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Publisher: Elsevier   (Total: 3031 journals)

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Showing 1 - 200 of 3031 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 20, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 16, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 79, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 22, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 27, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 302, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription  
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 195, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 9, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 21, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 5, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.383, h-index: 19)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 4)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 119, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 24, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 21, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 26, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 24, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 8, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 4)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 39, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 38, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 41, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 14)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 18, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 22)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 33, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 7, SJR: 0.764, h-index: 15)
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: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 5, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 21)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 6, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 20, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 14)
Advances in Pharmacology     Full-text available via subscription   (Followers: 13, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 17, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 56)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 1, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 332, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 7)
Advances in Surgery     Full-text available via subscription   (Followers: 6, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 28, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 14)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 12)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 42, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 303, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 4, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 7, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 389, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 29, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 36, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 48, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 3, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 5)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 7, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 5, SJR: 0.776, h-index: 35)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 6, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 45, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 45, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 47, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 34, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 25, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 31, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 48, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 173, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 51, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 2)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 22, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 23, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 32, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 13, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 52, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 3)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 152, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 7, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 10)
Anesthésie & Réanimation     Full-text available via subscription  
Anesthesiology Clinics     Full-text available via subscription   (Followers: 21, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 141, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

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Journal Cover Acta Materialia
  [SJR: 3.683]   [H-I: 202]   [195 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-6454
   Published by Elsevier Homepage  [3031 journals]
  • Revisiting the twinning mechanism in directional solidification of
           multi-crystalline silicon sheet
    • Authors: H.K. Lin; C.W. Lan
      Pages: 1 - 10
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): H.K. Lin, C.W. Lan
      The formation of the twin nucleus is an important phenomenon during the solidification of multi-crystalline silicon. However, the available model by Duffar and Nadri [Scripta Mater. 62(12) (2010) 955] was unable to predict a critical undercooling for twinning that was comparable with the experiments. Through the detailed analysis of the grain structures in the multi-crystalline silicon sheets grown by directional solidification, we find that the grain boundary plays a crucial role. By taking this into account, we revise the previous model. The free energy change (per unit length) when one or two facets anchor to the groove tri-junction and the critical undercooling for twinning are derived and compared with experiments. The predicted undercooling and the probability of forming a twinned nucleus at the groove based on the revised model are consistent with the experimental observations.
      Graphical abstract image

      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.077
      Issue No: Vol. 131 (2017)
       
  • Highly crystalline p-PbS thin films with tunable optical and hole
           transport parameters by chemical bath deposition
    • Authors: Rekha Bai; Dinesh Kumar; Sujeet Chaudhary; Dinesh K. Pandya
      Pages: 11 - 21
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): Rekha Bai, Dinesh Kumar, Sujeet Chaudhary, Dinesh K. Pandya
      Lead sulfide (PbS) thin films, consisting of well faceted (up to 400 nm) cubic-nanocrystals and possessing significantly improved opto-electronic parameters essential for photovoltaic applications, are grown by utilizing chemical bath deposition (CBD) technique with bath concentrations of 10–200 mM. X-ray diffraction (XRD) and Raman studies confirm the highly crystalline and pure phase of PbS. FESEM and HRTEM studies show that all the films possess uniform and compact (111) oriented nanocubic morphology. Bath concentration change provides tunability of nanocube size from 100 to 400 nm and the direct optical band gap from 1.50 to 0.94 eV. The PbS films exhibit p-type semiconducting behavior with hitherto unreported concurrent highest mobility of 29.3 cm2V−1s−1 and high carrier concentration of ∼1018 cm−3 with the lowest room temperature resistivity of 0.26 Ω–cm. The 25 mM and 10 mM films show significant surface plasmon absorption in 1200–2400 nm range making them suitable as efficient infrared absorbers in excitonic and multi-junction solar cells.
      Graphical abstract image

      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.062
      Issue No: Vol. 131 (2017)
       
  • Rapid solidification growth mode transitions in Al-Si alloys by dynamic
           transmission electron microscopy
    • Authors: John D. Roehling; Daniel R. Coughlin; John W. Gibbs; J. Kevin Baldwin; James C.E. Mertens; Geoffrey H. Campbell; Amy J. Clarke; Joseph T. McKeown
      Pages: 22 - 30
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): John D. Roehling, Daniel R. Coughlin, John W. Gibbs, J. Kevin Baldwin, James C.E. Mertens, Geoffrey H. Campbell, Amy J. Clarke, Joseph T. McKeown
      In situ dynamic transmission electron microscope (DTEM) imaging of Al-Si thin-film alloys was performed to investigate rapid solidification behavior. Solidification of alloys with compositions from 1 to 15 atomic percent Si was imaged during pulsed laser melting and subsequent solidification. Solely α-Al solidification was observed in Al-1Si and Al-3Si alloys, and solely kinetically modified eutectic growth was observed in Al-6Si and Al-9Si alloys. A transition in the solidification mode in eutectic and hypereutectic alloys (Al-12Si and Al-15Si) from nucleated α-Al dendrites at lower solidification velocities to planar eutectic growth at higher solidification velocities was observed, departing from trends previously seen in laser-track melting experiments. Comparisons of the growth modes and corresponding velocities are compared with previous solidification models, and implications regarding the models are discussed.
      Graphical abstract image

      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.061
      Issue No: Vol. 131 (2017)
       
  • The effect of the microstructure on the antiferromagnetic to ferromagnetic
           transition in FeRh alloys
    • Authors: A. Chirkova; F. Bittner; K. Nenkov; N.V. Baranov; L. Schultz; K. Nielsch; T.G. Woodcock
      Pages: 31 - 38
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): A. Chirkova, F. Bittner, K. Nenkov, N.V. Baranov, L. Schultz, K. Nielsch, T.G. Woodcock
      A detailed study of Fe48Rh52 samples heat treated at different temperatures (1123 K, 1273 K and 1423 K) has been performed using scanning and transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction and magnetic measurements. The microstructure of all samples consisted of α′ (B2) and γ (A1) phases. Although the chemical composition, chemical ordering and the lattice parameter of the magnetic α′ phase in all three samples did not vary with heat treatment temperature, the temperature of the metamagnetic transition between the antiferromagnetic (AFM) and ferromagnetic (FM) states varied by 50 K. No gradients in chemical composition on a length scale larger than approximately 10 nm exist at the α′/γ phase boundaries. Due to the 1% volume expansion of the α′ phase, which occurs during the AFM-FM transition, stress fields around the α′/γ phase boundaries are expected. The composition, lattice parameter, size, shape and distribution of the γ phase was shown to change with heat treatment temperature. Finite element models indicated that these microstructural parameters influence the magnitude and extent of the stress fields at the phase boundaries. The variation in the transition temperature is therefore ascribed to the differences in the stress fields.
      Graphical abstract image

      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.04.005
      Issue No: Vol. 131 (2017)
       
  • Stress-assisted grain growth in nanocrystalline metals: Grain boundary
           mediated mechanisms and stabilization through alloying
    • Authors: Yang Zhang; Garritt J. Tucker; Jason R. Trelewicz
      Pages: 39 - 47
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): Yang Zhang, Garritt J. Tucker, Jason R. Trelewicz
      The mechanisms of stress-assisted grain growth are explored using molecular dynamics simulations of nanoindentation in nanocrystalline Ni and Ni-1 at.% P as a function of grain size and deformation temperature. Grain coalescence is primarily confined to the high stress region beneath the simulated indentation zone in nanocrystalline Ni with a grain size of 3 nm. Grain orientation and atomic displacement vector mapping demonstrates that coalescence transpires through grain rotation and grain boundary migration, which are manifested in the grain interior and grain boundary components of the average microrotation. A doubling of the grain size to 6 nm and addition of 1 at.% P eliminates stress-assisted grain growth in Ni. In the absence of grain coalescence, deformation is accommodated by grain boundary-mediated dislocation plasticity and thermally activated in pure nanocrystalline Ni. By adding solute to the grain boundaries, the temperature-dependent deformation behavior observed in both the lattice and grain boundaries inverts, indicating that the individual processes of dislocation and grain boundary plasticity will exhibit different activity based on boundary chemistry and deformation temperature.
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      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.060
      Issue No: Vol. 131 (2017)
       
  • Thickness-dependent a1/a2 domain evolution in ferroelectric PbTiO3 films
    • Authors: S. Li; Y.L. Zhu; Y.L. Tang; Y. Liu; S.R. Zhang; Y.J. Wang; X.L. Ma
      Pages: 123 - 130
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): S. Li, Y.L. Zhu, Y.L. Tang, Y. Liu, S.R. Zhang, Y.J. Wang, X.L. Ma
      Ferroelectric a 1 /a 2 domain structure has great potentials in high dielectric capacitors and tunable microwave devices. Understanding its structure is crucial to better control the domain configurations for future applications. In this paper, PbTiO3 thin films with variant thicknesses are deposited on (110)-oriented GdScO3 substrates by Pulsed Laser Deposition (PLD) and investigated by using conventional transmission electron microscopy (TEM) and Cs-corrected Scanning TEM. Contrast analysis and electron diffractions reveal that PbTiO3 films are domain oriented consisting of a 1 /a 2 and a/c domain structure. The a 1 /a 2 domains are found to distribute periodically and its width increases with increasing film thickness following square root rule. Cs-corrected STEM imaging demonstrates that the domain walls of a 1 /a 2 domain structure have the rotation characteristic of 90° ferroelastic domain wall. The interchange of a 1 /a 2 domains induces the formation of vertex domains composed of two 90° and one 180° domain walls. Strains are mainly concentrated on the domain walls. The formation of this complex domain configuration is discussed in terms of the effect of the misfit strain, film thickness and cooling rate. These results provide novel information about a 1 /a 2 domain structures and are expected to shed some light on modulating a 1 /a 2 ferroelectric domain patterns in the design of ferroelectric-based devices.
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      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.064
      Issue No: Vol. 131 (2017)
       
