for Journals by Title or ISSN
for Articles by Keywords
help

Publisher: Elsevier   (Total: 3044 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 3044 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: 23, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 29, 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: 343, 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: 214, 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: 3)
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: 134, 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: 10, 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: 25, 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: 10, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, 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: 5)
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: 40, 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: 48, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
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: 21, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, 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: 7, 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: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19, 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: 2, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 348, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 7, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 16)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 317, 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: 408, 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: 9, 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: 47, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 48, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 45, 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: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 16, 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: 24, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 192, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 56, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 4)
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: 24, 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: 21, 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: 55, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 9)
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: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 37, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 166, 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: 156, 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]   [214 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-6454
   Published by Elsevier Homepage  [3044 journals]
  • Designing Mg alloys with high ductility: Reducing the strength
           discrepancies between soft deformation modes and hard deformation modes
    • 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
       
  • A new loop-punching mechanism for helium bubble growth in tungsten
    • 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
       
  • What governs ductility of ultrafine-grained metals' A microstructure
           based approach to necking instability
    • 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
       
  • Integrating multi-length scale high resolution 3D imaging and modelling in
           the characterisation and identification of mechanical failure sites in
           electrochemical dendrites
    • 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
       
  • Microstructural origins of high strength and high ductility in an
           AlCoCrFeNi2.1 eutectic high-entropy alloy
    • 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
       
  • Kinetics and dynamics of planar abnormal grain growth in nanocrystalline
           nickel
    • 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
       
  • Density power law and structures of metallic glasses
    • 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
       
  • Austenite avalanche evidenced by uniaxial stress in Ni-Mn-In Heusler
           single crystal
    • 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
       
  • Atomic structure and dynamic reconfiguration of layered defects in van der
           Waals layered Ge-Sb-Te based materials
    • 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
       
  • Hierarchical criteria to promote fast and selective αGB precipitation at
           β grain boundaries in β-metastable Ti-alloys
    • 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
       
  • On the high glass-forming ability of Pt-Cu-Ni/Co-P-based liquids
    • 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
       
  • Comparative studies on thermoelectric properties of p-type Mg2Sn0.75Ge0.25
           doped with lithium, sodium, and gallium
    • 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
       
  • Prediction of microscale plastic strain rate fields in two-phase
           composites subjected to an arbitrary macroscale strain rate using the
           materials knowledge system framework
    • 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
       
  • Diffusion processes during creep at intermediate temperatures in a
           Ni-based superalloy
    • 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
       
  • Predicting the morphologies of γʹ precipitates in cobalt-based
           superalloys
    • 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
       
  • Influence of β anisotropy on deformation processes operating in
           Ti-5Al-5Mo-5V-3Cr at room temperature
    • 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
       
  • Temperature-dependent micromechanical behavior of medium-Mn
           transformation-induced-plasticity steel studied by in situ synchrotron
           X-ray diffraction
    • 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
       
  • Solute-induced solid-solution softening and hardening in bcc tungsten
    • 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
       
  • Quantifying adhesion of ultra-thin multi-layer DLC coatings to Ni and Si
           substrates using shear, tension, and nanoscratch molecular dynamics
           simulations
    • 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
       
  • Solute segregation at the Al/θ′-Al2Cu interface in Al-Cu alloys
    • 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
       
  • Vacancy-tuned precipitation pathways in Al-1.7 Cu-0.025In-0.025Sb (at.%)
           alloy
    • 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
       
  • Roughening and destructive effects of sintering on micron-sized ZnO
           features
    • 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
       
  • Controlling grain structure and texture in Al-Mn from the competition
           between precipitation and recrystallization
    • 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
       
