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Showing 1 - 200 of 3183 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 100, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 38, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 6)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 437, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 302, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 25, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 17, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 182, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 29, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 11, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 33, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 50, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 65, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 24)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 20, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 12, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 8, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 26, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 17)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 66)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 419, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 37, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 53, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 384, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 472, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 45, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 7, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 63, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 46, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 12)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 36, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 36, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 51)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 248, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 66, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 24, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 209, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 217, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Acta Materialia
Journal Prestige (SJR): 3.263
Citation Impact (citeScore): 6
Number of Followers: 302  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1359-6454
Published by Elsevier Homepage  [3183 journals]
  • Isolation of a Ferroelectric Intermediate Phase in Antiferroelectric Dense
           Sodium Niobate Ceramics
    • Abstract: Publication date: Available online 22 August 2019Source: Acta MaterialiaAuthor(s): Hangfeng Zhang, Bin Yang, Haixue Yan, Isaac Abrahams Switchable ferroelectric/antiferroelectric ceramics are of significant interest for high power energy storage applications. Grain size control of this switching is an interesting approach to controlling polarization and hence dielectric properties. However, the use of this approach in technologically relevant ceramics is hindered by difficulty in fabricating dense ceramics with small grain sizes. Here an intermediate polar ferroelectric phase (P21ma) has been isolated in dense bulk sodium niobate ceramics by grain size control through spark plasma sintering methods. Our findings, supported by XRD, DSC, P-E (I-E) loops and dielectric characterization, provide evidence that the phase transition from the antiferroelectric (AFE) R-phase, in space group Pnmm, above 300 °C, to the AFE P-phase, in space group Pbma, at room temperature, always involves the polar intermediate P21ma phase and that the P21ma → Pbma transition can be suppressed by reducing grain size.Graphical abstractImage 1
  • Crystal orientation effect on fretting fatigue induced geometrically
    • Abstract: Publication date: Available online 21 August 2019Source: Acta MaterialiaAuthor(s): Qi-Nan Han, Shao-Shi Rui, Wenhui Qiu, Xianfeng Ma, Yue Su, Haitao Cui, Hongjian Zhang, Huiji Shi The effect of crystal orientation on fretting fatigue induced crack initiation and dislocation distribution is studied by in-situ SEM observation and electron back-scattered diffraction (EBSD) in this paper. Cracks and slip lines are observed in the fretting contact area of Ni-based single-crystal (NBSX) superalloys. The in-situ SEM observation captures different crack and slip line behaviors under different crystal orientations. The EBSD analysis results show obvious misorientation and orientation deviation in the fretting contact area. For both crystal orientations, the geometrically necessary dislocation (GND) density distributions in the contact area are obtained by using Hough-based EBSD methods. The peak position of grain reference orientation deviation (GROD) and GND density matches with the fretting fatigue crack formation position. EBSD analysis shows that the dislocation density distribution on each slip system is closely related to the crack initiation direction. The direction of slip system with the maximum dislocation density agrees with the crack initiation direction obtained by in-situ observation.Graphical abstractImage 1
  • In Situ Characterization of a High Work Hardening Ti-6Al-4V prepared by
           Electron Beam Melting
    • Abstract: Publication date: Available online 21 August 2019Source: Acta MaterialiaAuthor(s): K. Sofinowski, M. Šmíd, I. Kuběna, S. Vives, N. Casati, S. Godet, H. Van Swygenhoven A multi-phase Ti-6Al-4V prepared by electron beam melting and thermal post treatments has been shown to exhibit increased strength and ductility over standard wrought or hot isostatic pressed Ti-6Al-4V. The mechanical improvements are due to a prolonged, continuous work hardening effect not commonly observed in Ti alloys. In situ x-ray diffraction and high resolution digital image correlation are used to examine the strain partitioning between the phases during tensile loading with post-mortem electron microscopy to characterize the deformation behavior in each phase. Specimens heat treated between 850 and 980°C were tested and the effect of annealing temperature on the micromechanical response is discussed. It is shown that the work hardening is the result of composite load-sharing behavior between three mechanically distinct microstructures: large α lamellae and a martensitic region of fine acicular α' and a third phase not previously reported in this alloy.Graphical abstractImage 1
  • Radiation induced solute clustering in high-Ni reactor pressure vessel
    • Abstract: Publication date: Available online 21 August 2019Source: Acta MaterialiaAuthor(s): M.J. Konstantinović, I. Uytdenhouwen, G. Bonny, N. Castin, L. Malerba, P. Efsing The thermal stability and the structure of solute-vacancy clusters formed by neutron irradiation are studied by means of positron annihilation spectroscopy and hardness measurements of post-irradiation annealed reactor pressure vessel steels with high and low Ni contents. Two distinct recovery stages were observed and assigned to (a) the dissolution of vacancy clusters at about 650 K, and (b) the dissolution of solute-vacancy clusters at about 750 K. In steels with high Ni content, hardening mainly recovers during the second stage. Atomistic and coarse grain models suggest that during this stage, the removal of vacancies from vacancy-solute clusters leads to complete cluster dissolution, which indicates that solute clusters are radiation induced.x.Graphical abstractImage 1
  • 60 o +Shuffle+Dislocation+Pileup+against+Different+Grain+Boundaries+in+Silicon+Bicrystal+under+Shear&rft.title=Acta+Materialia&rft.issn=1359-6454&">Amorphization Induced by 60 o Shuffle Dislocation Pileup against
           Different Grain Boundaries in Silicon Bicrystal under Shear
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Hao Chen, Valery Levitas, Liming Xiong Molecular dynamics (MD) simulations of the amorphous band nucleation and growth ahead of the tip of a shuffle 60o dislocation pileup at different grain boundaries (GBs) in diamond-cubic (dc) silicon (Si) bicrystal under shear are performed. Amorphization initiates when the local resolved shear stress reaches approximately the same value required for amorphization in a perfect single crystal (8.6-9.3GPa) for the same amorphization plane. Since the local stresses at the tip of a dislocation pileup increase when the number of dislocations in the pileup is increased, the critical applied shear stress τap for the formation of an amorphous shear band significantly decreases with the dislocation accumulation at the GBs. In particular, when the number of the dislocations in a pileup increases from 3 to 8, the critical shear stress drops from 4.7GPa to 1.6GPa for both the Σ9 and Σ19 GBs and from 4.6GPa to 2.1GPa for the Σ3 GB, respectively. After the formation of steps and disordered embryos at the GBs, the atomistic mechanisms responsible for the subsequent amorphous shear band formations near different GBs are found to distinct from each other. For a high-angle GB, such as Σ3, an amorphous band propagates through the crystalline phase along the (112) plane. For the Σ9 GB, partial dislocations forming a stacking fault precede the formation of an amorphous band along the (110) plane. For the Σ19 GB, the one-layer stacking fault along the (111) plane transforms into an interesting intermediate phase: a two-layer band with the atomic bonds being aligned along the (111) plane (i.e., rotated by 30o with respect to the atomic bonds outside the band). This intermediate phase transforms to the amorphous band along the (111) plane under a further shearing. The obtained results represent an atomic-level confirmation of the effectiveness of dislocation pileup at the nucleation site for various strain-induced phase transformations (PTs), and exhibit some limitations.Graphical abstractImage 1
  • A Novel Liquid-Mediated Nucleation Mechanism for Explosive Crystallization
           in Amorphous Germanium
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Garth C. Egan, Tae Wook Heo, Amit Samanta, Geoffrey H. Campbell We report a novel mechanism for explosive crystallization in amorphous germanium (a-Ge), which operates through liquid-mediated nucleation occurring under extreme thermal gradient conditions. The crystallization kinetics of sputter-deposited films with thicknesses ranging from 30 to 150 nm were characterized using in situ movie-mode dynamic transmission electron microscopy (MM-DTEM). After localized heating from a short laser pulse, explosive liquid phase nucleation (LPN) was observed to occur during the early stage (50 nm) films deposited on silicon nitride substrates. The crystallization front propagated at ∼12-15 m/s and produced nanocrystalline microstructure with ∼50 nm grains. A mechanism involving the existence of a relatively thick (>100 nm) transient liquid layer and a high nucleation rate is proposed to explain the behavior. The key thermodynamic and kinetic features as well as the feasibility of the mechanism are further explored by employing parametric and systematic phase-field modeling and simulations.Graphical abstractImage 1
