Microstructure evolution in nanocrystalline NiTi alloy produced by HPT |
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| Authors: | R. Singh S.V. Divinski H. Rösner E.A. Prokofiev R.Z. Valiev G. Wilde |
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| Affiliation: | 1. Institut für Materialphysik, Westfälische Wihelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany;2. Institute of Physics of Advanced Materials, Ufa State Aviation University, 12 K. Marx Street, 450000 Ufa, Russian Federation;1. Osaka University, Graduate School of Engineering, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan;2. Fukui Institute of Technology, 3-6-1 Gakuen, Fukui-City, Fukui, 910-8505, Japan;1. School of Mechanical and Aerospace Engineering, Queen''s University Belfast, Northern Ireland, UK;2. Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China;1. Karadeniz Technical University, Science Faculty, Department of Physics, 61080 Trabzon, Turkey;2. Mersin University, Tarsus Faculty of Technology, Tarsus, Turkey;3. Adiyaman University, Department of Material Science Engineering, 02040 Adiyaman, Turkey;4. Mustafa Kemal University, Faculty of Arts and Sciences, Department of Physics, Antakya, Hatay, Turkey;5. UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan;1. Tomsk State University, Lenina Str. 36, Tomsk 634050, Russia;2. Texas A&M University, College Station, TX 77843, USA |
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| Abstract: | A slightly Ni-rich nano-NiTi alloy, deformed by high-pressure torsion (HPT) was investigated. By HPT, almost complete amorphization of initial B2 NiTi is obtained. Crystallization and microstructure evolution during isothermal treatment were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy.The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and the growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing reveals reproducibly non-monotonous trends with annealing time that cannot be explained solely by growth of crystalline volume fractions. The size of nanocrystals increases dramatically after annealing for 5 h. The effective activation enthalpies for stress relaxation (along with crystallization) and grain growth were estimated at 115 and 289 kJ/mol, respectively. The results are discussed with respect to the intricate interdependencies between synthesis and thermal processing pathways and the evolution of the nanoscale microstructure. |
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