  • Designing duplex, ultrafine-grained Fe-Mn-Al-C steels by tuning phase
           transformation and recrystallization kinetics
    • Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Jiali Zhang, Dierk Raabe, Cemal Cem Tasan
      A novel, lightweight Fe-25.7Mn-10.6Al-1.2C (wt.%) steel is designed by exploiting the concurrent progress of primary recrystallization and phase transformation, in order to produce an ultrafine-grained, duplex microstructure. The microstructure consists of recrystallized austenite grains surrounded by submicron-sized ferrite grains, and recovered austenite regions with preferential nano-κ-carbide precipitation. This partially recrystallized duplex microstructure demonstrates excellent strength-ductility combinations, e.g. a yield strength of 1251 MPa, an ultimate tensile strength of 1387 MPa, and a total elongation of 43%, arising from the composite response by virtue of diverging constituent strength and strain hardening behaviors.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Measured resolved shear stresses and Bishop-Hill stress states in
           individual grains of austenitic stainless steel
    • Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Nicolai Ytterdal Juul, Jette Oddershede, Armand Beaudoin, Kamalika Chatterjee, Margaret K.A. Koker, Darren Dale, Paul Shade, Grethe Winther
      The full three-dimensional stress state of 172 individual bulk grains in austenitic stainless steel 316 L at 0.1 and 1% sample elongation has been determined with sufficient accuracy to allow comparison with the theoretical Bishop-Hill stress states for plastically deforming grains as well as calculation of the resolved shear stresses on the individual slip systems. At 0.1%, the resolved shear stresses exhibit quite large variations between grains of similar orientation. When averaging over similarly oriented grains, the resolved shear stresses correspond to the Schmid factors for uniaxial tension. At 1%, only about half of the grains were close to a Bishop-Hill stress state. The stress state of the other half of the grains was closer to the applied uniaxial stress, in between Bishop-Hill states, or in some cases none of these. The orientation dependence of the assigned stress states deviate somewhat from the theoretical expectation. These deviations are found to originate from a larger tensile stress component than in the theoretical Bishop-Hill stress states and to be associated also with deviations from axisymmetric plastic strain. This conclusion was supported by finite-element crystal plasticity simulations.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Screw dislocation mediated solution strengthening of substitutional α-Ti
           alloys - First principles investigation
    • Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): P. Kwasniak, H. Garbacz
      The mechanical properties of hexagonal Ti alloys depend substantially on the glide of <a> type screw dislocations. The configurations and stabilities of these line defects are, however, known only in pure Ti and Ti + O solutions, where the locking-unlocking mechanism and a strong pinning effect control their activity. In this study, we investigated the unclear, screw dislocation mediated solution strengthening of substitutional α-Ti alloys. To this end, a first principle computational scheme was used to determine the structures and energies of the considered line defects during planar and cross-slip processes in the vicinity of the solute element. Two phenomena were determined that are crucial in terms of plastic deformation: (i) enhanced polymorphism of the dislocation cores leading to multiple new core configurations, and (ii) relatively large positive and negative interaction energies between the solutes and the line defects. Both these effects are strongly affected by the valence configuration of the alloying elements. Due to their pronounced structure and energy variations, dislocation planar and cross slip processes can occur under different scenarios, through diverse non-planar core geometries. Accordingly, an improvement in material strength is related to the overall energy amplitude of the dislocation states that can occur in the neighbourhood of the alloying element, which agrees well with experimental data. The calculations performed also indicate In as a potential alloy element for improving both the strength and ductility of Ti by stabilizing a special, compact core geometry able to spread on an arbitrary glide plane with a low energy barrier. All of the above effects are discussed in terms of the physical factors (solute size misfit, stacking fault energy and electronic structure) that affect the energy and geometry of dislocation cores.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Using heat treatments, high-pressure torsion and post-deformation
           annealing to optimize the properties of Ti-6Al-4V alloys
    • Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): Hamed Shahmir, Terence G. Langdon
      Experiments were conducted to investigate the processing parameters that may be used to optimize the properties of Ti-6Al-4V alloys. The alloy was initially subjected to two different heat treatments leading to the formation of martensitic α′ and lamellar α+β microstructures and then both materials were processed by high-pressure torsion (HPT) for 10 turns at room temperature. This gave significant grain refinement to the nanometer range in both conditions and the occurrence of an allotropic hcp to fcc phase transformation in the martensitic alloy. These nanostructured alloys were subjected to post-deformation annealing (PDA) at temperatures in the range of 473–1023 K. The results show the hardness increases slightly to 773 K due to α′+fcc→α+β+fcc and α→α+β phase transformations in the martensitic α′ and lamellar α+β alloys and then decreases up to 1023 K due to recrystallization and grain growth. An optimum property of a very high yield strength (∼1120 MPa) and ultimate tensile strength (∼1200 MPa), together with excellent ductility (elongation to failure of ∼26%), was achieved in the Ti-6Al-4V martensitic alloy processed by a combination of HPT followed by PDA at 873 K for 60 min.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Step-controlled Brownian motion of nanosized liquid Pb inclusions in a