  • Powder-spreading mechanisms in powder-bed-based additive manufacturing:
           experiments and computational modeling
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Hui Chen, Qingsong Wei, Yingjie Zhang, Fan Chen, Yusheng Shi, Wentao Yan The packing density of the powder layer plays a key role in the final quality of the parts fabricated via powder-bed-based (PBB) additive manufacturing. This paper presents a combined experimental and computational modeling study on the scraping type of powder-spreading process, in order to understand the fundamental mechanisms of the packing of the powder layer. The deposition mechanisms at the particulate scale, including particle contact stress and particle velocity, are investigated, using the discrete element method, while the macro-scale packing density is validated by experiments. It is found that there is a stress-dip at the bottom of powder pile scraped by the rake. This stress-dip makes the powder particles uniformly deposited. Three kinds of deposition mechanisms dominating the powder-spreading process are identified: cohesion effect, wall effect, and percolation effect. The cohesion effect, which leads to particle agglomerations and thus reduces the packing density, becomes stronger with the decrease of particle size. The wall effect, which leads to more vacancies in the powder layer, becomes stronger with the decrease of layer thickness or the increase of particle size. The percolation effect exists in bimodal powder particles, which leads to particle segregation within the powder layer and thus reduces the packing density. The three kinds of deposition mechanisms compete with each other during the powder-spreading process and make combined effects on the packing density of the powder layer.Graphical abstractImage 1
  • Physical metallurgy-guided machine learning and artificial intelligent
           design of ultrahigh-strength stainless steel
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Chunguang Shen, Chenchong Wang, Xiaolu Wei, Yong Li, Sybrand van der Zwaag, Wei Xu With the development of the materials genome philosophy and data mining methodologies, machine learning (ML) has been widely applied for discovering new materials in various systems including high-end steels with improved performance. Although recently, some attempts have been made to incorporate physical features in the ML process, its effects have not been demonstrated and systematically analysed nor experimentally validated with prototype alloys. To address this issue, a physical metallurgy (PM) -guided ML model was developed, wherein intermediate parameters were generated based on original inputs and PM principles, e.g., equilibrium volume fraction (Vf) and driving force (Df) for precipitation, and these were added to the original dataset vectors as extra dimensions to participate in and guide the ML process. As a result, the ML process becomes more robust when dealing with small datasets by improving the data quality and enriching data information. Therefore, a new material design method is proposed combining PM-guided ML regression, ML classifier and a genetic algorithm (GA). The model was successfully applied to the design of advanced ultrahigh-strength stainless steels using only a small database extracted from the literature. The proposed prototype alloy with a leaner chemistry but better mechanical properties has been produced experimentally and an excellent agreement was obtained for the predicted optimal parameter settings and the final properties. In addition, the present work also clearly demonstrated that implementation of PM parameters can improve the design accuracy and efficiency by eliminating intermediate solutions not obeying PM principles in the ML process. Furthermore, various important factors influencing the generalizability of the ML model are discussed in detail.Graphical abstractImage 1
  • Short-term creep behavior of an additive manufactured non-weldable
           Nickel-base superalloy evaluated by slow strain rate testing
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Jinghao Xu, Hans Gruber, Dunyong Deng, Ru Lin Peng, Johan J. Moverare Additive manufacturing (AM) of high γ′ strengthened Nickel-base superalloys, such as IN738LC, is of high interest for applications in hot section components for gas turbines. The creep property acts as the critical indicator of component performance under load at elevated temperature. However, it has been widely suggested that the suitable service condition of AM processed IN738LC is not yet fully clear. In order to evaluate the short-term creep behavior, slow strain rate tensile (SSRT) tests were performed. IN738LC bars were built by laser powder-bed-fusion (L-PBF) and then subjected to hot isostatic pressing (HIP) followed by the standard two-step heat treatment. The samples were subjected to SSRT testing at 850 °C under strain rates of 1×10-5/s, 1×10-6/s, and 1×10-7/s. In this research, the underlying creep deformation mechanism of AM processed IN738LC is investigated using the serial sectioning technique, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM). On the creep mechanism of AM polycrystalline IN738LC, grain boundary sliding is predominant. However, due to the interlock feature of grain boundaries in AM processed IN738LC, the grain structure retains its integrity after deformation. The dislocation motion acts as the major accommodation process of grain boundary sliding. Dislocations bypass the γ′ precipitates by Orowan looping and wavy slip. The rearrangement of screw dislocations is responsible for the formation of subgrains within the grain interior. This research elucidates the short-creep behavior of AM processed IN738LC. It also shed new light on the creep deformation mechanism of additive manufactured γ′ strengthened polycrystalline Nickel-base superalloys.Graphical abstractImage 1
  • Thick amorphous complexion formation and extreme thermal stability in
           ternary nanocrystalline Cu-Zr-Hf alloys
    • Abstract: Publication date: Available online 20 August 2019Source: Acta MaterialiaAuthor(s): Charlette M. Grigorian, Timothy J. Rupert Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with amorphous intergranular films, this paper investigates ternary nanocrystalline Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the formation of disordered complexions. Binary Cu-Zr and Cu-Hf alloys with similar initial grain sizes were also fabricated for comparison. The thermal stability of the nanocrystalline alloys was evaluated by annealing at 950 °C (>95% of the solidus temperatures), followed by detailed characterization of the grain boundary structure. All of the ternary alloys exhibited exceptional thermal stability comparable to that of the binary Cu-Zr alloy, and remained nanocrystalline even after two weeks of annealing at this extremely high temperature. Despite carbide formation and growth in these alloys during milling and annealing, the thermal stability of the ternary alloys is mainly attributed to the formation of thick amorphous intergranular films at high temperatures. Our results show that ternary alloy compositions have thicker boundary films compared to the binary alloys with similar global dopant concentrations. While it is not required for amorphous complexion formation, this work shows that having at least three elements present at the interface can lead to thicker grain boundary films, which is expected to maximize the previously reported toughening effect.Graphical abstractImage 1
  • Effects of thermal aging and low-fluence neutron irradiation on the
           mechanical property and microstructure of ferrite in cast austenitic
           stainless steels
    • Abstract: Publication date: Available online 19 August 2019Source: Acta MaterialiaAuthor(s): Siwei Chen, Yuichi Miyahara, Akiyoshi Nomoto, Kenji Nishida The effects of low-fluence neutron irradiation on hardening and microstructure evolution in ferrite of solution annealed or thermally aged CF3, CF3M, CF8 and CF8M cast austenitic stainless steels (CASSs) have been investigated by means of nanoindentation tests and atom probe tomography (APT). Thermal aging was performed at 400 ºC for 500 h. Neutron irradiation was carried out to a fluence of 4.84×1018 n/cm2 (E>1 MeV) at the temperature ranging from 289 to 292 ºC in the LVR-15 research reactor. Irradiation hardening in thermally-aged specimens was found to be similar with or smaller than that in the corresponding solution annealed specimens. Phase decomposition and formation of solute clusters acted two major factors for the hardening in ferrite with thermal aging and/or neutron irradiation. The phase decomposition of ferrite increased with either the thermal aging or the neutron irradiation for the solution annealed materials; however, the change in the phase decomposition of ferrite was neither significant nor apparent with the low-fluence neutron irradiation for the thermally-aged materials. Ni-Si-Mn enriched solute clusters were observed in the matrix of ferrite in the aged specimens, and the irradiated specimens with/without thermal aging. Mo in the CASSs appeared to inhibit the formation of solute clusters under the neutron irradiations. In the thermally-aged specimen with low-C and without Mo, neutron irradiation enhanced the formation of solute clusters significantly. For the first time we discussed the relationship between hardening and microstructure evolution in ferrite of CASSs with consideration of both thermal aging and neutron irradiation.Graphical abstractImage 1
  • Asymmetric flux-closure domains in compositionally graded nanoscale
           ferroelectrics and unusual switching of toroidal ordering by an
           irrotational electric field
    • Abstract: Publication date: Available online 19 August 2019Source: Acta MaterialiaAuthor(s): Le Van Lich, Minh-Tien Le, Tinh Quoc Bui, Thanh-Tung Nguyen, Takahiro Shimada, Takayuki Kitamura, Trong-Giang Nguyen, Van-Hai Dinh A reversal of polarization vortexlike domains in ferroelectric nanostructures plays important roles for next generations of electronic nanodevices. However, a direct switching of the polarization vortexlike domains in ferroelectrics is a nontrivial task since the toroidal moment is conjugated to a curled electric field rather than a homogeneous one. This work is dedicated to developing an approach to directly switch the toroidal ordering under an irrotational (homogeneous) electric field with the use of compositionally graded ferroelectric (cgFE) nanodot. The variation in material compositions induces an additionally broken spatial inversion symmetry at a scale beyond unit-cell level, giving rise to a formation of asymmetric flux-closure domain (FCD) in cgFE nanodot. More interestingly, such an asymmetric character facilitates to a switch of FCD by an irrotational electric field. In particular, the rotation of polarization can be directly switched from counter-clockwise to clockwise rotations and vice versa without a formation of intermediate domain structures during the switching process. This switching behavior is distinguished from that in homogeneous counterparts. We further demonstrate that the variation in material compositions tailors the distribution of electrostatic and total free energies in the cgFE nanodot that can control the annihilation/initiation process of FCD under irrotational electric field, providing fundamental reason for the direct switching of the toroidal moment. Another interesting issue is found that both the amplitude and frequency of applied electric field strongly affect the switching behavior of FCD in cgFE nanodot.Graphical abstractImage 1
