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.
KeywordsMartensitic phase transition NiTi Localization Single crystal
The support of NSF (CMMI-1536925 and DMR-1434613), ARO (W911NF-17-1-0225), XSEDE (TG-MSS140033), and ISU (Schafer 2050 Challenge Professorship and Vance Coffman Faculty Chair Professorship) is gratefully acknowledged.