           solid Al matrix
    • Abstract: Publication date: December 2017
      Source:Acta Materialia, Volume 141
      Author(s): T. Radetic, E. Johnson, D.L. Olmsted, Y. Yang, B.B. Laird, M. Asta, U. Dahmen
      We have made direct observations of the Brownian motion of individual nanosized liquid lead inclusions in solid aluminum by in-situ transmission electron microscopy. The process was found to depend strongly on the size of the inclusion and the anisotropy of the interfacial energy. The rate controlling mechanism was the nucleation of steps on facets of the equilibrium shape and the diffusion of Al along the liquid-solid interface. Because the Al-Pb interface undergoes a roughening transition at T r ≈ 820 K, the step nucleation barrier decreases with increasing temperature and vanishes completely at T r. By including the temperature dependence explicitly, we demonstrate that the contribution of the step energy to an Arrhenius plot of the data has a slope greater than the actual activation energy at temperature T by a factor T r/(T r -T). In addition, we show that the diffusion barrier for interfacial transport makes a substantial contribution. Our analysis reconciles a large discrepancy between activation energies obtained from the temperature and size dependences of the process and solves the apparent paradox posed by the observation that some particles are frozen in non-equilibrium shapes while nearby smaller particles are sufficiently mobile to undergo rapid Brownian motion.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Micro structures in the grain evolution during solidification of silicon:
           Phase field calculations
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): W. Miller, A. Popescu
      Two dimensional phase field simulations have been performed to study the influence of the growth kinetics and the surface energy on the growth behaviour of grains during solidification of Si. In particular, we studied the groove between two grains as recently observed by in situ observation [1]. Furthermore, we performed computations for different Σ boundaries and discuss the interplay between equilibrium of interfacial energies and growth kinetics.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Effects of ion irradiation on structural and mechanical properties of
           crystalline Fe/amorphous SiOC nanolaminates
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): A. Zare, Q. Su, J. Gigax, S.A. Shojaee, M. Nastasi, L. Shao, D.A. Lucca
      Irradiation-induced changes in the structural and mechanical properties of nanocrystalline Fe, amorphous silicon oxycarbide (SiOC), and Fe/SiOC nanolaminate films were studied using X-ray diffraction, atomic force microscopy, scanning/transmission electron microscopy, and micro/nanoindentation. The films were fabricated by magnetron sputtering and then irradiated at room temperature with 3.5 MeV Fe ions to damage levels of 10, 20, or 50 displacements per atom (dpa). Irradiation of the Fe films was found to increase the compressive residual stress and hardness. For the SiOC films, irradiation led to densification and a subsequent increase in elastic modulus and hardness. The as-deposited Fe/SiOC nanolaminate with individual layer thicknesses of 72 ± 10 nm exhibited a higher hardness compared to the Fe and SiOC films. Furthermore, cross-sectional scanning/transmission electron microscopy of the Fe/SiOC nanolaminate after indentation showed a reduction in the thickness of both the Fe and SiOC layers with no evidence of cracks, shear bands or interface delamination. The combination of increased hardness and deformability of the Fe/SiOC nanolaminate is the result of homogenous plastic co-deformation in the Fe and SiOC layers through the constraint of localized shear flow in the SiOC. Although irradiation of the Fe/SiOC nanolaminate led to recoil mixing of Fe into the SiOC layers, the nanolayered structure remained intact. Increasing the irradiation damage level from 10 to 50 dpa led to more recoil mixing and also a reduction in elastic modulus and hardness of the Fe/SiOC nanolaminate. The study suggests Fe/SiOC nanolaminates are a promising class of irradiation tolerant materials.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Natural metamaterial behavior across the phase transition for WxV1−xO2
           films revealed by terahertz spectroscopy
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Nicolas Émond, Badr Torriss, Denis Morris, Mohamed Chaker
      Metamaterials, which are made of repeated patterns of appropriately arranged small discrete structures, display unusual electromagnetic properties that overwhelm those of conventional materials. The modification of their properties is generally achieved by arranging the structures mechanically or electrically and requires rather complex designs. We report on the study of the complex conductivity of epitaxially-grown tungsten-doped vanadium dioxide (WxV1−xO2) thin films through the semiconductor-to-metal phase transition (SMT) using terahertz time-domain spectroscopy. The modelling of the terahertz conductivity across WxV1−xO2 SMT provides clear insights about the gradual nucleation of VO2 metallic domains among the semiconducting host and evidences the presence of strong carrier confinement and enhanced absorption close to the transition temperature, leading to a strong capacitive response of the electrons. The evolution of the SMT is also strongly affected by W doping, which reduces the scattering time in the metallic state, lowers the transition onset temperature and extends the temperature range over which the transition occurs. The WxV1−xO2 films thus forms an effective medium in the vicinity of the SMT and display the signature of a disordered metamaterial, which has significantly enhanced functionality thanks to its readily thermally-tunable properties over a wide range of temperatures close to room temperature.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Structural signature in Au-based amorphous alloys
