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Publisher: Elsevier   (Total: 3163 journals)

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Showing 1 - 200 of 3163 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 9)
AASRI Procedia     Open Access   (Followers: 14)
Academic Pediatrics     Hybrid Journal   (Followers: 30, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 22, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 88, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 35, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 395, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 27, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 2)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 242, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 10, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 27, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 6, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 6)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 16, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 8, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 9, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 22)
Advanced Cement Based Materials     Full-text available via subscription   (Followers: 3, SJR: 0.732, CiteScore: 3)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 137, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 12, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 22, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 14, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 29, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 7, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 3)
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: 27, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 19, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 8)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 23)
Advances in Ecological Research     Full-text available via subscription   (Followers: 42, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 27, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 43, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 53, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 8, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 22)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 37, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 14, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 21)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 1)
Advances in Organ Biology     Full-text available via subscription   (Followers: 1)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 16, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 6, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 10)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
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: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 59)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 5)
Advances in Space Research     Full-text available via subscription   (Followers: 385, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 10, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 17)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 46, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 337, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 10, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 437, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 43, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 1)
Agriculture and Natural Resources     Open Access   (Followers: 2)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 56, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 11, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 9)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 10, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 9, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 50, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 50, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 51, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 44, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 10)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 26, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 34, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 43)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 201, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 61, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 27, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 27, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 37, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 6)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 63, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 15, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 39, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 175, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 10, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)

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Journal Cover
Acta Materialia
Journal Prestige (SJR): 3.263
Citation Impact (citeScore): 6
Number of Followers: 242  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1359-6454
Published by Elsevier Homepage  [3163 journals]
  • Interface energetics and structure of the pearlitic microstructure in
           steels: An atomistic and continuum investigation
    • Authors: Matthew Guziewski; Shawn P. Coleman; Christopher R. Weinberger
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Matthew Guziewski, Shawn P. Coleman, Christopher R. Weinberger
      Atomistic modeling is used to investigate the energetics and structures of commonly reported orientation relationships between ferrite and cementite within pearlite: the Bagaryatskii, the Isaichev, and the Pitsch-Petch, as well as their associated near orientations. Dislocation arrays are found to form for all orientation relationships, with their spacing and direction a function of lattice mismatch. Within each orientation relationship, different interfacial chemistries are found to produce identical dislocation spacings and line directions, but differing interfacial energies. This chemistry component to the interfacial energy is characterized and it is determined that in addition to the lattice mismatch, there are two structural factors within the cementite terminating plane that affect the energetics: the presence of like site iron pairs and proximity of carbon atoms to the interface. Additionally, an alternate method for determining the interfacial energy of systems in which there are multiple chemical potentials for a single element is developed and implemented, an approach which is likely valid for other similar systems. The Isaichev orientation relationship is found to be the most favorable, while the “near” orientation relationships are found to be at least as energetically favorable as their parent orientation relationships. A continuum model based on O-lattice theory and anisotropic continuum theory was also applied to the atomistic results, yielding interfacial energy approximations that match well with those from atomistics and allowing for the characterization of the Burgers vectors, which are found to lie in high symmetry directions of the ferrite within the interface plane.
      Graphical abstract image

      PubDate: 2018-05-31T12:08:08Z
      DOI: 10.1016/j.actamat.2018.05.051
      Issue No: Vol. 155 (2018)
       
  • Elastic properties of AlxCrMnFeCoNi (0 ≤ x ≤ 5) high-entropy alloys
           from ab initio theory
    • Authors: Hualei Zhang; Xun Sun; Song Lu; Zhihua Dong; Xiangdong Ding; Yunzhi Wang; Levente Vitos
      Pages: 12 - 22
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Hualei Zhang, Xun Sun, Song Lu, Zhihua Dong, Xiangdong Ding, Yunzhi Wang, Levente Vitos
      Using ab initio calculations, we investigate the elastic properties of paramagnetic Al x CrMnFeCoNi (0 ≤ x ≤ 5) high-entropy alloys (HEAs) in both body-centered cubic (bcc) and face-centered cubic (fcc) structures. Comparison with available experimental data demonstrates that the employed approach describes accurately the elastic moduli. The predicted lattice constants increase monotonously with Al addition, whereas the elastic parameters exhibit complex composition dependences. The elastic anisotropy is unusually high for both phases. The brittle/ductile transitions formulated in terms of Cauchy pressure and Pugh ratio become consistent only when the strong elastic anisotropy is accounted for. The negative Cauchy pressure of CrMnFeCoNi is due to the relatively low bulk modulus and C 12 elastic constant, which in turn are consistent with the relatively low cohesive energy. The present findings in combination with the experimental data suggest anomalous metallic character for the HEAs system.
      Graphical abstract image

      PubDate: 2018-06-03T15:07:48Z
      DOI: 10.1016/j.actamat.2018.05.050
      Issue No: Vol. 155 (2018)
       
  • Glide and cross-slip of a-dislocations in Zr and Ti
    • Authors: D. Caillard; M. Gaumé; F. Onimus
      Pages: 23 - 34
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): D. Caillard, M. Gaumé, F. Onimus
      Slip systems involving dislocations with <a> Burgers vectors have been studied in hexagonal close packed Zr and Ti, by means of in situ straining experiments in a transmission electron microscope, at various temperatures and as a function of resolved shear stress. The results show that Zr and Ti are very similar in many respects. Prismatic slip is activated at rather low resolved shear stresses, and is controlled by the interaction between mobile dislocations and solute atoms (presumably oxygen). Pyramidal slip requires substantially higher resolved shear stresses and is characterized by straight screw dislocations moving by a kink-pair mechanism. Basal slip is activated at and above room temperature, for resolved shear stresses equal or higher than those in the prismatic planes. The slip traces are always wavy, presumably due to intensive cross slip from basal to prismatic planes. It also involves straight screw dislocations moving by a kink-pair mechanism. These microscopic observations are discussed in the light of some aspects of the mechanical behavior, in particular the increase of yield-stress at decreasing temperature and the discontinuity of activation area close to room temperature.
      Graphical abstract image

      PubDate: 2018-06-03T15:07:48Z
      DOI: 10.1016/j.actamat.2018.05.038
      Issue No: Vol. 155 (2018)
       
  • Universal aging characteristics of macroscopically and microscopically
           dissimilar metallic glasses
    • Authors: Kaikin Wong; Rithin P. Krishnan; Eric M. Dufresne; Koji Ohara; Alec R. Sandy; Suresh M. Chathoth
      Pages: 35 - 42
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Kaikin Wong, Rithin P. Krishnan, Eric M. Dufresne, Koji Ohara, Alec R. Sandy, Suresh M. Chathoth
      Supercooled liquids and glasses, due to their intrinsically unstable nature, are known to relax continuously until an equilibrium state is reached. By exploring atomic relaxation, aging and microscopic structure of chemically similar but physically dissimilar metallic glasses, we find that neither the relaxation time nor aging correlate with the free volume or density of the glasses. Furthermore, atomic relaxation time in these metallic glasses does not depend on the microscopic structure of the systems. The activation energy for the diffusion process indicates a completely different microscopic mechanism governing the atomic transport process. Nevertheless, the age-dependent relaxation time surprisingly exhibits a universal time-waiting time-temperature superposition. Our results provide a convincing proof of the universality in the aging of out-of-equilibrium materials.
      Graphical abstract image

      PubDate: 2018-06-03T15:07:48Z
      DOI: 10.1016/j.actamat.2018.05.059
      Issue No: Vol. 155 (2018)
       
  • A unified theory for microstructural alterations in bearing steels under
           rolling contact fatigue
    • Authors: Hanwei Fu; Pedro E.J. Rivera-Díaz-del-Castillo
      Pages: 43 - 55
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Hanwei Fu, Pedro E.J. Rivera-Díaz-del-Castillo
      Three major types of microstructural alterations occurring under rolling contact fatigue, white etching areas (WEAs), dark etching regions (DERs) and white etching bands (WEBs), are modelled under a unified approach: dislocation-assisted carbon migration theory. Following our previous work on DERs and WEBs, a novel model is proposed to describe dislocation cell formation in WEAs. The proposed model yields predictions of WEAs appearance, agreeing with experimental observations. Bearing life can be estimated by the WEA appearance model. The three microstructural alterations models are combined and, for the first time, it becomes possible to predict the occurrence and the formation progress of WEAs, DERs and WEBs with a unified theory. Microstructural alteration maps are plotted as a function of number of cycles, temperature, contact pressure and stress cycle frequency. The models are validated by the experimental results reported over the last 50 years.
      Graphical abstract image

      PubDate: 2018-06-06T07:44:56Z
      DOI: 10.1016/j.actamat.2018.05.056
      Issue No: Vol. 155 (2018)
       
