Phase field simulation on the martensite transformation and reorientation toughening behaviors of single crystal NiTi shape memory alloy: Effects of crystalline orientation and temperature

Based on the Ginzburg-Landau’s theory, a two-dimensional phase field model coupling martensite transformation/reorientation (MT/MR) and crack behavior was established. The crack propagation of single crystal NiTi shape memory alloy (SMA) and its dependence on the system’s crystalline orientation and temperature was studied by the phase filed simulations. The simulated results show that the proposed phase field model reasonably characterizes the crack propagation, MT/MR and stress–strain curve of single crystal NiTi SMA with different crystalline orientations and at various temperatures. The MT/MR toughening behaviors occur in the simulations, which depend greatly on the crystalline orientation and temperature: when the temperature is higher than the chemical equilibrium temperature, the MT toughening effect decreases with the increase of temperature; when the temperature is set to be lower than the chemical equilibrium temperature, the MR toughening effect decreases with the decrease of temperature. Generally, the closer the temperature to the chemical equilibrium temperature, the better the MT toughening effect and the weaker the orientation dependence is. However, the change of MR toughening capability with the temperature and crystalline orientation is complex because the twinned martensite phase at the crack tip can not only slow down the crack propagation rate, but also induce the crack bifurcation.