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Salman Ali Khan, X.D. Wang, Q.P. Cao, D.X. Zhang, J.Z. Jiang
      Here we elucidated that the anomalous shoulder at the left side of first main peak in structural factor is resulted from packing of AuAu bonds in the Au55Cu25Si20 amorphous alloy (AA), while the first main peak is largely from contributions of AuAu, AuCu and AuSi bonds. Local atomic packing of this glass is mainly composed of 9, 10 and 11-coordinated polyhedra rather than icosahedral-like clusters, in which the small sized clusters prefer avoiding each other while large ones prefer connecting themselves. This anomalous atomic packing structure limits its glass forming ability (GFA) and results in the anomalous shoulder of the first peak in structural factor. With the replacement of 5 at.% Cu atoms by Ag atoms, the spatial connectivity and the atomic packing density in Au55Cu20Ag5Si20 AA are largely increased, which homogenize atomic structures at least up to the second nearest neighbors and frustrate the geometry of competing crystalline-like nuclei, consequently, enhancing the GFA, as observed in experiments. This work illustrates how the atomic packing in an Au-based glass is altered by element substitution and sheds new insights to understanding of high GFA from the atomic scale and thus developing novel AAs with larger critical sizes.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Preferred diffusional pathways of intrinsic defects and silicon dopants in
           an ordered phase of In0.5Ga0.5As: A first-principles study
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Mardochee Reveil, Jingyang Wang, Michael O. Thompson, Paulette Clancy
      Integrating III-V semiconductors into next-generation silicon-based transistors is a promising alternative being considered as a route to faster and more energy-efficient electronic devices. These III-V materials will be doped, typically with Si as a dopant. However, dopant activation remains an issue, compounded by the fact there is still insufficient knowledge of the ease and preferred mechanistic pathways by which dopants, like Si, become activated within the III-V matrix. Using Density Functional Theory calculations, we have determined many of these critically important properties, namely, the energy barriers associated with the diffusion of both intrinsic point defects and silicon impurities in a prototypical ternary III-V material, here a CuAuI-ordered In 0.5 Ga 0.5 As. Refuting assumptions in the current literature, vacancy-assisted diffusion was found to be an unfavorable mechanism for this ordered ternary alloy, unlike in GaAs. Hence, substitutional Si atoms are essentially immobile on experimental timescales. While vacancies are nearly immobile, interstitials, especially split interstitials, can move easily within the crystal lattice. These defects become significant at high Si concentration leading to the unexpected phenomenon of enhanced diffusion of Si at high concentrations, which explains experimental observations.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Experimental quantification of mechanically induced boundary migration in
           nanocrystalline copper films
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Paul F. Rottmann, Kevin J. Hemker
      A new experimental technique is presented that combines in situ straining with transmission electron microscope-based automated crystal orientation mapping to document microstructural evolution with nanoscale resolution at sequential stages of deformation. Orientation maps of freestanding annealed nanocrystalline Cu films have been collected, and the resultant datasets provide direct measures of grain size, shape and orientation as well as local grain boundary character and position at various stages of applied strain. Numerous examples of stress-driven grain boundary and twin boundary migration were recorded and studied. Detailed analysis of the misorientation of mobile and immobile grain boundaries provided clear experimental evidence that a broad range of grain boundaries are susceptible to stress-assisted migration; no general correlation between grain boundary misorientation and mobility was detected. Incoherent Σ3 boundaries were observed to be significantly more mobile than coherent Σ3 twin boundaries. Nevertheless, deformation twins were observed to nucleate and grow from grain boundaries and triple points.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Atomistic simulations of Ni segregation to irradiation induced dislocation
           loops in Zr-Ni alloys
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Cong Dai, Peyman Saidi, Zhongwen Yao, Mark R. Daymond
      The role of Ni segregation on the stability of dislocation loops in the Zr-Ni binary system is elucidated by employing molecular dynamics/Monte Carlo simulations. The effect of the concentration of the alloying element on the strain energy around both interstitial and vacancy loops was investigated. Ni atoms are found to accumulate around the dislocation loops. Our results suggest that the driving force of Ni segregation to the loop is a combination effect of the release of the strain energy of the dislocation core and the reduction of energy arising due to annihilation of point defects associated with those Ni atoms previously substitutionally solute far from the loop. The anisotropic stress field of the dislocation loop is presented in cylindrical coordinates, and is used to explain the influence of the alloying element on the stability of the dislocation loop. Furthermore, cascade simulations in the vicinity of dislocation loops were employed in the irradiated Zr-Ni binary system, and a significant enhancement of the stability of the dislocation loops was related to the change of the stress field as well as the core energy of the loop due to the alloying segregation.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Folding in metal polycrystals: Microstructural origins and mechanics
