Bi-metallic model of the free recovery motion of ion irradiated Ti-rich NiTi shape memory alloy thin films

A bi-metal approach is used to model the free recovery motion of ion implanted Ti-rich NiTi sputtered films. For comparison and to validate the model, the thermo-mechanical properties of unirradiated films were explored, using an in-house built dead load tester and micro-tensile machine. There is good agreement between the measured recovery stresses in the unirradiated thin film and those that are predicted by model at the interface between the damage and undamaged layer. However, these stresses are too low to conclude that the loss in reversible motion observed in irradiated films are due to the overload of the damage layer and may result from other processes, such as structural and stress relaxations.