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Publisher: Elsevier   (Total: 3042 journals)

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Showing 1 - 200 of 3042 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: 17, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 81, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 23, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 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: 328, 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: 206, 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: 23, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 4, SJR: 0.383, h-index: 19)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 3)
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: 128, 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: 9, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 25, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 20, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 25, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 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: 10, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in 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: 40, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 40, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 48, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 12)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 25)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 35, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 25, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 13)
Advances in Pharmacology     Full-text available via subscription   (Followers: 15, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 59)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 2, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 340, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 6, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 15)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 309, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 8, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 400, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 38, 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: 50, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 5, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 6)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 8, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 4, SJR: 0.776, h-index: 35)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 7, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 48, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 48, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 44, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 36, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 16, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 30, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 24, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 34, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 179, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 55, 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: 23, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 24, 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: 33, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 55, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 9)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 160, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 8, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription  
Anesthesiology Clinics     Full-text available via subscription   (Followers: 22, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 153, 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]   [206 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-6454
   Published by Elsevier Homepage  [3042 journals]
  • Toughness enhancement and tribochemistry of the Nb-Ag-N films actuated by
           solute Ag
    • Authors: Ping Ren; Kan Zhang; Xin He; Suxuan Du; Xiaoyang Yang; Tao An; Mao Wen; Weitao Zheng
      Pages: 1 - 11
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): Ping Ren, Kan Zhang, Xin He, Suxuan Du, Xiaoyang Yang, Tao An, Mao Wen, Weitao Zheng
      The high-hardness nature of transition metal nitrides (TMN) has been widely exploited for industrial applications ranging from wear-resistance and cutting tools to scratch-resistant films. To design TMN-based films displaying a further improved toughness and a reduced friction represent urgent challenges. Up to now, creating a nanocomposite structure by introducing a very small content of the metal phase has been considered as a common strategy to enhance hardness and toughness. Herein, we present a new approach to incorporate few solute Ag atoms (∼1.5 at.%) into NbN film to form a Nb-Ag-N solid solution structure, achieving enhanced hardness and toughness, coupled with improved wear-resistance ability and remarkable drop in coefficient of friction (CoF). Hardness and toughness enhancement as well as the tribochemistry actuated by solute Ag have been investigated by combined experimental and density functional theory (DFT) analyses. Results show that the hardness enhancement induced by solute Ag stems from the combination of variation in microstructure and increment in bulk modulus B and C44. DFT calculations and electronic structure analyses further reveal that the presence of hybridizations between Ag 5s, 4d orbitals and N p-electrons is responsible for increment in B and C44; furthermore, the appearance of additional Ag eg states contributes to the improved toughness. Additionally, solute Ag can activate self-oxidation by forming Ag2O + Nb2O5 at the surface, which is beneficial for the formation of silver niobate (AgNbO3) during the sliding, thereby triggering the falling of the CoF at only 1.5 at.% Ag. Incorporation of few solute Ag atoms into TMN may provide a new strategy to improve the comprehensive properties including hardness, toughness, friction and wear-resistance.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.034
      Issue No: Vol. 137 (2017)
       
  • Effect of process parameters on phase stability and metal-insulator
           transition of vanadium dioxide (VO2) thin films by pulsed laser deposition
           
    • Authors: Ryan McGee; Ankur Goswami; Behnam Khorshidi; Kristi McGuire; Kalvin Schofield; Thomas Thundat
      Pages: 12 - 21
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): Ryan McGee, Ankur Goswami, Behnam Khorshidi, Kristi McGuire, Kalvin Schofield, Thomas Thundat
      Owing to remarkable thermochromic, electrochromic, and photochromic properties which arise from a first-order phase transition from insulator to metal at 68 °C, vanadium dioxide (VO2) has an enormous range of potential applications. However, due to such narrow thermodynamic stability, there is a major challenge surrounding selective phase deposition of vanadium dioxide thin films. Here, we present a report that establishes precise conditions for the deposition of three major polymorphs of VO2 by pulsed laser deposition. By a systematic study of the synergistic effects of the deposition conditions using a robust design of experiment (Taguchi design), we are able to deposit the VO2 (M1), VO2 (T), and VO2 (A) phases onto thermal oxide (Si/SiO2) substrates with remarkable precision. By electrically probing the temperature induced phase transformation from insulator to metal of each of these polymorphs, we find not only a strong dependence on the phase, but that the nature of the deposition conditions influences the magnitude and hysteresis width of the temperature cycle.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.025
      Issue No: Vol. 137 (2017)
       
  • A prominent driving force for the spallation of thermal barrier coatings:
           Chemistry dependent phase transformation of the bond coat
    • Authors: L.T. Wu; R.T. Wu; P. Xiao; T. Osada; K.I. Lee; M. Bai
      Pages: 22 - 35
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): L.T. Wu, R.T. Wu, P. Xiao, T. Osada, K.I. Lee, M. Bai
      The influence of substrate and bond coat chemistry on the degradation mechanism leading to the early spallation of thermal barrier coatings (TBCs) has not been well understood despite years of research effort. This is largely due to the sheer number of factors (i.e. interfacial rumpling and oxide growth kinetics) that all seem to contribute to the degradation of TBCs. To clarify the chemical effect, extensive characterizations and in-depth analysis near the oxide-bond coat interface, were carried out on the isothermally exposed TBC specimens. It is evident that the formation of γ′ along the grain boundaries can significantly enhance rumpling, while martensitic transformation during cooling creates out-of-plane stresses and causes crack nucleation at the oxide-bond coat interface. These partial phase transformations in the β bond coat system were determined to be a prominent driving force for the TBC spallation. To prevent the early spallation of TBCs, it is necessary to minimize the formation rate of γ′ and martensitic phases, which can be achieved by tailoring the inherent substrate/bond coat composition as elucidated in this paper.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.037
      Issue No: Vol. 137 (2017)
       
  • Morphology evolution of Ti3AlC carbide precipitates in high Nb containing
           TiAl alloys
    • Authors: Li Wang; Carolin Zenk; Andreas Stark; Peter Felfer; Heike Gabrisch; Mathias Göken; Uwe Lorenz; Florian Pyczak
      Pages: 36 - 44
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): Li Wang, Carolin Zenk, Andreas Stark, Peter Felfer, Heike Gabrisch, Mathias Göken, Uwe Lorenz, Florian Pyczak
      This work elucidates the morphology evolution of perovskite Ti3AlC carbides in a Ti-45Al-5Nb-0.75C alloy during ageing at 800 °C. The carbides in the γ matrix are initially needle-shaped with their long axis parallel to the [001] lattice direction of the γ matrix. After extended annealing, they decompose into small carbide sub-particles. By combining different transmission electron microscopy characterization methods and atom probe tomography it has been verified that the carbides first split into several parallel needles that are aligned along the [001]γ lattice direction. Later these parallel needles further decompose into numerous small sub-particles, while the matrix phase region between the sub-particles crystallographically reorients. To the authors' knowledge this is the first work which demonstrates such a precipitate splitting process in a matrix with a tetragonal crystal structure. It is proposed that the decomposition into small sub-particles is energetically favourable owing to the elastic interaction energy between the split sub-particles.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.018
      Issue No: Vol. 137 (2017)
       
  • Extrinsic contributions to piezoelectric Rayleigh behavior in morphotropic
           PbTiO3 - BiScO3
    • Authors: G. Tutuncu; J.S. Forrester; J. Chen; J.L. Jones
      Pages: 45 - 53
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): G. Tutuncu, J.S. Forrester, J. Chen, J.L. Jones
      In situ, high-energy, time-resolved X-ray diffraction experiments are utilized to quantify contributions from non-180° domain wall motion to the macroscopic electromechanical coupling effect in the morphotropic phase boundary composition 0.64PbTiO3-0.36BiScO3 during the application of weak electric field amplitudes. Macroscopic piezoelectric coefficient measurements are compared with diffraction data. The results demonstrate a linear contribution of electric-field-amplitude-dependent non-180° domain wall motion at small field amplitudes, and therefore domain wall motion contributes directly to the Rayleigh behavior of piezoelectric coefficients.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.032
      Issue No: Vol. 137 (2017)
       
  • Selected mode for rapidly growing needle-like dendrite controlled by heat
           and mass transport
    • Authors: D.V. Alexandrov; P.K. Galenko
      Pages: 64 - 70
      Abstract: Publication date: 15 September 2017
      Source:Acta Materialia, Volume 137
      Author(s): D.V. Alexandrov, P.K. Galenko
      The boundary integral method is developed for fast anisotropic interfaces. A general integro-differential equation for curved interfaces controlled by heat and mass transport is derived and applied to the problem of rapid dendritic growth. A selection criterion for the steady-state mode of growing parabolic interfaces is obtained and, in common solution with the undercooling balance, it is compared with experimental data on rapid dendritic solidification of deeply supercooled liquid droplets. In this comparison, transitions from solute diffusion-limited to thermo-solutal regime and, finally, to pure thermally controlled regime of the anisotropic dendrite are discussed and revealed. Limiting cases of known selection criteria for anisotropic dendrites growing at small and high growth Péclet numbers are provided.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.022
      Issue No: Vol. 137 (2017)
       