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Narayan K. Sundaram, Anirban Mahato, Yang Guo, Koushik Viswanathan, Srinivasan Chandrasekar
      Surface folding in large-strain deformation of metal polycrystals, mediated by unsteady sinuous plastic flow, was recently uncovered by direct observations. Here, we examine microstructural origins and mechanics of the folding process in polycrystalline aggregates, using computational methods and in situ, high-speed imaging experiments. Our model loading system is an indenter contact that imposes large strain deformation typical of metal forming, sliding and cutting. Folding arises primarily from intrinsic, grain-level flow stress variation in the polycrystalline ensemble. This flow stress heterogeneity is incorporated, spatially, in a continuum Lagrangian finite element framework, by partitioning the metal surface into grain-like structures. This pseudograin model captures all key aspects of the folding as observed by direct imaging, from fold nucleation via microstructure heterogeneity through various stages of fold development on the surface; surface strain fields; and deformation parameter effects such as indenter geometry and friction. The folding phenomenon is quite general, and provides a direct route for formation of surface defects and delamination wear particles. The microstructure-based simulation capability, thus validated, can be used as a virtual tool for analyzing large-strain plastic flow at surfaces and its consequences. Besides demonstrating the importance of folding in surface plasticity, the study points to a critical need to consider microstructure effects on local plasticity for sliding wear and deformation processing.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Electric field-induced phase transitions and composition-driven
           nanodomains in rhombohedral-tetragonal potassium-sodium niobate-based
           ceramics
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Xiang Lv, Jiagang Wu, Dingquan Xiao, Jianguo Zhu, Xixiang Zhang
      The mechanisms behind the high piezoelectricity of (K,Na)NbO3-based lead-free ceramics were investigated, including electric field-induced phase transitions and composition-driven nanodomains. The construction of a rhombohedral-tetragonal (R-T) phase boundary, confirmed using several advanced techniques, allowed a large piezoelectric constant (d 33) of 450 ± 5 pC/N to be obtained in (1-x)K0.4Na0.6Nb0.945Sb0.055O3-xBi0.5Na0.5(Hf1-y Sn y )O3 (0 ≤ x ≤ 0.06 and 0 ≤ y ≤ 0.5) ceramics possessing an ultralow ΔU T-R of 7.4 meV. More importantly, the existence of an intermediate phase, i.e., the electric-induced phase (EIP), bridging the rhombohedral R [P s//(111)] and tetragonal T [P s//(001)] phases during the polarization rotation was demonstrated. Striped nanodomains (∼40 nm) that easily responded to external stimulation were also observed in the ceramics with an R-T phase. Thus, the enhanced piezoelectric properties originated from EIP and the striped nanodomains.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • General evolution equation for the specific interface area of dendrites
           during alloy solidification
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): H. Neumann-Heyme, K. Eckert, C. Beckermann
      The specific area of the solid-liquid interface of an assembly of dendrites is an important integral measure of the morphology of the microstructure forming during alloy solidification. It represents the inverse of a characteristic length scale and is needed for the prediction of solidification defects and material properties. In the present study, the evolution of the interfacial area of dendrites is analysed using 3D phase-field simulations. A general evolution equation is developed for the specific interface area as a function of time and solid volume fraction that accounts for the effects of growth, curvature-driven coarsening and interface coalescence. The relation is validated using data from previously performed synchrotron X-ray tomography and isothermal coarsening experiments. It is found to be valid for arbitrary and even varying cooling rates and for a wide range of binary alloys. The rate constant in the evolution equation is successfully related to alloy properties.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Theoretical model and computer simulation of Metglas/PZT magnetoelectric
           composites for voltage tunable inductor applications
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Liwei D. Geng, Yongke Yan, Shashank Priya, Yu U. Wang