  • Direct observation of deformation twinning under stress gradient in
           body-centered cubic metals
    • Authors: Binbin Jiang; Aidong Tu; Hao Wang; Huichao Duan; Suyun He; Hengqiang Ye; Kui Du
      Pages: 56 - 68
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Binbin Jiang, Aidong Tu, Hao Wang, Huichao Duan, Suyun He, Hengqiang Ye, Kui Du
      In body-centered cubic (BCC) metals, plastic deformation usually takes place by deformation twinning under high strain rate. Although numerous efforts have been conducted on deformation twinning, the twinning mechanism is still shrouded in mystery. Here, we report a direct observation of deformation twinning in BCC tantalum and niobium by the use of in situ and aberration-corrected electron microscopy. Twin lamellae grow up from coherent twin boundaries by repeatedly extruding and subsequently expanding of bulges on the twin boundaries. A substantial stress gradient is detected around twin lamellae along the twinning direction. The twin growth can be described by a self-thickening mechanism through dislocation reactions at steps on coherent twin boundaries thus absent continuous supply of dislocations. The dislocation reactions can be activated and deactivated by the transition between normal step dislocations and complementary zonal dislocations. These results provide insights to deformation twinning in bulk BCC metals.
      Graphical abstract image

      PubDate: 2018-06-06T07:44:56Z
      DOI: 10.1016/j.actamat.2018.05.061
      Issue No: Vol. 155 (2018)
       
  • Density fluctuations with fractal order in metallic glasses detected by
           synchrotron X-ray nano-computed tomography
    • Authors: B. Huang; T.P. Ge; G.L. Liu; J.H. Luan; Q.F. He; Q.X. Yuan; W.X. Huang; K. Zhang; H.Y. Bai; C.H. Shek; C.T. Liu; Y. Yang; W.H. Wang
      Pages: 69 - 79
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): B. Huang, T.P. Ge, G.L. Liu, J.H. Luan, Q.F. He, Q.X. Yuan, W.X. Huang, K. Zhang, H.Y. Bai, C.H. Shek, C.T. Liu, Y. Yang, W.H. Wang
      We report density fluctuations spanning from nano-to micrometer scale in the three-dimensional (3D) space in metallic glasses (MGs) detected with synchrotron X-ray nano-computed tomography, which decouple with the chemical homogeneity. The MG quenched from fragile supercooled liquid exhibits a more heterogeneous microstructure with a gradient density fluctuation. Severe inhomogeneous deformation rejuvenates the microstructure of the MG with the creation of a large amount of low-density regions, which percolate into shear-band-like layers. Ramified 2.5-dimensional fractal low-density regions exist in all the MGs with the correlation length increasing with microstructural heterogeneity. The formation of the density fluctuations with fractal order in the MGs is discussed based on the percolation of low-density regions and shear transformation zones during the glass transition and deformation processes. Our results directly demonstrate the existence of fractal low-density entropic droplets in MGs affected by fragilities and thermomechanical histories, which could be significant for understanding and controlling the disordered structure of amorphous solids.
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      PubDate: 2018-06-06T07:44:56Z
      DOI: 10.1016/j.actamat.2018.05.064
      Issue No: Vol. 155 (2018)
       
  • Void growth and coalescence in a magnesium alloy studied by synchrotron
           radiation laminography
    • Authors: Babak Kondori; Thilo F. Morgeneyer; Lukas Helfen; A. Amine Benzerga
      Pages: 80 - 94
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Babak Kondori, Thilo F. Morgeneyer, Lukas Helfen, A. Amine Benzerga
      Damage accumulation is studied in a rolled, partially annealed magnesium alloy by means of synchrotron tomography. To avoid failure by plastic instability and generate an effective damage process zone, round notched bars are deformed up to crack initiation then sheet-like samples are cut out for subsequent tomography observations. The effect of the hydrostatic stress is explored by considering two notch radii. In a given specimen, advantage is taken of the naturally occurring gradients in plastic strain and stress triaxiality to gain insight into the various stages of damage progression, damage-to-fracture transition, as well as crack propagation. The key finding is that damage is quite diffuse in both types of specimens. The observations document extensive void nucleation, growth and coalescence, reminiscent of the most ductile and tough metallic materials. Crack growth is found to be inherently anisotropic. Crack initiation is found to occur predominately at the center of the specimen with a blunt notch, and near the notch root in the specimen with a sharp notch. Quantitative measurements based on about 1000 microvoids and blunted microcracks enable values of void volume fraction and microcrack blunting to be fairly estimated, at macroscopic crack initiation.
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      PubDate: 2018-06-09T11:17:46Z
      DOI: 10.1016/j.actamat.2018.05.026
      Issue No: Vol. 155 (2018)
       
  • Effect of Fe doping and magnetic field on martensitic transformation of
           Mn-Ni(Fe)-Sn metamagnetic shape memory alloys
    • Authors: P. Lázpita; M. Sasmaz; J.M. Barandiarán; V.A. Chernenko
      Pages: 95 - 103
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): P. Lázpita, M. Sasmaz, J.M. Barandiarán, V.A. Chernenko
      In this work we report the elaboration of a family of metamagnetic shape memory alloys with composition Mn49Ni42-x FexSn9 (x = 0, 2, 3, 4, 5 and 6 at.%) and the systematic study of their structure, martensitic transformation (MT) behavior and functional characteristics as a function of the Fe doping and magnetic field, up to 12 T. Regarding the influence of the magnetic field, we have tentatively divided the alloys into two groups: group I, alloys with x = 0, 2, 3 and 4 and group II, alloys with x = 5 and 6. Group II alloys exhibit an appreciable amount of dispersed γ-phase and a field-induced arrest of MT. The alloys from group I show a large magnetization drop at MT that proceeds steeply. This group also displays a monotonous evolution of all studied properties with pronounced metamagnetic effect and large magnetostrain effect, reaching 0.3%, in the alloy with x = 4.
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      PubDate: 2018-06-09T11:17:46Z
      DOI: 10.1016/j.actamat.2018.05.052
      Issue No: Vol. 155 (2018)
       
  • Dislocation-type evolution in quasi-statically compressed polycrystalline
           nickel
    • Authors: Chaoyi Zhu; Tyler Harrington; George T. Gray; Kenneth S. Vecchio
      Pages: 104 - 116
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Chaoyi Zhu, Tyler Harrington, George T. Gray, Kenneth S. Vecchio
      The nature of dislocation generation as a function of applied plastic strain in quasi-statically compressed polycrystalline pure nickel has been studied experimentally at ambient temperature. First, to ensure representative datasets of the geometrically-necessary dislocation densities (ρGND) associated with non-uniform plastic deformation, measurements over large (several millimeter square) areas were made using Hough-based EBSD methods. In addition, the total dislocation density (ρT) responsible for the overall work hardening is estimated from the measured flow stress based on Taylor's hardening model. Next, the statistically stored dislocation (SSD) density (ρSSD) is calculated by subtracting the GND density from the total dislocation density. The results demonstrate that in quasi-statically deformed nickel: i) the measured GND density varies linearly as a function of plastic strain in the range between 0.05 and 0.46; although Ashby's model predicts linearity for GND density evolution over entire range of strains, this study does not cover strains below 0.05; ii) the SSD density increases at a rate much faster than GND density; and iii) the SSD density exceeds the GND density at above 0.09 plastic strain. Both i) and ii) are in agreement with Ashby's prediction, while the magnitudes of GND density (iii) differ from Ashby's model prediction, particularly at large applied strains. Overall, this study enables the interplay of GNDs and SSDs in the hardening of nickel to be gleaned in a quantitative sense. This study illustrates that GNDs are the more important for the strength of polycrystalline metals in the early stages of work hardening, whereas SSDs contribute more to the strength at larger strains. Over the range of strain in this study, work hardening is predominantly through rapid multiplication of SSDs; whereas the GND density is initially higher than SSD density at 0.05 probably due to non-linear evolution of GNDs at low strains (<0.05), which will be the subject of future investigation.
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      PubDate: 2018-06-09T11:17:46Z
      DOI: 10.1016/j.actamat.2018.05.022
      Issue No: Vol. 155 (2018)
       
  • On the thermodynamics, kinetics, and sub-Tg relaxations of Mg-based bulk
           metallic glasses
    • Authors: Maximilian Frey; Ralf Busch; Wulff Possart; Isabella Gallino
      Pages: 117 - 127
      Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Maximilian Frey, Ralf Busch, Wulff Possart, Isabella Gallino
      The four Mg-based bulk metallic glass forming alloys Mg59.5Cu22.9Ag6.6Gd11, Mg61Cu28Gd11, Mg54Cu28Ag7Y11, and Mg65Cu25Y10 are investigated to gain insight into their thermodynamic and kinetic properties. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) in three point beam bending mode are used. The gathered data sets are used to evaluate the origin of the high glass forming ability of these systems, which is found in low thermodynamic driving forces for crystallization and sluggish kinetics. Furthermore, sub-Tg effects are observed via dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC) of as-cast samples. These are interpreted as related to the α-relaxation time spectrum instead of being caused by a Johari-Goldstein-type relaxation mechanism.
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      PubDate: 2018-06-09T11:17:46Z
      DOI: 10.1016/j.actamat.2018.05.063
      Issue No: Vol. 155 (2018)
       
