for Journals by Title or ISSN
for Articles by Keywords
help

Publisher: Elsevier   (Total: 3043 journals)

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Showing 1 - 200 of 3043 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 22, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 21, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 84, 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: 348, 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: 252, 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: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 23, 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: 5)
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: 135, 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: 25, 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 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: 26, 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: 41, 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: 41, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
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 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: 35, 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 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: 15, 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: 7, 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 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: 61)
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: 3, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 353, 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: 17)
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: 405, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 39, 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: 10, 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  
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: 8, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 48, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (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: 39, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 8, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 15, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 31, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 25, 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: 45, 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: 250, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 57, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5)
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: 22, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 34, 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: 57, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 11)
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: 167, 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: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 1)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 22, 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: 160, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (Followers: 1, SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Journal Cover Acta Materialia
  [SJR: 3.683]   [H-I: 202]   [252 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-6454
   Published by Elsevier Homepage  [3043 journals]
  • {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.
      Graphical abstract image

      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)
       
  • 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)
       
  • Nucleation kinetics in Al-Sm metallic glasses
    • Authors: L. Zhao; G.B. Bokas; J.H. Perepezko; I. Szlufarska
      Pages: 1 - 7
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): L. Zhao, G.B. Bokas, J.H. Perepezko, I. Szlufarska
      The isothermal nucleation kinetics in Al-Sm metallic glasses with low Sm concentrations ( x Sm ) was studied using molecular dynamics simulations in order to calculate time–temperature–transformation curves. The average delay time of Al nanocrystal nucleation was found to increase exponentially with x Sm , whereas the estimated critical cooling rate necessary to avoid crystallization decreases exponentially with x Sm . Sm solutes were found to suppress Al nucleation by increasing the attachment barrier and therefore by reducing the attachment frequency. The analysis shows that the attachment of Al to the evolving nucleus has the same characteristics as Al diffusion within the amorphous matrix and they both take place heterogeneously via collective movement of a group of Al atoms.
      Graphical abstract image

      PubDate: 2017-09-30T14:26:12Z
      DOI: 10.1016/j.actamat.2017.09.050
      Issue No: Vol. 142 (2017)
       
  • Simple and efficient synthesis of nanograin structured single phase filled
           skutterudite for high thermoelectric performance
    • Authors: Sanghoon Lee; Kyu Hyoung Lee; Young-Min Kim; Hyun Sik Kim; G. Jeffrey Snyder; Seunghyun Baik; Sung Wng Kim
      Pages: 8 - 17
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Sanghoon Lee, Kyu Hyoung Lee, Young-Min Kim, Hyun Sik Kim, G. Jeffrey Snyder, Seunghyun Baik, Sung Wng Kim
      Filled skutterudites are promising mid-to-high temperature range thermoelectric materials for power generation, however, a traditional melt-solidification process followed by annealing (TMA) and powder metallurgical sintering requires a long processing time more than 10 days to ensure the structural and compositional homogeniety of materials with a high thermoelectric conversion efficiency zT. To address this, we herein report a simple and efficient synthesis of high-performance n- and p-type filled skutterudites that successfully produces a complete single phase from single to multiple filled materials in a day. The nanograin (∼440 nm) structured bulks are prepared from the combined process of temperature-regulated melt spinning (MS) using ingots and short-time spark plasma sintering (SPS). The controlled phase evolution and transformation by adjusting rapid solidification and densification conditions are demonstrated by a comprehensive analysis including structure refinement and atomic-scale observation, verifying the desired occupancy and random distribution of filling elements, respectively. The maximum zT values of filled skutterudites fabricated here were 1.48 ± 0.17 at 800 K for n-type In0.12Yb0.20Co4.00Sb11.84 and 1.15 ± 0.13 at 750 K for p-type Ce0.91Fe3.40Co0.59Sb12.14, which are comparable to the highest zT values reported for filled skutterudites fabricated by TMA-based processes. Superior reproducibility achieved in shortened processing time enables the present synthetic process to be utilized for commercial manufacturing process that can be readily applied to massive production of bulk filled skutterudites for high-performance thermoelectric power generators.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.044
      Issue No: Vol. 142 (2017)
       
  • Grain boundary restructuring of multi-main-phase Nd-Ce-Fe-B sintered
           magnets with Nd hydrides
    • Authors: Tianyu Ma; Mi Yan; Kaiyun Wu; Bo Wu; Xiaolian Liu; Xuejiao Wang; Zeyu Qian; Chen Wu; Weixing Xia
      Pages: 18 - 28
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Tianyu Ma, Mi Yan, Kaiyun Wu, Bo Wu, Xiaolian Liu, Xuejiao Wang, Zeyu Qian, Chen Wu, Weixing Xia
      Multi-main-phase (MMP) Nd-Ce-Fe-B magnets prepared by sintering the mixture of Ce-free and Ce-containing RE2Fe14B (RE, rare earth) powders have been found to possess superior magnetic properties to the single-main-phase (SMP) ones. Purpose of this work is to further enhance the coercivity through restructuring the grain boundaries (GBs), which have strong influence on the short-range exchange coupling between adjacent grains. By incorporating 4 wt.% NdHx powders as the intergranular additive, coercivity of the (Pr, Nd)22.3Ce8.24FebalB0.98 (wt.%) MMP magnet has been substantially increased from 8.2 kOe to 13.1 kOe. Magnetic domain characterizations and the recoil loop measurements showed that the exchange coupling between adjacent grains has been weakened significantly due to the formation of continuous and smooth RE-rich GBs by the extra Nd after NdHx dehydrogenation. Elemental distribution analysis revealed that thicker Nd-rich 2:14:1 shells with stronger magnetocrystalline anisotropy have been formed in the outer region of the Ce-rich main phase grains, which is beneficial to enhance their effective anisotropy. In addition, the Ce-rich 2:14:1 shells surrounding the Nd-rich 2:14:1 grain cores became thinner, which is beneficial to weaken the magnetic dilution effect of such grains. Micromagnetic simulation results also suggest that the coercivity can be further enhanced once the grain boundary is nonmagnetic. Technically, enriching RE elements or reducing Fe content can weaken the ferromagnetism of the grain boundary phase as well as the exchange coupling between adjacent grains. The above findings might shed new insights into enhancing the coercivity of low cost Nd-Ce-Fe-B magnets.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.045
      Issue No: Vol. 142 (2017)
       
  • Mechanical properties of metal-ceramic nanolaminates: Effect of constraint
           and temperature
    • Authors: L.W. Yang; C. Mayer; N. Li; J.K. Baldwin; N.A. Mara; N. Chawla; J.M. Molina-Aldareguia; J. Llorca
      Pages: 37 - 48
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): L.W. Yang, C. Mayer, N. Li, J.K. Baldwin, N.A. Mara, N. Chawla, J.M. Molina-Aldareguia, J. Llorca
      Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanical response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). These mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.042
      Issue No: Vol. 142 (2017)
       