  • The premature necking of twinning-induced plasticity steels
    • Authors: C.L. Yang; Z.J. Zhang; P. Zhang; Z.F. Zhang
      Pages: 1 - 10
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): C.L. Yang, Z.J. Zhang, P. Zhang, Z.F. Zhang
      An unusual necking behavior was found in twinning-induced plasticity (TWIP) steels during tensile tests, which is quite different from that observed on most ductile metals. A sharp drop of the strain-hardening rate (Θ) arises before necking initiation, rather than after it, leading to the premature necking of TWIP steels. Through carefully examining the evolution of macroscopic defects at various tensile strains using three-dimensional X-ray tomography (3D-XRT), this premature necking behavior was attributed to the multiplication of macroscopic voids during plastic deformation. Combining with the previous theories and present characterizations on the evolution of macroscopic voids, the mechanism of the unusual necking behavior in TWIP steels was quantificationally revealed.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.042
      Issue No: Vol. 136 (2017)
       
  • A test of a phenomenological model of size dependent melting in Au
           nanoparticles
    • Authors: C. Dai; P. Saidi; H. Song; Z. Yao; M.R. Daymond; J.J. Hoyt
      Pages: 11 - 20
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): C. Dai, P. Saidi, H. Song, Z. Yao, M.R. Daymond, J.J. Hoyt
      It is well established that the melting point of a material decreases markedly as the system size approaches the nanoscale. However, despite over a century of study, the validity of any model for size dependent melting point depression has not been proven. In this work molecular dynamics simulations and a classical model of pure Au are used to perform a parameter free test of a phenomenological model of nanosphere melting. Consistent with model predictions, the simulations show that a premelted layer forms on the surface of the nanospheres at temperature well below the bulk melting point and the particle completely transforms to the liquid at a well defined instability temperature. The theoretical prediction of the instability temperature agrees very well with the simulation results, provided that the model is modified to include anisotropic surface properties.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.052
      Issue No: Vol. 136 (2017)
       
  • Diffusion-coupled cohesive interface simulations of stress corrosion
           intergranular cracking in polycrystalline materials
    • Authors: Chao Pu; Yanfei Gao; Yanli Wang; T.-L. Sham
      Pages: 21 - 31
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Chao Pu, Yanfei Gao, Yanli Wang, T.-L. Sham
      To study the stress corrosion intergranular cracking mechanism, a diffusion-coupled cohesive zone model (CZM) is proposed for the simulation of the stress-assisted diffusional process along grain boundaries and the mechanical response of grain boundary sliding and separation. This simulation methodology considers the synergistic effects of impurity diffusion driven by pressure gradient and degradation of grain boundary strength by impurity concentration. The diffusion-coupled CZM is combined with crystal plasticity finite element model (CPFEM) to simulate intergranular fracture of polycrystalline material under corrosive environment. Significant heterogeneity of the stress field and extensive impurity accumulation is observed at grain boundaries and junction points. Deformation mechanism maps are constructed with respect to the grain boundary degradation factor and applied strain rate, which dictate the transition from internal to near-surface intergranular fracture modes under various strain amplitudes and grain sizes.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.058
      Issue No: Vol. 136 (2017)
       
  • High Curie-temperature (TC) piezo-/ferroelectric single crystals with
           bismuth-based complex perovskites: Growth, structures and properties
    • Authors: Zenghui Liu; Hua Wu; Alisa Paterson; Zeng Luo; Wei Ren; Zuo-Guang Ye
      Pages: 32 - 38
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Zenghui Liu, Hua Wu, Alisa Paterson, Zeng Luo, Wei Ren, Zuo-Guang Ye
      Complex perovskite solid solutions based on Bi(B′B″)O3-PbTiO3 are potentially interesting ferroelectric and piezoelectric materials with high Curie temperature (T C). In this work, large-size (1-x)Bi(Zn1/2Ti1/2)O3-xPbTiO3 (BZT-PT), and (1-x)Bi(Zn2/3Nb1/3)O3-xPbTiO3 (BZN-PT) single crystals have been successfully grown by the high-temperature solution growth method and the top-cooled solution growth method. A comparative study of the (001)-oriented BZT-PT and BZN-PT crystals is carried out and significant differences are found in their structures and physical properties which are characterized by various techniques. The crystal structures of both crystals are refined to be of tetragonal symmetry by means of powder X-ray diffraction, but their local structures exhibit remarkable differences in terms of cationic displacements. The T C is determined to be around 572 °C and 424 °C for the BZT-PT and BZN-PT single crystals, respectively. The ferroic domain structures examined by polarized light microscopy based on optical crystallography are found to be different in the BZT-PT and BZN-PT crystals. The effects of domain structures on the different ferroelectric behaviors are investigated. The high T C and large coercive electric field, as well as the high remanent polarization of the BZT-PT and BZN-PT single crystals make them promising candidates for applications in high-power electromechanical transducers that can be operated in a wide temperature range.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.047
      Issue No: Vol. 136 (2017)
       
  • Hall-Petch relationship for austenitic stainless steels processed by large
           strain warm rolling
    • Authors: Z. Yanushkevich; S.V. Dobatkin; A. Belyakov; R. Kaibyshev
      Pages: 39 - 48
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Z. Yanushkevich, S.V. Dobatkin, A. Belyakov, R. Kaibyshev
      The deformation microstructures and their effect on the yield strength of austenitic stainless steels processed by large strain warm rolling were studied. The samples of 304 L and 316 L type steels were subjected to caliber bar rolling to total strains of 2 at temperatures of 773–1173 K. The structural changes were characterized by the development of continuous dynamic recrystallization. A decrease in the rolling temperature resulted in significant grain/subgrain refinement and an increase in the yield strength at room and elevated temperatures. A power law function was obtained between the deformation grain and subgrain sizes with a grain size exponent of 0.3. Therefore, the yield strength could be expressed by a modified Hall-Petch relationship including a term of substructural strengthening, which was evaluated using the obtained size relation. The numerical factors normalized by shear modulus for both structural and substructural strengthening terms depended quite weakly on tensile test temperature in the range of 293–873 K that suggested the deformation mechanisms being invariant up to 873 K. On the other hand, the thermally activated mechanisms led to the yield strength decreasing much faster than shear modulus as the tensile test temperature increased above 873 K.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.060
      Issue No: Vol. 136 (2017)
       
  • Stick-slip dynamics in a Ni62Nb38 metallic glass film during
           nanoscratching
    • Authors: D.X. Han; G. Wang; J.L. Ren; L.P. Yu; J. Yi; I. Hussain; S.X. Song; H. Xu; K.C. Chan; P.K. Liaw
      Pages: 49 - 60
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): D.X. Han, G. Wang, J.L. Ren, L.P. Yu, J. Yi, I. Hussain, S.X. Song, H. Xu, K.C. Chan, P.K. Liaw
      Stick-slip dynamics during nanoscratching is investigated for the Ni62Nb38 metallic glass. Detrended fluctuation analysis is introduced to explore the influence of loading force on the temporal scaling and stick-slip behavior. The self-similar characteristics and complexity in the temporal scale of the lateral force signal are investigated. A modified Cauchy class model is used for the stochastic stick-slip process, which connects the fractal dimension and the Hurst exponent and features the positive correlation process. The confidence intervals of the differential friction coefficient at different loading forces elucidate the inhomogeneous (and homogeneous) shear-branching processes during the nanoscratching process.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.061
      Issue No: Vol. 136 (2017)
       
  • On delamination toughening of a 14YWT nanostructured ferritic alloy
    • Authors: M.E. Alam; S. Pal; S.A. Maloy; G.R. Odette
      Pages: 61 - 73
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): M.E. Alam, S. Pal, S.A. Maloy, G.R. Odette
      The FCRD NFA-1 is a high strength, irradiation tolerant nanostructured ferritic alloy (NFA) produced by ball milling argon atomized Fe-14Cr-3W-0.35Ti-0.25Y (wt.%) and FeO powders, followed by hot extrusion at 850 °C, and subsequent annealing and cross-rolling at 1000 °C. The microstructure of the resulting ≈10 mm thick NFA-1 plate is dominated by ultrafine sub-micron pancake shaped grains, and a large population of microcracks lying on planes parallel to the plate faces. Pre-cracked fracture toughness tests in four different orientations (L-T, T-L, L-S and T-S) show stable crack growth by ductile tearing, with peak load KJc from ≈ 88 to 154 MPa√m at ambient temperature. Stable crack tearing persists down to ≈ −175 °C and is accompanied by extensive delamination due to the propagation of the microcracks. Depending on the specimen orientation, this unusual toughening mechanism is either due to a reduction of crack tip stresses in thin ligaments formed by the delaminations (L-T and T-L), or 90° deflection of cracks initially running normal to the delaminations (L-S and T-S), thereby suppressing cleavage in both cases. Understanding the fracture processes in NFA-1 is also important to its irradiation tolerance in nuclear service as well as its fabricability in making defect-free components such as thin-walled tubing.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.041
      Issue No: Vol. 136 (2017)
       
  • Composition dependence of diffusion and thermotransport in Ni-Al melts: A
           step towards molecular dynamics assisted databases
    • Authors: Elena V. Levchenko; Tanvir Ahmed; Alexander V. Evteev
      Pages: 74 - 89
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Elena V. Levchenko, Tanvir Ahmed, Alexander V. Evteev
      We present an extensive and self-consistent database of diffusion and thermotransport properties of molecular-dynamics models of Ni-Al melts with an embedded-atom method potential. The database is generated over wide temperature and composition ranges. A careful comparison with available fragmentary experimental data is made to ensure reliability of the employed model description of Ni-Al melts. A comprehensive analysis of the presented data is carried out and the emerging trends are discussed in details. In particular, a phenomenological model for the composition dependence of the enthalpy of mixing is introduced. This model accurately describes our simulation data for Ni-Al melts as well as enables an ease access to the partial enthalpies of species essential for precise characterization of thermotransport. Furthermore, an intriguing similarity between the shapes of the composition dependence of the Manning factor (which characterizes the interrelation between the collective and single-particle diffusion) and the enthalpy of mixing in Ni-Al melts is brought to attention. Meanwhile, our results for the reduced heat of transport (which characterizes the pure heat conduction initiated by collective diffusion in isothermal conditions) allow us to predict that, in Ni-Al melts, Ni and Al tend to migrate, respectively, to the cold and hot ends in the presence of a temperature gradient. Overall, we highlight a great importance of the presented study for developing and testing of theoretical frameworks to enable sophisticated control of the heat and mass transport in binary melts.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.056
      Issue No: Vol. 136 (2017)
       