  • Precipitation and Hardening in Irradiated Low Alloy Steels with a Wide
           Range of Ni and Mn Compositions
    • Abstract: Publication date: Available online 18 August 2019Source: Acta MaterialiaAuthor(s): N. Almirall, P.B. Wells, T. Yamamoto, K. Wilford, T. Williams, N. Riddle, G.R. Odette Mn-Ni-Si intermetallic precipitates (MNSPs) that are observed in some Fe-based alloys following thermal aging and irradiation are of considerable scientific and technical interest. For example, large volume fractions (f) of MNSPs form in reactor pressure vessel low alloy steels irradiated to high fluence, resulting in severe hardening induced embrittlement. Nine compositionally-tailored small heats of low Cu RPV-type steels, with an unusually wide range of dissolved Mn (0.06-1.34 at.%) and Ni (0.19-3.50 at.%) contents, were irradiated at ≈ 290°C to ≈ 1.4x1020 n/cm2 at an accelerated test reactor flux of ≈ 3.6x1012 n/cm2-s (E> 1 MeV). Atom probe tomography shows Mn-Ni interactions play the dominant role in determining the MNSP f, which correlates well with irradiation hardening. The wide range of alloy compositions results in corresponding variations in precipitates chemistries that are reasonably similar to various phases in the Mn-Ni-Si projection of the Fe based quaternary. Notably, f scales with ≈ Ni1.6Mn0.8. Thus f is modest even in advanced high 3.5 at.% Ni steels at very low Mn (Mn starvation); in this case Ni-silicide phase type compositions are observed.Graphical abstractImage 1
  • Designing solid solution hardening to retain uniform ductility while
           quadrupling yield strength
    • Abstract: Publication date: Available online 17 August 2019Source: Acta MaterialiaAuthor(s): Ping-Jiong Yang, Qing-Jie Li, Wei-Zhong Han, Ju Li, Evan Ma Single-phase metals can be strengthened via cold work, grain refinement, or solid solution hardening. But the yield strength elevation normally comes at the expense of ductility, i.e., a conspicuous decrease of the uniform elongation in uniaxial tension. This strength-ductility trade-off is often a result of inadequate strain hardening rate that can no longer keep up with the elevated flow stress to prevent plastic instability. Here we alleviate this dilemma by designing oxygen interstitial solution hardening in body-centered-cubic niobium: the strain hardening rate is exceptionally high, such that most of the uniform tensile ductility of Nb can be retained despite of quadrupled yield strength. The oxygen solutes impose random force field on moving dislocation line, promoting the formation of cross-kinks that dynamically accumulate vacancy-oxygen complexes. These obstacles enhance the trapping/multiplication of screw dislocations as well as cross-slip, all promoting strain hardening and strain de-localization. This approach utilizes only a low concentration of interstitial solutes to achieve effective strengthening and strain hardening simultaneously, and is an inexpensive and scalable route amenable to the processing of bulk samples.Graphical abstractImage 1
  • Effect of electrochemical charging on the hydrogen embrittlement
           susceptibility of Alloy 718
    • Abstract: Publication date: Available online 17 August 2019Source: Acta MaterialiaAuthor(s): X. Lu, D. Wang, D. Wan, Z.B. Zhang, N. Kheradmand, A. Barnoush The susceptibility of age-hardened nickel-based 718 superalloy to hydrogen embrittlement was studied by the controlled electrochemical charging combined with slow strain-rate tensile tests (SSRT) and advanced characterization techniques. We proposed some novel ideas of explaining hydrogen embrittlement mechanisms of the studied material in regard to two cracking morphologies: transgranular and intergranular cracking. It is for the first time to report that electrochemical charging alone could cause slip lines, surface and subsurface cracks on nickel-based superalloys. The formation of pre-damages was discussed by calculating the hydrogen concentration gradient generated during cathodic charging. Pre-damages were proved to result in transgranular cracks and lead to the evident reduction of mechanical properties. In addition, the STRONG (Slip Transfer Resistance of Neighbouring Grains) model was used to analyze the dependence of hydrogen-assisted intergranular cracking on the microscopic incompatibility of the grain boundaries. The results show that in the presence of hydrogen, grain boundaries with a lower dislocation slip transmission are more prone to cracking during loading and vice versa.Graphical abstractImage 1
  • A coupled microstructural-structural mechanism governing thermal
           depolarization delay in Na0.5Bi0.5TiO3-based piezoelectrics
    • Abstract: Publication date: Available online 15 August 2019Source: Acta MaterialiaAuthor(s): Dipak Kumar Khatua, Anupam Mishra, Naveen Kumar, Gobinda Das Adhikary, Uma Shankar, Bhaskar Majumdar, Rajeev Ranjan Driven by environmental concerns and governmental directives, a sustained research effort in the last decade and half has led to the development of lead-free alternatives which can potentially replace the commercial lead-based piezoceramics in niche applications. Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics have found acceptance as promising lead-free transducers in high power ultrasonic devices. An issue of concern however is the low depolarization temperature which limits the device’s tolerance for temperature rise during operation. While several strategies have been reported to improve thermal depolarization in NBT-based piezoceramics, there is a lack of consensus regarding the most fundamental factor/mechanism which enhances the depolarization temperature. In this paper we unravel a coupled microstructural-structural mechanism which controls the thermal depolarization in NBT-based piezoceramics. First, we demonstrate the phenomenon of a considerable increase in the depolarization temperature, without significantly losing the piezoelectric property in unmodified NBT by increasing the grain size. We then establish a grain size controlled structural mechanism and demonstrate that the rise in depolarization temperature is primarily associated with the bigger grains allowing relatively large lattice distortion to develop in the poling stabilized long range ferroelectric phase. We reconfirmed the validity of this mechanism in the model morphotropic phase boundary (MPB) composition 0.94Na0.5Bi0.5TiO3-0.06BaTiO3. For the sake of generalization, we demonstrate that the same mechanism is operative in another lead-based relaxor-ferroelectric system 0.62PbTiO3-0.38Bi(Ni0.5Hf0.5)O3. Our study provides the fundamental structural basis for understanding thermal depolarization delay in relaxor ferroelectric based piezoceramics.Graphical abstractImage 1
  • Interfacial Ponderomotive Force in Solids Leads to Field Induced
           Dissolution of Materials and Formation of Non-equilibrium Nanocomposites
    • Abstract: Publication date: Available online 14 August 2019Source: Acta MaterialiaAuthor(s): Amin Nozariasbmarz, Mahshid Hosseini, Daryoosh Vashaee We report that microwave radiation can decompose continuous solid-solution materials into their constituent phases – a process that is thermodynamically unfavorable at equilibrium. A detailed analysis of the interaction of the electromagnetic wave with the material showed that a strong ponderomotive force preferentially separates the constituent phases via an enhanced mass transport process amplified particularly near the interfaces. The proof of concept experiments showed that the material, whether it is a solid-solution of two elements, e.g. (Si1-xGex), or two compounds, e.g. (Bi2Te3)1-x(Sb2Te3)x, decomposes into the constituent phases when radiated by a polarized microwave field. The dissolution happens in the bulk of the material and even below the melting point. The degree of decomposition can be controlled by radiation parameters to produce structures composed of gradient phases of the solid-solution. This offers a novel and facile method for synthesizing gradient composite and complex structures for application in thermoelectricity as well as fabrication of core-shell structures for catalysts and biomedical applications.Graphical abstractImage 1
  • Relations between Material Properties and Barriers for Twin Boundary
           Motion in Ferroic Materials
    • Abstract: Publication date: Available online 14 August 2019Source: Acta MaterialiaAuthor(s): Bar Danino, Gil Gur-Arieh, Doron Shilo, Dan Mordehai Ferroic materials typically exhibit a microstructure that contains twins or domains separated by twin boundaries (walls). The deformation of these materials is governed by twin boundary motion under mechanical/electrical/magnetic driving force. The Landau-Ginzburg model is a widely accepted phenomenological model used to describe twin boundary properties. However, it is incapable of describing energy barriers for motion due to the lack of atomistic description. In this work, we present a model interatomic potential for studying the relations between the lattice barrier for twin boundary motion and measurable material properties. The interatomic potential emulates the continuum Landau-Ginzburg model and reproduces known results of twin boundary thickness and energy as a function of the model parameters. An atomic model system is constructed, with a single twin boundary separating crystals of different orientations and we employ the Nudged Elastic Band method to calculate the energy barriers for the motion of twin boundaries with different thicknesses under different externally-applied shear stresses. The results are summarized in a closed-form expression relating the energy barriers with material properties and the external loading. The energy barrier function extends the Landau-Ginzburg model and allows treating the motion of twin boundary as a thermally activated process.Graphical abstractImage 1
  • Strong metal–metal interaction and bonding nature in metal/oxide
           interfaces with large mismatches
