Thermal cycling and isothermal deformation response of polycrystalline NiTi: Simulations vs. experiment

A recent microstructure-based FEM model that couples crystal-based plasticity, the B2 ↔ B19′ phase transformation and anisotropic elasticity at the grain scale is calibrated to recent data for polycrystalline NiTi (49.9 at.% Ni). Inputs include anisotropic elastic properties, texture and differential scanning calorimetry data, as well as a subset of recent isothermal deformation and load-biased thermal cycling data. The model is assessed against additional experimental data. Several experimental trends are captured – in particular, the transformation strain during thermal cycling monotonically increases and reaches a peak with increasing bias stress. This is achieved, in part, by modifying the martensite hardening matrix proposed by Patoor et al. [Patoor E, Eberhardt A, Berveiller M. J Phys IV 1996;6:277]. Some experimental trends are underestimated – in particular, the ratcheting of macrostrain during thermal cycling. This may reflect a model limitation that transformation–plasticity coupling is captured on a coarse (grain) scale but not on a fine (martensitic plate) scale.