Wachtel, David Ehre, Anatoly I. Frenkel, Igor Lubomirsky
      10 mol% Gd-doped ceria (10GDC) ceramics, with grain size in the single micron range, display electrostrictive behavior under ambient conditions of temperature and pressure. In weak, quasi-static electric fields, i.e. <1 kV/cm, frequency <1 Hz, the longitudinal strain is measured to be proportional to the square of the applied electric field, albeit with the corresponding electrostrictive strain coefficient (M 33 ) displaying large variability between samples: −(2-20)·10−17 (m/V)2. Nevertheless, M 33 of all samples exceeds the values expected on the basis of the classical (Newnham) electrostriction scaling law by up to two orders of magnitude. A systematic study reveals the functional dependence of M 33 on frequency: above 10 Hz, M33 decreases to ≈10−18 (m/V)2, which may be characterized as non-Debye relaxation with non-ideality factor 0.35–1.13. For frequencies ≤1.5 Hz, increasing the field strength beyond 1 kV/cm results in an exponential decrease in M 33 : the longitudinal strain saturates at 1-4 ppm. Dielectric impedance spectra suggest that partitioning of the applied voltage between grain boundaries and grain cores may be a factor contributing both to the large variability in the electrostriction parameters, and to the strong dependence on electric field amplitude. The frequency dependence may have two sources: the slow electric field-driven reorganization of the Ce-containing active complexes in the electrostrictive medium as well as the influence of the grain boundaries. 10GDC ceramics may therefore be added to the list of non-classical electrostrictors which includes reduced and Gd-doped ceria thin films and (Nb,Y)-doped bismuth oxide ceramics.
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      PubDate: 2017-11-11T16:08:53Z
      DOI: 10.1016/j.actamat.2017.10.056
      Issue No: Vol. 144 (2017)
       
  • {101¯1} Twin boundary structures in a Mg–Gd alloy
    • Authors: Y.M. Zhu; S.W. Xu; J.F. Nie
      Pages: 1 - 12
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Y.M. Zhu, S.W. Xu, J.F. Nie
      In this work, we report our direct observations of atomic structures of both end and broad interfaces of { 10 1 ¯ 1 } twin boundary (TB) in a deformed and annealed Mg–Gd solid solution single phase alloy using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. The end interface is an asymmetric tilt boundary decorated by a periodic array of clusters comprising ordered Gd-rich columns. The broad interface consists of coherent { 10 1 ¯ 1 } twin boundaries that are disconnected by various steps and basal/pyramidal (BPy) facets, which all contain characteristic Gd segregation. The twin steps, including S1/1, S2/2, S3/2, S5/4, S7/6 and S7/7, are observed and classified in terms of their heights, orientations, and Burgers vectors. The S1/1 and S2/2 steps are not associated with any misfit dislocations, but S1/1 is always associated with an I1 stacking fault, which is free of Gd segregation, in the twin crystal. The S3/2, S5/4, S7/6 and S7/7 steps contain misfit dislocations but no stacking faults. The BPy facets, observed for the first time in the { 10 1 ¯ 1 } TB of Mg alloys, exhibit different widths and orientations, and they are associated with elastic strain arising from in-plane mismatch and plane disclination. A double-segregation-layer structure is also observed, with the coherent { 10 1 ¯ 1 } 1} TB lying on one of these two layers. These observations are discussed in terms of existing crystallographic models.
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      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.067
      Issue No: Vol. 143 (2017)
       
  • In situ dynamic TEM characterization of unsteady crystallization during
           laser processing of amorphous germanium
    • Authors: Garth C. Egan; Tian T. Li; John D. Roehling; Joseph T. McKeown; Geoffrey H. Campbell
      Pages: 13 - 19
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Garth C. Egan, Tian T. Li, John D. Roehling, Joseph T. McKeown, Geoffrey H. Campbell
      The unsteady propagation mechanism for the crystallization of amorphous germanium (a-Ge) was studied with in situ movie-mode dynamic transmission electron microscopy (MM-DTEM). Short laser pulses were used to heat sputter-deposited a-Ge films and the resulting crystallization process was imaged with up to 16 sequential 50 ns long electron pulses separated by a controlled delay that was varied between 0.5 and 5 μs The unsteady crystallization in the radial, net-growth direction was observed to occur at a decreasing rate of ∼1.5–0.2 m/s through a mechanism involving the formation of discrete ∼1.1 μm wide bands that grew with velocities of 9–12 m/s perpendicular to the radial direction and along the perimeter of the crystallized area. The crystallization rate and resulting microstructure were consistent with a liquid-mediated growth mechanism, which suggests that locally the band front reaches the amorphous melting temperature of Ge. A mechanism based on the notion of a critical temperature is proposed to explain the unsteady, banded behavior.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.10.003
      Issue No: Vol. 143 (2017)
       