  • Enhancement of current-perpendicular-to-plane giant magnetoresistive
           outputs by improving B2-order in polycrystalline Co2(Mn0.6Fe0.4)Ge Heusler
           alloy films with the insertion of amorphous CoFeBTa underlayer
    • Authors: S. Li; T. Nakatani; K. Masuda; Y. Sakuraba; X.D. Xu; T.T. Sasaki; H. Tajiri; Y. Miura; T. Furubayashi; K. Hono
      Pages: 49 - 57
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): S. Li, T. Nakatani, K. Masuda, Y. Sakuraba, X.D. Xu, T.T. Sasaki, H. Tajiri, Y. Miura, T. Furubayashi, K. Hono
      We studied the origin of the enhancement of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect by inserting a thin amorphous CoFeBTa (CFBT) underlayer below a Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy ferromagnetic (FM) layer. Large magnetoresistance ratio of ∼25% and resistance change-area product of ∼7.5 mΩ μm2 were obtained at room temperature by inserting a CFBT (1.2 nm) underlayer. X-ray diffraction (XRD) and transmission electron microscope analyses confirmed that the CMFG FM layer deposited on the CFBT underlayer was amorphous in the as-deposited state and crystallized to a B2-ordered polycrystalline film by annealing at 300 °C. The degree of B2 order (S B2) of the CMFG films was estimated by anomalous XRD using x-ray energies around the Co K-absorption edge. S B2 of the CMFG film deposited on the amorphous CFBT (1.2 nm) underlayer was ∼0.76, much larger than that of the CMFG film deposited on a crystalline CoFe underlayer (S B2 ∼0.47). First-principles calculations indicated that the spin polarization of the sp-conduction electrons in CMFG increases with increasing S B2, which accounts for the enhanced CPP-GMR effect in the pseudo spin-valve by inserting an amorphous CFBT underlayer.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.046
      Issue No: Vol. 142 (2017)
       
  • Effect of plastic anisotropy on the deformation behavior of bicrystalline
           aluminum films – Experiments and modeling
    • Authors: Ehsan Izadi; Saul Opie; Harn Lim; Pedro Peralta; Jagannathan Rajagopalan
      Pages: 58 - 70
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Ehsan Izadi, Saul Opie, Harn Lim, Pedro Peralta, Jagannathan Rajagopalan
      We investigated the effect of texture-induced plastic anisotropy on the deformation behavior of ultrafine-grained aluminum films with a bicrystalline texture (two grain variants). The films were uniaxially loaded along two different directions such that the heterogeneity in the plastic behavior of the two grain variants due to plastic anisotropy was minimized along one direction and maximized along the other. The bicrystalline films show smaller strain rate sensitivity and hysteresis of stress-strain response when they are deformed along the direction that minimizes plastic heterogeneity compared to the direction that maximizes it. Notable differences in flow stress and residual hardening were also found for the two loading directions. To quantitatively understand the effect of plastic anisotropy, we simulated the response of the films using three-dimensional finite elements with a microstructurally explicit model built from TEM automated crystal orientation mapping of the samples that includes a grain boundary region, along with crystal plasticity and anisotropic elasticity. The simulations reveal markedly different distribution of stresses and strains in the two grain variants when loading is performed along the two directions, which can be directly related to the ratio of Schmid factors of their most active slip systems.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.038
      Issue No: Vol. 142 (2017)
       
  • Effect of pre-existing defects in the parent fcc phase on atomistic
           mechanisms during the martensitic transformation in pure Fe: A molecular
           dynamics study
    • Authors: S. Karewar; J. Sietsma; M.J. Santofimia
      Pages: 71 - 81
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): S. Karewar, J. Sietsma, M.J. Santofimia
      Molecular dynamics (MD) simulations are used to study the effect of different defect configurations and their arrangements in the parent fcc phase on atomistic mechanisms during the martensitic transformation mechanisms in pure Fe. The defect configurations considered are stacking faults (SF) and twin boundaries (TB) in single crystal fcc. Three arrangements of these defect structures are considered: parallel TB, intersecting SF, and intersecting SF and TB. Each of these defect configurations affect the transformation mechanisms and transformation temperatures. Parallel TB are the lowest-barrier sites for the atomic shear and thus accelerate the transformation process. The fcc phase with parallel TB follows the Nishiyama-Wasserman (NW) martensitic transformation mechanism. On the other hand, intersecting SF impede the atomic shear and thus retard the transformation. The atomistic transformation mechanism in this case first follows the hcp to bcc Burgers path and then the fcc to bcc Olson-Cohen model. The intersecting SF and TB result in a combined effect of both the previous cases. The simulation results show the occurrence of different atomistic mechanisms during martensitic transformation depending on the type of defects present in the parent fcc phase.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.049
      Issue No: Vol. 142 (2017)
       
  • Hot cracking mechanism affecting a non-weldable Ni-based superalloy
           produced by selective electron Beam Melting
    • Authors: Edouard Chauvet; Paraskevas Kontis; Eric A. Jägle; Baptiste Gault; Dierk Raabe; Catherine Tassin; Jean-Jacques Blandin; Rémy Dendievel; Benjamin Vayre; Stéphane Abed; Guilhem Martin
      Pages: 82 - 94
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Edouard Chauvet, Paraskevas Kontis, Eric A. Jägle, Baptiste Gault, Dierk Raabe, Catherine Tassin, Jean-Jacques Blandin, Rémy Dendievel, Benjamin Vayre, Stéphane Abed, Guilhem Martin
      A non weldable nickel-based superalloy was fabricated by powder bed-based selective electron beam melting (S-EBM). The as-built samples exhibit a heterogeneous microstructure along the build direction. A gradient of columnar grain size as well as a significant gradient in the γ′ precipitate size were found along the build direction. Microstructural defects such as gas porosity inherited from the powders, shrinkage pores and cracks inherited from the S-EBM process were identified. The origins of those defects are discussed with a particular emphasis on crack formation. Cracks were consistently found to propagate intergranular and the effect of crystallographic misorientation on the cracking behavior was investigated. A clear correlation was identified between cracks and high angle grain boundaries (HAGB). The cracks were classified as hot cracks based on the observation of the fracture surface of micro-tensile specimens machined from as-built S-EBM samples. The conditions required to trigger hot cracking, namely, presence of a liquid film during the last stage of solidification and thermal stresses are discussed within the framework of additive manufacturing. Understanding the cracking mechanism enables to provide guidelines to obtain crack-free specimens of non-weldable Ni-based superalloys produced by S-EBM.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
      DOI: 10.1016/j.actamat.2017.09.047
      Issue No: Vol. 142 (2017)
       
  • Thermodynamic instability of a nanocrystalline, single-phase TiZrNbHfTa
           alloy and its impact on the mechanical properties
    • Authors: B. Schuh; B. Völker; J. Todt; N. Schell; L. Perrière; J. Li; J.P. Couzinié; A. Hohenwarter
      Pages: 201 - 212
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): B. Schuh, B. Völker, J. Todt, N. Schell, L. Perrière, J. Li, J.P. Couzinié, A. Hohenwarter
      An equiatomic, single-phase TiZrNbHfTa high-entropy alloy was subjected to high-pressure torsion, leading to a grain size below 100 nm. Introducing a nanocrystalline microstructure to the material should help to accelerate a possible phase decomposition of the material by having a high amount of fast diffusion pathways and possible nucleation sites in the form of grain boundaries. In order to test the materials thermodynamic stability the nanocrystalline high-entropy alloy. was subjected to various heat treatments for temperatures between 300 °C and 1100 °C. Isochronal heat treatments (1 h) resulted in a hardness increase from 420 HV1 for the as-processed state to 530 HV1 for an annealing temperature of 500 °C, while for temperatures of 700 °C and higher a softening compared to the as-processed state occurred. In order to clarify this unexpected annealing response, analysis of selected microstructural states was performed utilizing electron microscopy, x-ray diffraction as well as mechanical testing to gain further information on microstructure-property relationships. Complementary, thermodynamic simulations were performed via the Calphad approach and compared to the experimental results. A phase decomposition of the originally equimolar single-phase high-entropy alloy into a NbTa-rich body-centered cubic phase and ZrHf-rich phases, which occurred in two different crystal structures depending on the annealing temperature, was the main reason for the property changes. The obtained results not only give valuable new insights into the phase stability of the TiZrNbHfTa alloy, but also demonstrate the impact of the newly forming phases in regards to mechanical properties and its implication for a possible practical application of this alloy.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.035
      Issue No: Vol. 142 (2017)
       