  • Enhanced nanohardness and new insights into texture evolution and phase
           transformation of TiAl/TiB2 in-situ metal matrix composites prepared via
           selective laser melting
    • Authors: Wei Li; Yi Yang; Jie Liu; Yan Zhou; Ming Li; Shifeng Wen; Qingsong Wei; Chunze Yan; Yusheng Shi
      Pages: 90 - 104
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Wei Li, Yi Yang, Jie Liu, Yan Zhou, Ming Li, Shifeng Wen, Qingsong Wei, Chunze Yan, Yusheng Shi
      TiAl/TiB2 in-situ metal matrix composites (MMCs) with greatly enhanced nanohardness are prepared via selective laser melting (SLM) for the first time in this study. The effect of TiB2 reinforcement on the microstructural characteristics, texture evolution and phase transformation of TiAl-based alloy is investigated. The results show that with increasing the TiB2 content, the average grain size gradually decreases, and the crystallographic orientation transforms from a strong ( 0001 ) direction to ( 10 1 ¯ 1 ) and ( 11 2 ¯ 1 ) directions. Meanwhile, TiB2 has a great effect on the texture of SLM-processed TiAl/TiB2 MMCs. With increasing the TiB2 content, more textured TiAl/TiB2 MMCs can be produced. The TiAl/TiB2 MMCs are dominated by α2 phase and small amounts of γ, B2, TiB2 and TiB phases are also detected. α2 phase contains the most important texture components of prismatic fiber with { 10 1 ¯ 0 } < 11 2 ¯ 0> orientation, basal fiber with { 0001 } < 11 2 ¯ 0> orientation and pyramidal fiber with { 10 1 ¯ 1 } < 11 2 ¯ 0> and { 11 2 ¯ 2 } < 11 2 ¯ 3 > orientations. The TiB2 reinforcements are in the forms of the needlelike micro-TiB2 and irregular nano-TiB2 particles in the TiAl-based alloy matrix, and the nano-TiB2 particles are uniformly distributed with the size of 10 nm in length and 3–5 nm in width. The SLM-produced TiAl/TiB2 MMCs exhibit superior nanohardness of 10.57 ± 0.53 GPa, which is much higher than those of the traditional roll bonding fabricated TiB2 reinforced TiAl-based alloy. The findings would be a valuable reference for fabricating TiAl/TiB2 MMCs parts with controlled grain features, crystallographic texture and phase composition, enhanced mechanical properties and complex structures by SLM.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.07.003
      Issue No: Vol. 136 (2017)
       
  • Mesoscale simulation of elastocaloric cooling in SMA films
    • Authors: Frank Wendler; Hinnerk Ossmer; Christoph Chluba; Eckhard Quandt; Manfred Kohl
      Pages: 105 - 117
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Frank Wendler, Hinnerk Ossmer, Christoph Chluba, Eckhard Quandt, Manfred Kohl
      A model for the evolution of the mechanical and thermal properties of shape memory alloy (SMA) films during elastocaloric cycling is developed and compared with experiments. The focus is on Ti-Ni-Cu-Co films of 20 μm thickness showing ultra-low fatigue properties. The films undergo a highly localized pseudoelastic transformation under tensile load cycling featuring strain and temperature band patterns that depend on the loading conditions. The corresponding temperature change is of special interest for film-based elastocaloric cooling applications. Starting from a thermodynamics-based Gibbs free energy model comprising mechanical and chemical contributions, we include a martensite-austenite interface free energy term, for which formulations from a phase-field model are adapted. A 3D continuum mechanics description is modified to treat plane stress conditions appropriate for polycrystalline thin films. The nucleation mechanism of strain bands under dynamic loading is described by introducing a spatial random distribution of the transformation stress barriers reflecting the degree of material inhomogeneity. Heat transfer due to conduction and convection is taken into account. The simulations predict the correlated mechanical and thermal local response of the films including band formation and evolution, tilt angle as well as strain-rate dependence. Macroscopic stress-strain characteristics and thermal evolution curves well represent the experimental results.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.044
      Issue No: Vol. 136 (2017)
       
  • Lattice parameter misfit evolution during creep of a cobalt-based
           superalloy single crystal with cuboidal and rafted gamma-prime
           microstructures
    • Authors: James Coakley; Eric A. Lass; Dong Ma; Matthew Frost; Howard J. Stone; David N. Seidman; David C. Dunand
      Pages: 118 - 125
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): James Coakley, Eric A. Lass, Dong Ma, Matthew Frost, Howard J. Stone, David N. Seidman, David C. Dunand
      A [h00] oriented Co-based superalloy single crystal was crept under tension at 940 ° C / 100 MPa , resulting in a P-type raft morphology with extensive particle coalescence along the [h00] loading direction. However, particle coalescence was also observed in two perpendicular directions on the (h00) plane, normal to the loading axis. Tensile creep experiments were performed with in-situ neutron diffraction at 800 ° C / 500 MPa on this initially rafted γ ′ microstructure, and for comparison at (i) 900 ° C / 260 MPa , and at (ii) 750 ° C / 875 MPa , both with initially cuboidal γ ′ microstructures. The alloy was shown to exhibit a positive lattice parameter misfit, and during the first hour of creep at 900 ° C / 260 MPa , the lattice parameter evolution indicated changes in phase composition associated with γ ′ dissolution as the alloy achieved phase equilibrium at 900 ° C . For all three in-situ creep measurements, there was a significant divergence of the γ ′ and γ lattice parameters as creep proceeded. The lattice parameter misfit values between the precipitates and the matrix approached their unconstrained values during creep, and were notably large compared to those of Ni-based superalloys. This is indicative of a loss of coherency at the precipitate/matrix interfaces. Such a loss of coherency at the precipitate/matrix interfaces will likely degrade certain mechanical properties such as fatigue resistance, as has been shown for the Ni-based superalloys.
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      PubDate: 2017-07-07T08:41:10Z
      DOI: 10.1016/j.actamat.2017.06.025
      Issue No: Vol. 136 (2017)
       
  • Ductile fracture in notched bulk metallic glasses
    • Authors: J. Pan; Y.X. Wang; Y. Li
      Pages: 126 - 133
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): J. Pan, Y.X. Wang, Y. Li
      The deformation of bulk metallic glasses (BMGs) is generally driven by highly localized shear. Due to such inhomogeneous flow, failure occurs in a catastrophic brittle manner through rapid shear banding, often associated with very limited plastic strain macroscopically. Here, we demonstrate metal-like ductile fracture in Zr-based BMGs under tension, a completely opposite situation, by suppressing shear banding. In the absence of shear bands, nucleation of cavies/voids and subsequent void growth and coalescence dominate the initial plastic failure process, enabling BMGs to display the essential characteristics of ductile fracture, with deep dimples and cup-and-cone morphology. This ductile fracture only occurs in amorphous alloys, but not in the fully crystallized counterpart. Furthermore, the characteristic decohesion strength of the ductile fracture in Zr-based BMGs was found to be 1.75 GPa, one of the highest among engineering metals and alloys. These present findings reveal the previously hidden ductile behavior of BMGs, suggesting an alternative method to enhance the ductility of BMGs by removing shear banding.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.048
      Issue No: Vol. 136 (2017)
       
  • Cyclic compression response of micropillars extracted from textured
           nanocrystalline NiTi thin-walled tubes
    • Authors: Hassan Ghassemi-Armaki; Asher C. Leff; Mitra L. Taheri; J. Dahal; M. Kamarajugadda; K. Sharvan Kumar
      Pages: 134 - 147
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Hassan Ghassemi-Armaki, Asher C. Leff, Mitra L. Taheri, J. Dahal, M. Kamarajugadda, K. Sharvan Kumar
      Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. The cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of −5 °C is compared. The texture of the tube with the Af of −5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. These observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.043
      Issue No: Vol. 136 (2017)
       
  • Branching-induced grain boundary evolution during directional
           solidification of columnar dendritic grains
    • Authors: Chunwen Guo; Junjie Li; Honglei Yu; Zhijun Wang; Xin Lin; Jincheng Wang
      Pages: 148 - 163
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Chunwen Guo, Junjie Li, Honglei Yu, Zhijun Wang, Xin Lin, Jincheng Wang
      We present an investigation of secondary and tertiary branching behavior in diverging grain boundaries (GBs) between two columnar dendritic grains with different crystallographic orientations, both by two-dimensional phase-field simulations and thin-sample experiments. The stochasticity of the GB trajectories and the statistically averaged GB orientations were analyzed in detail. The side-branching dynamics and subsequent branch competition behaviors found in the simulations agreed well with the experimental results. When the orientations of two grains are given, the experimental results indicated that the average GB orientation was independent of the pulling velocity in the dendritic growth regime. The simulation and experimental results, as well as the results reported in the literature exhibit a uniform relation between the percentage of the whole gap region occupied by the favorably oriented grain and the difference in the absolute values of the secondary arm growth directions of the two competitive grains. By describing such a uniform relation with a simple fitting equation, we proposed a simple analytical model for the GB orientation at diverging GBs, which gives a more accurate description of GB orientation selection than the existing models.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.002
      Issue No: Vol. 136 (2017)
       