      Control of magnetic permeability through voltage promises to create novel electronic devices, such as voltage tunable inductors. The relationship between the structure and property of voltage tunable inductors comprising of magnetoelectric Metglas/PZT composites and the underlying domain-level mechanisms are investigated using theoretical analysis, computer simulation, and complementary experiments. A theoretical model is developed to analyze the roles of material anisotropy, inductor shape, and stress in controlling the Metglas permeability and its tunability. The analysis reveals key roles played by stress-induced anisotropy and the resultant ground magnetization state, and predicts two stress-dependent regimes of inductance tunability. The theory is validated using systematic experiments. The experimental results are used to determine the material and physical parameters. To further elucidate the underlying domain-level mechanisms responsible for controlling the behavior of voltage tunable inductor, phase field modeling is employed to simulate domain microstructures and magnetic permeability of Metglas/PZT composites under varying voltage. The computational results confirm the two regimes of inductance tunability and the controlling role of stress-induced anisotropy. The findings suggest engineering of internal bias stress as an effective means to optimize the inductance tunability of magnetoelectric Metglas/PZT composites.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Thermally activated dislocation plasticity in body-centered cubic chromium
           studied by high-temperature nanoindentation
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): In-Chul Choi, Christian Brandl, Ruth Schwaiger
      The deformation behavior of Chromium (Cr) was investigated with the goal to understand and quantify the thermally-activated dislocation plasticity and the transition to the temperature-/rate-independent regime in body-centered cubic (bcc) metals. High-temperature nanoindentation experiments were utilized to characterize the deformation behavior of bcc Cr from room temperature to 673 K. To validate the indentation method itself at elevated temperatures, we systematically studied the temperature-dependent indentation elastic modulus, which clearly shows a discontinuity at the magnetic phase transition at 308 K, which is quantitatively consistent with literature data. We characterized the kinetics of dislocation plasticity by analyzing the strain-rate sensitive behavior of the hardness at different temperatures. The observed signatures of the plastic relaxation mechanisms are discussed in the context of screw dislocation mobility governed by thermally-activated kink-pair nucleation, kink-drift or dislocation-impurity interaction.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Modulation of plastic flow in metallic glasses via nanoscale networks of
           chemical heterogeneities
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Jinwoo Kim, Hyun Seok Oh, Wan Kim, Pyuck-Pa Choi, Dierk Raabe, Eun Soo Park
      We systematically investigate the microstructures of metallic glasses with nanoscale networks of chemical heterogeneities introduced by the presence of a metastable miscibility gap, and their effects on modulating plastic flow of the alloys. Microstructural analysis of as-quenched alloys and the associated thermodynamic assessment in Cu-Zr-Al-Y metallic glass-forming system suggest that the existence of a metastable miscibility gap can induce not only phase-separated microstructures with sharp phase interfaces but also compositional fluctuations without a clear interface ranging from atomic scale to a few-nanometer scale in the fully amorphous alloys. The statistical analysis of shear avalanches in such compositionally heterogeneous metallic glasses reveals that chemical heterogeneities extending over a few nanometers promote a relatively large population of shear deformation units jammed before the nucleation of mature shear bands. This leads to the multiple nucleation of shear bands and sluggish deformation behavior along them. However, phase interfaces formed by phase separation inside the miscibility gap promote rapid propagation of shear bands at low flow stress, while compositional fluctuations creating non-sharp interfaces emerging at the outside of miscibility gap have relatively high resistance against shear band propagation. We hence suggest that the optimization of nanoscale compositional fluctuations in metallic glasses in terms of topology, percolation and magnitude can be an effective route for improving the materials' damage tolerance upon plastic flow.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Damage investigation and modeling of 3D woven ceramic matrix composites
           from X-ray tomography in-situ tensile tests
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Vincent Mazars, Olivier Caty, Guillaume Couégnat, Amine Bouterf, Stéphane Roux, Sébastien Denneulin, Jérôme Pailhès, Gérard L. Vignoles
      The present paper proposes an investigation of the failure events in a melt-infiltrated SiC/SiC composite. In-situ X-ray microtomography tensile tests were performed at room temperature and at 1250 °C in air. Digital Volume Correlation has been used to identify the damage mechanisms within the material at increasing loads and to propose a damage scenario. Realistic finite element meshes have been constructed from the 3D images to numerically reproduce the experiments at the meso-scale. Elastic simulations exhibit stress concentrations in the planes containing the weft tows. The first cracks and subsequent damage localization were found to appear within these planes thanks to the analysis of the in-situ tomographic data.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Influence of interphase boundary anisotropy on bulk eutectic
           solidification microstructures
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Supriyo Ghosh, Mathis Plapp