  • Surface-oxidized, freeze-cast cobalt foams: Microstructure, mechanical
           properties and electrochemical performance
    • Authors: Hyeji Park; Hoon-Hwe Cho; Kyungbae Kim; Kicheol Hong; Jae-Hun Kim; Heeman Choe; David C. Dunand
      Pages: 213 - 225
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Hyeji Park, Hoon-Hwe Cho, Kyungbae Kim, Kicheol Hong, Jae-Hun Kim, Heeman Choe, David C. Dunand
      Cobalt with anisotropic open porosity is fabricated by directional solidification of aqueous slurries of nanometric Co3O4 powder where ice dendrites push powders into aligned interdendritic spaces, followed by ice sublimation, reduction of the oxide to metallic Co powders, and sintering of these Co powders into parallel lamellae. As the Co3O4 powder slurry fraction decreases (from 10 to 4 vol%), Co lamellae width in the final foam also decreases (from 93 to 8 μm) while foam porosity increases (from 66 to 85%). A drop in solidification temperature (from −10 to −50 °C) decreases porosity (from 77 to 63%) and lamellae width (from 11 to 5 μm) at a constant 8 vol% slurry fraction. Finally, with increasing sintering time (for −10 °C solidification temperature and 8% slurry fraction), Co foam porosity decreases (from 77 to 68%) and lamella width strongly increases (from 10 to 59 μm), consistent with sintering-induced coalescence of lamellae. The Co foams exhibit high strength but relatively low stiffness as compared to simple theoretical models, consistent with internal Co lamella buckling. A uniform Co oxide layer is grown by oxidation to create an active coating on the Co lamellae useful for lithium-ion storage. A coin-cell test carried out on the oxidized Co foam demonstrates a capacity (1283 mAhg−1) almost twice that of a control oxidized Co foil anode, owing to its considerably larger surface area. Finite-element analysis is used to compute stresses and plastic strain evolutions during the lithiation process to understand the effect of oxide layer thickness and roughness, and micropores within the Co lamellae.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.066
      Issue No: Vol. 142 (2017)
       
  • Intrinsic impact toughness of relatively high strength alloys
    • Authors: Q.Q. Duan; R.T. Qu; P. Zhang; Z.J. Zhang; Z.F. Zhang
      Pages: 226 - 235
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Q.Q. Duan, R.T. Qu, P. Zhang, Z.J. Zhang, Z.F. Zhang
      Although the Charpy impact test has been routine for decades to assess the ductile or brittle nature of materials, the impact toughness, which is strongly sample-thickness dependent, is not an intrinsic property. By re-examining the energy absorption during fracturing of relatively high strength alloys, here we find a remarkably good linear relation between the impact energies and the fracture surface areas of samples with different thickness, and the slope essentially renders the intrinsic impact toughness. The new findings, which also provide a scaling law to well predict the thickness effect on the traditional impact toughness, may have broad applications for precisely determining the ductile-to-brittle transition temperature of small-dimensional devices, selecting materials according to their toughness at the thickness in usage, and evaluating the intrinsic toughness of emerging high strength materials with limited achievable size.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.064
      Issue No: Vol. 142 (2017)
       
  • Hydrogen embrittlement revealed via novel in situ fracture experiments
           using notched micro-cantilever specimens
    • Authors: Yun Deng; Afrooz Barnoush
      Pages: 236 - 247
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Yun Deng, Afrooz Barnoush
      The susceptibility of the FeAl intermetallic alloy to hydrogen-assisted cracking was investigated by in situ fracture experiments using notched micrometre-sized specimens using an Environmental Scanning Electron Microscope (ESEM). The notched beams were loaded under two different environmental conditions: one in high vacuum (5 × 10−4 Pa) to avoid hydrogen effects and one under a certain water vapor pressure (450 Pa) to promote hydrogen uptake. The fracture behaviour on a non-ASTM-standard micro-sized specimen was successfully studied by the experimental approach, and the microstructure of the whole crack area was analysed by Transmission Kikuchi Diffraction (TKD) and Transmission Electron Microscopy (TEM) techniques. Three crack growth stages were observed in all the specimens: i) elastic regime, ii) notch blunting and micro-crack formation; and iii) stable crack growth. We observed an accelerated crack propagation rate in specimens under hydrogen exposure. The hydrogen embrittlement phenomenon was found to occur because of the strong hydrogen-dislocation interactions. The combined effect of hydrogen-enhanced dislocation nucleation and hydrogen-restricted dislocation mobility is responsible for the hydrogen-enhanced cracking behaviour.
      Graphical abstract image

      PubDate: 2017-10-14T08:24:52Z
      DOI: 10.1016/j.actamat.2017.09.057
      Issue No: Vol. 142 (2017)
       
  • Designing Mg alloys with high ductility: Reducing the strength
           discrepancies between soft deformation modes and hard deformation modes
    • Authors: Guobao Liu; Jing Zhang; Guoqiang Xi; Rulin Zuo; Shuang Liu
      Pages: 1 - 9
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Guobao Liu, Jing Zhang, Guoqiang Xi, Rulin Zuo, Shuang Liu
      Two Mg alloys containing 0.03 at% and 0.18 at% Nd were designed to investigate the effects of solute concentration, and thermomechanical processing on the strengths of related deformation modes. Annealing treatments were conducted to stimulate grain coarsening for as-extruded alloys. In view of solute concentration effect, we conducted compressive tests and microstructure characterization to reveal and analyze the activities of the related deformation modes and their corresponding strengths. We find that the solute concentration of Nd does not affect the nucleation CRSS for {10-12} twinning. However, with the increase of Nd concentration, the nucleation CRSS for pyramidal <c+a>-slip was greatly reduced. We also use a thermomechanical processing route, in terms of pre-compression, unloading, intermediate annealing, and re-compression, to explore the effect of solute segregation on strengths of related deformation modes. It is found that the CRSS for the migration of {10-12} twinning dislocation increased significantly after the intermediate annealing treatment for Mg-0.18Nd alloy. We conclude that when designing high ductility Mg alloys, from the perspective of reducing the strength discrepancies between soft deformation modes and hard deformation modes, important factors including the type of alloying element, solute concentration, and pre-deformation strain need to be taken into account.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.006
      Issue No: Vol. 141 (2017)
       
  • A new loop-punching mechanism for helium bubble growth in tungsten
    • Authors: Hongxian Xie; Ning Gao; Ke Xu; Guang-Hong Lu; Tao Yu; Fuxing Yin
      Pages: 10 - 17
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Hongxian Xie, Ning Gao, Ke Xu, Guang-Hong Lu, Tao Yu, Fuxing Yin
      Growth of helium (He) bubbles with different initial sizes in tungsten (W) has been investigated by performing molecular dynamics simulations. Based on the simulation results a new loop punching mechanism for the large helium bubble growth is proposed. Different from the growth of small-size He bubbles by pushing out self-interstitial atoms and then rearranging into a prismatic dislocation loop, a large-size bubble grows by pushing out a dislocation, subsequently cross-slipping of its screw components and finally evolving into a prismatic dislocation loop. Such dislocations may react with each other to form a dislocation net around the bubble rather than to convert to prismatic dislocation loops.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.005
      Issue No: Vol. 141 (2017)
       
  • What governs ductility of ultrafine-grained metals' A microstructure
           based approach to necking instability
    • Authors: I.S. Yasnikov; Y. Estrin; A. Vinogradov
      Pages: 18 - 28
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): I.S. Yasnikov, Y. Estrin, A. Vinogradov
      We demonstrate that the conditions for plastic instability, which are traditionally obtained from solid mechanics considerations, also follow from linear stability analysis of the intrinsic evolution laws for the dislocation density. However, the strain rate sensitivity effect enters these conditions in a way different to the known Hart criterion. The necking strain predicted from the dislocation-based models shows good agreement with experimental data, highlighting the primary role played by dynamic dislocation recovery in the stability of uniform plastic flow. In particular, a sharp drop of ductility after plastic deformation to modest strains has been accounted for. A result of special interest with regard to ultrafine-grained materials is the predicted increase of their tensile ductility with increased strain imparted to them by prior severe plastic deformation. Importantly, ductility of such materials was found not to be governed primarily by increased strain rate sensitivity of the flow stress, as is commonly assumed in literature. Rather, it emerges as a result of a decrease in the rate of dynamic recovery of dislocations and the history of the pre-processing by severe plastic deformation.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.08.069
      Issue No: Vol. 141 (2017)
       