  • Ni-Mn-Ga micro-trusses via sintering of 3D-printed inks containing
           elemental powders
    • Authors: Shannon L. Taylor; Ramille N. Shah; David C. Dunand
      Pages: 20 - 29
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Shannon L. Taylor, Ramille N. Shah, David C. Dunand
      Ni-Mn-Ga magnetic shape memory alloy (SMA) micro-trusses, suitable for high magnetic field induced strains and/or a large magnetocaloric effect, are created via a new additive manufacturing method combining (i) 3D-printing of ∼400 μm struts with an ink containing a polymer binder and elemental Ni, Mn, and Ga powders, (ii) binder burn-out and metallic powder interdiffusion and homogenization to create the final alloy, and (iii) further sintering to increase strut density. Controlled amounts of hierarchical porosity, desirable to enable twinning in this polycrystalline alloy, are achieved after sintering: (i) continuous, ∼450 μm wide channels between the printed, ∼300 μm diameter Ni-Mn-Ga struts and (ii) microporosity within the struts, from 50 to 200 μm voids where the largest Ga powders initially resided, and from residual 5–25 μm pores between powders due to incomplete sintering. The micro-trusses, sintered at 1000 °C for 12 h, and chemically ordered for 10 h at 700 °C, with overall porosities of 73–76%, have uniform compositions near Ni-32Mn-18Ga (at.%) and are comprised of a non-modulated martensite phase. Reversible martensite/austenite transformations between 45 and 90 °C, Curie temperatures of 85–90 °C, and saturation magnetizations of up to 56 Am2/kg are achieved.
      Graphical abstract image

      PubDate: 2017-11-05T05:39:48Z
      DOI: 10.1016/j.actamat.2017.10.002
      Issue No: Vol. 143 (2017)
       
  • In situ studies on irradiation resistance of nanoporous Au through
           temperature-jump tests
    • Authors: Jin Li; C. Fan; Q. Li; H. Wang; X. Zhang
      Pages: 30 - 42
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Jin Li, C. Fan, Q. Li, H. Wang, X. Zhang
      Nanoporous materials have great potentials to alleviate irradiation-induced damage due to their giant surface-to-volume ratio. Previous in situ irradiation study on nanoporous Au at room temperature has shown the shrinkage of nanopores due to the absorption of irradiation-induced defects, and the shrinkage rate is pore-size-dependent. In this follow-up temperature-dependent study, we show that both defect density and nanopores evolve with irradiation temperature. Higher temperature results in lower defect density and reduced shrinkage rate of nanopores. The sink strength of nanopores as a function of temperature is estimated. Moreover, nanoporous Au exhibits significantly enhanced swelling resistance compared to coarse-grained Au. Potential mechanisms for temperature dependent irradiation resistance of nanoporous metals are discussed.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.054
      Issue No: Vol. 143 (2017)
       
  • Investigation on temporal evolution of the grain refinement in copper
           under high strain rate loading via in-situ synchrotron measurement and
           predictive modeling
    • Authors: Pooja Nitin Shah; Yung C. Shin; Tao Sun
      Pages: 43 - 54
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Pooja Nitin Shah, Yung C. Shin, Tao Sun
      Synchrotron X-rays are integrated with a modified Kolsky tension bar to conduct in situ characterization of the grain refinement mechanism operating during the dynamic deformation of metals. Copper with an initial average grain size of 36 μm is refined to 6.3 μm when loaded at a constant high strain rate of 1200 s−1. Synchrotron measurements revealed the temporal evolution of the grain refinement mechanism in terms of the initiation and rate of refinement throughout the loading test. A multiscale finite element based recrystallization model has been developed to predict the grain size evolution occurring during the dynamic deformation process. The model accurately predicts the initiation and temporal evolution of the refinement phenomenon with a predicted final average grain size of 2.4 μm.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.10.005
      Issue No: Vol. 143 (2017)
       