      The solidification of eutectic alloys generally produces two-phase microstructures. Their morphology is determined by the dynamics of the solid-liquid interfaces at the crystallization front. At the triple lines, where the liquid and the two solid phases meet, solid-liquid and solid-solid surface free energies are in local equilibrium. We perform three-dimensional phase-field simulations with a multi-phase-field model in which the surface free energies can be independently controlled. We find that an anisotropy of the interphase boundary (solid-solid) energy has a strong effect on the microstructural patterns. The lamellae tend to align with directions of minimal interphase boundary energy. For a two-fold anisotropy, as generally expected for interphase boundaries between two cubic crystals, regular lamellar arrays are formed, in strong contrast to the labyrinth patterns observed in isotropic systems. If two different grains compete, the one with the lowest interphase boundary energy always overgrows the other. These results are consistent with observations in bulk metallic eutectic samples, namely, the frequent occurrence of large regular lamellar arrays and the prevalence of grains with special orientation relationships.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • In-situ study of the dewetting behavior of Au/Ni bilayer films supported
           by a SiO2/Si substrate
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Xi Cen, Andrew M. Thron, Klaus van Benthem
      Solid state dewetting of Au/Ni bilayer films was investigated by in-situ cross-sectional TEM heating with energy-dispersive X-ray spectroscopy. The early stage of dewetting process revealed both grain boundary grooving at the surface of the Ni layer and void nucleation along the Au/Ni interface between Au grains. During annealing, inter-diffusion occurred and enhanced solubility was found between Au and Ni. Au diffused predominantly through Ni grain boundaries and decorated the Ni/substrate interface. The energetically preferred adsorption of Au at the Ni/SiO2 interface and at Ni grain boundaries, coupled with some alloying in the volume of the metal films delays the break-up of the bilayer film compared to pure Au or Ni films. The experimental observations confirm that dewetting kinetics of metal bilayer films are strongly affected by both partial alloying of the metals as well as the metal/metal interface.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • In-situ kinetics of modifications induced by swift heavy ions in Al2O3:
           Colour centre formation, structural modification and amorphization
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): C. Grygiel, F. Moisy, M. Sall, H. Lebius, E. Balanzat, T. Madi, T. Been, D. Marie, I. Monnet
      This paper details in-situ studies of modifications induced by swift heavy ion irradiation in α-Al2O3. This complex behaviour is intermediary between the behaviour of amorphizable and non-amorphizable materials, respectively. A unique combination of irradiation experiments was performed at the IRRSUD beam line of the GANIL facility, with three different characterisation techniques: in-situ UV–Vis absorption, in-situ grazing incidence X-Ray diffraction and ex-situ transmission electron microscopy. This allows a complete study of point defects, and by depth profile of structural and microstructural modifications created on the trajectory of the incident ion. The α-Al2O3 crystals have been irradiated by 92 MeV Xenon and 74 MeV Krypton ions, the irradiation conditions have been chosen rather similar with an energy range where the ratio between electronic and nuclear stopping power changes dramatically as function of depth penetration. The main contribution of electronic excitation, above the threshold for track formation, is present beneath the surface to finally get almost only elastic collisions at the end of the projected range. Amorphization kinetics by the overlapping of multiple ion tracks is observed. In the crystalline matrix, long range strains, unit-cell swelling, local microstrain, domain size decrease, disordering of oxygen sublattice as well as colour centre formation are found. This study highlights the relationship between ion energy losses into a material and its response. While amorphization requires electronic stopping values above a certain threshold, point defects are predominantly induced by elastic collisions, while some structural modifications of the crystalline matrix, such as unit-cell swelling, are due to contribution of both electronic and nuclear processes.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Investigations of deformation-induced δ → ζ phase transformation in
           zirconium hydride by in situ high-energy X-ray diffraction
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Shilei Li, Youkang Wang, Zifan Che, Gang Liu, Yang Ren, Yandong Wang
      In situ high-energy X-ray diffraction (HE-XRD) was used to study the micromechanical behavior of Zircaloy-4 during tensile loading, revealing for the first time a deformation-induced phase transformation from δ-hydride to ζ-Zr2H in the hydride at a critical stress of approximately 370 MPa. Detailed investigations using transmission electron microscopy confirmed that the ζ-Zr2H phase had a “hexagon-on-hexagon” orientation relationship with the α-Zr matrix, i.e., (0002)ζ//(0002)α and [2 1 ¯ 1 ¯ 0]ζ//[2 1 ¯ 1 ¯ 0]α. The ζ phase has almost the same lattice parameters for a and b and twice the c parameter as those of α-Zr. The affinity in crystal structure and lattice parameters between ζ-hydride and α-Zr suggests that ζ-Zr2H as an intermediate phase could be important to the dissolution and reprecipitation of δ-hydride during plastic deformation. The HE-XRD experiments provide evidence that the fracture of ζ-hydride plates aligned perpendicular to the loading direction (LD) causes the premature failure of the grains oriented with [0001]//LD in the matrix. The new finding regarding the deformation-induced phase transformation in the hydride is important to deepen the understanding of delayed hydride cracking in Zr alloys.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Dominating deformation mechanisms in ultrafine-grained chromium across
           length scales and temperatures
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): R. Fritz, D. Wimler, A. Leitner, V. Maier-Kiener, D. Kiener