  • Amorphous phase stability and the interplay between electronic structure
           and topology
    • Authors: Reza Mahjoub; Kevin J. Laws; Michael Ferry
      Pages: 131 - 140
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): Reza Mahjoub, Kevin J. Laws, Michael Ferry
      It is well-known that the stability of Pd-Si amorphous alloys can be improved substantially by minor additions of alloying elements such as Cu and Ag. Such improvement in stability is explained herein, whereby microscopic models based on efficient atomic packing and electronic structure were applied to the results of first principles simulations of Pd82Si18, Pd77.5Si16.5Cu8 and Pd75Si15Cu7Ag3 metallic glasses. It was revealed that while the atomic packing model fails to unequivocally explain the stabilizing effect of the binary Pd-Si alloy due to minor additions of Cu and/or Ag, the contribution of electronic states with lower energies to the stability of the amorphous structure is increased markedly. Further, the observed enhancement in the compressive ductility as a result of the addition of Ag to the Pd77.5Si16.5Cu8 alloy can be correlated to the combined effects of an increased heterogeneity in the local topology, weakened covalency and, hence, reduced directionality of Pd-Pd bonds as well as enhanced metallicity in the Pd75Si15Cu7Ag3 amorphous alloy. The analysis was further expanded to amorphous alloys where their characteristic binary prototypes are synthesised from late transition metals and non-metals as well as those comprising early transition metals and late transition metals. The findings shed light on the effects of minor alloying on the cooperative and competitive relationship between the topological and electronic structure of amorphous alloys.
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      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.070
      Issue No: Vol. 131 (2017)
       
  • Spherical nanoindentation, modeling and transmission electron microscopy
           evidence for ripplocations in Ti3SiC2
    • Authors: Justin Griggs; Andrew C. Lang; J. Gruber; G.J. Tucker; M.L. Taheri; M.W. Barsoum
      Pages: 141 - 155
      Abstract: Publication date: 1 June 2017
      Source:Acta Materialia, Volume 131
      Author(s): Justin Griggs, Andrew C. Lang, J. Gruber, G.J. Tucker, M.L. Taheri, M.W. Barsoum
      Herein we present experimental and modeling evidence for a new deformation micromechanism operating in layered solids termed a ripplocation. Select Ti3SiC2 grains were cyclically indented – either parallel or normal to the basal planes - with spherical tips with radii, R of 21 μm and 100 μm. When the load vs. displacement curves were converted to indentation stress vs. a/R curves, where a is the contact radius, fully and spontaneously reversible hysteresis loops were recorded. The energy dissipated per unit volume per cycle, Wd, was found to be a function of basal plane orientation; Wd was smaller when the basal planes were loaded edge on. Transmission electron microscope images of areas under the indentations revealed the existence of defects that previous work confirmed have a strain component along the c-axis and for which no g·b condition was found that resulted in their disappearance. These defects thus cannot be basal dislocations; their characteristics, however, are consistent with bulk ripplocations, BRs. It is the to-and-from movement of these BRs – and not basal dislocations as previously assumed - that is believed to be responsible for the fully and spontaneously reversible loops in Ti3SiC2 and possibly in most other layered solids. Consistent with the need of the basal planes to expand upon the introduction of BRs, the initial friction stress needed to move them was found to be almost three times lower when the basal planes were loaded edge-on. Molecular dynamics simulations on graphite at 10 K faithfully reproduce many features observed below the indenter in this, and previous, work on Ti3SiC2. The existence of BRs will require a revisiting and reassessment of our understanding of how layered solids - from geologic formations to 2D solids – deform.
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      PubDate: 2017-04-11T06:12:28Z
      DOI: 10.1016/j.actamat.2017.03.055
      Issue No: Vol. 131 (2017)
       
  • In-situ study of morphology and growth of primary α-Al(FeMnCr)Si
           intermetallics in an Al-Si alloy
    • Authors: Anton Bjurenstedt; Daniele Casari; Salem Seifeddine; Ragnvald H. Mathiesen; Arne K. Dahle
      Pages: 1 - 9
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Anton Bjurenstedt, Daniele Casari, Salem Seifeddine, Ragnvald H. Mathiesen, Arne K. Dahle
      Morphology and growth of primary α-Al(FeMnCr)Si intermetallics have been studied in-situ during solidification of a commercial secondary aluminum alloy employing X-radiographic imaging combined with deep-etching. The α-Al(FeMnCr)Si intermetallics were found to nucleate primarily on surface oxides, and the continued growth yielded both rhombic dodecahedrons and elongated rod-like morphologies. Both morphologies were observed as hopper and massive types, where the hopper intermetallics had the higher growth rates. The growth rate, which determines the type, appears to be linked to nucleation frequency; higher nucleation frequency promoted massive types and lower nucleation frequency promoted hopper intermetallics.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.026
      Issue No: Vol. 130 (2017)
       
  • Tailoring magnetic behavior of CoFeMnNiX (X = Al, Cr, Ga, and Sn) high
           entropy alloys by metal doping
    • Authors: Tingting Zuo; Michael C. Gao; Lizhi Ouyang; Xiao Yang; Yongqiang Cheng; Rui Feng; Shuying Chen; Peter K. Liaw; Jeffrey A. Hawk; Yong Zhang
      Pages: 10 - 18
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Tingting Zuo, Michael C. Gao, Lizhi Ouyang, Xiao Yang, Yongqiang Cheng, Rui Feng, Shuying Chen, Peter K. Liaw, Jeffrey A. Hawk, Yong Zhang
      Magnetic materials with excellent performances are desired for functional applications. Based on the high-entropy effect, a system of CoFeMnNiX (X = Al, Cr, Ga, and Sn) magnetic alloys are designed and investigated. The dramatic change in phase structures from face-centered-cubic (FCC) to ordered body-centered-cubic (BCC) phases, caused by adding Al, Ga, and Sn in CoFeMnNiX alloys, originates from the potent short-range chemical order in the liquid state predicted by ab initio molecular dynamics (AIMD) simulations. This phase transition leads to the significant enhancement of the saturation magnetization (Ms), e.g., the CoFeMnNiAl alloy has Ms of 147.86 Am2/kg. First-principles density functional theory (DFT) calculations on the electronic and magnetic structures reveal that the anti-ferromagnetism of Mn atoms in CoFeMnNi is suppressed especially in the CoFeMnNiAl HEA because Al changes the Fermi level and itinerant electron-spin coupling that lead to ferromagnetism.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.013
      Issue No: Vol. 130 (2017)
       
  • Ternary silicide formation from Ni-Pt, Ni-Pd and Pt-Pd alloys on Si(100):
           Nucleation and solid solubility of the monosilicides
    • Authors: A. Schrauwen; J. Demeulemeester; D. Deduytsche; W. Devulder; C. Detavernier; C.M. Comrie; K. Temst; A. Vantomme
      Pages: 19 - 27
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): A. Schrauwen, J. Demeulemeester, D. Deduytsche, W. Devulder, C. Detavernier, C.M. Comrie, K. Temst, A. Vantomme
      The solid solubility of the isomorphous monosilicides during the silicide reaction of Ni-Pt, Ni-Pd and Pt-Pd alloys on Si(100) is comparatively studied in the full composition range. Our study reveals that PtSi and PdSi, exhibiting a minor lattice mismatch, directly form a solid solution. In contrast, for larger differences in lattice parameters such as is the case for NiSi-PtSi and NiSi-PdSi, the mutually soluble phases coexist, prior to the formation of a solid solution at increased temperatures. Hence, it appears that the direct formation of a ternary monosilicide solid solution is inherently related to the lattice mismatch of the binary monosilicides. This finding provides an explanation for important differences observed in the elemental redistribution between the three systems, considered to be very similar up to now. Moreover, the different formation of a solid solution results in a fundamentally different nucleation of PdSi: while Ni lowers the nucleation barrier by reducing the contribution of the interface energy, Pt strongly increases the entropy of mixing which triggers the formation of the Pd-monosilicide at surprisingly low temperatures. Our results show that the lattice mismatch is a crucial parameter and determines the phase formation sequence and elemental redistribution during the silicide reaction.