  • Temperature dependence of the crystal structures and phase fractions of
           secondary phases in a Nd-Fe-B sintered magnet
    • Authors: Naruki Tsuji; Hiroyuki Okazaki; Wakana Ueno; Yoshinori Kotani; David Billington; Akira Yasui; Shogo Kawaguchi; Kunihisa Sugimoto; Kentaro Toyoki; Tomoki Fukagawa; Takeshi Nishiuchi; Yoshihiro Gohda; Satoshi Hirosawa; Kazuhiro Hono; Tetsuya Nakamura
      Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): Naruki Tsuji, Hiroyuki Okazaki, Wakana Ueno, Yoshinori Kotani, David Billington, Akira Yasui, Shogo Kawaguchi, Kunihisa Sugimoto, Kentaro Toyoki, Tomoki Fukagawa, Takeshi Nishiuchi, Yoshihiro Gohda, Satoshi Hirosawa, Kazuhiro Hono, Tetsuya Nakamura
      The constituent phases of a Nd14.2Fe79.4B6.3Cu0.1 sintered magnet and their crystal structures at ambient and elevated temperatures have been determined by synchrotron X-ray diffraction. At room temperature, dhcp-Nd, NdO x , hcp-Nd2O3, and Nd5Fe18B18 (Nd1.1Fe4B4) secondary phases have been identified in addition to the Nd2Fe14B main phase. The dhcp-Nd phase melts around 600 °C, corresponding to the eutectic temperature for the ternary Nd2Fe14B, Nd and Nd5Fe18B18 system. Below 600 °C, the variation of the lattice constants of the dhcp-Nd phase with temperature is strongly influenced by an internal stress from the spontaneous magnetostriction of the Nd2Fe14B phase. The difference of the lattice constants of the dhcp-Nd phase compared to those of pristine Nd metal is also significant, which is possibly associated with the inclusion of interstitial oxygen atoms at the 4f Wyckoff positions in the dhcp-Nd crystal. The validity of this scenario is confirmed by first-principles calculations of the equilibrium lattice constants of three-, four-, and nine-unit-cell supercells, in which different numbers of oxygen atoms quasi-randomly occupy some of the unoccupied 4f-sites.
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      PubDate: 2018-05-31T12:08:08Z
      DOI: 10.1016/j.actamat.2018.05.020
      Issue No: Vol. 154 (2018)
       
  • Effect of processing temperature on the microstructural characteristics of
           Cu-Ag nanocomposites: From supersaturation to complete phase decomposition
           
    • Authors: K.S. Kormout; P. Ghosh; A. Bachmaier; A. Hohenwarter; R. Pippan
      Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): K.S. Kormout, P. Ghosh, A. Bachmaier, A. Hohenwarter, R. Pippan
      Initially micrometer-sized powder blends of different compositions (Cu-6at%Ag, Cu-37 at%Ag and Cu-84 at%Ag corresponding to Cu-9vol%Ag, Cu-46 vol%Ag and Cu-89 vol%Ag) were deformed by high-pressure torsion for varying applied strain and temperature in order to study their effect on the degree of supersaturation and the prevailing deformation mechanisms. The resulting microstructures were comprehensively characterized with synchrotron X-ray diffraction and transmission electron microscopy. A gradual transition from complete supersaturation to complete phase separation was observed with increasing processing temperature. The critical temperature for full supersaturation strongly depended on the composition. In composites with low Ag and Cu contents single-phase alloys could be obtained up to processing temperatures of 100 °C. In the medium composition range strain localization in shear bands prevented full supersaturation for room temperature deformation. Only in regions deformed by shear bands a complete single-phase supersaturated solid solution was obtained, while the lamellar matrix retained a dual-phase structure. By lowering the processing temperature, using liquid nitrogen as coolant, a homogenous single-phase alloy could be also attained at medium compositions. The present results unravel a clear correlation between dominating deformation mechanisms and the degree of deformation-induced supersaturation.
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      PubDate: 2018-05-31T12:08:08Z
      DOI: 10.1016/j.actamat.2018.05.010
      Issue No: Vol. 154 (2018)
       
  • In situ synchrotron X-ray diffraction investigations of the physical
           mechanism of ultra-low strain hardening in Ti-30Zr-10Nb alloy
    • Authors: Z.W. Zhu; C.Y. Xiong; J. Wang; R.G. Li; Y. Ren; Y.D. Wang; Y. Li
      Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): Z.W. Zhu, C.Y. Xiong, J. Wang, R.G. Li, Y. Ren, Y.D. Wang, Y. Li
      A warm-rolled, metastable β-type Ti-30Zr-10Nb alloy exhibited a peculiar two-stage yielding behavior under uniaxial tensile loading, showing a first plastic stage with obvious strain hardening at 0.4%–10.4% strain and a second plastic stage with ultra-low strain hardening at 10.4%–23.5% strain. In situ high-energy X-ray diffraction (HE-XRD) was used to reveal the stress-induced martensitic transformation scenarios and physical mechanism of the different strain hardening rates. It was found that the deformation-induced phase transformation dominated the onset of the first plastic stage corresponding to the selection of favorable martensitic variants, and their elastic interaction contributed to the obvious strain hardening. HE-XRD experiments further verified that the ultra-low strain hardening rate in the second plastic stage was related to an interesting superelasticity of the martensite, which was characterized by the reversible, stress-induced reorientation of the martensite variants. This reorientation of the martensite variants was primarily due to the rigid lattice rotation of ∼23° about the [110]α″ axis toward the tensile direction. Our investigations provide in-depth understanding of the mechanism of the excellent plasticity with ultra-low strain hardening in β-type titanium alloys.
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      PubDate: 2018-05-31T12:08:08Z
      DOI: 10.1016/j.actamat.2018.05.034
      Issue No: Vol. 154 (2018)
       
  • Growth mode of austenite during reversion from martensite in
           Fe-2Mn-1.5Si-0.3C alloy: A transition in kinetics and morphology
    • Authors: Xianguang Zhang; Goro Miyamoto; Takeshi Kaneshita; Yasuki Yoshida; Yuki Toji; Tadashi Furuhara
      Pages: 1 - 13
      Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): Xianguang Zhang, Goro Miyamoto, Takeshi Kaneshita, Yasuki Yoshida, Yuki Toji, Tadashi Furuhara
      The kinetics and element partitioning during austenite (γ) reversion from lath martensite in Fe-2Mn-1.5Si-0.3C (mass%) alloy have been investigated. Two different types of γ in terms of crystallography, with Kurdjumov-Sachs (K-S) and without K-S orientation relationships with respect to the surrounding tempered martensite matrix, are formed. A transition in kinetics and element partitioning is related to the differences in crystallography. At low temperature, the growth of both types of γ is accompanied with the partitioning of Mn and Si. Consequently, the growth rates and appearance of the K-S and non K-S γ are similar and the reverted γ structure consists of acicular γ dominantly. On the other hand, at high temperature, only the K-S γ grows with partitioning of alloying elements in contrast to the partitionless growth of the non K-S γ, which leads to the formation of coarse globular γ. DICTRA simulation reveals that the variations in driving force for reversion and the interface mobility induce the transition of element partitioning. At large driving force and interface mobility, partitionless growth is possible and consequently coarse globular γ is formed by the fast growth of the non K-S γ at high temperature. On the other hand, reduction of the driving force or interface mobility induces the transition from partitionless to partitioning growth, which results in the dominant formation of thin acicular γ at low temperature.
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      PubDate: 2018-05-28T08:24:29Z
      DOI: 10.1016/j.actamat.2018.05.035
      Issue No: Vol. 154 (2018)
       
  • Multiscale field-induced structure of (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3
           ceramics from combined techniques
    • Authors: M. Otonicar; H. Ursic; M. Dragomir; A. Bradesko; G. Esteves; J.L. Jones; A. Bencan; B. Malic; T. Rojac
      Pages: 14 - 24
      Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): M. Otonicar, H. Ursic, M. Dragomir, A. Bradesko, G. Esteves, J.L. Jones, A. Bencan, B. Malic, T. Rojac
      The vast majority of studies on field-induced changes in (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) materials at the morphotropic phase boundary (MPB) have been performed on single crystals, while the more complex responses in polycrystalline materials have not yet been resolved. By using combined microscopy and diffraction techniques, this study aims to determine the structural changes induced by application of an electric field to two representative MPB compositions of the PMN–xPT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P4mm and Pm phases. Both ceramic compositions are characterized by a hierarchical domain structure with domains present at different length-scales. Based on the applied field measurements, major contributing effects in both compositions are outlined and discussed with respect to the processes related to the monoclinic phase and the adaptive phase theory. It is shown that the highly mobile domain walls are largely involved, along with the field-induced polarization rotation in the monoclinic PMN–30PT, and a phase transition to a mainly tetragonal structure in PMN–35PT. These multiscale results elucidate important aspects of field-induced changes in PMN–xPT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics.
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      PubDate: 2018-05-28T08:24:29Z
      DOI: 10.1016/j.actamat.2018.05.028
      Issue No: Vol. 154 (2018)
       