    • Abstract: Publication date: Available online 14 August 2019Source: Acta MaterialiaAuthor(s): Hongping Li, Mitsuhiro Saito, Chunlin Chen, Kazutoshi Inoue, Kazuto Akagi, Yuichi Ikuhara Metal/oxide heterointerfaces are ubiquitous in functional materials, and their microstructures frequently govern the macroscopic properties. It has been believed that the interfacial interactions are very weak at incoherent interfaces with large mismatches. Combining atomic-resolution scanning transmission electron microscopy with density functional theory calculations, we investigated the interaction and bonding reconstruction at Pd/ZnO{0001} interfaces, which have large mismatches. Molecular beam epitaxy was employed to grow Pd films on clean Zn-terminated ZnO(0001) and O-terminated ZnO(0001¯) polarized surfaces. Atomically sharp Zn-terminated interfaces formed on both substrates, and the large lattice misfit between the films and substrate was not strongly accommodated, suggesting the formation of incoherent regions. The interfacial atoms were located almost at bulk lattice points in the stoichiometric Zn-terminated Pd(111)/ZnO(0001) structure, whereas the interfacial Pd and Zn atoms underwent relatively large relaxations on the interfacial plane in the nonstoichiometric Zn-terminated Pd(111)/ZnO(0001¯) interface. Effective Pd-Zn chemical bonds were formed across both interfaces, but the bonding mechanisms were quite different, depending on the local atomic geometry. The Pd-Zn bonds exhibited site-dependent characteristics and gradually transitioned from covalent to ionic at the Pd(111)/ZnO(0001) interface, whereas most of Pd-Zn bonds exhibited strong covalent behavior at the Pd/ZnO(0001¯) interface. The adhesive energies indicated that the Zn-terminated Pd/ZnO(0001¯) interface is energetically preferable to the Zn-terminated Pd/ZnO(0001) interface. Thus, the interfacial interaction can be strong and direct metal–metal interactions can play a critical role in metal/oxide heterointerfaces with large mismatches, opening up a new avenue for understanding the origins of interface-related issues.Graphical abstractImage 1
  • Size-dependent failure of the strongest bulk metallic glass
    • Abstract: Publication date: Available online 14 August 2019Source: Acta MaterialiaAuthor(s): Ruitao Qu, Dominik Tönnies, Lin Tian, Zengqian Liu, Zhefeng Zhang, Cynthia A. Volkert Upon reducing the sample size into micrometer scale, an obvious brittle-to-ductile transition accompanied by a drastic change of failure mode from shattering to shear-banding was observed when compressing the brittle but strong Co55Ta10B35 bulk metallic glass (BMG). The shattering failure under macroscopic compression is dominated by splitting cracking, which completely differs from shear-banding and originates from extrinsic defects like inclusions. To reveal the critical conditions for shear-banding and splitting cracking, various micropillar specimens with intentionally introduced holes as extrinsic defects were tested, and the stress distributions at the failure moment were analyzed with finite element simulation. The shear plane criterion was found to be quite effective to estimate the nominal stress required for the failure dominated by shear-banding. However, brittle splitting cracking does not occur although the maximum tensile stress reaches the critical value, which is different from traditional brittle solids. To initiate splitting cracking, a high-tensile-stress region over a critical distance, which depends on defect size and fracture toughness of the BMG, is required. The critical conditions for shear failure and splitting cracking demonstrated in this approach can be used to estimate the failure conditions of various BMG components with complex geometries in a wide range of length scales, and to design tough composites based on brittle BMGs. As an example, a design criterion to avoid brittle splitting fracture of porous BMG materials is proposed.Graphical abstractImage 1
  • Microstructure and microchemistry study of irradiation-induced
           precipitates in proton irradiated ZrNb alloys
    • Abstract: Publication date: Available online 13 August 2019Source: Acta MaterialiaAuthor(s): Zefeng Yu, Chenyu Zhang, Paul M. Voyles, Lingfeng He, Xiang Liu, Kelly Nygren, Adrien Couet Proton irradiation induced Nb redistribution in Zr-xNb alloys (x = 0.4, 0.5, 1.0 wt.%) has been investigated using scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDS). Zr-xNb alloys are mainly composed of Zr matrix, native Zr-Nb-Fe phases, and β-Nb precipitates. After 2 MeV proton irradiation at 350 °C, a decrease of Nb content in native precipitates, as well as irradiation-induced precipitation of Nb-rich platelets (135 ± 69 nm long and 27 ± 12 nm wide) were found. Nb-rich platelets and Zr matrix form the Burgers orientation relationship, [11¯1]//[21¯1¯0] and (011)//(0002). The platelets were found to be mostly coherent with the matrix with a few dislocations near the ends of the precipitate. The coherent strain field has been measured in the matrix and platelets by the 4D-STEM technique. The growth of Nb-rich platelets is mainly driven by coherency and dislocation-induced strain fields. Irradiation may both enhance the diffusion and induce segregation of interstitial Nb to the ends of the irradiation induced platelets, further facilitating their growth.Graphical abstractImage 1
  • Kinetics of detwinning arising from annealing in chemical vapor deposited
    • Abstract: Publication date: Available online 13 August 2019Source: Acta MaterialiaAuthor(s): Hao Sun, Shaohua Fu, Chichi Chen, Zhirui Wang, Chandra Veer Singh Nickel carbonyl chemical vapor deposition (CVD) is a high-efficiency process used to produce nickel shell molds with high yield strength, reasonable ductility, and strong corrosion resistance. Such advantageous properties arise from the nanocrystals and nanotwins inside CVD nickel. However, the nanotwins do not persist at high temperatures, transforming into dislocation cells after 40-min annealing at 800°C. Using experimental examinations and computational simulations, we investigated the kinetics of detwinning in CVD nickel. TEM examinations showed that detwinning is realized by incoherent twin boundary (ITB) migration; meanwhile, plentiful dislocations are generated from CTBs. Our theoretical analysis revealed that these dislocations are necessary for the formation of the ITBs. Using molecular dynamics simulations, we found that the dislocations nucleated from CTBs during annealing are intrinsic grain boundary dislocations (IGBDs). Driven by the internal stress intensified by grain growth in the nanocrystalline regime, the IGBDs can separate from CTBs due to creep at 800°C, resulting in a higher dislocation density inside the twin lamella than the outside. These dislocations inside the twin lamella can trigger the formation of ITBs. Overall, unlike grain growth, stress is necessary for detwinning, so a monolithic nanotwin structure should be more stable than the nanotwins inside a nanocrystalline matrix within CVD nickel.Graphical abstractImage 1
  • High-fidelity 2D microstructure reconstruction via non-local patch-based
           image inpainting
    • Abstract: Publication date: Available online 12 August 2019Source: Acta MaterialiaAuthor(s): Anh Tran, Hoang Tran Microstructure reconstruction problems are usually limited to the representation with finitely many number of phases, e.g. binary and ternary. However, images of microstructure obtained through experimental, for example, using microscope, are often represented as a RGB or grayscale image. Because the phase-based representation is discrete, more rigid, and provides less flexibility in modeling the microstructure, as compared to RGB or grayscale image, there is a loss of information in the conversion. In this paper, a microstructure reconstruction method, which produces images at the fidelity of experimental microscopy, i.e. RGB or grayscale image, is proposed without introducing any physics-based microstructure descriptor. Furthermore, the image texture is preserved and the microstructure image is represented with continuous variables (as in RGB or grayscale images), instead of binary or categorical variables, which results in a high-fidelity image of microstructure reconstruction. The advantage of the proposed method is its quality of reconstruction, which can be applied to any other binary or multiphase 2D microstructure. The proposed method can be thought of as a subsampling approach to expand the microstructure dataset, while preserving its image texture. Moreover, the size of the reconstructed image is more flexible, compared to other machine learning microstructure reconstruction method, where the size must be fixed beforehand. In addition, the proposed method is capable of joining the microstructure images taken at different locations to reconstruct a larger microstructure image. A significant advantage of the proposed method is to remedy the data scarcity problem in materials science, where experimental data is scare and hard to obtain. The proposed method can also be applied to generate statistically equivalent microstructures, which has a strong implication in microstructure-related uncertainty quantification applications. The proposed microstructure reconstruction method is demonstrated with the UltraHigh Carbon Steel micrograph DataBase (UHCSDB).Graphical abstractImage 1
  • Distribution of boron and phosphorus and roles of co-doping in colloidal
           silicon nanocrystals
    • Abstract: Publication date: Available online 10 August 2019Source: Acta MaterialiaAuthor(s): Keita Nomoto, Hiroshi Sugimoto, Xiang-Yuan Cui, Anna V. Ceguerra, Minoru Fujii, Simon P. Ringer Boron (B) and phosphorous (P) co-doped colloidal silicon nanocrystals (Si NCs) have unique size-dependent optical properties, which lead to potential applications in optoelectronic and biomedical applications. However, the microstructure of the B and P co-doped colloidal Si NCs – in particular, the exact location of the dopant atoms in real space, has not been studied. A lack of understanding of this underlying question limits our ability to better control sample fabrication, as well as our ability to further develop the optical properties. To study the microstructure, a process enabling atom probe tomography (APT) of colloidal Si NCs was developed. A dispersion of colloidal Si NCs in a SiO2 sol-gel solution and a low temperature curing are demonstrated as the key sample preparation steps. Our APT results demonstrate that a B-rich region exists at the surface of the Si NCs, while P atoms are distributed within the Si NCs. First principles density functional theory calculations of a Si NC embedded in SiO2 matrix reveal that P atoms, which always prefer to reside inside a Si NC, significantly influence the distribution of B atoms. Specifically, P atoms lower the B diffusion barrier at Si/SiO2 interface and stabilize B atoms to reside within individual Si NCs. We propose that the B-modified surface changes the chemical properties of the Si NCs by (i) offering chemical resistance to attack by HF and (ii) enabling dispersibility in solution without aggregation.Graphical abstractImage 1
  • Effect of Temperature on the Transition in Deformation Modes in Mg Single