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.022
      Issue No: Vol. 130 (2017)
       
  • G phase precipitation and strengthening in ultra-high strength ferritic
           steels: Towards lean ‘maraging’ metallurgy
    • Authors: W.W. Sun; R.K.W. Marceau; M.J. Styles; D. Barbier; C.R. Hutchinson
      Pages: 28 - 46
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): W.W. Sun, R.K.W. Marceau, M.J. Styles, D. Barbier, C.R. Hutchinson
      Ultra-high strength steels are interesting materials for light-weighting applications in the transportation industries. A key requirement of these applications is weldability and consequently a low carbon content is desirable. Maraging steels are examples of ultra-high strength, low carbon steels but their disadvantage is their high cost due to the large Ni and/or Co additions required. This contribution is focussed on the development of steels with maraging-like strengths but with low solute contents (less than 10%). A series of alloy compositions were designed to exploit precipitation of the G phase in a ferritic matrix at temperatures of 450–600 °C in order to obtain yield strengths in excess of 2 GPa. The mechanical response of the materials was measured using tension and compression testing and the precipitate evolution has been characterized using atom probe tomography (APT) and in-situ small angle X-ray scattering (SAXS) at a synchrotron beamline. Precipitate number densities of 1025 m−3 are obtained, which are amongst the highest number densities so far observed in engineering alloys. The intrinsic strength of the G phase is shown to be proportional to its size, and deviations in the chemistry of the precipitates do not significantly affect their strengthening behaviour. An important outcome is that the common temper embrittlement issues known to occur during aging of martensite in the 450–600 °C range were mitigated in one alloy by starting with a cold-rolled and partially fragmented lath martensite instead of a freshly quenched martensite.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.032
      Issue No: Vol. 130 (2017)
       
  • Realization of highly conductive Ga-doped ZnO film with abnormally wide
           band-gap using magnetron sputtering by simply lowering working pressure
    • Authors: Hoang Ba Cuong; Che-Sin Lee; Sang-Hun Jeong; Byung-Teak Lee
      Pages: 47 - 55
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Hoang Ba Cuong, Che-Sin Lee, Sang-Hun Jeong, Byung-Teak Lee
      Sputter growth of highly conductive Ga-doped ZnO films with abnormally wide band-gap (Eg) is discussed in detail, as well as the accompanying defect behavior. It was observed that the optical Eg and the conductivity increased as the working pressure of the Ar plasma decreases. The ZnGaO films with Eg of 3.95 eV and resistivity of 2 × 10−4 Ω cm was obtained by simply lowering the working pressure to 0.3 Pa, which represent the highest Eg value so far reported for the ZnO-based transparent conducting materials with a resistivity lower than 10−3 Ω cm. It was proposed that this phenomenon may be attributed to the improved crystalline quality and the increased amount of the Ga incorporation into the Zn sites and the oxygen vacancy concentration. It was also suggested that the oxygen vacancy acts as the electron donor for the sputtered ZnO and ZnGaO films.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.033
      Issue No: Vol. 130 (2017)
       
  • A multi-scale correlative investigation of ductile fracture
    • Authors: M. Daly; T.L. Burnett; E.J. Pickering; O.C.G. Tuck; F. Léonard; R. Kelley; P.J. Withers; A.H. Sherry
      Pages: 56 - 68
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): M. Daly, T.L. Burnett, E.J. Pickering, O.C.G. Tuck, F. Léonard, R. Kelley, P.J. Withers, A.H. Sherry
      The use of novel multi-scale correlative methods, which involve the coordinated characterisation of matter across a range of length scales, are becoming of increasing value to materials scientists. Here, we describe for the first time how a multi-scale correlative approach can be used to investigate the nature of ductile fracture in metals. Specimens of a nuclear pressure vessel steel, SA508 Grade 3, are examined following ductile fracture using medium and high-resolution 3D X-ray computed tomography (CT) analyses, and a site-specific analysis using a dual beam plasma focused ion beam scanning electron microscope (PFIB-SEM). The methods are employed sequentially to characterise damage by void nucleation and growth in one volume of interest, allowing for the imaging of voids that ranged in size from less than 100 nm to over 100 μm. This enables the examination of voids initiated at carbide particles to be detected, as well as the large voids initiated at inclusions. We demonstrate that this multi-scale correlative approach is a powerful tool, which not only enhances our understanding of ductile failure through detailed characterisation of microstructure, but also provides quantitative information about the size, volume fractions and spatial distributions of voids that can be used to inform models of failure. It is found that the vast majority of large voids nucleated at MnS inclusions, and that the volume of a void varied according to the volume of its initiating inclusion raised to the power 3/2. The most severe voiding was concentrated within 500 μm of the fracture surface, but measurable damage was found to extend to a depth of at least 3 mm. Microvoids associated with carbides (carbide-initiated voids) were found to be concentrated around larger inclusion-initiated voids at depths of at least 400 μm. Methods for quantifying X-ray CT void data are discussed, and a procedure for using this data to calibrate parameters in the Gurson-Tvergaard Needleman (GTN) model for ductile failure is also introduced.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.028
      Issue No: Vol. 130 (2017)
       
  • The effect of matrix chemistry on dislocation evolution in an irradiated
           Zr alloy
    • Authors: A. Harte; D. Jädernäs; M. Topping; P. Frankel; C.P. Race; J. Romero; L. Hallstadius; E.C. Darby; M. Preuss
      Pages: 69 - 82
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): A. Harte, D. Jädernäs, M. Topping, P. Frankel, C.P. Race, J. Romero, L. Hallstadius, E.C. Darby, M. Preuss
      Advancements in transmission electron microscopy allow us to draw correlations between evolving matrix chemistry environments and the resulting dislocation structures that form. Such phenomena are essential in predicting the lifetime of neutron reactor components, but are not well understood at the fundamental level. We investigate the effect of nano-scale matrix chemical evolution in Zircaloy-2 on dislocation formation after emulating commercial reactor irradiation conditions on a proton beamline. Similarity in the dislocation type, morphology, density and evolution between the different irradiation types establishes proton irradiation in this regard. For the first time, we observe chemical segregation of Fe, Ni and Cr to a-loop positions in basal traces and the segregation of Sn in alternate rows, anticorrelated to the positions of the light transition elements. The resulting layered structure with a periodicity of ∼50 nm creates an even greater anisotropy than that usually associated with HCP materials. Concurrent analysis of chemical effects and dislocation spatial relationships provides evidence that may explain the delayed onset of c-loop nucleation and accelerated dimensional instability regimes in its dependence on the alignment of a-loops parallel to the trace of the basal plane. This demonstrates the applicability of chemical-structural correlations towards key research questions regarding deformation behaviour.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.024
      Issue No: Vol. 130 (2017)
       
  • Single-source-precursor derived RGO/CNTs-SiCN ceramic nanocomposite with
           ultra-high electromagnetic shielding effectiveness
    • Authors: Xingmin Liu; Zhaoju Yu; Ryo Ishikawa; Lingqi Chen; Xiaofei Liu; Xiaowei Yin; Yuichi Ikuhara; Ralf Riedel
      Pages: 83 - 93
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Xingmin Liu, Zhaoju Yu, Ryo Ishikawa, Lingqi Chen, Xiaofei Liu, Xiaowei Yin, Yuichi Ikuhara, Ralf Riedel
      For the first time, single-source-precursors (SSPs) were synthesized through chemical modification of a commercial poly(methylvinyl)silazane with chemically bonded graphene oxide and carbon nanotube hybrids (GO/CNTs). After pyrolysis of warm-pressed and consolidated SSP-powders at 1000 °C in Ar, monolithic SiCN ceramic nanocomposites modified with in-situ thermally reduced GO/CNTs, namely RGO/CNTs-SiCN, were successfully obtained. The SSP-derived nanocomposite exhibits significantly enhanced dielectric properties if compared with that of a physically-blended-precursor derived reference material. Moreover, the SSP-derived RGO/CNTs-SiCN composite containing 15.0 wt% GO/CNTs in the feed possesses an electromagnetic shielding effectiveness of 67.2 dB with a sample thickness of 2.00 mm, which is the highest value among all the reported graphene-based composites with comparable thickness.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.031
      Issue No: Vol. 130 (2017)
       
  • Integrated modeling of second phase precipitation in cold-worked 316
           stainless steels under irradiation
    • Authors: Mahmood Mamivand; Ying Yang; Jeremy Busby; Dane Morgan
      Pages: 94 - 110
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Mahmood Mamivand, Ying Yang, Jeremy Busby, Dane Morgan
      The current work combines the Cluster Dynamics (CD) technique and CALPHAD-based precipitation modeling to address the second phase precipitation in cold-worked (CW) 316 stainless steels (SS) under irradiation at 300–400 °C. CD provides the radiation enhanced diffusion and dislocation evolution as inputs for the precipitation model. The CALPHAD-based precipitation model treats the nucleation, growth and coarsening of precipitation processes based on classical nucleation theory and evolution equations, and simulates the composition, size and size distribution of precipitate phases. We benchmark the model against available experimental data at fast reactor conditions (9.4 × 10−7 dpa/s and 390 °C) and then use the model to predict the phase instability of CW 316 SS under light water reactor (LWR) extended life conditions (7 × 10−8 dpa/s and 275 °C). The model accurately predicts the γ′ (Ni3Si) precipitation evolution under fast reactor conditions and that the formation of this phase is dominated by radiation enhanced segregation. The model also predicts a carbide volume fraction that agrees well with available experimental data from a PWR reactor but is much higher than the volume fraction observed in fast reactors. We propose that radiation enhanced dissolution and/or carbon depletion at sinks that occurs at high flux could be the main sources of this inconsistency. The integrated model predicts ∼1.2% volume fraction for carbide and ∼3.0% volume fraction for γ′ for typical CW 316 SS (with 0.054 wt% carbon) under LWR extended life conditions. This work provides valuable insights into the magnitudes and mechanisms of precipitation in irradiated CW 316 SS for nuclear applications.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.025
      Issue No: Vol. 130 (2017)
       