  • Shape-memory characterization of NiTi microtubes fabricated through
           interdiffusion of Ti-Coated Ni wires
    • Abstract: Publication date: 1 September 2018
      Source:Acta Materialia, Volume 156
      Author(s): A.E. Paz y Puente, D.C. Dunand
      Near-equiatomic NiTi microtubes were fabricated using an additive alloying method consisting of two steps: (i) depositing a Ti-rich coating onto ductile, pure Ni wires (50 μm in diameter) via pack cementation, resulting in a Ni core coated with concentric NiTi2, NiTi and Ni3Ti shells, and (ii) homogenizing the coated wires to near-equiatomic NiTi composition via interdiffusion between core and shells, while concomitantly creating Kirkendall pores. Because of the spatial confinement and radial symmetry of the interdiffusing core/shell structure, the Kirkendall pores coalesce near the center of the wire and form a continuous longitudinal channel, thus creating a microtube. Both the mechanical and thermal response of the NiTi microtubes were characterized in this study using a combination of dynamic mechanical analysis and differential scanning calorimetry, respectively, in conjunction with conventional metallography and X-ray tomographic microscopy. Due to slight compositional variations, both shape-memory and superelastic behaviors were observed within the same microtube, which achieved a total tensile strain of ∼8% before failure: the largest contribution to the strain recovery was the thermal shape memory effect showing near complete strain recovery occurring during multiple cycles. A second microtube exhibited only superelastic behavior, achieving a maximum, recoverable strain of 2.5% at 110 MPa, likely limited by the presence of a remaining Ni3Ti core as a result of under-titanization. Finite-element analysis of elastic stresses in a wire segment modeled from actual tomography data illustrates the extent of stress concentrations due to inner and outer tube surface roughness. The stress concentrations are responsible for a 65% increase in the top 1% average von Mises stress, which may further affect the shape-memory behavior of the tubes.
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      PubDate: 2018-06-23T12:32:54Z
       
  • First-principles prediction of oxygen diffusivity near the (101¯2)
           twin boundary in titanium
    • Abstract: Publication date: 1 September 2018
      Source:Acta Materialia, Volume 156
      Author(s): M.S. Hooshmand, C. Niu, D.R. Trinkle, M. Ghazisaeidi
      We study the diffusivity of oxygen interstitials around a ( 10 1 ¯ 2 ) twin boundary in Titanium. First, we identify all possible stable interstitial sites around the twin boundary and compute the corresponding site energies and transition energy barriers for jumps between these sites, using density functional theory. We show that the site energies and the barriers are consistently lower than in bulk, suggesting the higher tendency of oxygen to segregate to the twin boundary region. Using the site and transition energies and an exact solution to the master equation, we then compute the diffusivity of oxygen in the presence of the twin boundary and find enhanced diffusivity around the boundary in all directions. Enhanced diffusivity towards the boundary determines the feasibility of oxygen segregation to favorable sites at the boundary, while increased diffusivity in the boundary plane provides a path for fast diffusion of oxygen. This result reveals the underlying mechanism governing the slow growth of ( 10 1 ¯ 2 ) twin by pinning at the segregated oxygen interstitials.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Anisotropic sintering behavior of freeze-cast ceramics by optical
           dilatometry and discrete-element simulations
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Aaron Lichtner, Denis Roussel, Daniel Röhrens, David Jauffres, Julie Villanova, Christophe L. Martin, Rajendra K. Bordia
      Directional freeze-casting of ceramic slurries followed by freeze drying and partial sintering results in materials with highly anisotropic properties parallel and transverse to the freezing direction. Physical measurements and optical dilatometry confirm that, during sintering, freeze-cast structures experience more strain along their freezing direction than transverse to it. Discrete Element (DEM) simulations of equivalent freeze-cast structures confirm this behavior. These simulations indicate that not only is sintering anisotropic on the macroscopic scale but within the walls and macropores themselves. It was determined that the anisotropic particle contact network that resulted from the aligned macropores led to anisotropic shrinkage during sintering.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Utilization of high entropy alloy characteristics in Er-Gd-Y-Al-Co high
           entropy bulk metallic glass
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Jinyeon Kim, Hyun Seok Oh, Jinwoo Kim, Chae Woo Ryu, Geun Woo Lee, Hye Jung Chang, Eun Soo Park
      In the present study, we carefully evaluate the role of high entropy alloy (HEA) characteristics on glass-forming ability (GFA) and mechanical responses in a newly developed Er-Gd-Y-Al-Co high entropy bulk metallic glass (HE-BMG) by comparison with the Er-Al-Co and Er-Y-Al-Co bulk metallic glasses (BMGs). The addition of multiple rare-earth elements (REs) to Er-Al-Co BMG results in both higher fragility according to Adam-Gibbs theory and slower crystallization kinetics according to confusion principle. Based on these mutual competitions, the Er18Gd18Y20Al24Co20 HE-BMG can be successfully fabricated up to 5 mm in diameter for glass formation. In particular, the HE-BMG exhibits unexpected structural bias and more fragile manner via preferential covalent bonding of Co-Al and various RE-Al clusters, which leads to larger deviation from the typical BMGs' behavior in the relation between fragility and elastic properties. Furthermore, the HE-BMG effectively retards crystallization kinetics, which was confirmed by exceptionally sluggish nanocrystallization of multi-precipitates from metastable liquid and longer post-recalescence plateau duration in cooling curve of solidification from stable liquid. Indeed, the increased structural instability due to HEA characteristics (preferential short-range order and sluggish crystallization) in HE-BMGs reduces cut-off size of self-organized shear avalanches and increases the number of chaotic shear avalanches, which can distribute the applied strain more homogeneously, resulting in enhanced intrinsic ductility. Consequently, these results provide a guideline on how to design HE-BMGs with promising properties by utilizing HEA characteristics, and thus can give us a strategy for bridging BMG and HEA.
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      PubDate: 2018-06-23T12:32:54Z
       
  • On the diffusive phase transformation mechanism assisted by extended
           dislocations during creep of a single crystal CoNi-based superalloy
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Surendra Kumar Makineni, Ankit Kumar, Malte Lenz, Paraskevas Kontis, Thorsten Meiners, Christopher Zenk, Stefan Zaefferer, Gunther Eggeler, Steffen Neumeier, Erdmann Spiecker, Dierk Raabe, Baptiste Gault
      We propose here a deformation-induced diffusive phase transformation mechanism occurring during shearing of γ′ ordered phase in a γ/γ′ single crystalline CoNi-based superalloy. Shearing involved the creation and motion of a high density of planar imperfections. Through correlative electron microscopy and atom probe tomography, we captured a superlattice intrinsic stacking fault (SISF) and its associated moving leading partial dislocation (LPD). The structure and composition of these imperfections reveal characteristic chemical – structural contrast. The SISF locally exhibits a D019 ordered structure coherently embedded in the L12 γ′ and enriched in W and Co. Interestingly, the LPD is enriched with Cr and Co, while the adjoining planes ahead of the LPD are enriched with Al. Quantitative analysis of the three-dimensional compositional field in the vicinity of imperfections sheds light onto a new in-plane diffusion mechanism as the LPD moves on specific {111} planes upon application of stress at high temperature.
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      PubDate: 2018-06-23T12:32:54Z
       
