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Open AccessArticle

The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics

Department of Materials Science and Engineering, National Chiao Tung University, Ta Hsueh Road, Hsinchu 300, Taiwan
Department of Mechanical Engineering, National Taiwan University, Taipei 106, Taiwan
Author to whom correspondence should be addressed.
Materials 2019, 12(1), 57;
Received: 26 November 2018 / Revised: 17 December 2018 / Accepted: 19 December 2018 / Published: 24 December 2018
(This article belongs to the Special Issue Shape Memory Alloys (SMAs) for Engineering Applications)
Superelasticity in shape memory alloys is an important feature for actuators and medical devices. However, the function of the devices is typically limited by mechanical bandwidth and fatigue, which are dominated by the microstructures. Thus, in order to correlate the mechanical response and the microstructures, the microstructural evolution in NiTi single crystals under the compression, tensile, and shearing tests is simulated by molecular dynamics (MD) in the current study. Then, the martensite variant identification method, which identifies the crystal variants/phases of each lattice based on the transformation matrix, is used to post-process the MD results. The results with the detailed information of variants and phases reveal many features that have good agreement with those reported in the literature, such as X-interfaces and the transitional orthorhombic phase between the austenite and monoclinic phases. A new twin structure consisting of diamond and wedge-shaped patterns is also discovered. The macroscopic behavior, such as stress-strain curves and the total energy profile, is linked with the distribution of dislocation and twin patterns. The results suggest that the loading cases of shear and compression allow a low critical strain for the onset of martensitic transformation and a better superelasticity behavior. Therefore, the two loading cases are suitable to apply to the NiTi actuators. The current work is expected to provide insight into the mechanical responses and design guideline for NiTi shape memory alloy actuators. View Full-Text
Keywords: shape memory alloys; superelasticity; molecular dynamics; crystal variants shape memory alloys; superelasticity; molecular dynamics; crystal variants
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Lu, H.-Y.; Chen, C.-H.; Tsou, N.-T. The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics. Materials 2019, 12, 57.

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