  • Damage evolution of ion irradiated defected-fluorite La2Zr2O7 epitaxial
           thin films
    • Authors: Tiffany C. Kaspar; Jonathan G. Gigax; Lin Shao; Mark E. Bowden; Tamas Varga; Vaithiyalingam Shutthanandan; Steven R. Spurgeon; Pengfei Yan; Chongmin Wang; Pradeep Ramuhalli; Charles H. Henager
      Pages: 111 - 120
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Tiffany C. Kaspar, Jonathan G. Gigax, Lin Shao, Mark E. Bowden, Tamas Varga, Vaithiyalingam Shutthanandan, Steven R. Spurgeon, Pengfei Yan, Chongmin Wang, Pradeep Ramuhalli, Charles H. Henager
      Pyrochlore-structure oxides, A 2 B 2O7, may exhibit remarkable radiation tolerance due to the ease with which they can accommodate disorder by transitioning to a defected fluorite structure. The mechanism of defect formation was explored by evaluating the radiation damage behavior of high quality epitaxial La2Zr2O7 thin films with the defected fluorite structure, irradiated with 1 MeV Zr+ at doses up to 10 displacements per atom (dpa). The level of film damage was evaluated as a function of dose by Rutherford backscattering spectrometry in the channeling geometry (RBS/c) and scanning transmission electron microscopy (STEM). At lower doses, the surface of the La2Zr2O7 film amorphized, and the amorphous fraction as a function of dose fit well to a stimulated amorphization model. As the dose increased, the surface amorphization slowed, and amorphization appeared at the interface. Even at a dose of 10 dpa, the core of the film remained crystalline, despite the prediction of amorphization from the model. To inform future ab initio simulations of La2Zr2O7, the bandgap of a thick La2Zr2O7 film was measured to be indirect at 4.96 eV, with a direct transition at 5.60 eV.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.01.012
      Issue No: Vol. 130 (2017)
       
  • Ductilization of aluminium alloy 6056 by friction stir processing
    • Authors: F. Hannard; S. Castin; E. Maire; R. Mokso; T. Pardoen; A. Simar
      Pages: 121 - 136
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): F. Hannard, S. Castin, E. Maire, R. Mokso, T. Pardoen, A. Simar
      The ductility of Al alloys is dictated by the nucleation, growth and coalescence of small internal voids originating from intermetallic particle fracture and from the presence of pre-existing porosity. The ductility is degraded when intermetallic particles are large and clustered. A low ductility adversely impacts both forming operations and the integrity of structural components. Local stirring using a friction stir processing (FSP) tool is shown here to very significantly increase the fracture strain of the Al alloy 6056 sometimes by more than a factor of two while making it more isotropic. Three reasons for the ductilization are unravelled based on 3D microtomography: (i) FSP breaks the large intermetallic particles into smaller, and thus stronger, fragments, (ii) FSP closes the pre-existing porosity; (iii) FSP randomizes the particle distribution. Hence, FSP positively impacts three of the main causes of ductility loss in metallic alloys. From an applicability viewpoint, this method has the potential to locally improve ductility of sheets at locations where forming involves large strains or of structural components at stress concentration points.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.01.047
      Issue No: Vol. 130 (2017)
       
  • First-principles modeling of anisotropic anodic dissolution of metals and
           alloys in corrosive environments
    • Authors: Hui Ma; Xing-Qiu Chen; Ronghan Li; Shoulong Wang; Junhua Dong; Wei Ke
      Pages: 137 - 146
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Hui Ma, Xing-Qiu Chen, Ronghan Li, Shoulong Wang, Junhua Dong, Wei Ke
      There have been extensive experimental observations of the anisotropic corrosion behavior of metals and alloys, and their mechanisms were assumed to be correlated with the so-called surface energy or the work function. However, to date, a specified mechanism or theory to interpret anisotropic corrosion behavior remains unclear. Here, we determine the anisotropic anodic dissolution of metals and alloys in corrosive environments by developing a formula to specify the relationship between the electrode potential (U) and the current density (I) by considering the basic parameters of our defined surface energy density ( E s u r f / ρ ) and the work function ( Φ ). Therefore, we build an ab initio model to evaluate the anisotropic anodic dissolution behavior of metals and alloys using the inputs obtained within density functional theory. This theory is further validated in the case of variations in the crystallographic planes of Mg. Moreover, some selected alloying additions such as Ga, Cd, Hg, In, As, and Cr are theoretically elucidated to effectively reduce the anodic dissolution rates of the Mg matrix to some extent, in close agreement with available experimental observations. This model is capable of predicting the anisotropic anodic dissolution behavior, providing a promising perspective for designing better corrosion-resistant alloys.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.027
      Issue No: Vol. 130 (2017)
       
  • Topological changes in coarsening networks
    • Authors: Dana Zöllner; Paulo Rangel Rios
      Pages: 147 - 154
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Dana Zöllner, Paulo Rangel Rios
      Curvature driven grain growth proceeds by the motion of curved grain boundaries in polycrystals leading to a decrease in the total interfacial free energy. However, grain growth cannot occur without the so-called topological transitions. Indeed, it is a mathematical impossibility that a decrease in the number of grains per unit volume may take place without the topological transition that corresponds to the grain disappearance. Nonetheless, despite their importance, no previous work has studied the topological transitions in detail that take place during the transient as well as the self-similar state of coarsening. In the present work, the three classical topological changes are tracked during 2-d grain growth simulated by a Monte Carlo method. It is shown and discussed how topological transitions reach a self-similar state together with the grain size and the number of edges (faces) per grain distribution.
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      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.040
      Issue No: Vol. 130 (2017)
       
  • Atomic-scale investigation of carbon atom migration in surface induced
           white layers in high-carbon medium chromium (AISI 52100) bearing steel
    • Authors: S.B. Hosseini; M. Thuvander; U. Klement; G. Sundell; K. Ryttberg
      Pages: 155 - 163
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): S.B. Hosseini, M. Thuvander, U. Klement, G. Sundell, K. Ryttberg
      The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the Ac1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ-carbides (cementite). The APT results reveal that the original θ-carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains.
      Graphical abstract image

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.030
      Issue No: Vol. 130 (2017)
       
  • Determination of the five parameter grain boundary character distribution
           of nanocrystalline alpha-zirconium thin films using transmission electron
           microscopy
    • Authors: I. Ghamarian; P. Samimi; G.S. Rohrer; P.C. Collins
      Pages: 164 - 176
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): I. Ghamarian, P. Samimi, G.S. Rohrer, P.C. Collins
      Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physical vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTAR™/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium.
      Graphical abstract image

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.041
      Issue No: Vol. 130 (2017)
       
  • Correlation of splat state with deposition characteristics of cold sprayed
           niobium coatings
    • Authors: S. Kumar; M. Ramakrishna; N.M. Chavan; S.V. Joshi
      Pages: 177 - 195
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): S. Kumar, M. Ramakrishna, N.M. Chavan, S.V. Joshi
      The cold spray technique has a great potential to deposit refractory metals for a variety of potential applications. Cold spraying of different metals have been addressed comprehensively to understand the deposition characteristics of the coatings. Since there is no available data on the deposition characteristics of cold sprayed Niobium, impact behavior of splats at different deposition conditions were simulated and numerically analyzed using Finite Element Modeling (FEM) and correlated with the experimental observations that highlight the role of the velocity and temperature of the particle upon impact on the bonding features. The increase in temperature of the splat drastically reduces the flow stress at the interface leading to best inter-splat bonding state. The synergistic effect of the temperature and the velocity leads to the formation of very dense, defect free niobium coating associated with deformation localization including interface melting. Formation of nanocrystalline grains at the inter-splat boundary was confirmed through TEM and compared with the FEM findings. Finally, understanding the deformation and deposition behavior of refractory metal such as niobium will be helpful to engineer the coatings for potential applications.