  • Integrating multi-length scale high resolution 3D imaging and modelling in
           the characterisation and identification of mechanical failure sites in
           electrochemical dendrites
    • Authors: Moshiel Biton; Farid Tariq; Vladimir Yufit; Zhangwei Chen; Nigel Brandon
      Pages: 39 - 46
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Moshiel Biton, Farid Tariq, Vladimir Yufit, Zhangwei Chen, Nigel Brandon
      The Zn-air battery system is attractive because of its potentially high power density, environmental compatibility and low-cost materials [1]. This paper is focused on understanding the degradation of Zn air batteries, in particular the evolution of Zn dendrites, one of the main degradation mechanisms. Complementary tomographic techniques allow the direct 3D imaging and characterisation of complex microstructures, including the observation and quantification of dendrite growth. Here we present results from 3D x-ray and FIB-SEM tomography of Zn dendrite formation in a zinc-air battery, down to resolutions of tens of nanometers, enabling analysis of complex micro-structures. This approach is shown to be effective in understanding how electrochemical dendrites grow, and demonstrates that tomography coupled with modelling can provide new insights into dendrite growth in electrochemical systems.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.008
      Issue No: Vol. 141 (2017)
       
  • Microstructural origins of high strength and high ductility in an
           AlCoCrFeNi2.1 eutectic high-entropy alloy
    • Authors: Xuzhou Gao; Yiping Lu; Bo Zhang; Ningning Liang; Guanzhong Wu; Gang Sha; Jizi Liu; Yonghao Zhao
      Pages: 59 - 66
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Xuzhou Gao, Yiping Lu, Bo Zhang, Ningning Liang, Guanzhong Wu, Gang Sha, Jizi Liu, Yonghao Zhao
      Recent studies indicate that eutectic high-entropy alloys can simultaneously possess high strength and high ductility, which have potential applications in industrial fields. Nevertheless, microstructural origins of the excellent strength–ductility combination remain unclear. In this study, an AlCoCrFeNi2.1 eutectic high-entropy alloy was prepared with face-centered cubic (FCC)(L12)/body-centered-cubic (BCC)(B2) modulated lamellar structures and a remarkable combination of ultimate tensile strength (1351 MPa) and ductility (15.4%) using the classical casting technique. Post-deformation transmission electron microscopy revealed that the FCC(L12) phase was deformed in a matter of planar dislocation slip, with a slip system of {111} <110>, and stacking faults due to low stacking fault energy. Due to extreme solute drag, high densities of dislocations are distributed homogeneously at {111} slip plane. In the BCC(B2) phase, some dislocations exist on two {110} slip bands. The atom probe tomography analysis revealed a high density of Cr-enriched nano-precipitates, which strengthened the BCC(B2) phase by Orowan mechanisms. Fracture surface observation revealed a ductile fracture in the FCC(L12) phase and a brittle-like fracture in the BCC(B2) lamella. The underlying mechanism for the high strength and high ductility of AlCoCrFeNi2.1 eutectic high-entropy alloy was finally analyzed based on the coupling between the ductile FCC(L12) and brittle BCC(B2) phases.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.07.041
      Issue No: Vol. 141 (2017)
       
  • Kinetics and dynamics of planar abnormal grain growth in nanocrystalline
           nickel
    • Authors: J.E. Darnbrough; F. Christien; P.E.J. Flewitt
      Pages: 67 - 74
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): J.E. Darnbrough, F. Christien, P.E.J. Flewitt
      Growth of abnormally large grains has been observed previously in nanocrystalline Nickel both in-directly by electron imaging after heat treatment and by in-situ resistivity measurement. However the form and rate of the growth has been derived indirectly. This work makes use of in-situ heat treatment combined with back scattered electron imaging illustrates that the abnormal micro-planar faceted grains grow with a dependence not only on the surrounding but also as the orientation of the growing facet. This observation has shown that the grains grow in a semi-constrained manner such that high index faces such as {211} grow faster than stable {111} faces.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.08.068
      Issue No: Vol. 141 (2017)
       
  • Density power law and structures of metallic glasses
    • Authors: Min Wu; Jianlin Cheng; John S. Tse; Yuanming Pan; Lin Zhang
      Pages: 75 - 82
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Min Wu, Jianlin Cheng, John S. Tse, Yuanming Pan, Lin Zhang
      The existence of a universal power law relating the position of the first sharp diffraction peak (q, FSDP) to the density (ρ or the volume V) with a constant exponent <3 has been debated in the last decade. A constant dimensionality is important because it reflects the fractal topology of the glass structures. In this study, the validity of the Ehrenfest equation applied to multi-component metallic glasses is examined using first-principles molecular dynamics calculations. The results show that the Ehrenfest coefficient depends on the local structures of the glasses and is not a constant for all glasses. Moreover, since the diffraction pattern is determined by the scattering between atom pairs, in a multi-component glass, the X-ray diffraction FSDP is only sensitive to the heavy atoms, and the observed P-q relationship does not necessary correspond to the P V equation of state of the bulk material and is not always a suitable indicator for monitoring structural phase transitions or volume changes. On the other hand, for suitable systems, neutron diffraction is a reliable method to determine the structural features of both heavy and light atoms. In this study, the simulated neutron diffraction patterns of Ca72·7Al27.3 metallic glasses show a clear splitting of the FSDP at the pressure where the pressure-induced polyamorphism transition occurs. From the presented results, there is no justification for expecting the existence of a universal power scaling law with a constant exponent for all glasses.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.014
      Issue No: Vol. 141 (2017)
       
  • Austenite avalanche evidenced by uniaxial stress in Ni-Mn-In Heusler
           single crystal
    • Authors: L. Porcar; P. Courtois; J. Debray; D. Bourgault
      Pages: 83 - 91
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): L. Porcar, P. Courtois, J. Debray, D. Bourgault
      The martensitic transformation in Ni50Mn34.5In15.5 single crystal was studied by electrical resistivity measurements under controlled and constant uniaxial stress. We observed that the kinetics of the transformation under uniaxial stress, defined as the derivative of the volume fraction of martensite (austenite) with respect to time, present two maxima during heating at a constant rate of 3 K/min. An additional energy is required for the complete transformation to happen and there is a distortion in the hysteretic cycle depending on the rate. The interaction between transformed volume and untransformed volume and inter-variant conversion could be responsible for this distortion adding a local internal stress in the material. The transformation during heating is consequently isothermal. However, a new increase of the austenite restoration rate occurs in an avalanche form when additional superheating leads to an increase in the driving force that does not compensate any more the total strain energy.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.001
      Issue No: Vol. 141 (2017)
       
