Phase field simulation to one-way shape memory effect of NiTi shape memory alloy single crystal

摘要

Based on the Ginzburg-Landau theory and in the framework of thermodynamics, a three-dimensional phase field model was developed to simulate the one-way shape memory effect (OWSME) of NiTi shape memory alloy (SMA) single crystal originated from the martensite transformation and reorientation. A new reorientation strain was simultaneously introduced when a transformation strain was considered in the proposed model, and the phase field equations corresponding to the martensite transformation and reorientation were derived, respectively. From the simulations to the OWSME, it is found that: the martensite variants are grown in a self-coordinating manner and combined by twinned interfaces to reduce the local elastic energy during the temperature-induced transformation from B2 phase to B19' one; then, the stress-induced martensite reorientation is completed through the migration of twinned interfaces and the variants with optimal orientations are obtained during the subsequent loading, and a residual strain is produced after the unloading; during the further heating after the unloading, a uniform temperature-induced reverse transformation from the single-oriented martensite variant to B2 austenite phase occurs, and the residual strain produced by the stress-induced martensite reorientation is progressively recovered.