    • Abstract: Publication date: Available online 10 August 2019Source: Acta MaterialiaAuthor(s): Gi-Dong Sim, Kelvin Y. Xie, Kevin J. Hemker, Jaafar A. El-Awady Here, an experimental study utilizing in-situ scanning electron microscopy (SEM) micro-compression testing and post-mortem transmission electron microscopy (TEM) imaging is presented to quantify the effect of temperature on the transition in deformation modes in twin-oriented Mg single crystals. Single crystal micropillars were fabricated using FIB milling, then tested by in-situ SEM micro-compression from 20⁰C to 225⁰C. It is observed that plasticity in the deformed Mg microcrystals at temperatures at and below 100oC is governed by {101¯2} extension twinning. However, an anomalous increase of the flow stresses is observed at 100oC, which is likely due to paucity of dislocation sources that are required to promote twin boundary migration. At 150oC and above, extension twinning is suppressed and a continuous plastic flow and strain softening induced by prismatic dislocation mediated plasticity is observed. By comparing the current results with those from bulk scale studies for other hexagonal-closed-pack single crystals (e.g. titanium (Ti) and zirconium (Zr)), a general trend for the effect of temperature on the transition in deformation modes in HCP materials is proposed.Graphical abstractImage 1
  • Effective cluster interactions and pre–precipitate morphology in
           binary Al-based alloys
    • Abstract: Publication date: Available online 10 August 2019Source: Acta MaterialiaAuthor(s): O.I. Gorbatov, A.Yu. Stroev, Yu.N. Gornostyrev, P.A. Korzhavyi The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of ab initio calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.Graphical abstractImage 1
  • Assessment of ductile character in superhard Ta-C-N thin films
    • Abstract: Publication date: Available online 10 August 2019Source: Acta MaterialiaAuthor(s): T. Glechner, R. Hahn, T. Wojcik, D. Holec, S. Kolozsvári, H. Zaid, S. Kodambaka, P.H. Mayrhofer, H. Riedl Using a combination of density functional theory calculations and nanomechanical testing of sputter-deposited, 110-oriented Ta0.47C0.34N0.19 thin films, we show that non-metal alloying – substituting C with N atoms – in TaC results in a super-hard material with enhanced ductility. Based on the calculated elastic constants, with Pugh and Pettifor criteria for ductile character, we predict that stoichiometric and sub-stoichiometric Ta-C-N alloys are more ductile than Ta-C compounds. From nanoindentation of the as-deposited coating, we measure hardness of 43 ± 1.4 GPa. In situ scanning electron microscopy (SEM) based micro-compression of cylindrical pillars, prepared via focused ion beam milling of the coating, revealed that Ta-C-N alloys are ductile and undergo plastic deformation with a yield strength of 17 ± 1.4 GPa. The post-compression SEM images of the pillars show {111} as the active slip system operating during compression. Additional in situ SEM based cantilever tests suggest that the Ta-C-N films exhibit superior fracture toughness compared to Ta-C coatings. Our results provide a new perspective on the role of alloying on the mechanical behavior of ultra-high temperature compounds such as transition-metal carbides.Graphical abstractImage 1
  • Pseudo-topotactic growth of diamond nanofibers
    • Abstract: Publication date: Available online 8 August 2019Source: Acta MaterialiaAuthor(s): J. Narayan, A. Bhaumik, A. Haque We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure nanodiamonds along the growth directions. Subsequent laser pluses melt regions below nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of nanodiamond fibers can be increased, as each pulse results in ∼50nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C-C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp3 bonding (σ∗), and absence of 284 eV peak for sp2 (π∗) graphitic bonding. The characteristic diamond Raman peak at 1332 cm-1 is found to downshift to 1321cm-1 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.Graphical abstractImage 1
  • X-ray characterization of the micromechanical response ahead of a
           propagating small fatigue crack in a Ni-based superalloy
    • Abstract: Publication date: Available online 8 August 2019Source: Acta MaterialiaAuthor(s): Diwakar P. Naragani, Paul A. Shade, Peter Kenesei, Hemant Sharma, Michael D. Sangid The small fatigue crack (SFC) growth regime in polycrystalline alloys is complex due to the heterogeneity in the local micromechanical fields, which result in high variability in crack propagation directions and growth rates. In this study, we employ a suite of techniques, based on high-energy synchrotron-based X-ray experiments that allow us to track a nucleated crack, propagating through the bulk of a Ni-based superalloy specimen during cyclic loading. Absorption contrast tomography is used to resolve the intricate 3D crack morphology and spatial position of the crack front. Initial near-field high-energy X-ray diffraction microscopy (HEDM) is used for high-resolution characterization of the grain structure, elucidating grain orientations, shapes, and boundaries. Cyclic loading is periodically interrupted to conduct far-field HEDM to determine the centroid position, average orientation, and average lattice strain tensor for each grain within the volume of interest. Reciprocal space analysis is used to further examine the deformation state of grains that plasticize in the vicinity of the crack. Analysis of the local micromechanical state in the grains ahead of the crack front is used to rationalize the advancing small crack path and growth rate. Specifically, the most active slip system in a grain, determined by the maximum resolved shear stress, aligns with the crack growth direction; and the degree of microplasticity ahead of the crack tip helps to identify directions for potential occurrences of crack arrest or propagation. The findings suggest that both the slip system level stresses and microplasticity events within grains are necessary to get a complete description of the SFC progression. Further, this detailed dataset, produced by a suite of X-ray characterization techniques, can provide the necessary validation, at the appropriate length-scale, for SFC models.Graphical abstractImage 1
  • Cup-cone structure in spallation of bulk metallic glasses
    • Abstract: Publication date: Available online 8 August 2019Source: Acta MaterialiaAuthor(s): X.C. Tang, C. Li, H.Y. Li, X.H. Xiao, L. Lu, X.H. Yao, S.N. Luo A special spallation morphology in bulk metallic glass, named as the “cup-cone” structure, is of particular interest since it manifests a unique “ductile–brittle” transition. To gain insights into the underlying mechanism for the formation of a cup-cone structure, we conduct planar impact experiments at various impact velocities, as well as finite element method analysis. Spall strength increases with increasing impact velocity. Scanning electron microscopy and X-ray computed tomography are performed on postmortem samples to characterize cup-cone structures; their average size and spacing decrease as impact velocity increases, and they dominate fracture morphology at high impact velocities. Cups and cones are generally distributed on the side away from and on the side closer to the target free surface, respectively. The initial nucleation sites of voids become the conical vertices of cup-cones, and the subsequent nucleation sites form along the conical surface and coalesce into the cracks and fracture surfaces.Graphical abstractImage 1
  • Insight into silicon-carbon multilayer films as anode materials for
    • Abstract: Publication date: Available online 8 August 2019Source: Acta MaterialiaAuthor(s): Zhen Zhang, Ningbo Liao, Hongming Zhou, Wei Xue The combination of silicon and carbon layers exhibits superior lithium capacity and rate performance; however, the corresponding lithiation mechanism on the atomic-scale is not clear. In this work, the impact of the carbon layer on the electrochemical performance of silicon-carbon film systems as the lithium anode is investigated by a combination of experiments and first principles calculations. Experimental results show that the sample with the thickest carbon layer presents the smallest first cycle discharge capacities (2814mAhg-1); however, this sample also results in the largest capacity retentions after 100 cycles (69%) and the rate capability test (48.4%). Based on first principles calculations, the average length of the Li-Si bond near the silicon-carbon interface is significantly shorter than that in silicon, indicating an irreversible capacity loss. The structure with the largest carbon layer thickness corresponds to enhanced reversible capacity, electronic conductivity and lithium diffusion coefficient, which is consistent with experimental results. Our calculations provide a deeper understanding of irreversible capacity loss and how the primary nanostructure contributes to superior rate performance for silicon-carbon film anode materials.Graphical abstractImage 1
  • Phase transformation mechanisms during Quenching and Partitioning of a
           ductile cast iron
    • Abstract: Publication date: Available online 7 August 2019Source: Acta MaterialiaAuthor(s): Arthur S. Nishikawa, Goro Miyamoto, Tadashi Furuhara, André P. Tschiptschin, Hélio Goldenstein The modification of the matrix of ductile cast irons by heat treatments has been of interest of researchers for many years. Among these treatments, in the last years the Quenching & Partitioning (Q&P) process has emerged as a viable way to produce microstructures containing controlled amounts of martensite and retained austenite, providing a good combination of strength and ductility. In this work, the different mechanisms of phase transformations occurring during the Q&P heat treatment applied to a ductile cast iron alloy is investigated. Microsegregation, inherent to cast irons, was analyzed by means of Electron Probe Microanalysis (EPMA). Microstructural characterization was performed with Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD), while kinetics of carbon redistribution and competitive reactions were studied using dilatometry and in situ synchrotron X-ray diffraction. It was found that either transition carbides or cementite precipitate in martensite depending on the partitioning temperature. Despite of carbides precipitation, evidence of carbon partitioning from martensite to austenite was obtained. Formation of bainitic ferrite occurs during the partitioning step, further contributing to carbon enrichment of austenite. The experimental results are compared with a local field model that computes the local kinetics of carbon redistribution by simultaneously considering carbides precipitation and growth of bainitic ferrite. Results showed that kinetics of carbon partitioning from martensite to austenite depends on the carbides free energy. More stable carbides do not dissolve and prevent the escape of carbon from martensite. Fast carbon partitioning occurs by dissolution of less stable carbides, but it is slowed down as growth of bainitic ferrite proceeds. This result is explained by the overlapping of the diffusion fields (soft impingement) of the carbon partitioned from martensite and the carbon rejected from growth of bainitic ferrite.Graphical abstractImage 1
  • The effect of Zr substitution on saturation magnetization in