  • Alloying effects on the microstructure and mechanical properties of
           nanocrystalline Cu-based alloyed thin films: Miscible Cu-Ti vs immiscible
           Cu-Mo
    • Authors: J.Y. Zhang; J.T. Zhao; X.G. Li; Y.Q. Wang; K. Wu; G. Liu; J. Sun
      Pages: 55 - 66
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): J.Y. Zhang, J.T. Zhao, X.G. Li, Y.Q. Wang, K. Wu, G. Liu, J. Sun
      Tuning the microstructure to optimize the mechanical performance of nanocrystalline Cu thin films via the alloying strategy is quite important for their application in microdevices. In this work, we prepared nanocrystalline miscible Cu-Ti and immiscible Cu-Mo alloyed thin films to investigate alloying effects on the microstructure and mechanical properties of Cu thin films in terms of mixing enthalpies. It is found that the dopants of both Ti and Mo can notably refine the grains, and in particular promote the formation of nanotwins below a critical content of solute, beyond which the formation of nanotwins is notably suppressed. The nonmonotonic solute concentration-dependent twinning behavior observed in Cu-Ti and Cu-Mo alloyed thin films is explained by the coupling effects between grain size and grain boundary segregated dopants that affects the stimulated slip process of partials. The increased hardness of both Cu-Ti and Cu-Mo systems with increasing the solute contents are quantitatively explained by combining several strengthening mechanisms, including solid solution strengthening, grain/twin boundary (GB/TB) strengthening, solute segregation-induced strengthening. It unexpectedly appears that with increasing the solute contents, the Cu-Ti system exhibits monotonically reduced positive strain rate sensitivity (SRS, m), whereas the Cu-Mo system manifests almost constant negative SRS. The fundamental difference in SRS m between Cu-Ti and Cu-Mo is rationalized in terms of the interactions between solute atomic clusters and dislocations based on the cross-core diffusion mechanism.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.039
      Issue No: Vol. 143 (2017)
       
  • In-situ strength of individual silicon particles within an aluminium
           casting alloy
    • Authors: M.G. Mueller; G. Žagar; A. Mortensen
      Pages: 67 - 76
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): M.G. Mueller, G. Žagar, A. Mortensen
      Measurements of local strength are performed in-situ on individual silicon particles that constitute the second phase of aluminium alloy A356. Particles are shaped using Focused Ion Beam (FIB) milling such that, upon the application of a compressive force on the particle, a volume of material unaffected by FIB milling is subjected to bending. Silicon particles in this commercial aluminium casting alloy are shown to be capable of locally sustaining tensile stresses as high as 16 GPa, i.e., approaching theoretical strength. The reason why such strengths are not reached by most alloy Si particles is shown to be the presence of specific surface defects, the effect of which is assessed. The most deleterious defects are interfaces between merged silicon crystals; therefore, eliminating these might lead to significantly enhanced strength and ductility in this widely-used casting alloy family.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.058
      Issue No: Vol. 143 (2017)
       
  • Size effects on intergranular crack growth mechanisms in ultrathin
           nanocrystalline gold free-standing films
    • Authors: Ehsan Hosseinian; Saurabh Gupta; Olivier N. Pierron; Marc Legros
      Pages: 77 - 87
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Ehsan Hosseinian, Saurabh Gupta, Olivier N. Pierron, Marc Legros
      This study investigated the combined effects of thickness (30 vs 100 nm) and average grain size (40 vs 70 nm for the thicker films) on the crack propagation mechanisms in ultrathin nanocrystalline gold microbeams, using a microelectromechanical system device to perform in situ transmission electron microscope (TEM) tensile experiments. Monotonic tensile tests of the two types of microbeams show similar strength levels (∼400 MPa) and ductility (∼2%). However, the thicker specimens exhibit a much more ductile behavior under repeated stress relaxation experiments, which the in situ TEM experiments revealed to be related to differences in intergranular crack propagation mechanisms. The governing crack growth process is in both cases dominated by grain boundary dislocation activities leading to grain boundary sliding. For the thinner specimens, secondary nanocracks are generated (as a result of grain boundary sliding) ahead of the main crack and coalesce together. Instead, secondary nanocracks do not form ahead of the main crack for the thicker specimens; the main crack extends as a result of sustained grain boundary sliding at the crack tip.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.10.004
      Issue No: Vol. 143 (2017)
       