  • A new insight into the ∑=2 grain boundary characteristics in WC powder
           and in WC-Co sintered materials
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Maxime Pellan, Sabine Lay, Jean-Michel Missiaen, Susanne Norgren, Jenny Angseryd, Ernesto Coronel, Tomas Persson
      In order to gain a better understanding of the WC-Co sintering process, the change in ∑ = 2 grain boundaries was studied in two series of alloys with different carbon contents and increasing Co content in the 10–50 vol% range. The samples were sintered at 1410 °C for 1 h and 5 h. The frequency of ∑ = 2 grain boundaries and the rotation angle distribution were determined using electron backscatter diffraction (EBSD) in order to make a statistical analysis of the effect of composition and sintering time on the special boundary characteristics. Complementary TEM observations were conducted for a more thorough determination of the rotation aspects (angle/axis). The rotation angle is scattered in the WC powder with a maximum peak close to 90°, as expected for ∑ = 2 grain boundaries. However, the average rotation angle tends towards 88.7° in sintered alloys. This deviation is explained by a dislocation array compensating for the misfit and angular deviation in the grain boundary. Its characteristics are calculated using the 0-lattice approach and the associated elastic energy is evaluated from these data. The observed angular deviation is consistent with a minimum elastic energy of the boundary. Particle rearrangement, which can occur during liquid phase sintering, might explain the slight rotation of adjacent crystals in the sintered materials, in order to find a lower energy configuration. A mechanism involving stacking faults in successive prismatic planes is also proposed to explain the formation of ∑ = 2 boundaries and their high frequency in the powder.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Control of surface potential and hydroxyapatite formation on TiO2 scales
           containing nitrogen-related defects
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Masami Hashimoto, Takafumi Ogawa, Satoshi Kitaoka, Shunsuke Muto, Maiko Furuya, Hiroyasu Kanetaka, Masayuki Abe, Hayato Yamashita
      The hydroxyapatite (HAp) formation ability and related surface potentials of rutile-type TiO2 scales formed on Ti are controlled by varying the Ti heat treatment conditions in a N2 atmosphere containing a trace amount of O2. The zeta potentials of the samples heated at 873 and 973 K for 1 h are large negative and positive values, respectively, where HAp formation on the surface is enhanced in both cases. Upon longer heat treatment at those temperatures, the HAp forming ability diminishes and the zeta potential becomes more neutral. Kelvin probe force microscopy indicates that, under dry conditions, the surface charges on the TiO2 scales formed at 873 and 973 K in 1 h are positive and negative, respectively, opposite to the signs of the zeta potentials measured under wet conditions. Scanning transmission electron microscopy, electron energy loss spectroscopy, and calculations of defect formation energies reveal that nitrogen atoms incorporated into TiO2 during scale formation produce the charged defects ( N O ) O − 1 and ( N 2 ) O + 2 for the scales formed in 1 h at 873 and 973 K, respectively. In the case of longer treatments, nitrogen-related defects presumably transform into more stable states, such as N 2 gas, in voids, resulting in a neutral surface. The present findings lead to physical models of surface charge distributions that elucidate the relationship between nitrogen-related defects, charged surfaces, and HAp formation mechanisms.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Thermodynamics of radiation induced amorphization and thermal annealing of
           Dy2Sn2O7 pyrochlore
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Cheng-Kai Chung, Maik Lang, Hongwu Xu, Alexandra Navrotsky
      Thermodynamics and annealing behavior of swift heavy ion amorphized Dy2Sn2O7 pyrochlore were studied. Its amorphization enthalpy, defined as the total energetic difference between the irradiation amorphized and undamaged Dy2Sn2O7 states, was determined to be 283.6 ± 6.5 kJ/mol by high temperature oxide melt drop solution calorimetry. It has been an enigma that stannate and some other pyrochlores do not follow the general rA/rB−radiation resistance relation seen in most pyrochlore systems. In this work, we use the amorphization enthalpy, which reflects all the complex chemical and structural characteristics, as a more effective parameter to correlate the radiation damage resistance of pyrochlores with their compositions. It successfully explains the superior radiation damage resistance of the stannate pyrochlores compared with titanate pyrochlores. Differential scanning calorimetry (DSC) reveals a strong exothermic event starting at 978 K, which is attributed to long-range recrystallization based on X-ray diffraction (XRD) analysis, similar to the effect previously observed in Dy2Ti2O7. A second pronounced heat event beginning at ∼1148 K, which results from local structural rearrangement, is clearly decoupled from the first event for irradiated Dy2Sn2O7. Both the heat releases measured by DSC on heating to 1023 and 1473 K, and the excess enthalpies of the annealed samples indicate that the recovery to the original, ordered state was not fully achieved up to even 1473 K, despite XRD showing the apparent restoration of crystalline pyrochlore structure. The remaining metastability may be attributed to local disorder in the form of weberite-like short-range domains in the recrystallized material. Intriguingly, the second event for different pyrochlores generally starts at similar temperatures while the onset of the long range recrystallization is compositionally dependent. The amorphization and thermal annealing behavior observed in irradiated Dy2Sn2O7 may provide insights into the general mechanisms of radiation damage and recovery of pyrochlores relevant to their nuclear applications.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Synchrotron quantification of graphite nodule evolution during the
           solidification of cast iron
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): M.A. Azeem, M.K. Bjerre, R.C. Atwood, N. Tiedje, P.D. Lee
      In cast iron, graphite develops in conjunction with the metallic matrix during solidification. The morphology and distribution of the embedded graphite is pivotal for mechanical properties from yield strength to fatigue. A novel high temperature environmental cell was developed and combined with in situ synchrotron tomography to investigate and quantify microstructural evolution, including graphite nodule nucleation and growth rates in ductile cast iron. The mechanisms of degenerate graphite nodule formation were also revealed. The formation of a coherent primary gamma phase dendritic network before the graphite nucleation is demonstrated. The graphite nodule nucleation rate, mobility and growth rates are compared to classical models, highlighting the limitations in these models. The results provide unique insights to tune the temperature pathways during cast iron solidification to achieve desired uniform rounded graphite morphologies and size distributions.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Contribution of irradiation-induced defects to hardening of a low-copper
           reactor pressure vessel steel
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Masaki Shimodaira, Takeshi Toyama, Kenta Yoshida, Koji Inoue, Naoki Ebisawa, Keiko Tomura, Toshimasa Yoshiie, Milan J. Konstantinović, Robert Gérard, Yasuyoshi Nagai
      We investigated the fluence dependence of irradiation-induced solute cluster, dislocation loop, and very small defect to reveal the hardening mechanism in surveillance test specimens from a reactor pressure vessel steel with low-Cu content (0.04 wt%) using atom probe tomography (APT), weak-beam scanning transmission electron microscopy (WB-STEM), and positron annihilation spectroscopy. A high number density (>1023 m−3) of solute clusters mainly composed of Ni, Mn, and Si atoms were found in highly neutron irradiated specimens (∼1024 neutrons m−2 (E > 1 MeV)) by APT. These solute clusters were one of the main sources of hardening as reported previously. On the other hand, it was also revealed that dislocation loops were formed with a number density of ∼1022 m−3 in the high-fluence specimens by WB-STEM. The estimated hardening due to dislocation loops was more than half of the actual hardening, showing that dislocation loops are also main source of irradiation hardening at high neutron fluence with the solid experimental evidences. Regarding specimens subjected to a low neutron fluence (∼1023 neutrons m−2), very small defects, not detected by either WB-STEM or APT, were formed by positron annihilation spectroscopy. This result suggested that, at a low neutron fluence, the defects were the initial hardening source and they may grow the dislocation loops observed by WB-STEM at high fluence range.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Radiation damage reduction by grain-boundary biased defect migration in
           nanocrystalline Cu
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Miaomiao Jin, Penghui Cao, Sidney Yip, Michael P. Short
      Nanocrystalline materials with a high density of grain boundaries have long been reported to alleviate radiation damage. However, a full mechanistic understanding of defect reduction, particularly the interaction mechanisms between grain boundaries and clustered defects during irradiation, remains an open question. Here we present atomistic simulations of prolonged radiation damage evolution in Cu bicrystals with increasing radiation dose. Our results reveal the atomic details of defect nucleation and migration, and the mechanisms for the annihilation of defect clusters during irradiation. Stacking fault tetrahedra formed due to radiation damage cascades show preferential migration to irradiated grain boundary. Interstitial-loaded grain boundaries are observed to be dynamically resilient, and persistently interact with the stacking fault tetrahedra, revealing a self-healing response to radiation damage. The results show a synergistic effect of grain boundaries on defect annihilation at small grain spacings of less than 6 nm, giving rise to a drastic decrease in the density of defect clusters. These findings, along with the mechanistic insights, present an integrated perspective on interface-mediated damage reduction in radiation-resistant nanomaterials.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Compact reconstruction of orientation distributions using generalized
           spherical harmonics to advance large-scale crystal plasticity modeling:
           Verification using cubic, hexagonal, and orthorhombic polycrystals
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Adnan Eghtesad, Timothy J. Barrett, Marko Knezevic
      Compaction of crystallographic texture data is highly desirable in crystal plasticity simulations because the computational time involved in such calculations scales linearly with the number of crystal orientations. In a recent publication, we have reported a rigorous procedure for reducing large datasets of crystal orientations for cubic-orthotropic and hexagonal-orthotropic polycrystalline metals using symmetrized generalized spherical harmonics (GSH) functions. The procedure relies on a quantitative description of crystallographic texture using an orientation distribution function (ODF) and its series representation using GSH. The core procedure consists of matching the spectral representation of a full-size ODF containing any number of crystal orientations with that of an ODF containing a compact set of orientations. In this paper, we generalize the procedure to any crystal structure with no restrictions to sample symmetry. These major extensions are accompanied by dealing with significantly more dimensions as well as imaginary terms. Two approaches for generating an initial set of orientations in the compact ODF are explored, one based on binning of a given fundamental zone in the Bunge-Euler orientation space and another that takes advantage of MTEX to maximize the compaction. The overall procedure has been successfully applied to compaction of large ODFs for cubic, hexagonal, and orthorhombic polycrystalline metals with orthotropic and no sample symmetry. It is quantitatively demonstrated that texture evolution, twin volume fraction evolution, stress-strain response, and geometrical changes of samples can be accurately simulated to large plastic strains with compact ODFs using crystal plasticity finite element models.
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      PubDate: 2018-06-23T12:32:54Z
       