           (Sm1-xZrx)(Fe0.8Co0.2)12 compound with the ThMn12 structure
    • Abstract: Publication date: Available online 6 August 2019Source: Acta MaterialiaAuthor(s): P. Tozman, Y.K. Takahashi, H. Sepehri-Amin, D. Ogawa, S. Hirosawa, K. Hono Zr is one of the essential elements to stabilize the ThMn12 structure in rare earth (R) transition metal (M) hard magnetic compounds, RM12. In this work, the effects of Zr on the intrinsic hard magnetic properties of (Sm1-x Zrx)(Fe0.8Co0.2)12 compounds are investigated using epitaxially grown thin films. The increase of Zr substitution for Sm from x = 0 to 0.26 for (Sm1-x Zrx)(Fe0.8Co0.2)12 increases saturation magnetization (μ0Ms) from 1.78 T to 1.90 T, the highest value reported for hard magnetic compounds. The largest μ0Ha and Tc for Zr-doped samples were found to be 9.8 T and 671 K for x = 0.18 which is superior to those for Nd2Fe14B. Sm-rich Sm1.30Zr0.27(Fe0.8Co0.2)12, obtained as sub-μm thick films, has remanence, μ0Mr of 1 T, which appears to be useful for near-field applications such as micro-electro-machines and magnetic recording media if microstructure can be optimized to obtain a sufficient coercivity.Graphical abstractImage 1
  • Temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B
           sintered magnet based on first-order reversal curve analysis
    • Abstract: Publication date: Available online 6 August 2019Source: Acta MaterialiaAuthor(s): Satoshi Okamoto, Kazunori Miyazawa, Takahiro Yomogita, Nobuaki Kikuchi, Osamu Kitakami, Kentaro Toyoki, David Billington, Yoshinori Kotani, Tetsuya Nakamura, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Yukio Takada, Takashi Sato, Yuji Kaneko, Akira Kato A Ga-doped Nd-Fe-B sintered magnet has attracted significant attention as a heavy-rare-earth-free high-performance magnet. We have studied the temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on the first-order reversal curve (FORC) analysis. The FORC diagram pattern of the Ga-doped Nd-Fe-B sintered magnet changes from single spot in the high field region at room temperature to double spots in the low and high field regions at 200 °C, indicating that the dominant magnetization reversal process changes from single domain type to multidomain type. The single domain magnetization reversal at room temperature is well confirmed by using the soft X-ray magnetic circular dichroism microscopy observation. This change in the magnetization reversal process is well discussed by the temperature dependent local demagnetization field and the saturation field of multidomain state. Moreover, we have demonstrated the quantitative analysis of the FORC diagram pattern, which makes a deeper understanding of the magnetization reversal process of the Ga-doped Nd-Fe-B sintered magnet.Graphical abstractImage 1
  • A new phenomenological approach for modeling strain hardening behavior of
           face centered cubic materials
    • Abstract: Publication date: Available online 5 August 2019Source: Acta MaterialiaAuthor(s): Sumeet Mishra, Manasij Yadava, Kaustubh N. Kulkarni, N.P. Gurao A new methodology for analyzing strain hardening behavior of face centered cubic materials based on transition from restricted glide/single slip to multiple slip has been developed. The proposed modification considers strain dependence of orientation factor spanning between lower bound iso-stress Sachs model and upper bound iso-strain Taylor model. The modifications are suitably incorporated in the classical two internal variable model to develop a new slip activity based strain hardening model. The proposed model is shown to be performing better than the existing one parameter forest strengthening model and two internal variable model in predicting strain hardening behavior in the presence of wide range of microstructural features such as solutes, semi-coherent and incoherent precipitates, grain sizeand twins. Experimental validation of the proposed concept of transition in slip behavior is shown in terms of evolution of dislocation density and character from X-ray diffraction and surface roughness, slip lines and micro-texture from in-situ electron back scatter diffraction tests.Graphical abstractImage 1
  • Monoclinic angle, shear response, and minimum energy pathways of NiTiCu
           martensite phases from ab initio calculations
    • Abstract: Publication date: Available online 5 August 2019Source: Acta MaterialiaAuthor(s): Sam Bakhtiari, Jefferson Zhe Liu, Yinong Liu, Hong Yang Ti50Ni50-xCux alloys are observed to exhibit multiple martensitic transformations from B2 to an orthorhombic B19 and a monoclinic B19′ phase. In addition, DFT calculations have predicted a B19ʺ phase with a higher monoclinic angle as the thermodynamically stable ground state. This study investigated the effects of Cu content and shear stress on the monoclinic angles, phase stabilities of the various martensites, the minimum energy pathways, and the relative total energies among the phases in this pseudo-equiatomic Ti(Ni50-xCux) system. A new monoclinic phase (B19M) with a monoclinic angle lower than that of B19′ was found at above a critical Cu content. This confirms the formation of an intermediate phase in the martensitic transformation sequence of the pseudo-equiatomic Ti(Ni50-xCux) system but contradicts the crystal structure of the experimentally observed phase. It was found that the monoclinic angles of both B19M and B19ʺ decrease with increasing the magnitude of an opposing shear stress to their monoclinic distortion. At above certain critical values of the opposing shear stress, the B19M and B19ʺ phases destabilise and transform to lower monoclinic angle phases. In addition, the evidence suggests that the experimentally observed monoclinic B19′ phase is in fact a distorted B19ʺ with a reduced monoclinic angle under an opposing shear stress. With the same argument, the experimentally reported B19 phase is a metastable phase formed under the effect of an opposing shear stress to the monoclinic distortion of B19M.Graphical abstractImage 1
  • A new scenario for ‹c› vacancy loop formation in zirconium based on
           atomic-scale modeling
    • Abstract: Publication date: Available online 3 August 2019Source: Acta MaterialiaAuthor(s): B. Christiaen, C. Domain, L. Thuinet, A. Ambard, A. Legris The growth of zirconium alloys under irradiation is a phenomenon experimentally identified and associated with the development beyond a threshold dose of dislocation loops with vacancy character having a Burgers vector with a component parallel to the c axis. In this work, by combining atomic simulations (DFT and empirical potential) and continuous modeling, we show that prismatic stacking fault pyramids or bipyramids whose base rests on the basal plane of the hcp structure are likely precursors to the formation of c vacancy loops. In other words, these would not be formed by progressive accretion of vacancies but rather by collapse of the pyramids or bipyramids beyond a certain size. This mechanism could explain the fact that the ‹c› vacancy loops are never observed below a size of the order of 10 nm and their appearance at high fluence.Graphical abstractImage 1
  • Creep failure of honeycombs made by rapid prototyping
    • Abstract: Publication date: Available online 3 August 2019Source: Acta MaterialiaAuthor(s): P.E. Seiler, H.C. Tankasala, N.A. Fleck Additive manufacture and rapid prototyping are versatile methods for the generation of lattice materials for applications in the creep regime. However, these techniques introduce defects that can degrade the macroscopic creep strength. In the present study, the uniaxial tensile response of two-dimensional PMMA lattices is measured in the visco-plastic regime: tests are performed at 100 °C which is slightly below the glass transition temperature Tg of PMMA. Both as-manufactured defects (Plateau borders and strut thickness variation) and as-designed defects (missing cell walls, solid inclusions, and randomly perturbed joints) are introduced. The dispersion in macroscopic strength is measured for relative densities in the range of 0.07 to 0.19. It is observed that initial failure of the lattice is diffuse in nature: struts fail at a number of uncorrelated locations, followed by the development of a single macroscopic crack transverse to the loading direction. In contrast, the same PMMA lattice fails in a correlated, brittle manner at room temperature. An FE study is performed to gain insight into the diffuse failure mode and the role played by as-manufactured defects, including the dispersion in tensile strength of individual struts of the lattice. A high damage tolerance to as-designed defects is observed experimentally: there is negligible knock-down in strength due to the removal of cell walls or to the presence of solid inclusions. These findings aid the design and manufacture of damage tolerant lattices in the creep regime.Graphical abstractElastic-brittle versus visco-plastic failure ofPMMA lattices.Image 1
  • Direct observation of the displacement field and microcracking in a glass
           by means of X-ray tomography during in situ Vickers indentation experiment
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Tanguy Lacondemine, Julien Réthoré, Éric Maire, Fabrice Célarié, Patrick Houizot, Clément Roux-Langlois, Christian M. Schlepütz, Tanguy Rouxel The actual displacement field in a glass during an in-situ Vickers indentation experiment was determined by means of X-ray tomography, thanks to the addition of 4 vol. % of X-ray absorbing particles, which acted as a speckle to further proceed through digital volume correlation. This displacement was found to agree well with the occurrence of densification beneath the contact area. The intensity of the densification contribution (Blister field proposed by Yoffe) was characterized and provides evidence for the significant contribution of densification to the mechanical fields. Densification accounts for 27 % of the volume of the imprint for the studied glass, that is expected to be less sensitive to densification than amorphous silica or window glass. A major consequence is that indentation cracking methods for the evaluation of the fracture toughness, when they are based on volume conservation, as in the case of Hill-Eshelby plastic inclusion theory, are not suitable to glass. The onset for the formation of the subsurface lateral crack was also detected. The corresponding stress is ≈ 14 GPa and is in agreement with the intrinsic glass strength.Graphical abstractImage 1
  • The interaction between vacancies and twin walls, junctions, and kinks,
           and their mechanical properties in ferroelastic materials