  • Computation of entropies and phase equilibria in refractory V-Nb-Mo-Ta-W
           high-entropy alloys
    • Authors: Yi Wang; Ming Yan; Qiang Zhu; Williams Yi Wang; Yidong Wu; Xidong Hui; Richard Otis; Shun-Li Shang; Zi-Kui Liu; Long-Qing Chen
      Pages: 88 - 101
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Yi Wang, Ming Yan, Qiang Zhu, Williams Yi Wang, Yidong Wu, Xidong Hui, Richard Otis, Shun-Li Shang, Zi-Kui Liu, Long-Qing Chen
      We have applied the first-principles phonon method to the refractory V-Nb-Mo-Ta-W high-entropy alloys (HEAs) to predict the major phase separations in the temperature-compositional space and hence the associated entropy changes within the systems, taking into account vibrational, electronic, and configurational contributions to the total entropy. The first-principles calculations covered 178 phases ranging from pure elements, the ordered B2, B32, B23, B22, hR8, hR7, tI6, C15, and D03 binary phases, two ordered MoNbTaW quaternary phases, and the partially disordered and completely disordered bcc phases. By sorting their relative phase stabilities with the Dantzig's simplex minimization algorithm, the possibilities of phase separation for the refractory quaternary and quinary HEAs were thermodynamically found in the temperature range of 500–907 K.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.10.017
      Issue No: Vol. 143 (2017)
       
  • Strong electron-polarized atom chain in amorphous phase-change memory
           GeSbTe alloy
    • Authors: Nian-Ke Chen; Xian-Bin Li; Xue-Peng Wang; Wei Quan Tian; Shengbai Zhang; Hong-Bo Sun
      Pages: 102 - 106
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): Nian-Ke Chen, Xian-Bin Li, Xue-Peng Wang, Wei Quan Tian, Shengbai Zhang, Hong-Bo Sun
      Phase-change memory (PCM) material is the promising material system for nonvolatile-memory technology. Performance optimization of PCM device urgently requires the deeper clarification of its material “Gene”. In this study, through first-principles calculations, p-orbital-aligned atom chains are identified to play important roles in governing optoelectronic reflectivity in amorphous Ge2Sb2Te5. These atom chains make the electronic state of the amorphous Ge2Sb2Te5 hold strong electron-polarized components, thereby governing the optical property. The present study offers a new understanding of “Gene” for PCM materials which benefit the material design and the performance improvement of PCM devices.
      Graphical abstract image

      PubDate: 2017-11-05T05:39:48Z
      DOI: 10.1016/j.actamat.2017.10.013
      Issue No: Vol. 143 (2017)
       
  • Micro-plasticity and recent insights from intermittent and small-scale
           plasticity
    • Authors: R. Maaß; P.M. Derlet
      Pages: 338 - 363
      Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143
      Author(s): R. Maaß, P.M. Derlet
      Prior to macroscopic yielding, most materials undergo a regime of plastic activity that cannot be resolved in conventional bulk deformation experiments. In this pre-yield, or micro-plastic regime, it is the initial three dimensional defect network that is probed and the intermittently evolving microstructure admits small increments in plastic strain. By reducing the sample size, this intermittent activity becomes increasingly apparent and can be routinely observed through small-scale mechanical testing. In some cases, the intermittent activity was shown to exhibit aspects of scale-free behavior, prompting a paradigm shift away from traditional microstructure-dependent unit mechanisms that may be associated with a well-defined length and stress scale. In this article, we discuss and review connections between classical micro-plasticity and intermittent flow across all length scales, with the aim of highlighting the value of miniaturized testing as a means to unravel this very early regime of bulk plasticity.

      PubDate: 2017-11-05T05:39:48Z
      DOI: 10.1016/j.actamat.2017.06.023
      Issue No: Vol. 143 (2017)
       
  • Editors for Acta Materialia
    • Abstract: Publication date: 15 January 2018
      Source:Acta Materialia, Volume 143


      PubDate: 2017-11-05T05:39:48Z
       
 
 
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