  • Interaction and infiltration behavior of Eyjafjallajökull, Sakurajima
           volcanic ashes and a synthetic CMAS containing FeO with/in EB-PVD
           ZrO2-65 wt% Y2 O3 coating at high temperature
    • Authors: R. Naraparaju; Juan J. Gomez Chavez; U. Schulz; C.V. Ramana
      Pages: 164 - 180
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): R. Naraparaju, Juan J. Gomez Chavez, U. Schulz, C.V. Ramana
      Yttria rich-zirconia thermal barrier coatings (TBCs) with a nominal composition of 65 wt % Y2O3 balanced ZrO2 were deposited by electron-beam physical vapor deposition (EB-PVD) and tested for calcium-magnesium-aluminum-silicate (CMAS) infiltration resistance. The infiltration studies were performed with a set of one synthetized CMAS composition and two real volcanic ashes from the Eyjafjallajökull volcano located in Iceland and the Sakurajima volcano located in southern Japan. The coatings were tested at 1250 °C for short term (5 min) and long term (intervals from 1 to 20 h). The results indicate a significantly different reaction process for the synthesized CMAS compared with the natural volcanic ashes. The yttria-rich zirconia coatings demonstrate promising results against infiltration by vigorously reacting against the molten glass inducing its crystallization by forming apatite and garnet phases. The formed reaction products effectively sealed the columnar gaps of the TBC and generated a uniform reaction layer that prevented further infiltration.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.055
      Issue No: Vol. 136 (2017)
       
  • Cu-Zr nanoglasses: Atomic structure, thermal stability and indentation
           properties
    • Authors: Sree Harsha Nandam; Yulia Ivanisenko; Ruth Schwaiger; Zbigniew Śniadecki; Xiaoke Mu; Di Wang; Reda Chellali; Torben Boll; Askar Kilmametov; Thomas Bergfeldt; Herbert Gleiter; Horst Hahn
      Pages: 181 - 189
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Sree Harsha Nandam, Yulia Ivanisenko, Ruth Schwaiger, Zbigniew Śniadecki, Xiaoke Mu, Di Wang, Reda Chellali, Torben Boll, Askar Kilmametov, Thomas Bergfeldt, Herbert Gleiter, Horst Hahn
      The structure of Cu50Zr50 metallic nanoglasses, their thermal stability and mechanical performance are studied in the present paper. Elemental segregation of Cu and Zr is observed in consolidated nanoglasses. A segregation model is proposed with Cu rich interfaces and Zr rich relaxed cores which explains the observed thermal and mechanical properties of nanoglasses. The interfacial regions with high free volume and enriched with Cu act as nucleating sites for the crystallization reaction, increasing the crystallization temperatures in nanoglasses compared to the melt-spun ribbon of the same composition. The hardness and Young's modulus increase as well for the nanoglasses compared to melt-spun ribbons. Metallic nanoglasses deform homogenously, while melt-spun ribbons reveal the formation of shear bands during indentation. It is proposed that the interfacial regions, which are sources of high free volume act as nucleating sites for the formation of numerous shear transformation zones giving rise to homogeneous deformation in nanoglasses.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.001
      Issue No: Vol. 136 (2017)
       
  • Role of dislocation pile-ups in nucleation-controlled size-dependent
           strength of Fe nanowires
    • Authors: Roman Kositski; Dan Mordehai
      Pages: 190 - 201
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Roman Kositski, Dan Mordehai
      We studied the strength of Fe faceted nanowires under diametrical compression using molecular dynamics simulations. We show that a series of consecutive events of dislocation nucleations occurs at the vertices of the nanowire, and two edge dislocation pile-ups are formed before a catastrophic event occurs, previously named a cross-split of edge dislocations. The compressive stress at which dislocations are nucleated depends on the specimen's size and obeys a power-law, with an exponent that depends on the number of dislocations already nucleated into the pile-up. The role of the dislocation pile-up is discussed and, on the basis of classical nucleation theory, we examine the contribution of the dislocation pile-up to the nucleation conditions at the vertices of the nanowire. We found that three contributions need to be accounted for: the stress gradient at the vertices, the back stress from the nucleated pile-up, and the image stresses due to the confined volume of the nanowire. In addition, the proposed model agrees with the distribution of the dislocations inside the pile-up. We ratify that cross-splitting occurs at the head of the pile-up when the distance between the two leading dislocations is about twice their Burgers vectors. Considering this value as the limit for dislocation core coalescence, the results of our model and molecular dynamic simulations for the stresses needed for cross-splitting were in excellent agreement. Based on these results, we found the dependency of the critical stress needed for cross-splitting on the size. Finally, we extend the discussion to the general role of dislocation pile-ups in nucleation-controlled plasticity.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.057
      Issue No: Vol. 136 (2017)
       
  • Microstructural characterization of boron-rich boron carbide
    • Authors: Kelvin Y. Xie; Vladislav Domnich; Lukasz Farbaniec; Bin Chen; Kanak Kuwelkar; Luoning Ma; James W. McCauley; Richard A. Haber; K.T. Ramesh; Mingwei Chen; Kevin J. Hemker
      Pages: 202 - 214
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Kelvin Y. Xie, Vladislav Domnich, Lukasz Farbaniec, Bin Chen, Kanak Kuwelkar, Luoning Ma, James W. McCauley, Richard A. Haber, K.T. Ramesh, Mingwei Chen, Kevin J. Hemker
      Boron carbide has a wide range of solubility, but the effects of stoichiometry on its microstructure and mechanical response are not well understood. In this study, detailed microstructural characterization was carried out on three hot-pressed B-rich boron carbide samples. Lattice parameter measurements from XRD identified the compositions to be B4.2C, B5.6C and B7.6C. Local substitutional disorder was observed by Raman spectroscopy, particularly for more B-rich samples. Electron energy loss spectroscopy observations suggest that excess boron preferentially substitutes for carbon atoms in the B11C icosahedra; after which additional boron modifies the CBC chains. Moreover, the boron content has salient effects on boron carbide densification and microstructure. Improved densification was observed in the more B-rich samples (B5.6C and B7.6C), and there is a transition from few or no intragranular planar defects (B4.2C), to numerous stacking faults (B5.6C), to copious twins (B7.6C). Nanoindentation experiments revealed that the highest value for B4.2C is statistically larger than that for B5.6C or B7.6C, suggesting that the hardness of boron carbide is reduced by boron substitution.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.063
      Issue No: Vol. 136 (2017)
       
  • A first principles study of the stacking fault energies for fcc Co-based
           binary alloys
    • Authors: Li-Yun Tian; Raquel Lizárraga; Henrik Larsson; Erik Holmström; Levente Vitos
      Pages: 215 - 223
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Li-Yun Tian, Raquel Lizárraga, Henrik Larsson, Erik Holmström, Levente Vitos
      The stacking fault energy is closely related to structural phase transformations and can help to understand plastic deformation mechanisms in materials. Here we perform first principles calculations of the stacking fault energy in the face centered cubic (fcc) Cobalt-based binary alloys Co1−x M x , where M = Cr, Fe, Ni, Mo, Ru, Rh, Pd and W. We investigate the concentration range between 0 and 30 at.% of the alloying element. The results are discussed in connection to the phase transition between the low-temperature hexagonal close packed (hcp) and the fcc structures observed in Co and its alloys. By analyzing the stacking fault energies, we show that alloying Co with Cr, Ru, and Rh promotes the hcp phase formation while Fe, Ni and Pd favor the fcc phase instead. The effect of Mo and W on the phase transition differs from the other elements, that is, for concentrations below 10% the intrinsic stacking fault energy is lower than that for pure fcc Co and the energy barrier is higher, whereas above 10% the situation reverses. We carry out also thermodynamic calculations using the ThermoCalc software. The trends of the ab initio stacking fault energy are found to agree well with those of the molar Gibbs energy differences and the phase transition temperature in the binary phase diagrams and give a solid support for the phase stability of these alloys.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.010
      Issue No: Vol. 136 (2017)
       
  • Thermodynamics versus kinetics of grain growth control in nanocrystalline
           zirconia
    • Authors: Nazia Nafsin; Jeffery A. Aguiar; Toshihiro Aoki; Andrew M. Thron; Klaus van Benthem; Ricardo H.R. Castro
      Pages: 224 - 234
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Nazia Nafsin, Jeffery A. Aguiar, Toshihiro Aoki, Andrew M. Thron, Klaus van Benthem, Ricardo H.R. Castro
      This work presents a thorough analysis of the grain growth behavior of gadolinium doped yttria stabilized zirconia (YSZ). The effect of the dopant on the thermodynamics as well as on the kinetics of the process is reported by providing extensive experimental data. While normal grain growth following a parabolic growth relation was observed, gadolinium inhibited the process proportionally to its concentration. By using microcalorimetry, we showed that the dopant decreases the grain boundary energy of YSZ, and hence reduces the driving force for growth. Analysis of the growth profile at different temperatures and times indicate that gadolinium does not significantly affect the grain boundary mobility or the activation energy for grain growth. The results rationalize that the dopant is acting on a mostly thermodynamic basis and opens good perspective for design of coarsening control focused on the system energetics.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.005
      Issue No: Vol. 136 (2017)
       
