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 (Ms) remains constant during incomplete forward transformations, resulting in a constant-stress range between the arrest temperature and Ms. 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.