Modeling the Microstructure Evolutions of NiTi Thin Film During Tension

A microscale phase field model for the multivariant martensitic phase transformation is advanced and utilized for studying the pseudoelastic behavior of a thin film of equiatomic single crystal NiTi under tensile loading. The thermomechanical model includes the strain softening as a mechanism leading to strain (transformation) localization and discrete microstructure formation. To avoid a small scale limitation, gradient term is dropped. Numerical solutions have shown a negligible mesh sensitivity for different element shapes and densities, which is due to rate-dependent kinetic equations for phase transformation. Microstructure evolution and corresponding stress-strain curves are presented for several cases. Obtained stress-strain curves, band-like martensitic microstructure, a sudden drop in the stress at the beginning of the martensitic transformation, residual austenite, and multiple stress oscillations due to nucleation events are qualitatively similar to those in known experiments.