  • Atomic structure and dynamic reconfiguration of layered defects in van der
           Waals layered Ge-Sb-Te based materials
    • Authors: Andriy Lotnyk; Ulrich Ross; Torben Dankwort; Isom Hilmi; Lorenz Kienle; Bernd Rauschenbach
      Pages: 92 - 96
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Andriy Lotnyk, Ulrich Ross, Torben Dankwort, Isom Hilmi, Lorenz Kienle, Bernd Rauschenbach
      Ge-Sb-Te based phase change alloys are currently used in optical data storage and are regarded as promising candidates to replace Flash memories. Detailed knowledge of structural defects in these materials is crucial for further understanding of the switching mechanisms, e.g., in recently proposed interfacial phase change memory. In the present work, atomic structure and dynamics of layered defects frequently reported in van der Waals bonded Ge-Sb-Te based materials and GeTeSb2Te3 based superlattices are studied using advanced transmission electron microscopy. It is shown that the defects are confined into two atomic layers of GeSb and Te and represent localized stacking faults. In situ experiments revealed that the GeSb and Te bilayers can be easily reconfigured into such bilayer stacking faults with subsequent formation of a new van der Waals gap, indicating a mechanism of structural reconfiguration of building blocks in layered Ge-Sb-Te compounds. Overall the results of the present work shed insights into the dynamics of van der Waals gaps rearrangement and mechanism of the layer exchange process in layered functional chalcogenide compounds, also relevant for an understanding of switching mechanisms in interfacial phase change alloys.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.012
      Issue No: Vol. 141 (2017)
       
  • Hierarchical criteria to promote fast and selective αGB precipitation at
           β grain boundaries in β-metastable Ti-alloys
    • Authors: Tao Liu; Lionel Germain; Julien Teixeira; Elisabeth Aeby-Gautier; Nathalie Gey
      Pages: 97 - 108
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Tao Liu, Lionel Germain, Julien Teixeira, Elisabeth Aeby-Gautier, Nathalie Gey
      Early grain boundary (GB) decoration was analyzed in a β-metastable titanium alloy by using electron backscatter imaging and diffraction. More than 1000 GBs were analyzed and classified as 'special' or 'general' GBs: A boundary is called 'special' if it is able to form an αGB layer satisfying the Burgers Orientation Relationship (BOR) with both grains within an angular deviation θ2-BOR; the others are called 'general' GBs. First, the result gives the probability of a GB to transform early according to a disorientation criterion. 49.5°, 60°/<110> special HAGBs are clearly identified as preferential GBs for early precipitations whereas 60°/<111> special HAGBs behave as general GBs. Second, the probability for transformed GBs to respect the double-BOR variant selection (VS) criterion according to θ2-BOR deviation is evaluated. The probability is close to 100% for GBs with θ2-BOR up to 10°, random for GBs with θ2-BOR over 16°, and decreases progressively but remains higher than random with θ2-BOR in between, i.e. an intermediate domain. In addition the habit plane (HP) VS criterion was considered based only on single trace analysis between HP and GB plane (GBP). In most cases, the HP closeness to the GBP was not a relevant VS criterion.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.08.063
      Issue No: Vol. 141 (2017)
       
  • On the high glass-forming ability of Pt-Cu-Ni/Co-P-based liquids
    • Authors: Oliver Gross; Sascha S. Riegler; Moritz Stolpe; Benedikt Bochtler; Alexander Kuball; Simon Hechler; Ralf Busch; Isabella Gallino
      Pages: 109 - 119
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Oliver Gross, Sascha S. Riegler, Moritz Stolpe, Benedikt Bochtler, Alexander Kuball, Simon Hechler, Ralf Busch, Isabella Gallino
      The continuous and isothermal crystallization diagrams of the Pt42.5Cu27Ni9.5P21 and the Pt60Cu16Co2P22 bulk glass forming compositions are determined using calorimetric experiments. In the case of the Pt42.5Cu27Ni9.5P21 bulk metallic glass, the formation of the primary crystalline phase can be prevented by rapid cooling in a conventional DSC. In contrast, for similar cooling conditions, the formation of the primary precipitating compound in Pt60Cu16Co2P22 cannot be prevented in a conventional DSC as also observed in in-situ synchrotron X-ray scattering experiments. This is attributed to a critical overheating, above which remaining structures dissolve, resulting in a drastic increase of the degree of undercooling, similar to what is observed in Zr-based BMGs. Using the classical nucleation theory, the combined thermodynamic and kinetic data are used to model the isothermal crystallization data for Pt42.5Cu27Ni9.5P21, yielding an interfacial energy value of 0.11 J/m2 between the primary nucleating crystal and the liquid. This value is three times higher than the value for good Zr-based glass-formers, suggesting that the interfacial energy plays a pivotal role in the exceptionally high glass-forming ability of Pt-P-based systems and compensates for the fragile liquid behavior and the large driving force for crystallization.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.013
      Issue No: Vol. 141 (2017)
       
  • Comparative studies on thermoelectric properties of p-type Mg2Sn0.75Ge0.25
           doped with lithium, sodium, and gallium
    • Authors: Udara Saparamadu; Johannes de Boor; Jun Mao; Shaowei Song; Fei Tian; Weishu Liu; Qinyong Zhang; Zhifeng Ren
      Pages: 154 - 162
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Udara Saparamadu, Johannes de Boor, Jun Mao, Shaowei Song, Fei Tian, Weishu Liu, Qinyong Zhang, Zhifeng Ren
      Mg(Sn,Si) and Mg(Sn,Ge) are promising n-type thermoelectric materials with good thermoelectric properties in the temperature range of 300–800 K. For power generation, similar thermoelectric performance of p-type materials is equally important. However, p-type material performance is much worse than the n-type, because achieving optimized carrier concentration has been difficult for the p-type Mg2X (X = Sn, Si). In this study we systematically compared the effect of the dopants Li, Na, and Ga and found that the highest carrier concentrations are achievable in Li-doped samples. Due to the relatively high content of Sn, carrier concentration of > 5 × 1019 cm−3 were achieved for all dopants. Analysis of the transport data in the framework of a single parabolic band model showed similar and carrier concentration independent effective masses for all dopants. Our results therefore indicate a rigid band structure for p-type Mg2X for the studied dopants, in contrast to previous reports. Higher carrier mobilities have been achieved for Li-doped samples compared to the previous reports. Larger Hall mobilities leads to a higher peak power factor. Due to the higher carrier concentration, the onset of intrinsic excitations (bipolar effect) effectively shifts to higher temperature compared to the other two dopants, which results in a peak figure of merit of ∼0.5 at 723 K for Li doped samples.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.009
      Issue No: Vol. 141 (2017)
       
  • Prediction of microscale plastic strain rate fields in two-phase
           composites subjected to an arbitrary macroscale strain rate using the
           materials knowledge system framework
    • Authors: David Montes de Oca Zapiain; Evdokia Popova; Surya R. Kalidindi
      Pages: 230 - 240
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): David Montes de Oca Zapiain, Evdokia Popova, Surya R. Kalidindi
      In this work, a data-driven reduced-order model is presented to predict the microscale spatial distribution of the plastic strain rate tensor in an isotropic two-phase composite subjected to an arbitrary macroscopically imposed strain rate tensor. This model was built using the framework of localization linkages called Material Knowledge Systems (MKS), which has been demonstrated to exhibit a remarkable combination of accuracy and low computational cost. In prior work, the MKS framework was successfully used to predict the local strain rate fields in multiphase composites subjected to a selected macroscale strain rate tensor. In this work, the MKS framework is extended to include the complete set of all macroscale strain rate tensors that could be applied. This is accomplished by developing novel representations that allow a parametrization of the localization kernel over the complete space of unit symmetric traceless second-rank tensors and implementing them with the required fast computational strategies. The MKS localization linkage produced in this work was calibrated and validated to results from microscale finite element models.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.016
      Issue No: Vol. 141 (2017)
       
