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Abstract The one-way shape memory effect of NiTi shape memory alloy nano-single crystal was investigated by the molecular dynamics simulations based on a second nearest neighbor modified embedded atom interaction potential. The deformation behavior and microstructural evolution of the NiTi nano-single crystal during temperature-induced martensitic transformation and stress-induced martensitic reorientation were elucidated in detail, and the effect of loading rate on the one-way shape memory effect in a nanoscale was discussed. Simulated results show that different martensite variants are coexisted when the nano-single crystal is cooled below the martensite finish temperature and then the martensitic reorientation occurs during the stress loading process. The residual strain after unloading gradually decreases with the increase of temperature, but cannot fully recover even if the temperature is much higher than the austenite finish temperature, since the irreversible plastic deformation occurs during the martensite reorientation. It is also found that the austenite transformation temperature of the single crystal during the subsequent heating after the stress-induced martensitic reorientation is much higher than that without undergoing the martensitic reorientation. On the one hand, the plastic deformation will disturb the stress field in the single crystal, resulting in a pinning effect on the martensitic reverse transformation; then, a larger driving force is needed to trigger the martensitic reverse transformation. On the other hand, since the interface morphology among various reoriented martensite variants is different from that among twinned martensite variants, the martensite interfacial energy will be changed by the martensitic reorientation, which affecting the critical temperatures of martensite transformation. In addition, it is found that the martensitic reorientation depends on the loading rate strongly. With the increase of the loading rate, the modulus and critical stress of martensitic reorientation increase gradually, which are caused by the viscosity of the movement of interfaces among different martensite variants. Finally, simulated results show that the evolutions of atomic structures are different at various loading rates in the subsequent cooling process. All the above results will provide a basis for the research on the molecular dynamics simulations on the shape memory effect of NiTi shape memory alloy polycrystal.
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Received: 21 October 2019
Published: 28 April 2020
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2020, Vol. 41 