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Xiaomei He, Suzhi Li, Xiangdong Ding, Jun Sun, Sverre M. Selbach, Ekhard K.H. Salje Vacancies strongly interact with twin boundaries and often change dramatically the properties of a ferroelastic material. However, the understanding of this behavior at an atomic-level is still deficient. Here we study vacancy diffusion processes across very large length- and time-scales using a combination of molecular dynamics and Monte Carlo simulations. We find that vacancies reduce their energy by residing at twin boundaries, kinks inside domain boundaries, and junctions between domain boundaries. Vacancies have the largest binding energy inside junctions and co-migrate with the motion of the junctions. For the weaker trapping inside twin boundaries, a “ghost line” may be generated because vacancies do not necessarily diffuse with moving boundaries and are left behind, leaving a trace of a previous position of the domain boundary. Needle twins act as channels for fast diffusion with almost one order of magnitude higher vacancy diffusivity than in bulk. The relative concentration of vacancies at twin boundaries (ρVa) is a function of the average vacancy concentration (CVa) with ρVa ∼ CVaα and α = 0.61, in contrast to that of immobile vacancies case with α = 0.4. The concentration of vacancies at twin boundaries is enriched ca. 5 times at low temperatures. With increasing temperature, the enrichment drops as the trapping potential at the twin boundaries decreases (thermal release). The distribution of energy-drop upon twin pattern evolution follows a power law. The exponent ε increases from ∼1.44 to 2.0 when the vacancy concentration increases. The power law exponent is the same in the athermal region, while Vogel-Fulcher behavior is found at high temperatures.Graphical abstractImage 1
  • Macro-to nanoscopic in situ investigation on yielding mechanisms in
           ultrafine grained medium Mn steels: role of the austenite-ferrite
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Binhan Sun, Yan Ma, Nicolas Vanderesse, Rama Srinivas Varanasi, Wenwen Song, Philippe Bocher, Dirk Ponge, Dierk Raabe Ultrafine austenite-ferrite duplex medium Mn steels often show a discontinuous yielding phenomenon, which is not commonly observed in other composite-like multiphase materials. The underlying dislocation-based mechanisms are not understood. Here we show that medium Mn steels with an austenite matrix (austenite fraction ∼65 vol.%) can exhibit pronounced discontinuous yielding. A combination of multiple in situ characterization techniques from macroscopic (a few millimeters) down to nanoscopic scale (below 100 nm) is utilized to investigate this phenomenon. We observe that both austenite and ferrite are plastically deformed before the macroscopic yield point. In this microplastic regime, plastic deformation starts in the austenite phase before ferrite yields. The austenite-ferrite interfaces act as preferable nucleation sites for new partial dislocations in austenite and for full dislocations in ferrite. The large total interface area, caused by the submicron grain size, can provide a high density of dislocation sources and lead to a rapid increase of mobile dislocations, which is believed to be the major reason accounting for discontinuous yielding in such steels. We simultaneously study the Lüders banding behavior and the local deformation-induced martensite forming inside the Lüders bands. We find that grain size and the austenite stability against deformation-driven martensite formation are two important microstructural factors controlling the Lüders band characteristics in terms of the number of band nucleation sites and their propagation velocity. These factors thus govern the early yielding stages of medium Mn steels, due to their crucial influence on mobile dislocation generations and local work hardening.Graphical abstractImage 1
  • Application of Gaussian Process regression models for capturing the
           evolution of microstructure statistics in aging of Nickel-based
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Yuksel C. Yabansu, Almambet Iskakov, Anna Kapustina, Sudhir Rajagopalan, Surya R. Kalidindi Nickel-based superalloys, used extensively in advanced gas turbine engines, exhibit complex microstructures that evolve during exposure to high temperatures (i.e., aging treatments). In this work, we examine critically if the principal component (PC) representation of rotationally invariant 2-point spatial correlations can adequately capture the salient features of the microstructure evolution in the thermal aging of the superalloys. For this purpose, an experimental study involving microstructure characterization of 27 differently aged (i.e., different combinations of temperature and time of exposure) samples was designed and conducted. Of these, 23 samples were employed for training a Gaussian Process Regression (GPR) model that took the aging temperature and the aging time as inputs, and predicted the microstructure statistics as output. The viability of the approach described above was evaluated critically by comparing the predictions for the four samples that were not used in the training of the GPR model. Furthermore, a new strategy was developed and implemented to generate digital microstructures corresponding to the predicted microstructure statistics. The predicted microstructures were found to be in good agreement with the experimentally measured one, validating the novel framework presented in this work.Graphical abstractImage 1
  • On the interaction of precipitates and tensile twins in magnesium alloys
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): C. Liu, P. Shanthraj, J.D. Robson, M. Diehl, S. Dong, J. Dong, W. Ding, D. Raabe Although magnesium alloys deform extensively through shear strains and crystallographic re-orientations associated with the growth of twins, little is known about the strengthening mechanisms associated with this deformation mode. A crystal plasticity based phase field model for twinning is employed in this work to study the strengthening mechanisms resulting from the interaction between twin growth and precipitates. The full-field simulations reveal in great detail the pinning and de-pinning of a twin boundary at individual precipitates, resulting in a maximum resistance to twin growth when the precipitate is partially embedded in the twin. Furthermore, statistically representative precipitate distributions are used to systematically investigate the influence of key microstructural parameters such as precipitate orientation, volume fraction, size, and aspect ratio on the resistance to twin growth. The results indicate that the effective critical resolved shear stress (CRSS) for twin growth increases linearly with precipitate volume fraction and aspect ratio. For a constant volume fraction of precipitates, reduction of the precipitate size below a critical level produces a strong increase in the CRSS due to the Orowan-like strengthening mechanism between the twin interface and precipitates. Above this level the CRSS is size independent. The results are quantitatively and qualitatively comparable with experimental measurements and predictions of mean-field strengthening models. Based on the results, guidelines for the design of high strength magnesium alloys are discussed.Graphical abstractImage 1
  • Effects of Water on the Mechanical Properties of Silica Glass using
           Molecular Dynamics
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Hai Mei, Yongjian Yang, Adri C.T. van Duin, Susan B. Sinnott, John C. Mauro, Lisheng Liu, Zhengyi Fu Understanding the effects of water on the mechanical properties of silica glass is important for many applications of silicate glasses. In this study, the effects of water on both elastic and plastic properties of pure silica glass are investigated. The introduction of molecular water leads to an increase of Young’s modulus of silica glass at low water content, while hydroxyl exhibits an opposite effect. While hydroxyl groups decrease both strength and fracture toughness of the glass via destructing the silica network connectivity, molecular water undermines these properties by effectively driving the silica network to a “strained” configuration in absence of external stress. The water effect can be characterized in terms of the change of Si-O bond length and Si-O-Si bond angle. The plateau in the stress-strain curves of silica with the existence of molecular water in compact tension is associated with the Si-O bond breaking followed by formation of silanol groups. Moreover, the introduction of molecular water lowers the critical tensile stress where the plateau occurs.Graphical abstractImage 1
  • Segregation-driven grain boundary spinodal decomposition as a pathway for
           phase nucleation in a high-entropy alloy
    • Abstract: Publication date: Available online 30 July 2019Source: Acta MaterialiaAuthor(s): Linlin Li, Zhiming Li, Alisson Kwiatkowski da Silva, Zirong Peng, Huan Zhao, Baptiste Gault, Dierk Raabe Elemental segregation to grain boundaries (GBs) can induce structural and chemical transitions at GBs along with significant changes in material properties. The presence of multiple principal elements interacting in high-entropy alloys (HEAs) makes the GB segregation and interfacial phase transformation a rather challenging subject to investigate. Here, we explored the temporal evolution of the chemistry for general high-angle GBs in a typical equiatomic FeMnNiCoCr HEA during aging heat treatment through detailed atom probe tomography (APT) analysis. We found that the five principal elements segregate heterogeneously at the GBs. More specifically, Ni and Mn co-segregate to some regions of the GBs along with the depletion of Fe, Co and Cr, while Cr is enriched in other regions of the GBs where Ni and Mn are depleted. The redistribution of these elements on the GBs follow a periodic characteristic, spinodal-like compositional modulation. The accumulation of elements at the GBs can create local compositions by shifting their state from a solid solution (like in the adjacent bulk region) into a spinodal regime to promote interfacial phase-like transitions as segregation proceeds. These results not only shed light on phase precursor states and the associated nucleation mechanism at GBs in alloy systems with multiple principal elements but also help to guide the microstructure design of advanced HEAs in which formation of embrittling phases at interfaces must be avoided.Graphical abstractImage 1
  • Direct TEM observation of α/γ interface migration during cyclic partial
           phase transformations at intercritical temperatures in an Fe-0.1C -0.5Mn
    • Abstract: Publication date: Available online 28 July 2019Source: Acta MaterialiaAuthor(s): J. Nutter, H. Farahani, W.M. Rainforth, S. van der Zwaag The kinetic behaviour of austenite/ferrite interfaces in a low carbon – 0.5 mass% Mn containing steel during Cyclic Partial Phase Transformation (CPPT) experiments has been investigated using hot stage Transmission Electron Microscopy (TEM). Individual interfaces were observed to display behaviour typical of CPPT experiments as recorded in macroscopic dilatometry experiments and demonstrated i) the “normal”, ii) inverse transformations and iii) a stagnant stage in which the interface migrates at a very low velocity as a result of the interface passing through a Mn enriched zone due to the preceding transformation. The length of the stagnant stage determined from the TEM observations shows excellent agreement with that measured from dilatometry and kinetic modelling, whilst the distance migrated from the interface shows some disparities which are primarily attributed to differences in assumptions about grain geometry and nucleation. No special interface features were observed when the interface changed direction and passed through the previously Mn-enriched zones. General observations on the interaction of the transformation interface with microstructural features are also reported.Graphical abstractImage 1