  • Diffusion processes during creep at intermediate temperatures in a
           Ni-based superalloy
    • Authors: T.M. Smith; Y. Rao; Y. Wang; M. Ghazisaeidi; M.J. Mills
      Pages: 261 - 272
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): T.M. Smith, Y. Rao, Y. Wang, M. Ghazisaeidi, M.J. Mills
      The local compositional changes associated with stacking fault and microtwin formation during creep at intermediate temperatures in a commercial Ni-base disk superalloy are explored. In order to investigate microtwin formation, an [001] single crystal of ME3 was tested in compression at 760 °C under a stress of 414 MPa – a stress-temperature regime found to promote microtwinning. Atomic resolution scanning transmission electron microscopy combined with state-of-the-art energy dispersive X-ray (EDX) spectroscopy analysis reveals the presence of Co and Cr rich Cottrell atmospheres around leading dislocations responsible for the creation of SISFs, SESFs, and microtwins. This analysis also highlights the role that tertiary γ particles inside γ′ precipitates have on γ′ shearing deformation mechanisms. Through the use of CALPHAD calculations, combined with new experimental observations, new insights into the rate-controlling processes during creep deformation are discussed.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.027
      Issue No: Vol. 141 (2017)
       
  • Predicting the morphologies of γʹ precipitates in cobalt-based
           superalloys
    • Authors: A.M. Jokisaari; S.S. Naghavi; C. Wolverton; P.W. Voorhees; O.G. Heinonen
      Pages: 273 - 284
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): A.M. Jokisaari, S.S. Naghavi, C. Wolverton, P.W. Voorhees, O.G. Heinonen
      Cobalt-based alloys with γ / γ ′ microstructures have the potential to become the next generation of superalloys, but alloy compositions and processing steps must be optimized to improve coarsening, creep, and rafting behavior. While these behaviors are different than in nickel-based superalloys, alloy development can be accelerated by understanding the thermodynamic factors influencing microstructure evolution. In this work, we develop a phase field model informed by first-principles density functional theory and experimental data to predict the equilibrium shapes of Co-Al-W γ ′ precipitates. Three-dimensional simulations of single and multiple precipitates are performed to understand the effect of elastic and interfacial energy on coarsened and rafted microstructures; the elastic energy is dependent on the elastic stiffnesses, misfit strain, precipitate size, applied stress, and precipitate spatial distribution. We observe characteristic microstructures dependent on the type of applied stress that have the same γ ′ morphology and orientation seen in experiments, indicating that the elastic stresses arising from coherent γ / γ ′ interfaces are important for morphological evolution during creep. The results also indicate that the narrow γ channels between γ ′ precipitates are energetically favored, and provide an explanation for the experimentally observed directional coarsening that occurs without any applied stress.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.003
      Issue No: Vol. 141 (2017)
       
  • Influence of β anisotropy on deformation processes operating in
           Ti-5Al-5Mo-5V-3Cr at room temperature
    • Authors: S. Hémery; P. Villechaise
      Pages: 285 - 293
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): S. Hémery, P. Villechaise
      In the past, little attention was paid to the effects of the high β fraction retained at room temperature on the deformation behavior of β metastable titanium alloys. As it significantly differs from more conventional α/β alloys, mostly constituted of α phase, a thorough investigation appears as mandatory. This is the aim of the present study through a detailed characterization of the operating deformation processes combined with an evaluation of the strain field heterogeneities. Tensile tests conducted in a scanning electron microscope coupled with markers tracking and electron back-scattered diffraction techniques enabled an in situ monitoring of the early activity of deformation systems. A major influence of the elastic anisotropy of the β phase on the highly heterogeneous deformation behavior was revealed in the elastic and plastic regimes. The underlying mechanisms controlling the onset and the development of plasticity in β metastable titanium alloys are clarified and discussed accordingly.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.023
      Issue No: Vol. 141 (2017)
       
  • Temperature-dependent micromechanical behavior of medium-Mn
           transformation-induced-plasticity steel studied by in situ synchrotron
           X-ray diffraction
    • Authors: Minghe Zhang; Longfei Li; Jie Ding; Qingbao Wu; Yan-Dong Wang; Jonathan Almer; Fangmin Guo; Yang Ren
      Pages: 294 - 303
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Minghe Zhang, Longfei Li, Jie Ding, Qingbao Wu, Yan-Dong Wang, Jonathan Almer, Fangmin Guo, Yang Ren
      The temperature-dependent micromechanical behavior of medium-Mn transformation-induced-plasticity (TRIP) steel with a nominal chemical composition of Fe-0.1C-10Mn-2Al (mass%) fabricated by intercritical annealing 650 °C for 1 h after cold-rolling, was investigated using in situ high-energy X-ray diffraction (HE-XRD) with uniaxial tensile tests at temperatures of 100, 25 and −50 °C. We find that as the deformation temperature decreases, the Lüders strain decreases and more austenite transforms to martensite during Lüders band propagation. The Lüders bands are associated with sudden changes of lattice strain in austenite. At 100 °C, austenite is too stable to transform to martensite, resulting in limited work-hardening capability and a relatively low strain to failure. At 25 °C, the austenite is found to transform in bursts during applied loading. These transformations correlate with stepwise peak broadening in the austenite phase and are attributed to Portevin-Le Châtelier (PLC) band propagation. At −50 °C, we observe a more intense TRIP effect which suppresses PLC band formation and leads to a high ultimate tensile strength. In addition to the TRIP effect, we find that work hardening in the deformation-induced martensite phase plays an important role in the plastic stability at low temperature, by accommodating stress compatibility between grains and phases. Our studies provide the first direct experimental evidence for the existence of large stress concentrations in the austenite phase near the Lüders band propagation front. These observations help to deepen understanding of the complex temperature-dependent micromechanical behaviors of advanced medium-Mn TRIP steels.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.030
      Issue No: Vol. 141 (2017)
       
  • Solute-induced solid-solution softening and hardening in bcc tungsten
    • Authors: Yong-Jie Hu; Michael R. Fellinger; Brady G. Bulter; Yi Wang; Kristopher A. Darling; Laszlo J. Kecskes; Dallas R. Trinkle; Zi-Kui Liu
      Pages: 304 - 316
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Yong-Jie Hu, Michael R. Fellinger, Brady G. Bulter, Yi Wang, Kristopher A. Darling, Laszlo J. Kecskes, Dallas R. Trinkle, Zi-Kui Liu
      The solute-induced softening and hardening effects in bcc W for twenty-one substitutional alloying elements (Al, Co, Cr, Fe, Hf, Ir, Mn, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Ru, Ta, Tc, Ti, V and Zr) are examined to search for a similar softening effect as that observed with Re. The changes in energy barriers of dislocation motion caused by solute-dislocation interactions are directly computed via a first-principles approach with flexible boundary conditions. The effect of solutes on the critical resolved shear stress of the ½ <111> screw dislocation in bcc W at room temperature is quantitatively predicted, as a function of alloy concentration, via a mesoscopic solid-solution model using the first-principles results as input. Al and Mn are proposed to be promising substitutes for Re as these two elements introduce similar softening effects as Re in bcc W. In addition, the trends of the solute-dislocation interactions, and their correlations to the dislocation core structure geometries are discussed.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.019
      Issue No: Vol. 141 (2017)
       
  • Quantifying adhesion of ultra-thin multi-layer DLC coatings to Ni and Si
           substrates using shear, tension, and nanoscratch molecular dynamics
           simulations
    • Authors: Michael R. Price; Bart Raeymaekers
      Pages: 317 - 326
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Michael R. Price, Bart Raeymaekers
      Ultra-thin diamond-like carbon (DLC) coatings are used in many engineering applications including hard disk drives, automobile engines, and MEMS/NEMS devices to protect delicate substrates against wear and corrosion. However, they are susceptible to brittle cracking and delamination due to high intrinsic stress and poor adhesion to many substrates. Inclusion of an intermediate layer can prevent delamination of the coating. We perform simple shear and tension loading and nanoscratch molecular dynamics simulations to quantify the effect of coating layer thickness and composition on the adhesion of the ultra-thin multi-layer DLC coatings used in hard disk drives to their substrate. We observe that an intermediate Si layer improves adhesion of DLC coatings to Ni substrates compared to coatings without one, and that an optimum thickness of the Si layer exists. We also find that an intermediate DLC layer with sp 3 fraction lower than the outermost DLC coating layer protects the substrate from plastic deformation under external loading, and that it improves adhesion to Si but not Ni substrates compared to coatings with no intermediate layer.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.031
      Issue No: Vol. 141 (2017)
       