  • Growth competition between columnar dendritic grains – Cellular
           automaton versus phase field modeling
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): A. Pineau, G. Guillemot, D. Tourret, A. Karma, Ch.-A. Gandin
      Cellular Automaton (CA) simulations of two-dimensional growth competition among columnar dendritic grains are carried out for a succinonitrile - 0.4 wt% acetone alloy. This is achieved by computing the Grain Boundary (GB) orientation during directional solidification of a bi-crystal in a frozen temperature gradient approximation, each crystal being defined by its own orientation. Comparisons are subsequently conducted with recent Phase Field (PF) results derived under the same conditions as well as with the Geometrical Limit (GL) criterion and the Favorably Orientated Grain (FOG) criterion. The GL criterion is defined mathematically considering infinitely small branching within each grain in directions perpendicular to the main dendrite arms growth directions. The FOG criterion states survival of the grain having the growth direction best aligned with the temperature gradient. The GB orientation is investigated by CA simulations as a function of the cell size, the cell neighborhood and the position used to compute the growth velocity. Results reveal that sufficiently small cells lead to the convergence of the GB orientation towards the GL criterion, while sufficiently large cells lead to the FOG criterion. Within a range of intermediate cell size, excellent agreement is found with a revised version of the FOG criterion (rev-FOG) extracted from PF simulations over a wide range of grain orientations. The cell size needs to be of the order of the maximum step between primary stationary dendrite tips of the two competing grains. The Moore neighborhood provides better results than the von Neumann neighborhood. Noticeable improvement is also observed when computing the growth velocity at the leading dendrite tip positions compared to using the cell center approximation. With computational times several orders of magnitudes lower than PF, the CA method offers a realistic and useful alternative for direct simulations of solidification grain structures in casting processes. This work is also an example of upscaling between models, showing how PF dedicated to model phenomena at the scale of the solid-liquid interface and sidebranching competition can be used to evaluate and calibrate CA developed for large scale simulations.
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      PubDate: 2018-06-20T06:14:10Z
       
  • Nontrivial temperature behavior of the carrier concentration in graphene
           on ferroelectric substrate with domain walls
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Anatolii I. Kurchak, Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Maksym V. Strikha
      This work explores a nontrivial temperature behavior of the carriers concentration, which governs the conductance of the graphene channel on ferroelectric substrate with domain walls that is a basic element for field effect transistors of new generation. We revealed the transition from a single to double antiferroelectric-like hysteresis loop of the concentration voltage dependence that happens with the temperature increase and then exist in a wide temperature range (350–500) K. We have shown that the double loops of polarization and concentration can have irregular shape that remains irregular as long as the computation takes place, and the voltage position of the different features (jumps, secondary maxima, etc) changes from one period to another, leading to the impression of quasi-chaotic behavior. It appeared that these effects originate from the nonlinear screening of ferroelectric polarization by graphene carriers, as well as it is conditioned by the temperature evolution of the domain structure kinetics in ferroelectric substrate. The nonlinearity rules the voltage behavior of polarization screening by graphene 2D-layer and at the same time induces the motion of separated domain walls accompanied by the motion of p-n junction along the graphene channel. Since the domain walls structure, period and kinetics can be controlled by changing the temperature, we concluded that the considered nano-structures based on graphene-on-ferroelectric are promising for the fabrication of new generation of modulators based on the graphene p-n junctions.
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      PubDate: 2018-06-20T06:14:10Z
       
  • Modelling and neutron diffraction characterization of the interfacial
           bonding of spray formed dissimilar steels
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): T.L. Lee, J. Mi, S. Ren, S. Zhao, J. Fan, S. Kabra, S. Zhang, P.S. Grant
      The spray forming of thick, dissimilar steel clad tubes with the objective of achieving a high integrity metallurgical bond across the cladding-substrate interface able to withstand residual stresses and subsequent thermo-mechanical processing was investigated by large scale experiments, modelling and extensive microstructural characterization including microscopy, X-ray tomography, neutron scattering and mechanical testing. The simulated residual stress distributions across the cladding-substrate interface, accounting for any as-sprayed porosity and the distribution of martensitic and retained austenite phases, were compared with neutron diffraction measurements and differences used to infer the load transfer behaviour and thus the mechanical integrity of the interface. The mechanical properties of the interfaces were then also measured directly by shear testing. The link between substrate pre-heating, the spray forming temperature, and the resulting preform temperature, porosity, phase fractions, residual stress, strength and integrity of the interface were established and quantified explicitly.
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      PubDate: 2018-06-20T06:14:10Z
       
  • A comparative study of structural and electrical properties in lead-free
           BCZT ceramics: Influence of the synthesis method
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Indrani Coondoo, Neeraj Panwar, Denis Alikin, Igor Bdikin, Saikh S. Islam, Anton Turygin, Vladimir Ya Shur, Andrei L. Kholkin
      In the present work, various grain size phenomena were studied in promising lead-free piezoelectric ceramics (Ba0.85Ca0.15) (Zr0.10Ti0.90)O3 fabricated via chemical and conventional oxide methods. Phase composition was ascertained by the Rietveld refinement. Average grain size estimated from the microstructure was ∼1.5 μm in the sol-gel derived ceramic (SG-BCZT) which was much smaller than that obtained in coarse grained (∼27 μm) sample prepared by solid state method (SS-BCZT). Systematic investigation of various functional properties viz. dielectric, ferroelectric, piezoelectric and impedance emphasized the profound influence of grain size effects. The increase in grain boundary volume fraction enhanced diffuseness while lowered the dielectric peak in SG-BCZT. Similarly, increase in elastic stiffness and progressive hindrance to domain wall movements, resulted in a decrease of the remnant polarization and the associated piezoelectric charge coefficient values in small-grained SG-BCZT sample. Accordingly, higher Young's modulus value of 158.3 GPa was observed in SG-BCZT as compared to 117.9 GPa in SS-BCZT. Local-area piezoresponse force microscopy (PFM) images revealed lamellar domains with periodicity 250 ± 90 nm in SS-BCZT while small sized fractal-like irregular domains with an estimated domain width of 150 ± 60 nm were registered in SG-BCZT. Complex impedance spectroscopy results along with grain boundary conductivity were also guided by grain size effect. The mechanisms of grain size driven effects and their impact on the functional properties were discussed.
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      PubDate: 2018-06-20T06:14:10Z
       
  • In-situ high temperature micromechanical testing of ultrafine grained
           yttria-stabilized zirconia processed by spark plasma sintering
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Jaehun Cho, Jin Li, Q. Li, Jie Ding, Han Wang, S. Xue, T.B. Holland, A.K. Mukherjee, Haiyan Wang, X. Zhang
      Yttria-stabilized zirconia (YSZ) exhibits both enhanced strength and fracture toughness attributed to transformation-induced plasticity. Recent studies show that miniaturization of YSZ to the microscale enhances the effectiveness of stress-induced phase transformation by reducing mismatch stress among incommensurate grains. However, the fundamental understandings on the high temperature micromechanical behaviors of ultrafine grained YSZ remain limited. Here, we report on the high temperature (up to 670 °C) in-situ micromechanical testing of spark plasma sintered YSZ. The mechanical behaviors of YSZ tested below 400 °C are highlighted by large inelastic strain (∼7%) due primarily to phase transformation toughening. Beyond 400 °C, martensitic transformation toughening is gradually superseded by grain boundary sliding triggered by ultrafine grains. The micropillars tested at 670 °C exhibit significantly enhanced plastic flow, arising mainly from dislocation activity along with grain boundary sliding.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Study of slip activity in a Mg-Y alloy by in situ high energy X-ray
           diffraction microscopy and elastic viscoplastic self-consistent modeling
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Leyun Wang, Zhonghe Huang, Huamiao Wang, Alireza Maldar, Sangbong Yi, Jun-Sang Park, Peter Kenesei, Erica Lilleodden, Xiaoqin Zeng
      Slip activity from various slip modes largely determines the yield strength and ductility of Mg alloys. Solid solution elements in Mg can change the slip activity dramatically. In this paper, far-field high energy X-ray diffraction microscopy (FF-HEDM) is employed to study slip activity in a Mg-3wt%Y alloy during an in situ tensile experiment. The specimen was incrementally loaded up to 3% engineering strain along the rolling direction. At each load step, FF-HEDM data were collected to track the crystallographic orientation, center of mass, and stress tensor changes of nearly 1000 grains in the probed volume. By analyzing the change in orientation and stress tensor of individual grains at different load steps, it is possible to identify the activated slip systems and measure their critical resolved shear stress (CRSS) values. Prismatic slip and pyramidal I <a> slip are found to be very active in this alloy. The estimated CRSS values for basal slip, prismatic slip and pyramidal I <a> slip are 12 MPa, 38 MPa, and 36 MPa, respectively. These CRSS values were applied in a dislocation-based elastic viscoplastic self-consistent (EVPSC) model that successfully simulated the tensile stress-strain curve from the FF-HEDM experiment. The model also qualitatively predicted the crystal rotation in most of the selected grains, though it underestimated the internal stress and the magnitude of crystal rotation in these grains. Influence of solute Y on the strength and ductility of Mg alloys is discussed.
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      PubDate: 2018-06-18T15:11:13Z
       