  • Characterization of Local Morphology and Availability of Triple-Phase
           Boundaries in Solid Oxide Cell Electrodes
    • Abstract: Publication date: Available online 27 July 2019Source: Acta MaterialiaAuthor(s): G. Rinaldi, A. Nakajo, P. Burdet, M. Cantoni, W.K.S. Chiu, J. Van herle The performance of solid oxide cells is known to be dependent upon the density of three phase boundaries (TPB), but the potential for improving their effective electrocatalytic activity by morphological adjustments is imprecisely known. A spilling algorithm was developed to characterize the surfaces available for diffusion at TPBs. It scans each slice in 3-D imaging dataset to measure the interfaces between the solid and the pore phases at each TPB. Because of the stereological approach, these surfaces are defined as “available lengths” (LA). The measurement was tested on artificial packed spheres structures with controlled properties and a percolation theory-based model before application to a real Ni-YSZ. The LA distributions cover 2 orders of magnitude. The subset shorter than the extent of diffusion profiles reported in the literature is in the range of 3% and 20% for Ni and YSZ, respectively, suggesting possible limitations of their effective electrocatalytic properties. The average LA is larger on YSZ than on Ni, which is a trend opposite to the phase diameter. The available length analysis revealed microstructural characteristics that stem from the manufacturing route and cannot be identified by the inspection of standard metric and topological properties. A strong correlation between the available length and the extension of TPB lines is observed for Ni but for YSZ, despite the predominance of convex shapes, which likely originates from the Ni reduction. This suggests possibilities for controlling the available length by the manufacturing route, depending specifically to the electrocatalytic properties of the phases in composite materials.Graphical abstractImage 1
  • Mechanical Response of a Bicontinuous Copper-Molybdenum Nano-composite:
           Experiments and Simulations
    • Abstract: Publication date: Available online 27 July 2019Source: Acta MaterialiaAuthor(s): Nathan Beets, Yuchi Cui, Diana Farkas, Amit Misra We present the results of a combined experimental and simulation-based study of the mechanical response of a bicontinuous copper-molybdenum nanocomposite, where high strength and good plastic deformability were observed. The experimental sample, prepared by co-sputtering Cu and Mo, achieved a feature size of around 15 nm. Corresponding digital nanostructures with feature sizes between 9 to 15 nm were generated using a phase field model. Virtual compression testing was performed using molecular dynamics simulation. The resultant mechanical response of these samples was analyzed at the macroscopic and atomistic levels. Strain partitioning was observed, where most of the plastic deformation occurs through dislocations that are emitted from the interface into the FCC Cu phase. The interface also acts as a barrier to dislocation propagation. The nanocomposites exhibit high strain hardening rate and plastic co-deformation in Cu and Mo intertwined phases. No shear banding is observed after 30% compression in both experiment and simulation. The bicontinuous, intertwined morphology of metallic FCC/BCC nanocomposites is effective in producing high yield strengths, high strain hardening rate and uniform distribution of plasticity in the sample volume.Graphical abstractImage 1
  • Alloys-By-Design: Application to titanium alloys for optimal
    • Abstract: Publication date: Available online 24 July 2019Source: Acta MaterialiaAuthor(s): E. Alabort, D. Barba, M.R. Shagiev, M.A. Murzinova, R.M. Galeyev, O.R. Valiakhmetov, A.F. Aletdinov, R.C. Reed An alloy design approach for titanium alloys is presented. New alloys are isolated, manufactured and tested with an emphasis on the superplastic response. The superplastic effect is found to be optimal between 650 to 750∘C at strain rates between 8.3×10 and 8.3×10/s – this is a substantial improvement in terms of temperature and deformation rates over traditional titanium alloys such as Ti-6Al-4V. Elongations approaching ∼2000% are demonstrated. Electron backscatter diffraction studies confirm a randomisation of texture and absence of significant intragranular dislocation density, confirming superplasticity and thus grain-boundary sliding as the overarching deformation mechanism. At strain rates faster than 0.01/s, the alloys exhibit large elongations (∼200-500%) but softening is evident and lower ductility results. Our results reveal that the physical factors controlling the alloy composition/property/manufacturing interrelationship are understood and quantified. Physically-based constitutive equations are presented and used to demonstrate the practical advantages of the designed alloys.Graphical abstractImage 1
  • Density, Distribution and Nature of Planar Faults in Silver Antimony
           Telluride for Thermoelectric Applications
    • Abstract: Publication date: Available online 23 July 2019Source: Acta MaterialiaAuthor(s): Lamya Abdellaoui, Siyuan Zhang, Stefan Zaefferer, Ruben Bueno-Villoro, Andrei Baranovskiy, Oana Cojocaru-Mirédin, Yuan Yu, Yaron Amouyal, Dierk Raabe, Gerald Jeffrey Snyder, Christina Scheu Defects such as planar faults in thermoelectric materials improve their performance by scattering phonons with short and medium mean free paths (3∼100 nm), thereby reducing the lattice thermal conductivity,κl. Understanding statistically the microscopic distribution of these extended defects within the grains and in low angle grain boundaries is necessary to tailor and develop materials with optimal thermoelectric performance for waste heat harvesting. Herein, we analyze these defects from the millimeter down to the nanometer scale in AgSbTe2 thermoelectric material with low angle grain boundaries. The investigations were performed using electron channeling contrast imaging combined with transmission electron microscopy. The microstructure study was complemented by estimating the effect of planar faults on the phonon scattering using the Debye Callaway model. AgSbTe2 is a promising thermoelectric material, which exhibits extremely low thermal conductivity, κ, of 0.5 Wm-1K-1 at room temperature. In contrast to conventional alloys or intermetallic materials, in the present material small angle grain boundaries are not composed of individual dislocations but of a dense arrangement of stacked planar faults with fault densities up to NPF=1.6⋅108m−1. We explain their abundance based on their low interfacial energy of about 186 mJm-2 calculated by ab-initio calculations. The current findings show, that it is possible to reach very high densities of phonon-scattering planar faults by the correct microstructure engineering in AgSbTe2 thermoelectric materials.Graphical abstractImage 1
  • Thermodynamic Assessment of the Solar-to-fuel Performance of
           La0.6Sr0.4Mn1-yCryO3-δ Perovskite Solid Solution Series
    • Abstract: Publication date: Available online 18 July 2019Source: Acta MaterialiaAuthor(s): Alexander H. Bork, Erwin Povoden-Karadeniz, Alfonso J. Carrillo, Jennifer L.M. Rupp In the search of new materials for the solar-to-fuel technology, we turn to the material class of perovskites that offer wide possibilities in manipulation of its chemistry and redox activity. Here, we access the role of Cr in the La0.6Sr0.4Mn1-yCryO3-δ perovskite solid solution hitherto unexplored for two-step solar thermochemical fuel production. A multi-component Calphad defect model for the system La-Sr-Cr-Mn-O is therefore optimized and used for computations of oxygen nonstoichiometries and redox thermodynamics of the La0.6Sr0.4Mn1-yCryO3-δ solution series in the temperature range of 1073 to 1873 K as a potential operation window for solar-to-fuel conversion. Modeling results reveal two advantages of substituting manganese by chromium. Firstly, it is possible to reduce the heat capacity with up to 10 %, to a value of 132 J mol-1 K-1. Secondly, the thermodynamic driving force for solar-to-fuel conversion increases and the Cr-doped materials provide higher yield and efficiency at isothermal operation. The proposed model allows for continuous simulative scanning of redox thermodynamics from zero Cr-doping to a fully substituted chromite perovskite. For isothermal water splitting, the composition La0.6Sr0.4Mn0.2Cr0.8O3-δ displays the highest fuel yield and efficiency of 2.7 % due to a high thermodynamic driving force at elevated temperature for this composition. These predictive insights give prospects for engineering the thermodynamics of the oxygen release reaction in perovskites towards higher fuel production and efficiency in solar-to-fuel reactors with isothermal operation.Graphical abstractImage 1
  • High-temperature X-ray absorption spectroscopy study of thermochromic
           copper molybdate
    • Abstract: Publication date: Available online 21 June 2019Source: Acta MaterialiaAuthor(s): Inga Jonane, Andris Anspoks, Giuliana Aquilanti, Alexei Kuzmin X-ray absorption spectroscopy at the Cu and Mo K-edges was used to study the effect of heating on the local atomic structure and dynamics in copper molybdate (α-CuMoO4) in the temperature range from 296 to 973 K. The reverse Monte-Carlo (RMC) method was successfully employed to perform accurate simulations of EXAFS spectra at both absorption edges simultaneously. The method allowed us to determine structural models of α-CuMoO4 being consistent with the experimental EXAFS data. These models were further used to follow temperature dependencies of the local environment of copper and molybdenum atoms and to obtain the mean-square relative displacements for Cu–O and Mo–O atom pairs. Moreover, the same models were able to interpret strong temperature-dependence of the Cu K-edge XANES spectra. We found that the local environment of copper atoms is more affected by thermal disorder than that of molybdenum atoms. While the MoO4 tetrahedra behave mostly as the rigid units, a reduction of correlation in atomic motion between copper and axial oxygen atoms occurs upon heating. This dynamic effect seems to be the main responsible for the temperature-induced changes in the O2−→Cu2+ charge transfer processes and, thus, is the origin of the thermochromic properties of α-CuMoO4 upon heating above room temperature.Graphical abstractImage 1
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Heriot-Watt University
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