  • Investigation on thermal transport and structural properties of
           InFeO3(ZnO)m with modulated layer structures
    • Authors: Xiaoxuan Zhang; Haijun Wu; Yanling Pei; Yiming Zhou; Shengkai Gong; Jiaqing He; Li-Dong Zhao
      Pages: 235 - 241
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Xiaoxuan Zhang, Haijun Wu, Yanling Pei, Yiming Zhou, Shengkai Gong, Jiaqing He, Li-Dong Zhao
      We investigate the thermal transport and structural properties of InFeO3(ZnO)m (m = 1, 2, 3, 4, 5) with modulated layer structure, through high resolution transmission electron microscopy and theoretical calculation. Interestingly, we find that the thermal conductivities dependent on the m numbers and stacked layers. Elastic properties indicate that InFeO3(ZnO)m with m odd numbers possesses weaker chemical bonding and lower thermal conductivity than those of InFeO3(ZnO)m with m even numbers. The calculated thermal conductivities show well consistent with the experimental data through integrating the contributions from Umklapp phonon-phonon scattering, stacking faults and optical branch. The results show that thermal conductivities of InFeO3(ZnO)m are predominantly determined by stacking faults, especially in the low temperature range. Our finding provides new insight into seeking the materials with low thermal conductivity through artificially designing layer structures.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.012
      Issue No: Vol. 136 (2017)
       
  • Element-specific amorphization of vacancy-ordered GeSbTe for ternary-state
           phase change memory
    • Authors: Xue-Peng Wang; Xian-Bin Li; Nian-Ke Chen; Qi-Dai Chen; Xiao-Dong Han; Shengbai Zhang; Hong-Bo Sun
      Pages: 242 - 248
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Xue-Peng Wang, Xian-Bin Li, Nian-Ke Chen, Qi-Dai Chen, Xiao-Dong Han, Shengbai Zhang, Hong-Bo Sun
      GeSbTe alloys have the ability of rapidly transforming between amorphous and crystalline phases. Therefore, they can be used in the non-volatile phase change memory. Recently, a vacancy-ordered cubic Ge2Sb2Te5 (VOC GST) phase change material where the vacancies are highly ordered in the (111) plane, has been experimentally demonstrated by STEM. However, studies are mainly on the structural characterization, rather than on the phase change behavior and possible applications of the VOC GST. Here, using first-principles molecular dynamic simulations, we study the melt-quenched amorphization process and its possible applications. We find that the VOC GST exhibits a quasi-two-dimensional amorphization process that is triggered by the diffusion of Ge atoms but not others. A partial amorphous (P-amor) phase is obtained, which can act as an intermediate state between the pure amorphous and pure crystalline phases for possible ternary-state data storage.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.006
      Issue No: Vol. 136 (2017)
       
  • First-principles calculations of stacking fault energies in Mg-Y, Mg-Al
           and Mg-Zn alloys and implications for 〈c+a〉 activity
    • Authors: Binglun Yin; Zhaoxuan Wu; W.A. Curtin
      Pages: 249 - 261
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Binglun Yin, Zhaoxuan Wu, W.A. Curtin
      Mg-3wt.%RE alloys show substantially enhanced 〈 c + a 〉 activity as compared to pure Mg or other Mg-Al, Mg-Zn alloys of similar grain sizes. Activation of 〈 c + a 〉 slip has been postulated to be associated with the reduction of the basal I 1 stacking fault (SF) energy upon alloying with RE elements. However, the underlying mechanism and any special role of the RE solutes, as compared to Al and Zn, remain unclear. Here, precise first-principles methods and calculations are used to assess all relevant SF energies as a function of Y, Al and Zn concentrations in the dilute limit relevant to current experiments. Results show that solute effects vary among different solutes and among different SFs of the same solute. However, the effects of Y on basal plane SF energies can also be achieved by Al at similar/twice the concentrations and the effect of Y on the pyramidal (Pyr.) II plane can be achieved by Zn at similar concentrations. Enhanced 〈 c + a 〉 activity in Mg-3wt.%RE alloys thus does not appear to be directly related to these SF energies, in contrast to current widely-accepted postulates. The average reductions in Pyr. II and I SF energies by Y also have little influence on the strong thermodynamic driving force for the transition of easy-glide Pyr. II and I dislocations into sessile basal-plane-dissociated structures. Y solutes only stand out in affecting the relative pyramidal SF energies differently than Al and Zn, which is not considered in any mechanisms proposed to date. These results highlight the importance of precise first-principles calculations in study of solid solution alloying at appropriate solute concentrations, which allows for the quantitative assessment of potential dislocation phenomena related to ductility.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.062
      Issue No: Vol. 136 (2017)
       
  • Ab initio assisted design of quinary dual-phase high-entropy alloys with
           transformation-induced plasticity
    • Authors: Zhiming Li; Fritz Körmann; Blazej Grabowski; Jörg Neugebauer; Dierk Raabe
      Pages: 262 - 270
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Zhiming Li, Fritz Körmann, Blazej Grabowski, Jörg Neugebauer, Dierk Raabe
      We introduce a new class of high-entropy alloys (HEAs), i.e., quinary (five-component) dual-phase (DP) HEAs revealing transformation-induced plasticity (TRIP), designed by using a quantum mechanically based and experimentally validated approach. Ab initio simulations of thermodynamic phase stabilities of Co20Cr20Fe40-xMn20Nix (x = 0–20 at. %) HEAs were performed to screen for promising compositions showing the TRIP-DP effect. The theoretical predictions reveal several promising alloys, which have been cast and systematically characterized with respect to their room temperature phase constituents, microstructures, element distributions and compositional homogeneity, tensile properties and deformation mechanisms. The study demonstrates the strength of ab initio calculations to predict the behavior of multi-component HEAs on the macroscopic scale from the atomistic level. As a prototype example a non-equiatomic Co20Cr20Fe34Mn20Ni6 HEA, selected based on our ab initio simulations, reveals the TRIP-DP effect and hence exhibits higher tensile strength and strain-hardening ability compared to the corresponding equiatomic CoCrFeMnNi alloy.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.023
      Issue No: Vol. 136 (2017)
       
  • Stress-induced phase transition in lead-free relaxor ferroelectric
           composites
    • Authors: Lukas M. Riemer; K.V. Lalitha; Xijie Jiang; Na Liu; Christian Dietz; Robert W. Stark; Pedro B. Groszewicz; Gerd Buntkowsky; Jun Chen; Shan-Tao Zhang; Jürgen Rödel; Jurij Koruza
      Pages: 271 - 280
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Lukas M. Riemer, K.V. Lalitha, Xijie Jiang, Na Liu, Christian Dietz, Robert W. Stark, Pedro B. Groszewicz, Gerd Buntkowsky, Jun Chen, Shan-Tao Zhang, Jürgen Rödel, Jurij Koruza
      Piezoelectric materials are considered an enabling technology generating an annual turnover of about 20 billion $. At present, lead-based materials dominate the market with the known risk to health and environment. One of the three key competitors for their replacement is the class of sodium bismuth titanate (NBT)-based relaxor ferroelectrics, the use of which is limited by thermal depolarization. An increased thermal stability has recently been experimentally demonstrated for composites of Na1/2Bi1/2TiO3-6BaTiO3 with ZnO inclusions (NBT-6BT:xZnO). However, the exact mechanism for this enhancement still remains to be clarified. In this study, piezoresponse force microscopy and 23Na NMR spectroscopy were used to demonstrate that the incorporation of ZnO leads to a stabilization of the induced ferroelectric state at room temperature. Temperature-dependent measurements of the relative dielectric permittivity ε′(T), the piezoelectric coefficient d 33 and the strain response revealed an increase of the working temperature by 37 °C. A simple mechanics model suggests that thermal deviatoric stresses stabilize the ferroelectric phase and increase, as well as broaden, the temperature range of depolarization. Our results reveal a generally applicable mechanism of enhancing phase stability in relaxor ferroelectric materials, which is also valid for phase diagrams of other ceramic matrix composites.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.008
      Issue No: Vol. 136 (2017)
       
  • On the influence of microcantilever pre-crack geometries on the apparent
           fracture toughness of brittle materials
    • Authors: Steffen Brinckmann; Kurt Matoy; Christoph Kirchlechner; Gerhard Dehm
      Pages: 281 - 287
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Steffen Brinckmann, Kurt Matoy, Christoph Kirchlechner, Gerhard Dehm
      Focused ion beam machined microcantilevers are frequently used for fracture mechanics analysis of inhomogeneous solids at the micrometer scale. A finite element method study about the influence of the pre-crack geometry on the apparent fracture toughness is provided. We discuss the influence of material bridges and the effect of rounded pre-crack corners when two dimensional models are employed to evaluate the fracture toughness. We conclude with a guideline for introducing an optimized pre-crack.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.014
      Issue No: Vol. 136 (2017)
       