  • Solute segregation at the Al/θ′-Al2Cu interface in Al-Cu alloys
    • Authors: Dongwon Shin; Amit Shyam; Sangkeun Lee; Yukinori Yamamoto; J. Allen Haynes
      Pages: 327 - 340
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Dongwon Shin, Amit Shyam, Sangkeun Lee, Yukinori Yamamoto, J. Allen Haynes
      A recent investigation has confirmed that solute atoms segregated to the interfaces between aluminum and θ′-Al2Cu can extend the stability of metastable θ′ to higher temperatures. Herein, we present an extensive first-principles database of the segregation energies of 34 elements to the Al/θ′ interface and identify key descriptors that can guide the design of higher temperature Al-Cu alloys. We find that the segregation energies are strongly correlated with the size and volume of solute atoms and their solubilities within θ′. We provide a physical/chemical basis to the experimentally observed elemental hierarchy in terms of the ability of individual elements to stabilize the Al/θ′ interface. Finally, we suggest a new microalloying strategy that offers opportunities to further increase the critical temperature limit of Al-Cu alloys.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.020
      Issue No: Vol. 141 (2017)
       
  • Vacancy-tuned precipitation pathways in Al-1.7 Cu-0.025In-0.025Sb (at.%)
           alloy
    • Authors: Yong Zhang; Zezhong Zhang; Nikhil V. Medhekar; Laure Bourgeois
      Pages: 341 - 351
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Yong Zhang, Zezhong Zhang, Nikhil V. Medhekar, Laure Bourgeois
      Microalloying is a routine method to optimize precipitation and mechanical properties in light metals. Here we study how In and Sb (0.025 at.%) additions in an Al-1.7 at.% Cu alloy benefit precipitation during ageing and investigate the underlying mechanism using scanning transmission electron microscopy and density functional theory (DFT) calculations. The combined additions accelerate precipitation kinetics and increase peak hardness through two different ways. In samples aged directly at low temperatures (≤200 °C) after solid solution treatment, cubic close-packed InSb nanocrystals form first. The truncated {002} surfaces of InSb particles induce the preferential nucleation of Guinier-Preston (GP) zones, θ″ and θ′ successively. However, in samples aged at 250 °C, precipitation of θ′ precedes that of InSb particles. Supersaturated vacancies trapped by In and Sb solute atoms/clusters play a critical role in switching the precipitation sequence. By tuning how strong the binding between a vacancy and solute atoms is, we successfully invert the temperature dependence of the precipitation sequence. These findings will contribute to understanding precipitation mechanisms and optimizing precipitate distribution in aluminium precipitation hardenable alloys.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.025
      Issue No: Vol. 141 (2017)
       
  • Roughening and destructive effects of sintering on micron-sized ZnO
           features
    • Authors: Hong-fei Ju; Kaijie Ning; Kathy Lu
      Pages: 352 - 359
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Hong-fei Ju, Kaijie Ning, Kathy Lu
      Microfabrication of ceramic features has become a critical issue in realizing the miniaturization of devices. Micron-sized ZnO features attract much attention because of their unique properties of direct wide bandgap, high exciton binding energy, good piezoelectrics, and easy doping for devices. However, limited effort has been devoted to understanding the sintering behaviors of micron-sized ZnO features. In this study, micron-sized ZnO ridges were prepared via centrifuge-aided micromolding and sintered at 950 °C for different time in air atmosphere. The sintering process destructs the ZnO ridges via abnormal grain growth and surface roughening. The relationship difference in grain growth vs. densification between the bulk and the features is elucidated, and gas evaporation during sintering is the major contributor to grain growth. Destruction prediction of ridge features using sintering time and bulk relative density is established based on grain growth and densification. Feature surface roughening is further analyzed with respect to thermodynamic fundamentals.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.034
      Issue No: Vol. 141 (2017)
       
  • Controlling grain structure and texture in Al-Mn from the competition
           between precipitation and recrystallization
    • Authors: K. Huang; K. Zhang; K. Marthinsen; R.E. Logé
      Pages: 360 - 373
      Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): K. Huang, K. Zhang, K. Marthinsen, R.E. Logé
      The recrystallization behaviour of Al-Mn alloys (AA3xxx series alloys) is affected by randomly distributed dispersoids present before annealing, by dispersoids precipitated at grain/subgrain boundaries before the onset of recrystallization, and by dispersoids concurrently precipitated during recrystallization. In this study, the effects of these three populations of dispersoids on the recrystallization behaviour of a cold rolled AA3xxx alloy were analysed and compared using four temperature-time paths to different target temperatures. Changing the temperature-time path modifies the extent of recovery, the dispersoid structures, as well as the absolute recrystallization temperature, which then influences the final grain structure and recrystallization texture. In particular, an in-depth investigation on how different populations of dispersoids affect the main recrystallization texture components of AA3xxx alloys, i.e., P{011}〈566〉, ND-Cube {001}〈310〉, and Cube {001}〈100〉, has been carried out. The results clearly show that, as compared to isothermal annealing, annealing with more elaborate heating and annealing schedules (temperature-time paths) all lead to increased strength of the P texture component and decreased intensities of both the Cube and ND-rotated Cube texture components. The increase of P texture strength and average grain size is most significant when recrystallization occurs concurrently with precipitation. The controlling mechanisms behind this behaviour and the possibility to use them to tailor the grain structure and texture of similar alloys are further discussed.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
      DOI: 10.1016/j.actamat.2017.09.032
      Issue No: Vol. 141 (2017)
       
