期刊
ACTA MATERIALIA
卷 194, 期 -, 页码 565-576出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2020.05.004
关键词
High-energy X-ray diffraction; Nanocrystalline material; Ni-Ti; Shape memory alloy; R phase reorientation
资金
- National Key R&D Program of China [2018YFB1105100]
- NSFC [51971244, 51731010]
- Science Foundation of China University of Petroleum, Beijing [2462018BJC005]
- Australian Research Council [DP180101744, DP180101955]
- US Department of Energy, Office of Science and Office of Basic Energy Science [DE-AC0206CH11357]
This study investigated the mechanisms and temperature dependence of the R phase variant reorientation deformation in a nanocrystalline NiTi wire by means of in-situ synchrotron high-energy X-ray diffraction technique during tensile deformation. The NiTi wire exhibited a single stage B2 -> R transformation upon cooling with the R -> B19' martensitic transformation completely suppressed down to the liquid nitrogen temperature. The R phase variant reorientation deformation in tension was revealed to proceed in a Luders-manner, as evidenced by sudden changes of diffraction peak intensity and increases of lattice elastic strains of the R phase during the deformation. The variant reorientation obeys the principles to yield maximum crystallographic strain in the direction of the applied load. Thus, the variants with larger d-spacing values aligned to the axis of tension grew at the expense of those of lower d-spacing values. The increases of lattice elastic strains are attributed to the internal load transfer among the different crystallographic variants during the R phase reorientation. The crystallographic strain of R phase reorientation was found to increase with decreasing the deformation temperature. This corresponds directly to the continued evolution of the structure of the R phase of increased structural distortion relative the B2 phase with decreasing the temperature. This reflects the second order nature of the R phase. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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