  • A multiscale shear-transformation-zone (STZ) model and simulation of
           plasticity in amorphous solids
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Shingo Urata, Shaofan Li
      In this work, we have developed a multiscale shear-transformation-zone (STZ) model to simulate inelastic deformations in amorphous materials at macroscale without using phenomenological constitutive modeling. The main novelties of the multiscale method are two: (1) the multiscale method employs an atomistic-based representative sampling cell (RS-cell) that is embedded in every quadrature points of macroscale finite elements, and it generically contains potential shear-transformation-zones. Thus the evolution of RS-cells can naturally allow molecular clusters having irreversible microstructure rearrangements at microscale in response to applied loads, and subsequently translate the effects of the irreversible rearrangements of molecular clusters in each RS-cell to inelastic responses at the continuum scale, i.e. delineating the defect-mediated amorphous plasticity, and (2) the method uses a Parrinello-Rahman molecular mechanics based the Cauchy-Born rule to construct an atomistically-informed constitutive model at continuum level, which is able to quantitatively measure amorphous plasticity behaviors, including plastic flow stress, inelastic hysteresis loops under cyclic loading, and strain localizations at macroscale. By doing so, we have successfully simulated plastic deformation in the Lennard-Jones binary glass (LJBG) at macroscale level. Moreover, we have shown that the multiscale shear-transformation-zone can capture cyclic plasticity and the shear band formations in LJBG material.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Multi−interface spin exchange regulated biased magnetoelectric coupling
           in Cluster−assembled multiferroic heterostructural films
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Yulong Bai, Bo Yang, Hao Zhang, Xin Wu, Ning Jiang, Shifeng Zhao
      Cluster−assembled Ni−NiO core−shell structures were periodically immersed into multiferroic Bi5Ti3FeO15 (BTFO) film matrices to form pseudo 1–3 BTFO/Ni−NiO/BTFO heterostructural films with multiferroic/antiferromagnetic/ferromagnetic (MF/AFM/FM) multi−interfaces. A biased magnetoelectric coupling effect was obtained at room temperature by a magnetic annealing process. The biased direction depends on the orientation of the annealing magnetic field, with magnetoelectric coefficient curves moving to left after positive annealing magnetic field, while moving to right with negative annealing magnetic field. This biased magnetoelectric effect originates from the multi−interface spin exchange coupling. The immersion of cluster−assembled Ni−NiO core−shells in the multiferroic matrices enhance the interfacial coupling effect due to the large surface-to-volume ratio. Thus, the interfacial spin exchange induced biased magnetoelectric effect is enhanced and reversible. The work provides an avenue on the weak magnetic field detection, spintronic devices and multistate switching memories.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Effects of surface modifications on the fatigue life of unconstrained
           Ni-Mn-Ga single crystals in a rotating magnetic field
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Hu Zhang, Andrew Armstrong, Peter Müllner
      Long-term fatigue life during high-cycle magnetic-mechanical actuation is crucial to the application of Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs). It has been reported that long fatigue life can be achieved by both reducing surface damage and constraining Ni-Mn-Ga single crystals to exhibit much lower strain than the theoretical limit. In the present study, the fatigue life of Ni-Mn-Ga single crystal samples treated with various surface modifications was investigated in a rotary fatigue testing instrument. The apparatus minimally constrained the samples and allowed for magnetic-field-induced strain (MFIS) close to the theoretical limit. We first treated the samples with electropolishing, which we found created more surface defects than those of the mechanically polished sample. These defects acted as dispersed pinning sites for twin boundaries and nucleated cracks easily due to the localized stress concentration, resulting in reduced fatigue life. We then studied the introduction of residual compressive stresses imparted by micropeening. Although micropeening increased surface roughness, it produced a uniform surface morphology and a finely twinned structure. We argue that the large groups of dislocations did not pile up and the stress distribution was more homogeneous due to the fine twin structure, lowering the crack nucleation rate. Consequently, the fatigue life of unconstrained Ni-Mn-Ga single crystals with large MFIS was significantly improved by the micropeening treatment.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Atomistic simulations of interaction between basal dislocations
           and three-dimensional twins in magnesium
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Mingyu Gong, Guisen Liu, Jian Wang, Laurent Capolungo, Carlos N. Tomé
      Dislocation slip and twinning are equally important in the plastic deformation of hexagonal close packed crystals. Basal slip and extension 10 1 ¯ 2 < 1 ¯ 011 > twins can be activated concurrently in magnesium and, as a result, complex dislocation-dislocation, twin-twin, and dislocation-twin interactions take place and determine the hardening behavior. Here, using atomistic simulations, we study the latter mechanism, namely, the interactions between basal < a > dislocations and a three-dimensional (3D) { 10 1 ¯ 2 } twin. According to our findings, a basal screw dislocation can fully transform into the twin via multiple cross-slip between basal and prismatic planes in the matrix. This process causes the formation of jogs and basal stacking faults in the matrix, and prismatic < a > dislocations in the twin. We also find that a basal mixed dislocation cannot directly transform into the twin. Instead, it dissociates into twinning dislocations, resulting in a change in twin thickness and the formation of basal/prismatic steps. When the dislocation interacts with the lateral twin boundary, slip transformation in the twin is accomplished through the gliding of either ½< a + c> or < a + c > on the prismatic plane in the twin. Accompanying the gliding of ½< a + c >, a prismatic stacking fault is created inside the twin. By accounting for the 3D character of the dislocation-twin reactions, our results extend our understanding of slip transformation into a twin, the formation of basal and prismatic stacking faults in matrix and twin, and the role that local stresses and the lateral boundary of the twin play in this process.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Quantifying the grain boundary segregation strengthening induced by
           post-ECAP aging in an Al-5Cu alloy
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Hailong Jia, Ruben Bjørge, Lingfei Cao, Hui Song, Knut Marthinsen, Yanjun Li
      Hardening on annealing (HOA) has been frequently observed in nanostructured metals and alloys. For nanostructured materials obtained by severe plastic deformation (SPD), HOA has been attributed to the reduction of dislocation sources within grains and grain boundary relaxation during annealing. In the present work, it is shown that when a bimodal grain structured (a mixture of micron-sized and ultrafine grains) Al-5Cu alloy prepared by equal channel angular pressing (ECAP) was subjected to post-ECAP natural and artificial aging treatments, the alloy shows a completely different precipitation behavior with an accelerated precipitation kinetics. No coherent θ'' or semi-coherent θ' precipitates form in the bulk of grains, while a large fraction of stable incoherent θ precipitates form along high angle boundaries. After artificial aging at low temperatures for a short time, a significant improvement of both ultimate tensile strength and uniform elongation was achieved without sacrificing the yield strength. A systematic microstructure characterization by EBSD, TEM and APT has been carried out to investigate the evolution of grain size, dislocation density and solid solution level of Cu as well as the precipitation of Al-Cu precipitates during natural and artificial aging treatments. A quantitative evaluation of different supposed strengthening mechanisms revealed that the segregation of Cu elements at grain boundaries plays a more important role than grain boundary relaxation and the dislocation source-limited strengthening to compensate the yield strength reduction caused by the decrease in dislocation density and solute content of Cu in solid solution.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Germanium substitution endowing Cr3+-doped zinc aluminate phosphors with
           bright and super-long near-infrared persistent luminescence
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Yi Zhang, Rui Huang, Hongliang Li, Dejian Hou, Zhenxu Lin, Jie Song, Yuzheng Guo, Huihong Lin, Chao Song, Zewen Lin, John Robertson
      We present novel near-infrared (NIR) Cr3+-doped non-gallate super-long-persistence phosphors (Zn1+xAl2-2xGexO4:Cr3+) by Germanium substitution in the original ZnAl2O4:Cr3+. Unlike the negligible NIR persistent luminescence of ZnAl2O4:Cr3+ upon UV or visible light excitation, the Ge substituted phosphors feature strong and super-long-persistent luminescence at approximately 650–750 nm for more than 120 h. The relation between the Ge substitution and the defect trapping states is investigated systematically. The experimental results combined with the first-principles calculations reveal that Ge Zn ○○ and Ge Al ○ in the spinel structure would introduce shallow and deep defect states in the band gap to serve as new efficient traps, which are mainly responsible for the strong and super-long-persistent luminescence upon UV or visible light excitation. The present advanced phosphors is an alternative candidate for applications in biomedical imaging and night-vision surveillance.
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      PubDate: 2018-06-18T15:11:13Z
       
