Phase field modeling for cyclic phase transition of NiTi shape memory alloy single crystal with super-elasticity

From the Ginzburg-Landau's theory and thermodynamics, a three-dimensional phase field model was developed to simulate the cyclic phase transition of the NiTi shape memory alloy (SMA) single crystal with super-elasticity. The phase transition from the austenite phase to martensite one and its reverse were numerically simulated by the developed phase field model considering the repeated tension-unloading. The simulations indicated the nucleation and evolution of the multi-variant martensite and austenite phases in a scale of single crystal during the cyclic phase transition. It is found that the NiTi SMA single crystal with super-elasticity exhibits a remarkable localized deformation, accompanied by a local softening feature. Moreover, the microstructure evolution of the NiTi single crystal during the cyclic deformation was investigated. It is shown that the super-elasticity of the NiTi single crystal degrades gradually until it reaches to a stable state after certain load cycles, and a progressive accumulation of remnant martensite phase occurs, simultaneously; the phase transition of the NiTi single crystal gradually alters from a local mode into a uniform one, which comes from the internal defects and their evolutions; a large number of remnant martensite phase occurs because the enriched defects can greatly prevent the occurrence of reverse phase transition. (C) 2017 Elsevier B.V. All rights reserved.