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.023
      Issue No: Vol. 130 (2017)
       
  • Taming martensitic transformation via concentration modulation at
           nanoscale
    • Authors: Jiaming Zhu; Yipeng Gao; Dong Wang; Tong-Yi Zhang; Yunzhi Wang
      Pages: 196 - 207
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Jiaming Zhu, Yipeng Gao, Dong Wang, Tong-Yi Zhang, Yunzhi Wang
      Martensitic transformation (MT) is typically a strongly first-order transition with autocatalysis in nucleation followed by rapid growth. It usually takes place within a narrow temperature or stress range, making its utilization in a controllable manner difficult. We show by computer simulations how MTs can be tailored by concentration modulation at the nanoscale in the parent phase, which induces spatial variations of both the stability of martensite and the transformation strain and tunes the overall MT kinetics from a typical first-order transition into a high-order like continuous transition. Such a unique MT characteristic reduces or even eliminates the transformation hysteresis and produces quasi-linear elasticity with ultra-low apparent elastic modulus.
      Graphical abstract image

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.042
      Issue No: Vol. 130 (2017)
       
  • Large area flexible polymer solar cells with high efficiency enabled by
           imprinted Ag grid and modified buffer layer
    • Authors: Shudi Lu; Jie Lin; Kong Liu; Shizhong Yue; Kuankuan Ren; Furui Tan; Zhijie Wang; Peng Jin; Shengchun Qu; Zhanguo Wang
      Pages: 208 - 214
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Shudi Lu, Jie Lin, Kong Liu, Shizhong Yue, Kuankuan Ren, Furui Tan, Zhijie Wang, Peng Jin, Shengchun Qu, Zhanguo Wang
      To take a full advantage of polymer semiconductors on realization of large-area flexible photovoltaic devices, herein, we fabricate polymer solar cells on the basis of polyethylene terephthalate (PET) with imprinted Ag grid as transparent electrode. The key fabrication procedure is the adoption of a modified PEDOT:PSS (PH1000) solution for spin-coating the buffer layer to form a compact contact with the substrate. In comparison with the devices with intrinsic PEDOT:PSS buffer layer, the advanced devices present a much higher efficiency of 6.51%, even in a large device area of 2.25 cm2. Subsequent characterizations reveal that such devices show an impressive performance stability as the bending angle is enlarged to 180° and bending time is up to 1000 cycles. Not only providing a general methodology to construct high efficient and flexible polymer solar cells, this paper also involves deep insights on device working mechanism in bending conditions.
      Graphical abstract image

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.050
      Issue No: Vol. 130 (2017)
       
  • Coupled experimental and computational investigation of omega phase
           evolution in a high misfit titanium-vanadium alloy
    • Authors: D. Choudhuri; Y. Zheng; T. Alam; R. Shi; M. Hendrickson; S. Banerjee; Y. Wang; S.G. Srinivasan; H. Fraser; R. Banerjee
      Pages: 215 - 228
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): D. Choudhuri, Y. Zheng, T. Alam, R. Shi, M. Hendrickson, S. Banerjee, Y. Wang, S.G. Srinivasan, H. Fraser, R. Banerjee
      Morphological and compositional evolution of omega (ω) precipitates in a model Titanium-20 wt%Vanadium (or 19 at.%V) alloy has been systematically investigated by coupling transmission electron microscopy and atom probe tomography with atomistic ab initio and continuum microelasticity computations. The initial water quenched microstructure comprised of a fine scale distribution of athermal ω precipitates, which form congruently from the β phase via a complete displacive collapse of {222}β planes, that has been rationalized based on DFT computations. Subsequent annealing at 300 °C, over progressively increasing time periods, resulted in isothermal evolution of the ω precipitates, whose morphology changes from ellipsoidal to cuboidal, accompanied with V rejection. The highly V-enriched β matrix consisted of short VV bond lengths, further distorting the bcc lattice, and increasing the β/ω misfit. This facilitates the change in the morphology of omega precipitates from ellipsoidal to cuboidal resulting in a {001}β habit plane for these precipitates. The coupled experimental and computational approach permits rationalizing the evolution of ω precipitate morphology and composition in such high β−ω misfit β-Ti alloys.
      Graphical abstract image

      PubDate: 2017-03-27T13:19:03Z
      DOI: 10.1016/j.actamat.2017.03.047
      Issue No: Vol. 130 (2017)
       
  • Phase transitions as a tool for tailoring magnetostriction in intrinsic
           Fe-Ga composites
    • Authors: V.V. Palacheva; A. Emdadi; F. Emeis; I.A. Bobrikov; A.M. Balagurov; S.V. Divinski; G. Wilde; I.S. Golovin
      Pages: 229 - 239
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): V.V. Palacheva, A. Emdadi, F. Emeis, I.A. Bobrikov, A.M. Balagurov, S.V. Divinski, G. Wilde, I.S. Golovin
      Fe-Ga alloys exhibit unique functional properties such as magnetostriction that can be varied from the highest positive values among iron-based alloys to negative values including zero magnetostriction, if proper compositions and heat treatments are chosen. This remarkable behavior is related to rather complex phase transformation sequences in this alloy family that are still unresolved. In earlier studies, the phase transformations in Fe-Ga alloys were studied by X-ray diffraction, which provides structural information limited to the near-surface sample area. In this paper, we use electron back-scatter diffraction and in situ neutron diffraction to characterize the D03 and L12 phases that originate from the fcc and bcc phases in the Fe-27Ga type bulk alloy, respectively. Different ratios between these phases, characterized by magnetostriction values of different signs, were achieved using an isothermal annealing treatment that produces an intrinsic composite in the alloy. Depending on the relative fraction of the D03 and L12 phases, the magnetostriction values of the alloy, λS, vary from +100 to −50 ppm, including the value of λS = 0 for the alloy with L12:D03 = 2:1 achieved after 600 min annealing at 400 °C, thus demonstrating the controlled adjustment of magnetostriction in these advanced alloys.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.049
      Issue No: Vol. 130 (2017)
       
  • Zinc blende–wurtzite polytypism in nanocrystalline ZnO films
    • Authors: A. Brian Aebersold; Lorenzo Fanni; Aïcha Hessler-Wyser; Sylvain Nicolay; Christophe Ballif; Cécile Hébert; Duncan T.L. Alexander
      Pages: 240 - 248
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): A. Brian Aebersold, Lorenzo Fanni, Aïcha Hessler-Wyser, Sylvain Nicolay, Christophe Ballif, Cécile Hébert, Duncan T.L. Alexander
      ZnO is commonly observed and assumed to crystallize fully in a wurtzite structure. Indeed, while polytypism between a wurtzite and a zinc blende phase is often seen in some II-VI compounds, it has only rarely been observed in ZnO. Here, by means of automated crystal orientation mapping and high-resolution imaging in transmission electron microscopy, we identify nanometer-sized regions of zinc blende forming during the growth of compact nanocrystalline metal–organic chemical vapor deposited ZnO films. We analyze a c-fiber-textured wurtzite ZnO film, where the columnar grain growth, typical for polycrystalline films, is interrupted by the formation of these zinc blende regions. These regions in turn provide surfaces for the heteroepitaxial renucleation of newly oriented wurtzite grains. In contrast to the columnar grains, which grow fastest along their c-axis, these new grains are identified to grow fastest along their basal plane. By means of convergent beam electron diffraction, we show that this difference in fast growth direction relates to the polarity of exposed facets. A growth model is proposed, showing how this polytypism affects the microstructure evolution of the film in ways that were not predicted by existing film growth models.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.021
      Issue No: Vol. 130 (2017)
       
  • Giant dielectric permittivity and high tunability in Y-doped SrTiO3
           ceramics tailored by sintering atmosphere
    • Authors: Alexander Tkach; Olena Okhay; Abílio Almeida; Paula M. Vilarinho
      Pages: 249 - 260
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Alexander Tkach, Olena Okhay, Abílio Almeida, Paula M. Vilarinho
      Development of giant-permittivity and high-tunability dielectric materials has attracted great interest because of growing demand for smaller and faster energy-storage and electronic devices. Materials such as CaCu3Ti4O12, displaying the giant dielectric permittivity due to extrinsic Maxwell-Wagner interfacial polarization effect, have previously been reported. Ferroelectric materials possessing intrinsic ionic polarization due to a phase transition to the polar state have also been indicated to possess a high tunability of the dielectric permittivity by dc electric field. Here, a class of the giant-permittivity materials based on SrTiO3 ceramics doped with up to 1% of yttrium and their processing concept, which yields the dielectric permittivity up to ∼209,000 at 10 kHz for nitrogen sintering atmosphere, and the relative tunability up to ∼74% under 20 kV cm−1 for oxygen sintering atmosphere, is reported. The high tunability is proved to be due to polar clusters created at low temperatures by off-central Y3+ ions on Sr2+ sites. The giant permittivity is explained by a coupling of the polar clusters relaxation mode with the donor substitution induced electrons at low temperatures and by the Maxwell-Wagner relaxation around room temperature. Besides the fundamental understanding, this discovery opens a new development window for high-frequency and low-temperature electronic and energy-storage applications.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.051
      Issue No: Vol. 130 (2017)
       
  • Strong and ductile age-hardening Mg-Al-Ca-Mn alloy that can be extruded as
           fast as aluminum alloys
    • Authors: T. Nakata; C. Xu; R. Ajima; K. Shimizu; S. Hanaki; T.T. Sasaki; L. Ma; K. Hono; S. Kamado
      Pages: 261 - 270
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): T. Nakata, C. Xu, R. Ajima, K. Shimizu, S. Hanaki, T.T. Sasaki, L. Ma, K. Hono, S. Kamado
      We have developed a wrought magnesium alloy, Mg-1.3Al-0.3Ca-0.4Mn (wt.%) or AXM10304, that can be extruded at a very high die-exist speed of 24 m/min, comparable to the extrusion speed for aluminum alloys, and that exhibits an excellent combination of strength and elongation after an age-hardening, i.e., a tensile 0.2% proof stress of 287 MPa and an elongation of 20%. The high tensile proof stress is attributed to the dispersion of a high number density of monolayer Guinier Preston (G.P.) zones dispersed in grains with an average grain size of 17 μm and <10 1 ¯ 0> fiber texture typical of Mg alloy extrusions. The uniform dispersion of the G.P. zones facilitates cross-slip, and the G.P. zones do not work as crack initiation and propagation site, so the degradation of the elongation after the age-hardening is prevented. The combination of strength and elongation of the extruded and age-hardened AXM10304 is superior to those of Mg-6Al-1Zn (AZ61) and Mg-6.0Zn-0.5Zr (ZK60) commercial alloys and comparable to those of 6000 series of aluminum alloys without any expensive ingredients. Therefore, this alloy may open up a new application areas where weight reduction is of a priority issue.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.046
      Issue No: Vol. 130 (2017)
       