  • On the origin of the improvement of shape memory effect by precipitating
           VC in Fe–Mn–Si-based shape memory alloys
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): M.J. Lai, Y.J. Li, L. Lillpopp, D. Ponge, S. Will, D. Raabe
      We studied the role of VC precipitation in improving the shape memory effect (SME) of the as-solution treated Fe–Mn–Si-based shape memory alloys by examining the microstructures developed during aging and deformation using transmission electron microscopy and electron channeling contrast imaging. Our results suggest that VC particles are not the only product of aging. Upon aging at 650 °C, the precipitation of VC particles is accompanied by the formation of profuse dislocations (2.26 ± 0.098 × 1013 m−2). In this case, the SME is not improved compared to the as-solution treated reference state. Upon aging at high temperatures (700–900 °C), a number of stacking faults are formed accompanying the VC precipitation and the SME is significantly improved, where the recovery ratios reach almost twice that of the as-solution treated state (<50%). For these high-temperature aged states, in situ straining experiments reveal that the stacking faults rather than the VC particles play an important role in the stress-induced martensitic transformation, leading to the formation of very thin (<3 nm) martensite plates with a single crystallographic variant within each grain. These martensite plates are in contrast to the very thick (from tens to hundreds of nanometers) and multi-variant martensite plates that prevail in the as-solution treated state. By comparing the characteristics of the martensite plates between the as-solution treated and the high-temperature aged states, the reasons for the improvement of SME by precipitating VC were discussed.
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      PubDate: 2018-06-18T15:11:13Z
       
  • Experimental and modeling study of compressive creep in 3D-woven Ni-based
           superalloys
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Hoon-Hwe Cho, Dinc Erdeniz, Keith W. Sharp, David C. Dunand
      Micro-architectured Ni-based superalloy structures, with Ni-20Cr-3Ti-2Al (wt.%) composition and γ/γ′-microstructure, are created by a multi-step process: (i) non-crimp orthogonal 3D-weaving of ductile, 202 μm diameter Ni-20%Cr wires, (ii) gas-phase alloying with Al and Ti, (iii) simultaneous transient-liquid phase (TLP) bonding between wires and homogenization within wires via interdiffusion, (iv) solutionizing to create a single-phase solid solution, and (v) aging to precipitate the γ′ phase. The creep behavior of these 3D-woven γ/γ′ nickel-based superalloys is studied under uniaxial compression via experiments at 825 °C and via finite element (FE) analysis, using a 3D model of the woven structures obtained through X-ray micro-tomography. The creep strain rate for the woven Ni-based superalloy is higher than that for the bulk superalloy due to the lower solid volume fraction of the woven structure, while the creep exponents are identical. The compressive creep behavior is sensitive to the geometry of the woven structures: fewer wires perpendicular to the load and fewer bonds between wires cause lower creep resistance of the woven structure, due to a reduction in load transfer from the longitudinal wires (which are primarily load-bearing) and the perpendicular wires. Creep buckling of longitudinal wires drastically reduces creep resistance of the woven structure, confirming the importance of maintaining longitudinal wires vertical and parallel to the uniaxial compression direction. Finally, reducing wire cross-section, e.g., via oxidation, reduces creep resistance. The oxidation kinetics of the wire structures at 750, 825, and 900 °C displayed parabolic rate constants comparable to commercial Ni-based superalloys, but indicates that up to 35% of the wire cross-section is oxidized after 7 days at 825 °C, such that oxidation-resistant coatings are needed for long-term use in oxidative environment.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Phase-field simulation of domain walls in rhombohedral ferroelectric
           single crystals
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Peng Lv, Christopher S. Lynch
      Domain engineered ferroelectric relaxor-PbTiO3 single crystals exhibit ultrahigh piezoelectric coefficients. A 10th order Landau-Devonshire energy function for rhombohedral PIN-PMN-PT ferroelectric single crystals was implemented in a phase-field model to study the behavior of domain walls under external electric field. The domain formation and domain wall evolution were simulated. A new way to apply periodic boundary conditions was implemented to accommodate nonzero strain during the domain formation and evolution. It was found that 71 and 109 domain walls reacted differently to external electric field along the [110] direction. A domain wall broadening effect was observed in the 71 domain walls when the electric field was below the coercive field. When the electric field exceeded the coercive field, homogeneous polarization switching occurred with no motion of the 71 domain walls. Heterogeneous polarization switching occurred by the sweeping of the 109 domain walls. The evolution mechanism of the two types of domain walls helps explain the behavior of engineered domain structures subjected to external electric field.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Twinned nanoporous gold with enhanced tensile strength
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): Eun-Ji Gwak, Hansol Jeon, Eunji Song, Na-Ri Kang, Ju-Young Kim
      Enhancing tensile strength is crucial to increasing the applicability of nanoporous materials including nanoporous gold (np-Au) that show mechanical weakness because of their nanoporous structure despite other superior characteristics. We fabricated twinned and textured np-Au foils with an average twin spacing of 7.9 nm. The foils exhibit an ultimate tensile strength (UTS) of 87.5 MPa when the loading axis is normal to the twin boundaries. This UTS value is approximately three times greater than that for np-Au with rare twins of 27.4 MPa. The high UTS can be ascribed to the twin boundaries acting as effective barriers to dislocation slip, resulting in the strain-hardening of the load-bearing ligaments.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Hydrogen-induced accelerated grain growth in vanadium
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): May L. Martin, Astrid Pundt, Reiner Kirchheim
      Grain growth in nanocrystalline vanadium films was studied at 600 and 700 °C in vacuum and in hydrogen atmosphere with partial pressures ranging from 1 to 1000 Pa. It is shown that grain growth is significantly increased in the presence of hydrogen. Thus the expected effect of retarding grain growth either by reducing grain boundary energy due to hydrogen segregation or by hydrogen drag on the moving boundary did not occur. Two explanations are given for the accelerated grain growth. First, hydrogen reduces the formation energy of ledges, assuming these ledges are required for initiating and advancing boundary motion. Second, grain growth requires the annihilation of excess volume which may be enhanced by reducing the formation energy of vacancies in the presence of hydrogen.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Complete ductility in NdFeB-type alloys using the Hydrogen Ductilisation
           Process (HyDP)
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): O.P. Brooks, A. Walton, W. Zhou, D. Brown, I.R. Harris
      The work outlined in this paper demonstrates significant improvements in ductility during the Hydrogen Ductilisation Process (HyDP) [1] of a Neomax-type alloy and, for the first time, complete ductility of a sub-stoichiometric alloy. In previous studies, the uniformity of the ductilisation transformation was limited by the presence of the NdFe4B4 phase not undergoing complete disproportionation, which left extremely brittle, micron-scale islands in a highly ductile disproportionated matrix. The present works investigated the influence of a significantly longer (18 h) hydrogen treatment of the Neomax-type alloy to observe whether the completely disproportionated NdFe4B4 phase is as ductile as the disproportionated matrix. It has been observed that, when the NdFe4B4 phase is completely disproportionated, it exhibits similar ductility to that of the disproportionated matrix, showing no sign of cracking under a compressive load. However, inhomogeneity in the book mould material leads to varying quantities of NdFe4B4 phase and thus, varying levels of disproportionation. Despite this, significant improvements were observed in the mechanical behaviour of the Neomax-type alloy. The longer disproportionation treatment also results in larger grains and thus, a lower final coercivity in the recombined state than that of the previous 5 h treatment. For comparison, the mechanical behaviour of a sub-stoichiometric alloy, which did not contain any NdFe4B4 phase, has also been studied. The compression behaviour of this sub-stoichiometric alloy in the disproportionated state was found to be completely ductile. It is clear from this work that it is possible to create a completely ductile NdFeB material directly from the solid cast alloy which, in the future, could have significant implications for NdFeB magnet production.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Grading the magnetic anisotropy and engineering the domain wall dynamics
           in Fe-rich microwires by stress-annealing
    • Abstract: Publication date: 15 August 2018
      Source:Acta Materialia, Volume 155
      Author(s): V. Zhukova, J.M. Blanco, P. Corte-Leon, M. Ipatov, M. Churyukanova, S. Taskaev, A. Zhukov
      We have studied the magnetic properties and domain wall dynamics in Fe-rich microwires subjected to stress-annealing. The hysteresis loops of Fe-rich microwires were considerably affected by stress-annealing. We obtained drastic decrease in coercivity and change in the character of hysteresis loops from rectangular to linear in stress-annealed Fe-rich microwires. For the wires after stress-annealing at variable temperatures we obtained a graded magnetic behavior with local hysteresis loops shapes and features (coercivity, remanent magnetization) changing along the sample length. In the samples subjected to local stress-annealing we created an artificial source of domain wall injection allowing the manipulation of domain wall dynamics. The observed stress-induced anisotropy could be related to the internal stress relaxation after annealing and the interplay of compressive “back-stresses” arisen after stress annealing and axial internal stresses.
      Graphical abstract image

      PubDate: 2018-06-18T15:11:13Z
       
  • Editors for Acta Materialia
    • Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154


      PubDate: 2018-06-18T15:11:13Z
       
  • Launching Materialia
    • Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154
      Author(s): Christopher A. Schuh, Kazuhiro Hono, William R. Wagner, Baptiste Gault, Joseph D'Angelo, George T. Gray


      PubDate: 2018-06-18T15:11:13Z
       
  • Acta Materialia and Scripta Materialia Outstanding Reviewers in 2017
    • Abstract: Publication date: 1 August 2018
      Source:Acta Materialia, Volume 154


      PubDate: 2018-06-18T15:11:13Z
       
 
 
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