  • Diffusion mechanisms of C in 100, 110 and 111 Fe surfaces studied using
           kinetic activation-relaxation technique
    • Authors: Oscar A. Restrepo; Charlotte S. Becquart; Fedwa El-Mellouhi; Othmane Bouhali; Normand Mousseau
      Pages: 303 - 314
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Oscar A. Restrepo, Charlotte S. Becquart, Fedwa El-Mellouhi, Othmane Bouhali, Normand Mousseau
      The physics of Fe-C surface interactions is of fundamental importance to phenomena such as corrosion, catalysis, synthesis of graphene, new steels, etc. To better understand this question, we perform an extensive characterization of the energy landscape for carbon diffusion from bulk to surfaces for bcc iron at low C concentration. C diffusion mechanisms over the three main Fe-surfaces – (100), (110) and (111) – are studied computationally using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Migration and adsorption energies on surfaces as well as absorption energies into the subsurfaces are predicted and then compared to density functional theory (DFT) and experiment. The energy landscape along C-diffusion pathways from bulk to surface is constructed allowing a more extensive characterization of the diffusion pathways between surface and subsurface. In particular, effective migration energies from (100), (110) and (111) surfaces, to the bulk octahedral site are found to be around ∼1.6 eV, ∼1.2 eV and ∼1.3 eV respectively suggesting that C insertion into the bulk cannot take place in pure crystalline Fe, irrespective of the exposed surface.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.009
      Issue No: Vol. 136 (2017)
       
  • Extreme reduction of thermal conductivity by embedding Al2O3 nanoparticles
           into single-crystalline Bi nanowires
    • Authors: Jong Wook Roh; Jinhee Ham; Jeongmin Kim; Hongjae Moon; Hyun Sik Kim; Wooyoung Lee
      Pages: 315 - 322
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Jong Wook Roh, Jinhee Ham, Jeongmin Kim, Hongjae Moon, Hyun Sik Kim, Wooyoung Lee
      Al2O3 nanoparticles-embedded single-crystalline Bi nanowires were successfully synthesized without using any templates via the spontaneous growth of Bi thin films covered with Al2O3 nanoparticles. It is experimentally confirmed that Al2O3 nanoparticles were embedded into the single-crystalline Bi nanowires by using the high-resolution transmission electron microscopy and energy dispersive X-ray spectrometry. The temperature-dependent thermal conductivities of individual Al2O3 nanoparticles-embedded single-crystalline Bi nanowires were measured directly using suspended micro-devices. The thermal conductivities of the Al2O3 nanoparticles-embedded Bi nanowires were found to be extremely low compared with those of pure Bi nanowires of similar diameters. Moreover, the thermal conductivity of the Al2O3 nanoparticles-embedded Bi nanowires was not size-dependent, i.e., it did not vary for nanowires with significantly different diameters. This result suggests that the phonon-boundary scattering is not the dominant phonon scattering mechanism in these systems while the phonon-boundary scattering is dominant in the pure single-crystalline nanowires. From the experimental measurements and theoretical calculation, these drastic reduction and unique tendency in the thermal conductivities of Al2O3 nanoparticles-embedded Bi nanowires were explained by the combined effect of the phonon-boundary scattering and impurity scattering occurring between the embedded Al2O3 nanoparticles and Bi matrix.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.020
      Issue No: Vol. 136 (2017)
       
  • Effect of saddle point anisotropy of point defects on their absorption by
           dislocations and cavities
    • Authors: D. Carpentier; T. Jourdan; Y. Le Bouar; M.-C. Marinica
      Pages: 323 - 334
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): D. Carpentier, T. Jourdan, Y. Le Bouar, M.-C. Marinica
      Developing predictive models for the microstructure evolution of materials requires an accurate description of the point defects fluxes to the different sinks, such as dislocations, grain boundaries and cavities. This work aims at improving the evaluation of sink strengths of dislocations and cavities using object kinetic Monte-Carlo simulations parametrized with density functional theory calculations. The present accurate description of point defects migration enables quantitative assessment of the influence of the point defects anisotropy at saddle point. The results in aluminum show that the anisotropy at saddle point has a large influence on sink strengths. In particular, this anisotropy leads to the cavity being a biased sink. These results are explained by the analysis of the point defect trajectories to the sinks, which are shown to be strongly affected by the saddle point anisotropy.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.013
      Issue No: Vol. 136 (2017)
       
  • Influence of growth velocity variations on the pattern formation during
           the directional solidification of ternary eutectic Al-Ag-Cu
    • Authors: Johannes Hötzer; Philipp Steinmetz; Anne Dennstedt; Amber Genau; Michael Kellner; Irmak Sargin; Britta Nestler
      Pages: 335 - 346
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Johannes Hötzer, Philipp Steinmetz, Anne Dennstedt, Amber Genau, Michael Kellner, Irmak Sargin, Britta Nestler
      In order to control the evolving microstructure in complex eutectics and other multi-phase systems, it is important to understand the adjustment mechanisms and the parameters that determine pattern evolution. Here, a combined experimental and simulation approach is taken to investigate the response of a three-phase eutectic system to changes in solidification velocity. Using Al-Ag-Cu as a model system, large scale three-dimensional phase-field simulations are compared to directionally solidified samples containing both, velocity increases and decreases. The experimental results are obtained by synchrotron tomography for detailed consideration of the microstructure directly before and after a targeted velocity change and by traditional SEM analysis of sample cross sections to capture effects over longer length scales. In addition to qualitative analysis of the images, the microstructures are statistically assessed using phase fractions, shape factor and nearest neighbor statistics. Both, simulation and experiment show an immediate change in phase fraction as a result of a change in growth velocity. Adjustment of the microstructural pattern occurs more slowly over a relatively long length scale, due to splitting, merging and overgrowing events. Novel quantification techniques emphasize that ternary eutectic phase arrangements are complex and continuously evolving structures which, even under ideal conditions, do not reach steady state growth as quickly as previously believed.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.007
      Issue No: Vol. 136 (2017)
       
  • Shear and shuffling accomplishing polymorphic fcc γ → hcp
           ε → bct α martensitic phase transformation
    • Authors: Xu-Sheng Yang; Sheng Sun; Hai-Hui Ruan; San-Qiang Shi; Tong-Yi Zhang
      Pages: 347 - 354
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Xu-Sheng Yang, Sheng Sun, Hai-Hui Ruan, San-Qiang Shi, Tong-Yi Zhang
      Martensitic transformation (MT) has extreme science merits and engineering significance. However, the underlying displacive atom collective movements for the transition from face-centered cubic structure (fcc-γ) austenite to body-centered tetragonal structure (bct-α) martensite has not been uncovered due to the lack of directly experimental evidence. Here, we examined the Plastic Deformation-Induced Martensitic Transformation (PDIMT) from fcc-γ to bct-α in AISI 304 stainless steel by High-resolution Transmission Electron Microscopy (HRTEM). The HRTEM observations exhibit a novel polymorphic fcc-γ → hcp-ε → bct-α PDIMT mechanism, which is further confirmed by the Molecular Dynamics (MD) simulations. The transition from fcc-γ to hcp-ε is accomplished by gliding Shockley partial dislocations on every second (111)γ planes. The transition from hcp-ε to bct-α is executed by gliding half-Shockley partial dislocation dipoles on every second (0001)ε planes and the gliding is simultaneously accompanied by atom shuffling. The dipole shear is conducted in a sandwich manner, meaning that a half-Shockley partial dislocation glides on one side of a (0001)ε plane and its partner of the dipole glides on the other side of the same (0001)ε plane. The novel findings will have great impact on the microstructural control in metals and alloys by PDIMT and stimulate innovative ideas to understand other solid phase transition mechanisms.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.016
      Issue No: Vol. 136 (2017)
       
  • Ballistic-diffusive phonon heat transport across grain boundaries
    • Authors: Xiang Chen; Weixuan Li; Liming Xiong; Yang Li; Shengfeng Yang; Zexi Zheng; David L. McDowell; Youping Chen
      Pages: 355 - 365
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Xiang Chen, Weixuan Li, Liming Xiong, Yang Li, Shengfeng Yang, Zexi Zheng, David L. McDowell, Youping Chen
      The propagation of a heat pulse in a single crystal and across grain boundaries (GBs) is simulated using a concurrent atomistic-continuum method furnished with a coherent phonon pulse model. With a heat pulse constructed based on a Bose-Einstein distribution of phonons, this work has reproduced the phenomenon of phonon focusing in single and polycrystalline materials. Simulation results provide visual evidence that the propagation of a heat pulse in crystalline solids with or without GBs is partially ballistic and partially diffusive, i.e., there is a co-existence of ballistic and diffusive thermal transport, with the long-wavelength phonons traveling ballistically while the short-wavelength phonons scatter with each other and travel diffusively. To gain a quantitative understanding of GB thermal resistance, the kinetic energy transmitted across GBs is monitored on the fly and the time-dependent energy transmission for each specimen is measured; the contributions of coherent and incoherent phonon transport to the energy transmission are estimated. Simulation results reveal that the presence of GBs modifies the nature of thermal transport, with the coherent long-wavelength phonons dominating the heat conduction in materials with GBs. In addition, it is found that phonon-GB interactions can result in reconstruction of GBs.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.054
      Issue No: Vol. 136 (2017)
       
  • The formation mechanism of the nanocrystalline cells in Sm2Fe17Nx powder
           during overnitridation
    • Authors: Akihide Hosokawa; Kenta Takagi
      Pages: 366 - 377
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Akihide Hosokawa, Kenta Takagi
      It is known that an overnitridation process significantly improves the coercivity of coarse Sm-(Fe,M)-N magnet powder (M = Cr, Mn, Ti, V) and also introduces a unique microstructure in the particles wherein nanocrystalline cells are separated by amorphous walls (=frequently called nano-cell like structure). It has however been reported that those nanocrystalline cells rotate spontaneously during overnitridation and thus the final powder product becomes unfortunately isotropic. The phenomena have widely been known for more than two decades but the formation/rotation mechanism of the nano-cell like structure is not well understood yet. In this study, the evolutions of the magnetic properties and the microstructure during overnitridation were investigated in greater detail. The multi-scale microstructural observation technique that combines the recent electron microscopic machines disclosed what was occurring in the particles during overnitridation; it was found that the local nitrogen content and the microstructure in a particle are highly heterogeneous and the spontaneous rotation, surprisingly, do not occur.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.019
      Issue No: Vol. 136 (2017)
       