  • On the crystallography and composition of topologically close-packed
           phases in ATI 718Plus®
    • Authors: Robert Krakow; Duncan N. Johnstone; Alexander S. Eggeman; Daniela Hünert; Mark C. Hardy; Catherine M.F. Rae; Paul A. Midgley
      Pages: 271 - 280
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Robert Krakow, Duncan N. Johnstone, Alexander S. Eggeman, Daniela Hünert, Mark C. Hardy, Catherine M.F. Rae, Paul A. Midgley
      ATI 718Plus® is a nickel-based superalloy developed to replace Inconel 718 in aero engines for static and rotating applications. Here, the long-term stability of the alloy was studied and it was found that topologically close-packed (TCP) phases can form at the γ-η interface or, less frequently, at grain boundaries. Conventional and scanning transmission electron microscopy techniques were applied to elucidate the crystal structure and composition of these TCP precipitates. The precipitates were found to be tetragonal sigma phase and hexagonal C14 Laves phase, both being enriched in Cr, Co, Fe and Mo though sigma has a higher Cr and lower Nb content. The precipitates were observed to be heavily faulted along multiple planes. In addition, the disorientations between the TCP phases and neighbouring η/γ were determined using scanning precession electron diffraction and evaluated in axis-angle space. This work therefore provides a series of compositional and crystallographic insights that may be used to guide future alloy design.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.038
      Issue No: Vol. 130 (2017)
       
  • Effect of the modulation ratio on the interface structure of TiAlN/TiN and
           TiAlN/ZrN multilayers: First-principles and experimental investigations
    • Authors: Yu X. Xu; Li Chen; Fei Pei; Ke K. Chang; Yong Du
      Pages: 281 - 288
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Yu X. Xu, Li Chen, Fei Pei, Ke K. Chang, Yong Du
      The interface structure of the multilayered transition metal nitride coatings, which are widely used for various industrial applications, plays a crucial role in their properties. Here, first-principles calculations combined with key experiments are used to investigate the interface structures of TiAlN/TiN and TiAlN/ZrN multilayers with varied modulation ratios. Based on first-principles energetics calculations, it was found that TiAlN/TiN multilayers favour the coherent growth, independent of the modulation ratio of TiAlN to TiN, whereas the modulation ratio of TiAlN to ZrN has an important effect on the interface structure of TiAlN/ZrN multilayers. This prediction is in agreement with our experimental investigations. For TiAlN/TiN and TiAlN/ZrN multilayers with modulation periods of 4–6 nm and varied modulation ratios, the coherent interfaces between the TiAlN and TiN sublayers are observed in all TiAlN/TiN multilayers, while only the TiAlN/ZrN multilayer with a lower modulation ratio of TiAlN to ZrN exhibits the overall metastable epitaxial growth. The formation of metastable coherent interfaces in TiAlN/ZrN multilayers can be attributed to the nonequilibrium deposition process with the presence of defects, such as interface dislocations.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.053
      Issue No: Vol. 130 (2017)
       
  • Enhancing the performance of Ce:YAG phosphor-in-silica-glass by
           controlling interface reaction
    • Authors: Beiying Zhou; Wei Luo; Sheng Liu; Shijia Gu; Mengchen Lu; Yan Zhang; Yuchi Fan; Wan Jiang; Lianjun Wang
      Pages: 289 - 296
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Beiying Zhou, Wei Luo, Sheng Liu, Shijia Gu, Mengchen Lu, Yan Zhang, Yuchi Fan, Wan Jiang, Lianjun Wang
      Dispersing the Ce3+ doped yttrium aluminum garnet (Ce:YAG) phosphor in the glass matrix has been widely investigated to replace conventional organic resin or silicone packaging. However, the reaction layer formed between commercial phosphors and glass matrix severely degrades the optical performance of Ce:YAG phosphor in silica glass (PiSG) materials. This paper demonstrates an ultra-fast method for preparing high performance PiSG materials. Instead of traditional melting process, the highly transparent PiSG samples can be rapidly fabricated from mixtures of commercial Ce:YAG phosphor and mesoporous SiO2 (SBA-15) powders using spark plasma sintering (SPS) at relatively low temperature (1000 °C) within short time (10 min). Owing to the inhibition of the deleterious interface reactions between Ce:YAG phosphor and silica glass matrix, the phosphor has been perfectly preserved, and the internal relative quantum yield of the PiSG sample reaches as high as 93.5% when excited at 455 nm, which is the highest efficiency in current research. Furthermore, combining the PiSG sample, we successfully fabricate a light-emitting diode (LED) module exhibiting a superior performance with luminous efficacy of 127.9 lm/W, correlated color temperature of 5877 K and color rendering index of 69 at the operating current of 120 mA. This work on the high performance LED modules provides not only a new approach to fabricate the functional glass-based materials that is sensitive to the high temperature, but also a possibility to extend the lifetime and improve the optical performances of the glass based LEDs.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.057
      Issue No: Vol. 130 (2017)
       
  • In situ synchrotron high-energy X-ray diffraction study of microscopic
           deformation behavior of a hard-soft dual phase composite containing phase
           transforming matrix
    • Authors: Junsong Zhang; Shijie Hao; Daqiang Jiang; Yong Huan; Lishan Cui; Yinong Liu; Hong Yang; Yang Ren
      Pages: 297 - 309
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Junsong Zhang, Shijie Hao, Daqiang Jiang, Yong Huan, Lishan Cui, Yinong Liu, Hong Yang, Yang Ren
      This study explored a novel intermetallic composite design concept based on the principle of lattice strain matching enabled by the collective atomic load transfer. It investigated the hard-soft microscopic deformation behavior of a Ti3Sn/TiNi eutectic hard-soft dual phase composite by means of in situ synchrotron high-energy X-ray diffraction (HE-XRD) during compression. The composite provides a unique micromechanical system with distinctive deformation behaviors and mechanisms from the two components, with the soft TiNi matrix deforming in full compliance via martensite variant reorientation and the hard Ti3Sn lamellae deforming predominantly by rigid body rotation, producing a crystallographic texture for the TiNi matrix and a preferred alignment for the Ti3Sn lamellae. HE-XRD reveals continued martensite variant reorientation during plastic deformation well beyond the stress plateau of TiNi. The hard and brittle Ti3Sn is also found to produce an exceptionally large elastic strain of 1.95% in the composite. This is attributed to the effect of lattice strain matching between the transformation lattice distortion of the TiNi matrix and the elastic strain of Ti3Sn lamellae. With such unique micromechanic characteristics, the composite exhibits high strength and large ductility.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.052
      Issue No: Vol. 130 (2017)
       
  • Atomistic study of nucleation and migration of the basal/prismatic
           interfaces in Mg single crystals
    • Authors: Qun Zu; Xiao-Zhi Tang; Shuang Xu; Ya-Fang Guo
      Pages: 310 - 318
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Qun Zu, Xiao-Zhi Tang, Shuang Xu, Ya-Fang Guo
      The formation of the basal/prismatic (BP) interfaces during nucleation and growth of a reoriented crystal in Mg single crystals under c-axis tension is investigated by molecular dynamics simulations. The BP interfaces nucleate by a shuffling mechanism via local atomic rearrangement. Both two-layer disconnection and one-layer disconnection contribute to the migration of the BP interfaces. The three-dimensional analysis reveals that the two-layer disconnection forms at the junction between the partial pyramidal dislocation and BP interface. The BP interfacial disconnections prefer to move towards the [ 1 2 ¯ 10 ] direction rather than the [ 1 ¯ 010 ] /[0001] direction due to the accumulation of mismatches along the [ 1 ¯ 010 ] /[0001] direction. Moreover, the BP interface can transform to the { 10 1 ¯ 2 } twin boundary and vice versa. The transformation from a BP interface to a twin boundary occurs through the diagonal pile-up of BP interface disconnections, and the reverse transformation involves an upright pile-up process. Both BP transformation and { 10 1 ¯ 2 } twinning can effectively accommodate the applied tensile strain along the c-axis. The co-existing BP interfaces and { 10 1 ¯ 2 } twin boundaries allow for large deviations of a twin interface from the { 10 1 ¯ 2 } twin plane.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.035
      Issue No: Vol. 130 (2017)
       