      The microstructure influence on the thermally activated deformation behaviour of chromium is investigated for a more fundamental understanding of the deformation mechanisms contributing to plasticity in bcc metals. Therefore, scale-bridging experiments at variable temperatures and varying strain-rates are performed, encompassing macroscopic compression tests in direct correlation to local in-situ SEM micro-compression experiments on taper-free pillars and advanced nanoindentation testing. For the first time, it is demonstrated that, independent of stress state, sample volume and surface fraction, a distinct temperature-dependent transition of the dominating deformation mechanism occurs. While at low temperatures the lattice resistance dominates, exceeding a critical temperature the dislocation interaction with grain boundaries becomes the rate limiting step. Finally, based on the vastly different fractions of grain boundaries in the tested sample volumes, a comprehensive model on the deformation of bcc metals, in particular at small scales or for confined volumes is derived.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Structural investigation of phase segregation in Mn2CrGa-based alloys
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): X.-Z. Li, W.-Y. Zhang, D.J. Sellmyer
      Alloys with nominal compositions of Mn2CrGa1-xAlx (x = 0.0, 0.2, 0.5, 1.0) have been studied by X-ray powder diffraction (XRD). Detailed structural investigation of the alloys with x = 0.2 and 0.5 has been further carried out using transmission electron microscopy (TEM). The alloys, in the typical Heusler composition, were prepared using rapid quenching and subsequent annealing. The XRD analysis revealed that a disordered cubic phase was present in the alloys with x = 0.0 and 1.0 while a spinodal decomposition with phase separation has been observed in the alloys with x = 0.2 and 0.5. TEM study confirms a segregation of two crystalline phases, one of them a cubic phase with the β–Mn prototype structure and the other a new crystalline phase with a tetragonal structure. Energy-dispersive X-ray spectroscopy (EDS) analysis was used to determine the compositions of the two crystalline phases. The mass ratio of the tetragonal phase and the β–Mn prototype cubic phase is derived as t/c ≈ 2.41 by fitting the average compositions of the two crystalline phases to the nominal composition. The orientational relationship of two crystalline structures has been determined by selected-area electron diffraction (SAED) and stereogram analysis. The structures of the two crystalline phases have been investigated by high-resolution transmission electron microscopy (HRTEM) and image simulation. The structural model of the tetragonal phase is proposed and compared with the experimental results in SAED and HRTEM studies.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Materials selection rules for amorphous complexion formation in binary
           metallic alloys
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): Jennifer D. Schuler, Timothy J. Rupert
      Complexions are phase-like interfacial features that can influence a wide variety of properties, but the ability to predict which material systems can sustain these features remains limited. Amorphous complexions are of particular interest due to their ability to enhance diffusion and damage tolerance mechanisms, as a result of the excess free volume present in these structures. In this paper, we propose a set of materials selection rules aimed at predicting the formation of amorphous complexions, with an emphasis on (1) encouraging the segregation of dopants to the interfaces and (2) lowering the formation energy for a glassy structure. To validate these predictions, binary Cu-rich metallic alloys encompassing a range of thermodynamic parameter values were created using sputter deposition and subsequently heat treated to allow for segregation and transformation of the boundary structure. All of the alloys studied here experienced dopant segregation to the grain boundary, but exhibited different interfacial structures. Cu-Zr and Cu-Hf formed nanoscale amorphous intergranular complexions while Cu-Nb and Cu-Mo retained crystalline order at their grain boundaries, which can mainly be attributed to differences in the enthalpy of mixing. Finally, using our newly formed materials selection rules, we extend our scope to a Ni-based alloy to further validate our hypothesis, as well as make predictions for a wide variety of transition metal alloys.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
  • Shear-band thickness and shear-band cavities in a Zr-based metallic glass
    • Abstract: Publication date: November 2017
      Source:Acta Materialia, Volume 140
      Author(s): C. Liu, V. Roddatis, P. Kenesei, R. Maaß
      Strain localization into shear bands in metallic glasses is typically described as a mechanism that occurs at the nano-scale, leaving behind a shear defect with a thickness of 10–20 nm. Here we sample the structure of a single system-spanning shear band that has carried all plastic flow with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and high-energy x-ray tomography (XRT). It is found that the shear-band thickness and the density change relative to the matrix sensitively depend on position along the shear band. A wide distribution of shear-band thickness (10 nm–210 nm) and density change (−1% to −12%) is revealed. There is no obvious correlation between shear-band thickness and density change, but larger thicknesses correspond typically to higher density changes. More than 100 micron-size shear-band cavities were identified on the shear-band plane, and their three-dimensional arrangement suggests a strongly fluctuating local curvature of the shear plane. These findings urge for a more complex view of a shear band than a simple nano-scale planar defect.
      Graphical abstract image

      PubDate: 2017-09-23T20:54:07Z
       
 
 
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: 54.225.39.142
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2016