  • Misfit-driven β′′′ precipitate composition and
           morphology in Mg-Nd alloys
    • Authors: Stephen DeWitt; Ellen L.S. Solomon; Anirudh Raju Natarajan; Vicente Araullo-Peters; Shiva Rudraraju; Larry K. Aagesen; Brian Puchala; Emmanuelle A. Marquis; Anton van der Ven; Katsuyo Thornton; John E. Allison
      Pages: 378 - 389
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Stephen DeWitt, Ellen L.S. Solomon, Anirudh Raju Natarajan, Vicente Araullo-Peters, Shiva Rudraraju, Larry K. Aagesen, Brian Puchala, Emmanuelle A. Marquis, Anton van der Ven, Katsuyo Thornton, John E. Allison
      We report on a combined computational and experimental examination of coherent precipitation in a Mg-Nd alloy, a prototypical Mg-rare earth alloy. Three-dimensional phase field simulations are conducted to predict the composition and morphology of β ′ ′ ′ precipitates, a unique family of hierarchically ordered phases that are metastable in a wide Nd concentration range. Predictions are compared to experimental high-angle annular dark-field scanning transmission electron microscopy observations. The phase field model thermodynamic description is parameterized entirely from first-principles calculations. The simulations predict an elevated Nd composition in β ′ ′ ′ that is above the stress-free equilibrium value. The elevated Nd concentration in β ′ ′ ′ is in very good agreement with experimental observations and arises from a large misfit strain energy penalty and the low curvature of the β ′ ′ ′ free energy well. The phase field simulations predict that isolated precipitates are lenticular with a (100) habit plane, and are approximately equiaxial when viewed along the [100] direction. The predicted habit plane and precipitate dimensions are shown to be generally consistent with experimental observations, within the uncertainty introduced by density functional theory calculations of the stress-free transformation (misfit) strain and by precipitate interactions not accounted for in the simulations. Contrary to the predictions for isolated precipitates, some experimentally observed precipitates are elongated along the [001] direction relative to the [010] direction. This elongation is frequently correlated with a particular arrangement of two orientation variants of β ′ ′ ′ . A phase field simulation of two precipitates in this arrangement is shown to exhibit similar [001] elongation.
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      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.053
      Issue No: Vol. 136 (2017)
       
  • Dislocation loop evolution during in-situ ion irradiation of model FeCrAl
           alloys
    • Authors: Jack C. Haley; Samuel A. Briggs; Philip D. Edmondson; Kumar Sridharan; Steve G. Roberts; Sergio Lozano-Perez; Kevin G. Field
      Pages: 390 - 401
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Jack C. Haley, Samuel A. Briggs, Philip D. Edmondson, Kumar Sridharan, Steve G. Roberts, Sergio Lozano-Perez, Kevin G. Field
      Model FeCrAl alloys of Fe-10%Cr-5%Al, Fe-12%Cr-4.5%Al, Fe-15%Cr-4%Al, and Fe-18%Cr-3%Al (in wt %) were irradiated with 1 MeV Kr++ ions in-situ with transmission electron microscopy to a dose of 2.5 displacements per atom (dpa) at 320 °C. In all cases, the microstructural damage consisted of dislocation loops with ½〈111〉 and 〈100〉 Burgers vectors. The proportion of ½〈111〉 dislocation loops varied from ∼50% in the Fe-10%Cr-5%Al model alloy and the Fe-18Cr%-3%Al model alloy to a peak of ∼80% in the model Fe-15%Cr-4.5%Al alloy. The dislocation loop volume density increased with dose for all alloys and showed signs of approaching an upper limit. The total loop populations at 2.5 dpa had a slight (and possibly insignificant) decline as the chromium content was increased from 10 to 15 wt %, but the Fe-18%Cr-3%Al alloy had a dislocation loop population ∼50% smaller than the other model alloys. The largest dislocation loops in each alloy had image sizes of close to 20 nm in the micrographs, and the median diameters for all alloys ranged from 6 to 8 nm. Nature analysis by the inside-outside method indicated most dislocation loops were interstitial type.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.011
      Issue No: Vol. 136 (2017)
       
  • Micromechanical behaviour of a two-phase Ti alloy studied using grazing
           incidence diffraction and a self-consistent model
    • Authors: Y. Zhao; S. Wroński; A. Baczmański; L. Le Joncour; M. Marciszko; T. Tokarski; M. Wróbel; M. François; B. Panicaud
      Pages: 402 - 414
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Y. Zhao, S. Wroński, A. Baczmański, L. Le Joncour, M. Marciszko, T. Tokarski, M. Wróbel, M. François, B. Panicaud
      The mechanical behaviour of each phase in two-phase titanium Ti-18 was studied at room temperature under a low strain rate tensile test until fracture. Due to its selectivity, the X-ray diffraction method was applied for in-situ tensile test to analyse the behaviour of each phase in the direction perpendicular to the loading force. In addition, the biaxial stress states of the initial sample, as well as those of the sample during the tensile test, were determined using multi-reflection grazing incidence X-ray diffraction (MGIXD). The experimental data were compared with the prediction of an elasto-plastic self-consistent model in order to study slips on crystallographic planes and mechanical effects occurring during plastic deformation.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.06.022
      Issue No: Vol. 136 (2017)
       
  • Hydrogen enhances the radiation resistance of amorphous silicon
           oxycarbides
    • Authors: Hepeng Ding; Michael J. Demkowicz
      Pages: 415 - 424
      Abstract: Publication date: 1 September 2017
      Source:Acta Materialia, Volume 136
      Author(s): Hepeng Ding, Michael J. Demkowicz
      We use first principles molecular dynamics to investigate unit displacement processes in amorphous silicon oxycarbides (SiOC) and demonstrate that the introduction of hydrogen (H) into these materials enhances their radiation resistance. Our simulations show that 100 eV knock-ons in H-free SiOC redistribute C through the formation of CO and CC bonds. H counteracts this trend by passivating dangling O bonds and preventing C from coming out of solution. This effect arises from the exceptionally high mobility of H, which leads to the saturation of radiation-induced O and C radicals even before the thermal-spike induced by a high-energy knock-on dies down. Our work suggests that fully hydrogenated SiOC is a promising radiation-resistant material for future nuclear energy applications.
      Graphical abstract image

      PubDate: 2017-07-20T13:41:59Z
      DOI: 10.1016/j.actamat.2017.07.017
      Issue No: Vol. 136 (2017)
       
  • Comparison of densification kinetics of a TiAl powder by spark plasma
           sintering and hot pressing
    • Authors: Zofia Trzaska; Guillaume Bonnefont; Gilbert Fantozzi; Jean-Philippe Monchoux
      Pages: 1 - 13
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Zofia Trzaska, Guillaume Bonnefont, Gilbert Fantozzi, Jean-Philippe Monchoux
      Densification kinetics by spark plasma sintering (SPS) and hot pressing (HP) have been compared, under isothermal conditions and with heating rates of 20 °C/min. Careful calibration of sample temperature has been carried out to obtain comparable results. In all cases, densification kinetics did not exhibit significant differences, ruling out any influence of the SPS current. The stress exponent n and the activation energy Q of the Norton law describing deformation at high temperature of the powder particles have been determined by isothermal experiments at different stresses and temperatures, respectively. The values obtained, n = 1.9 ± 0.3 and Q = 308 ± 20 kJ/mol for SPS, n = 1.5 ± 0.3 and Q = 276 ± 40 kJ/mol for HP, come close in both techniques. Using these values, anisothermal densification kinetics at heating rates of 20°C/min and 100 °C/min, typical of the SPS, could be analytically reproduced, using literature models. The activation parameters suggest that SPS densification kinetics occurs by dislocation climb controlled by Al bulk diffusion, that is, by classical metallurgical mechanisms.
      Graphical abstract image

      PubDate: 2017-06-13T12:04:53Z
      DOI: 10.1016/j.actamat.2017.06.004
      Issue No: Vol. 135 (2017)
       
  • Individual effect of recrystallisation nucleation sites on texture
           weakening in a magnesium alloy: Part 1- double twins
    • Authors: Dikai Guan; W. Mark Rainforth; Junheng Gao; Joanne Sharp; Brad Wynne; Le Ma
      Pages: 14 - 24
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Dikai Guan, W. Mark Rainforth, Junheng Gao, Joanne Sharp, Brad Wynne, Le Ma
      Recrystallised grain nucleation, grain growth and corresponding texture evolution in a cold-rolled rare earth containing WE43 Mg alloy during annealing at 490 °C was fully tracked using a quasi-in-situ electron backscatter diffraction method. The results show nucleation sites, such as double twins, can weaken the deformed texture and for the first time provide direct evidence that recrystallised grains originating from double twins can form the rare earth texture during annealing. Precipitation and recrystallisation occurred concurrently during most of the annealing period, with precipitates forming preferentially along prior grain and twin boundaries. These precipitates effectively retard the recrystallisation due to particle pinning leading to an excessively long time for the completion of recrystallisation. A large portion of recrystallised grains were observed to have 〈0001〉 poles tilted 20–45° away from the normal direction. The RE texture emerges during the nucleation of recrystallised grains and is maintained during subsequent uniform grain growth, which results in a stable RE texture being developed as recrystallisation progresses. The uniform grain growth could be attributed to solute drag suppressing the grain boundary mobility of those grains that had recrystallised with a basal texture and precipitate pinning restricting potential orientated grain growth.
      Graphical abstract image