  • Dependence of twinned volume fraction on loading mode and Schmid factor in
           randomly textured magnesium
    • Authors: Jan Čapek; Kristián Máthis; Bjørn Clausen; Matthew Barnett
      Pages: 319 - 328
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Jan Čapek, Kristián Máthis, Bjørn Clausen, Matthew Barnett
      The twinning activity in random textured cast magnesium during room temperature tension and compression tests was monitored by neutron diffraction (ND). Variation of integrated intensities of selected diffraction peaks, characterizing the twinned volume in particularly oriented grains was compared with calculated Schmid factors for extension twinning of these grains. It is shown that in tension there is a direct proportion between the twinned volume and the maximum value of the Schmid factor for a given grain orientation. In contrast, in compression this relation is not valid. The twinned volume in this case is influenced by both deviation of the grain from the ideal orientation and its rotation around the c-axis. The experimental results are in good agreement with those obtained from elasto-plastic self-consistent (EPSC) modeling.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.017
      Issue No: Vol. 130 (2017)
       
  • Liquid-like grain boundary complexion and sub-eutectic activated sintering
           in CuO-doped TiO2
    • Authors: Jiuyuan Nie; Jonathan M. Chan; Mingde Qin; Naixie Zhou; Jian Luo
      Pages: 329 - 338
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): Jiuyuan Nie, Jonathan M. Chan, Mingde Qin, Naixie Zhou, Jian Luo
      The eutectic temperature and composition of the TiO2-CuO system were carefully measured to be 1010 ± 10 °C and 83CuO:17TiO2, respectively. Subsequently, a TiO2-CuO phase diagram was computed, representing a correction and major improvement from the phase diagram available in literature. Dilatometry measurements and isothermal sintering experiments unequivocally demonstrated the activated (enhanced) sintering of TiO2 with the addition of CuO, occurring at as low as >300 °C below the eutectic temperature. High resolution transmission electron microscopy (HRTEM) characterization of water-quenched specimens revealed the formation of nanometer-thick, liquid-like, intergranular films (IGFs), a type of grain boundary (GB) complexion (a.k.a. 2-D interfacial phase), concurrently with accelerated densification and well below the bulk eutectic temperature. Consequently, activated sintering is explained from the enhanced mass transport in this premelting-like complexion. An interfacial thermodynamic model was used to quantitatively explain and justify the stabilization of liquid-like IGFs below the eutectic temperature and the temperature-dependent IGF thicknesses measured by HRTEM. A GB λ diagram was computed, for the first time for a ceramic system, to represent the thermodynamic tendency for general GBs in CuO-doped TiO2 to disorder.
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      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.03.037
      Issue No: Vol. 130 (2017)
       
  • On the strain-induced stabilization of microstructural features formed
           along dislocations
    • Authors: M.H. Jhon; D.C. Chrzan; A.M. Glaeser
      Pages: 339 - 346
      Abstract: Publication date: 15 May 2017
      Source:Acta Materialia, Volume 130
      Author(s): M.H. Jhon, D.C. Chrzan, A.M. Glaeser
      Capillarity-driven mass transport limits the stability of microstructures with a high surface-to-volume ratio. Fiber reinforcements, dendritic structures, and other wire-like morphologies may be susceptible to Rayleigh instabilities and to concurrent or subsequent coarsening. Decreases in the characteristic length scales of microstructures to the nanoscale make such forms of evolution and instability evident at lower values of homologous temperature, consistent with expectations based on size scaling. Herein, we present a simple continuum theory that predicts that sufficiently small second-phase wires exhibiting dislocation character are stable to both Rayleigh instabilities and coarsening. Thus, defects such as hollow-core dislocations will tend to be stabilized while a freestanding nanowire will tend to be unstable. More generally, the effects of surface-energy anisotropy and strain energy on morphological stability are evaluated in a manner that allows their individual and combined effects on stability to be assessed and mapped.
      Graphical abstract image

      PubDate: 2017-04-04T03:18:01Z
      DOI: 10.1016/j.actamat.2017.02.032
      Issue No: Vol. 130 (2017)
       
  • Size effect on deformation twinning in face-centred cubic single crystals:
           Experiments and modelling
    • Authors: Z.Y. Liang; J.T.M. De Hosson; M.X. Huang
      Pages: 1 - 10
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Z.Y. Liang, J.T.M. De Hosson, M.X. Huang
      In addition to slip by dislocation glide, deformation twinning in small-sized metallic crystals also exhibits size effect, namely the twinning stress increases with decreasing sample size. In order to understand the underpinning mechanisms responsible for such effect, systematic experiments were carried out on the small-sized single-crystalline pillars of a twinning-induced plasticity steel with a face-centred cubic structure. The flow stress increases considerably with decreasing pillar diameter from 3 to 0.5 μm, demonstrating a substantial size effect with a power exponent of 0.43. Detailed microstructural characterization reveals that the plastic deformation of the present pillars is dominant by twinning, primarily via twin growth, indicating that the size effect should be related to deformation twinning instead of slip by dislocation glide. Subsequent modelling works indicate that twinning can be accomplished by the dissociation of the ion-radiation-induced vacancy Frank loops in the damaged subsurface layer of the pillars, and the size effect is attributed to the ion-radiation-induced compressive stress in the subsurface layer, which decreases with pillar diameter.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.063
      Issue No: Vol. 129 (2017)
       
  • Microstructural evolution of cold-sprayed Inconel 625 superalloy coatings
           on low alloy steel substrate
    • Authors: Atanu Chaudhuri; Y. Raghupathy; Dheepa Srinivasan; Satyam Suwas; Chandan Srivastava
      Pages: 11 - 25
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Atanu Chaudhuri, Y. Raghupathy, Dheepa Srinivasan, Satyam Suwas, Chandan Srivastava
      This study illustrates microstructural evolution of INCONEL 625 superalloy coatings cold-sprayed on a 4130 chrome alloy steel with medium carbon content. INCONEL 625 powder (5–25 μm) were successfully cold sprayed without any oxidation. The comprehensive microstructure analysis of the as-sprayed coatings and of the substrate-coating interface was carried out using EBSD, TEM, and XRD. The coating microstructure at the substrate-coating interface was markedly different from the microstructure away from the interface. The coating microstructure at steel-coating interface consisted of a fine layer of small grains. The microstructure beyond this fine layer can be divided into splats, inter splat and intra splat boundaries. Both splat and splat boundaries exhibited deformation induced dislocations. Dynamic recovery of dislocations-ridden regions inside the splat was responsible for the development of sub grain structure inside a splat with both low and high angle grain boundaries. Splat-splat (inter splat) boundary consisted of a relatively high density of dislocations and shear bands as a result of adiabatic shear flow localisation. This flow instability is believed to enhance the microstructural integrity by eliminating porosity at splat-splat boundaries. Based on the microstructural analysis using electron microscopy, a plausible mechanism for the development of microstructure has been proposed in this work. Cold spray technique can thus be deployed to develop high quality coatings of commercial importance.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.070
      Issue No: Vol. 129 (2017)
       
  • Oxygen octahedral coupling and structural reconstruction at the
           intergrowth interface in bilayered Ca3Mn2O7
    • Authors: Jiangbo Lu; Chao Ma
      Pages: 26 - 32
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Jiangbo Lu, Chao Ma
      Nanoscale intergrowth is a ubiquitous phenomenon in layered manganites, and the interaction with the host material results in structural reconstruction around the interface, which plays an important role in the physical properties, similar to the interface effect happening in oxide heterostructures. In this work, by combining the aberration-corrected scanning transmission electron microscopy and density functional theory calculations, the oxygen octahedral coupling at the interface was directly visualized and quantified at atomic scale, and the role of oxygen octahedral coupling in the microstructure and electronic structure of bilayered Ca3Mn2O7 were studied. The intergrowth induced interfacial phases show different octahedral tilting angles which depend on the form of nanoscale intergrowth, and thus are structurally and electronically different from bulk materials. These findings can well explain the observed mixture of tetragonal and orthorhombic phases in Ca3Mn2O7 at room temperature, and also offers great insights into understanding of peculiar magnetism induced by the presence of intergrowth. Since the tilting angle of these intergrowth induced phases can be controlled by the thickness and density of the intergrowth, the latter could have the potential to be used to tune the physical properties.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.075
      Issue No: Vol. 129 (2017)
       
  • Fatigue mediated lattice rotation in Al alloys
    • Authors: R. Goswami; S.B. Qadri; C.S. Pande
      Pages: 33 - 40
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): R. Goswami, S.B. Qadri, C.S. Pande
      A significant lattice rotation in the plastic zone of a fatigue crack at room temperature in highly oriented Al 1100 and Al 7075 alloys has been observed by employing X-ray diffraction (XRD) and transmission electron microscopy (TEM). The intensity of 111 peak gradually increases as compared to the intensity of 200 peak as we approach the crack, suggesting lattice rotation. The texture was seen to change gradually from nearly cubic, away from the crack, to a more random orientation close to the crack. We ascribe the lattice rotation to the increase in dislocation density in the plastic zone. The estimated average angle of rotation is approximately 11°, which is sufficient to disturb the cube texture close to the crack. In addition, the observed plastic zone, as estimated by the lattice rotation, is order of magnitude higher as compared to the theoretically predicted plastic zone. This is of great importance, as it leads to a new insight of the underlying physics of the deformation process in the plastic zone under cyclic loading.