  • First-principles study of the third-order elastic constants and related
           anharmonic properties in refractory high-entropy alloys
    • Authors: Xiaoqing
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Xiaoqing Li
      The third-order elastic constants (TOECs) and elastic anharmonic behavior in four body-centered cubic refractory high-entropy alloys (HEAs) based on elements of the fourth, fifth, and sixth groups are investigated using density-functional simulations. We find that the values of the TOECs C 111 are the largest in magnitude among the studied six independent TOECs and strongly increase with increasing average valence electron concentration (VEC). Interestingly, the TOEC C 456 undergos a sign change as a function of the VEC. Using the obtained TOECs, we investigate the mode Grüneisen constants γ i as well as the low temperature limit γ ¯ , derive the long-wavelength acoustic nonlinearity parameters β, and reveal the pressure derivatives of effective elastic constants and polycrystalline moduli as a function of the VEC. Our results show that β displays a different directional order along the pure mode [ 100 ] , [ 110 ] , and [ 111 ] directions for the four considered refractory HEAs. Furthermore, we show that the directional order of β is not correlated to the crystal symmetry. With the help of the obtained pressure derivatives of polycrystalline moduli, we predict the low temperature volume expansion coefficient.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • On the microstructural origins of martensitic transformation arrest in a
           NiCoMnIn magnetic shape memory alloy
    • Authors: N.M. Bruno; Salas Wang Igor Roshchin Santamarta Arroyave Duong Y.I.
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): N.M. Bruno, D. Salas, S. Wang, Igor V. Roshchin, R. Santamarta, R. Arroyave, T. Duong, Y.I. Chumlyakov, I. Karaman
      The martensitic transformation arrest phenomenon in Ni45Co5Mn36.6In13.4 meta-magnetic shape memory alloy (MMSMA) single crystals was investigated as a function of secondary annealing heat treatments, using thermo-magnetometry and transmission electron microscopy (TEM). Dark-field images of the austenite phase at room temperature revealed the long range L21 and B2 ordered microstructural landscape with different morphologies in the annealed single crystals. Their measured thermomagnetic responses demonstrated full transformation arrest after certain heat treatments and unique microstructural morphologies. Martensitic transformation hysteresis, range, and enthalpy were measured in the annealed partially- or non-arrested single crystals. With the data, herein, we found that the samples with long range L21 ordering exhibit martensitic transformation at higher temperatures than some of the crystals of the same composition showing predominantly B2 order. This finding opposes the previous reports on the effect of annealing on the martensitic transformation characteristics of MMSMAs. We provide evidence that long range order promoted with high temperature annealing is not the only microstructural feature capable of influencing the martensitic transition in NiCoMnIn MMSMAs. Data suggests that quenched in vacancies, in addition to long range order, also influence the transformation characteristics.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • Designing disordered hyperuniform two-phase materials with novel physical
           properties
    • Authors: Chen Torquato
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): D. Chen, S. Torquato
      Heterogeneous materials consisting of different phases are ideally suited to achieve a broad spectrum of desirable bulk physical properties by combining the best features of the constituents through the strategic spatial arrangement of the different phases. Disordered hyperuniform heterogeneous materials are new, exotic amorphous matter that behave like crystals in the manner in which they suppress volume-fraction fluctuations at large length scales, and yet are isotropic with no Bragg peaks. In this paper, we formulate for the first time a Fourier-space numerical construction procedure to design at will a wide class of disordered hyperuniform two-phase materials with prescribed spectral densities, which enables one to tune the degree and length scales at which this suppression occurs. We demonstrate that the anomalous suppression of volume-fraction fluctuations in such two-phase materials endow them with novel and often optimal transport and electromagnetic properties. Specifically, we construct a family of phase-inversion-symmetric materials with variable topological connectedness properties that remarkably achieves a well-known explicit formula for the effective electrical (thermal) conductivity. Moreover, we design disordered stealthy hyperuniform dispersion that possesses nearly optimal effective conductivity while being statistically isotropic. Interestingly, all of our designed materials are transparent to electromagnetic radiation for certain wavelengths, which is a common attribute of all hyperuniform materials. Our constructed materials can be readily realized by 3D printing and lithographic technologies. We expect that our designs will be potentially useful for energy-saving materials, batteries and aerospace applications.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • Molecular design of confined organic network hybrids with controlled
           deformation rate sensitivity and moisture resistance
    • Authors: Yichuan Ding; Qiran Xiao Reinhold Dauskardt
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Yichuan Ding, Qiran Xiao, Reinhold H. Dauskardt
      We demonstrate molecular design strategies for engineering the deformation rate sensitivity and fracture resistance of organic-inorganic hybrid films in moist environment. Hybrids with intimate mixing of inorganic and organic molecular networks were synthesized with an epoxy-functionalized silane, (3-glycidoxypropyl) trimethoxysilane and an acetate-stabilized zirconium alkoxide, tetra-n-propoxyzirconium. The highly confined non-hydrolysable organic molecular network connectivity was systematically manipulated by tuning the epoxy ring opening polymerization reaction and the incorporation of carbon bridges of selected lengths. By investigating the corresponding time-dependent crack growth in moist environments, new insights into the fundamental molecular-scale relaxation and cracking mechanisms of the hybrids are provided. These processes were found to be impacted by the confined organic network connectivity which results in significant changes in the deformation rate sensitivity and fracture resistance. With increasing non-hydrolysable organic network connectivity, mechanical behavior that varied from almost perfectly elastic to increasingly viscoelastic could be obtained in a controlled fashion. The related resistance to cracking in moist environments was found to be significantly improved. These findings provide a basis for the rational design of functional hybrids with precisely defined mechanical properties.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • Metastable solidification of hypereutectic Co2Si-CoSi composition:
           Microstructural studies and in-situ observations
    • Authors: Yeqing Wang; Jianrong Gao Matthias Kolbe Andrew (Chih-Pin) Chuang Yang
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Yeqing Wang, Jianrong Gao, Matthias Kolbe, Andrew (Chih-Pin) Chuang, Yang Ren, Douglas Matson
      Metastable solidification of undercooled Co60Si40 melts was investigated by microstructural studies and in-situ high-energy X-ray diffraction. Five solidification paths were identified. Three of them were observed at low undercoolings, which show uncoupled and coupled growth of stable β-Co2Si and CoSi compounds. The other paths were observed at high undercoolings, which show peritectic and primary crystallization of a metastable Co5Si3 compound. The β-Co2Si and Co5Si3 compounds crystallize into a hexagonal crystal structure and experience solid-state decomposition. Microstructure formation depends on solidification path. The coupled and uncoupled growth of the stable compounds produces a regular lamellar eutectic structure and an anomalous eutectic structure, respectively. The crystallization and solid-state decomposition of the metastable Co5Si3 compound brings about a fine-grained two-phase mixture, which represents another type of anomalous eutectic structure. The results provide proof of two rare mechanisms of anomalous eutectic formation and shed light onto metastable phase relations in the undercooled region of the CoSi system.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • The role of W on the thermal stability of nanocrystalline NiTiWx thin
           films
    • Authors: Aslan Ahadi; Arvind Kalidindi Junpei Sakurai Yoshitaka Matsushita Koichi Tsuchiya
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Aslan Ahadi, Arvind R. Kalidindi, Junpei Sakurai, Yoshitaka Matsushita, Koichi Tsuchiya, Christopher A. Schuh
      This paper investigates the effect of minority W additions on the thermal stability of nanocrystalline NiTi thin films. The films were produced in an amorphous state, and the addition of W was found to increase the activation energy for crystallization and lead to finer grain sizes after crystallization. In the crystallized films, W was observed to both segregate to the NiTi grain boundaries and to phase separate into fine precipitates; together these effects contribute to the stability of the nanocrystalline state up to 1200 °C. Using in-situ transmission electron microscopy, grain growth was observed concomitantly with coarsening of W precipitates, indicating that a primary mechanism for stability is Zener pinning by the W precipitates. At the same temperature where coarsening begins to occur rapidly, grain boundaries were also observed to undergo a transformation to thick, amorphous complexions. Monte Carlo simulations showed that W segregation to grain boundaries increases with temperature, which contributes to an increased rate of coarsening and loss of stability against grain growth.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
  • On the characterisation of antisite defects and ordering in
           off-stoichiometric Fe2VAl-based Heusler compounds by X-ray anomalous
           diffraction
    • Authors: Camille van; der Rest Alain Schmitz Pascal Jacques
      Abstract: Publication date: 1 January 2018
      Source:Acta Materialia, Volume 142
      Author(s): Camille van der Rest, Alain Schmitz, Pascal J. Jacques
      Compounds based on Fe2VAl are good candidates for low grade heat harvesting owing to the thermoelectric effect. However, it is claimed that their thermoelectric properties are badly influenced by antisite defects, especially at higher temperatures. The present study investigates order-disorder transitions in Fe2VAl ternary Heusler compounds. An inherent problem of these compounds is the close atomic numbers of Fe and V, leading to similar x-ray atomic scattering factors. Hence, the D03 and L21 structures, corresponding to Fe-V antisite defects, are hardly distinguishable by X-ray diffraction. In this work, anomalous scattering and neutron diffraction were successfully combined with differential scanning calorimetry to highlight the order-disorder transitions in Fe2VAl-based compounds. A model has been developed to quantify the ordering parameters. From these results, specific heat-treatments were defined to promote the formation of the L21 ordered phase.
      Graphical abstract image

      PubDate: 2017-10-08T13:52:09Z
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
Home (Search)
Subjects A-Z
Publishers A-Z
Customise
APIs
Your IP address: 54.166.199.178
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2016