      PubDate: 2017-06-13T12:04:53Z
      DOI: 10.1016/j.actamat.2017.06.015
      Issue No: Vol. 135 (2017)
       
  • Vacancy mediated alloying strengthening effects on γ/γ′ interface of
           Ni-based single crystal superalloys: A first-principles study
    • Authors: Wenyue Zhao; Zhimei Sun; Shengkai Gong
      Pages: 25 - 34
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Wenyue Zhao, Zhimei Sun, Shengkai Gong
      The vacancy effects on the site preferences of alloying elements Re, Mo, Ta and Cr at γ/γ′ interface are studied using first-principles density functional theory. The alloying strengthening mechanism mediated by vacancy is also evaluated via calculating the Griffith work of fracture for γ/γ′ interface as well as the energy barrier of vacancy migration at the interface. The calculated results show that a Ni vacancy on (001)γ′ plane does not change the most preferable substitution position of the alloying elements at corner-point Ni site on (001)γ except Cr. These alloying elements in γ′ enhance the interfacial bonding strength of γ/γ′ interface even with the presence of a neighboring vacancy, among which Re exhibits the best strengthening effect. The improvement in the γ/γ′ interfacial strength is ascribed to the increased chemical bonding strength between the alloying atom and the nearest-neighbor host atom. Furthermore, a single Ni vacancy has higher migration energy barriers around the alloying solutes especially Re solute substituting on (001)γ at γ/γ′ interface, although the alloying solutes at these preferable sites have no contribution to the interfacial bonding strength.
      Graphical abstract image

      PubDate: 2017-06-13T12:04:53Z
      DOI: 10.1016/j.actamat.2017.05.074
      Issue No: Vol. 135 (2017)
       
  • Interconfigurational and intraconfigurational transitions of Yb2+ and Yb3+
           ions in hydroxyapatite: A cathodoluminescence study
    • Authors: Luz A. Zavala; Paloma Fernández; Ekaterina Novitskaya; Jorge N. Díaz; Manuel Herrera; Olivia A. Graeve
      Pages: 35 - 43
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Luz A. Zavala, Paloma Fernández, Ekaterina Novitskaya, Jorge N. Díaz, Manuel Herrera, Olivia A. Graeve
      We present a cathodoluminescence (CL) study of the interconfigurational transitions of Yb2+ and intraconfigurational transitions of Yb3+ dopant ions in hydroxyapatite (HAp) powders. Our results demonstrate that strong electric fields present in the HAp lattice induce manifold levels in the electronic configuration of the ytterbium ions, due to splitting of the 4f 135d 1 orbitals. CL spectra of Yb2+ display a series of sharp peaks centered at 3.27, 2.98, 2.85, 2.53, 2.27, 2.09 and 1.63 eV, corresponding to transitions between multiple levels produced by a trigonal distortion of the regular octahedral crystal field of the Yb2+ 4f 135d 1 configuration. CL spectra of Yb3+ display four emissions centered at 1.17, 1.21, 1.24 and 1.27 eV, generated by intraconfigurational transitions between the 2F5/2 and 2F7/2 states of Yb3+ ions. Two types of samples were synthesized at different pH values, resulting in variations of the valence of the ytterbium ions, such that the ratios of Yb2+/Yb3+ were 0.31 and 0.55 in calcined powders synthesized at pH values of 6 and 4, respectively, as determined from X-ray photoelectron spectroscopy. Infrared CL images of the two samples show an inhomogeneous spatial distribution of the Yb3+ dopant in the powders. Thermal treatment of the samples, at 873 K in an oxygen atmosphere, result in quenching of the Yb2+ luminescence due to oxidation of the Yb2+ into Yb3+.
      Graphical abstract image

      PubDate: 2017-06-13T12:04:53Z
      DOI: 10.1016/j.actamat.2017.06.003
      Issue No: Vol. 135 (2017)
       
  • Near-isotropic elastic properties and high shear deformation resistance:
           Making low symmetry and open structured YbAlB14, LuAlB14 and ScMgB14
           superhard
    • Authors: Yanchun Zhou; Fu-Zhi Dai; Huimin Xiang; Zhihai Feng
      Pages: 44 - 53
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Yanchun Zhou, Fu-Zhi Dai, Huimin Xiang, Zhihai Feng
      Superhard materials are usually found in high symmetry and high bond density compounds like diamond and cubic BN. Herein, using a combination of first-principles calculations and the microscopic and macroscopic models for hardness prediction, three new possible superhard boron-rich metal borides with low symmetry and open structure are predicted. The predicted hardness values are 37.9 GPa, 37.5 GPa and 41.3 GPa for YbAlB14, LuAlB14 and ScMgB14, respectively, from the macroscopic model and 45.1 GPa, 50.8 GPa and 50.4 GPa, respectively, from the microscopic model. The reliability of this work is supported by comparing the measured hardness of AlMgB14 and Y0.62Al0.71B14 with the calculated Vickers hardness of AlMgB14 and YAlB14. The metal elements are found to influence the anisotropy of BB bonds and elastic properties beside transferring valence electrons to the boron framework and stabilizing the crystal structure. From elastic property angle, it is the near-isotropic elastic modulus and high shear deformation resistance underpinned by the nearly isotropic BB bonding that warrant these low symmetry and open structured ternary borides superhard.
      Graphical abstract image

      PubDate: 2017-06-18T16:58:00Z
      DOI: 10.1016/j.actamat.2017.06.016
      Issue No: Vol. 135 (2017)
       
  • Irradiation-induced damage evolution in concentrated Ni-based alloys
    • Authors: Gihan Velişa; Mohammad W. Ullah; Haizhou Xue; Ke Jin; Miguel L. Crespillo; Hongbin Bei; William J. Weber; Yanwen Zhang
      Pages: 54 - 60
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Gihan Velişa, Mohammad W. Ullah, Haizhou Xue, Ke Jin, Miguel L. Crespillo, Hongbin Bei, William J. Weber, Yanwen Zhang
      Understanding the effects of chemical complexity from the number, type and concentration of alloying elements in single-phase concentred solid-solution alloys (SP-CSAs) on defect dynamics and microstructure evolution is pivotal for developing next-generation radiation-tolerant structural alloys. A specially chosen set of SP-CSAs with different chemical complexity (Ni80Fe20, Ni80Cr20 and Ni40Fe40Cr20) are investigated using 1.5 MeV Mn ions over a wide fluence range, from 2 × 1013 to 1 × 1016 ions cm−2 at room temperature. Based on an integrated study of Rutherford backscattering spectroscopy in channeling geometry and molecular dynamics simulations, the results demonstrate that Ni40Fe40Cr20 is more radiation tolerant than Ni80Fe20, Ni80Cr20 and elemental Ni in the low fluence regime. While chemical complexity of this set of SP-CSAs is clearly demonstrated to affect defect evolution through suppressed defect production and enhanced recombination at early stages, the effect of the mixed ferro- and anti-ferromagnetic interactions is not the only controlling factor responsible for the improved radiation performance. The observed strong alloying effect on defect evolution is attributed to the altered defect migration mobilities of defect clusters in these alloys, an intrinsic characteristic of the complex energy landscapes in CSAs.
      Graphical abstract image

      PubDate: 2017-06-18T16:58:00Z
      DOI: 10.1016/j.actamat.2017.06.002
      Issue No: Vol. 135 (2017)
       
  • Reaction of amorphous/crystalline SiOC/Fe interfaces by thermal annealing
    • Authors: Qing Su; Mikhail Zhernenkov; Hepeng Ding; Lloyd Price; Daniel Haskel; Erik Benjamin Watkins; Jaroslaw Majewski; Lin Shao; Michael J. Demkowicz; Michael Nastasi
      Pages: 61 - 67
      Abstract: Publication date: 15 August 2017
      Source:Acta Materialia, Volume 135
      Author(s): Qing Su, Mikhail Zhernenkov, Hepeng Ding, Lloyd Price, Daniel Haskel, Erik Benjamin Watkins, Jaroslaw Majewski, Lin Shao, Michael J. Demkowicz, Michael Nastasi
      The development of revolutionary new alloys and composites is crucial to meeting materials requirements for next generation nuclear reactors. The newly developed amorphous silicon oxycarbide (SiOC) and crystalline Fe composite system has shown radiation tolerance over a wide range of temperatures. To advance understanding of this new composite, we investigate the structure and thermal stability of the interface between amorphous SiOC and crystalline Fe by combining various experimental techniques and simulation methods. We show that the SiOC/Fe interface is thermally stable up to at least 400 °C. When the annealing temperature reaches 600 °C, an intermixed region forms at this interface. This region appears to be a crystalline phase that forms an incoherent interface with the Fe layer. Density functional theory (DFT) Molecular dynamics (MD) is performed on the homogeneous SiFeOC phase to study the early stages of formation of the intermixed layer. Both experimental and simulation results suggest this phase has the fayalite crystal structure. The physical processes involved in the formation of the intermixed region are discussed.
      Graphical abstract image

      PubDate: 2017-06-18T16:58:00Z
      DOI: 10.1016/j.actamat.2017.06.020
      Issue No: Vol. 135 (2017)
       
 
 
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