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.061
      Issue No: Vol. 129 (2017)
       
  • Macroscale and microscale fracture toughness of microporous sintered Ag
           for applications in power electronic devices
    • Authors: Chuantong Chen; Shijo Nagao; Katsuaki Suganuma; Jinting Jiu; Tohru Sugahara; Hao Zhang; Tomohito Iwashige; Kazuhiko Sugiura; Kazuhiro Tsuruta
      Pages: 41 - 51
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Chuantong Chen, Shijo Nagao, Katsuaki Suganuma, Jinting Jiu, Tohru Sugahara, Hao Zhang, Tomohito Iwashige, Kazuhiko Sugiura, Kazuhiro Tsuruta
      The application of microporous sintered silver (Ag) as a bonding material to replace conventional die-bonding materials in power electronic devices has attracted considerable interest. Characterization of the mechanical properties of microporous Ag will enable its use in applications such as lead-free solder electronics and provide a fundamental understanding of its design principles. However, the material typically suffers from thermal and mechanical stress during its production fabrication, and service. In this work, we have studied the effect of microporous Ag specimen size on fracture toughness from the microscale to the macroscale. A focused ion beam was used to fabricate 20-, 10- and 5-μm-wide microscale specimens, which were of the same order of magnitude as the pore networks in the microporous Ag. Micro-cantilever bending tests revealed that fracture toughness decreased as the specimen size decreased. Conventional middle-cracked tensile tests were performed to determine the fracture toughness of the macroscale specimens. The microscale and macroscale fracture toughness results showed a clear size effect, which is discussed in terms of both the deformation behavior of crack tip and the influence of pore networks within Ag with different specimen sizes. Finite element model simulations showed that stress at the crack tip increased as the specimen size increased, which led to larger plastic deformation and more energy being consumed when the specimen fractured.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.065
      Issue No: Vol. 129 (2017)
       
  • Massive nanoprecipitation in an Fe-19Ni-xAl maraging steel triggered by
           the intrinsic heat treatment during laser metal deposition
    • Authors: Philipp Kürnsteiner; Markus B. Wilms; Andreas Weisheit; Pere Barriobero-Vila; Eric A. Jägle; Dierk Raabe
      Pages: 52 - 60
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Philipp Kürnsteiner, Markus B. Wilms, Andreas Weisheit, Pere Barriobero-Vila, Eric A. Jägle, Dierk Raabe
      Due to the layer-by-layer build-up of additively manufactured parts, the deposited material experiences a cyclic re-heating in the form of a sequence of temperature pulses. In the current work, this “intrinsic heat treatment (IHT)” was exploited to induce the precipitation of NiAl nanoparticles in an Fe-19Ni-xAl (at%) model maraging steel, a system known for rapid clustering. We used Laser Metal Deposition (LMD) to synthesize compositionally graded specimens. This allowed for the efficient screening of effects associated with varying Al contents ranging from 0 to 25 at% and for identifying promising concentrations for further studies. Based on the existence of the desired martensitic matrix, an upper bound for the Al concentration of 15 at% was defined. Owing to the presence of NiAl precipitates as observed by Atom Probe Tomography (APT), a lower bound of 3–5 at% Al was established. Within this concentration window, increasing the Al concentration gave rise to an increase in hardness by 225 HV due to an exceptionally high number density of 1025 NiAl precipitates per m3, as measured by APT. This work demonstrates the possibility of exploiting the IHT of the LMD process for the production of samples that are precipitation strengthened during the additive manufacturing process without need for any further heat treatment.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.069
      Issue No: Vol. 129 (2017)
       
  • Thermal disorder and correlation effects in anti-perovskite-type copper
           nitride
    • Authors: Janis Timoshenko; Andris Anspoks; Alexandr Kalinko; Alexei Kuzmin
      Pages: 61 - 71
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Janis Timoshenko, Andris Anspoks, Alexandr Kalinko, Alexei Kuzmin
      Reverse Monte Carlo simulations coupled with evolutionary algorithm were employed for the analysis of the temperature dependent (10–300 K) Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra of polycrystalline copper nitride (Cu3N) with the goal to extract information on the thermal disorder and interatomic correlations in anti-perovskite-type crystal lattice. The obtained results are discussed in comparison with metallic copper and perovskite-type rhenium trioxide. The analysis of EXAFS spectra suggests that the anisotropy of copper atom vibrations is significantly enhanced upon increasing temperature, leading to pronounced tilting motion of NCu6 octahedra. Strong correlation in the motion of atoms was found along –N–Cu–N– atomic chains but it reduces rapidly with an increase of interatomic distance. Finally, anticorrelated motion of neighboring Cu atoms occurs along Cu–Cu bonds and is consistent with breathing-type motion of NCu6 octahedra.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.074
      Issue No: Vol. 129 (2017)
       
  • Effect of nanoscale α2 precipitation on strain localisation in a
           two-phase Ti-alloy
    • Authors: D. Lunt; T. Busolo; X. Xu; J. Quinta da Fonseca; M. Preuss
      Pages: 72 - 82
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): D. Lunt, T. Busolo, X. Xu, J. Quinta da Fonseca, M. Preuss
      Many commercial Ti-alloys contain 6 wt% Aluminium and these alloys are prone to precipitation of α2 (Ti3Al). Here, we investigate and quantify the effect of α2 precipitation on strain localisation behaviour for Ti-6Al-4V with an equiaxed microstructure using High Resolution Digital Image Correlation (HR-DIC) in combination with Electron Back Scatter Diffraction (EBSD). HR-DIC has enabled us to quantify strain localisation, which shows that at 1% applied strain the strain heterogeneity in terms of maximum shear strain is about twice in the sample containing α2 precipitates compared to the α2-free sample. Theoretical slip trace angles for all possible slip systems were calculated using Electron Back Scatter Diffraction (EBSD) orientation data and cross-correlated with experimental slip trace angles measured from nanoscale shear strain maps recorded by HR-DIC to predict the active slip domain. It has been found that while slip type activity in terms of frequency is strongly dependent on texture in respect to loading direction, the actual shear strain contribution from prismatic slip does increase significantly in the presence of α2 precipitation. This experimental observation supports previous calculations of Anti-Phase Boundary (APB) energies for α2 precipitates [1] where widely dissociated partial dislocations on the prismatic plane show a lower APB energy than the APB energy associated with shearing on the basal plane in α2.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.068
      Issue No: Vol. 129 (2017)
       
  • Interfacial free energy and stiffness of aluminum during rapid
           solidification
    • Authors: Nicholas T. Brown; Enrique Martinez; Jianmin Qu
      Pages: 83 - 90
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): Nicholas T. Brown, Enrique Martinez, Jianmin Qu
      Using molecular dynamics simulations and the capillary fluctuation method, we have calculated the anisotropic crystal-melt interfacial free energy and stiffness of aluminum in a rapid solidification system where a temperature gradient is applied to enforce thermal non-equilibrium. To calculate these material properties, the standard capillary fluctuation method typically used for systems in equilibrium has been modified to incorporate a second-order Taylor expansion of the interfacial free energy term. The result is a robust method for calculating interfacial energy, stiffness and anisotropy as a function of temperature gradient using the fluctuations in the defined interface height. This work includes the calculation of interface characteristics for temperature gradients ranging from 11 to 34 K/nm. The captured results are compared to a thermal equilibrium case using the same model and simulation technique with a zero gradient definition. We define the temperature gradient as the change in temperature over height perpendicular to the crystal-melt interface. The gradients are applied in MD simulations using defined thermostat regions on a stable solid-liquid interface initially in thermal equilibrium. The results of this work show that the interfacial stiffness and free energy for aluminum are dependent on the magnitude of the temperature gradient, however the anisotropic parameters remain independent of the non-equilibrium conditions applied in this analysis. The relationships of the interfacial free energy/stiffness are determined to be linearly related to the thermal gradient, and can be interpolated to find material characteristics at additional temperature gradients.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.033
      Issue No: Vol. 129 (2017)
       
  • Dislocation-twin boundary interaction in small scale Cu bi-crystals loaded
           in different crystallographic directions
    • Authors: N.V. Malyar; J.-S. Micha; G. Dehm; C. Kirchlechner
      Pages: 91 - 97
      Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129
      Author(s): N.V. Malyar, J.-S. Micha, G. Dehm, C. Kirchlechner
      The mechanical behavior of several 5 × 5 micron sized Cu bi-crystals with a single coherent Σ 3 { 11 1 } twin boundary (TB) is studied by in situ Laue microdiffraction (μLaue) compression with the aim to unravel the slip transfer mechanisms through TBs. Single crystalline pillars (SCP) are additionally tested and used as reference samples. Engineering stress-strain curves and post mortem scanning electron microscopy (SEM) images were correlated to the local evolution of the TB angle, the storage of geometrically necessary dislocations and crystal orientations investigated by in situ X-ray Laue microdiffraction (μLaue). Both μLaue and post mortem SEM demonstrate multiple transmission events through the TB without significant storage of geometrically necessary dislocations in the crystals or at the boundary, independent on the compression direction. Nevertheless, at engineering strains larger than 5% a small dislocation pile-up was once observed temporarily at the boundary. Upper and lower bounds for the transmission stress are discussed based on the current experimental results.
      Graphical abstract image

      PubDate: 2017-03-08T23:48:51Z
      DOI: 10.1016/j.actamat.2017.02.067
      Issue No: Vol. 129 (2017)
       
  • Editors for Acta Materialia
    • Abstract: Publication date: 1 May 2017
      Source:Acta Materialia, Volume 129


      PubDate: 2017-04-04T03:18:01Z
       
 
 
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