Incomplete martensitic transformations in NiTi thin films

Nickel-titanium thin films were deposited onto silicon substrates and subjected to incomplete martensitic transformations. With wafer curvature methods, we observed a stress discontinuity that seems analogous to the splitting of the endothermic peaks measured by differential scanning calorimetry due to the temperature memory effect. The martensite start temperature (M_s) remains constant during incomplete forward transformations, resulting in a constant-stress range between the arrest temperature and M_s. However, incomplete reverse transformations start immediately at the arrest temperature. X-ray diffraction measurements confirm these path-dependent behaviors, which are consistent with the thermodynamic model of martensitic transformations.