Post-annealing of ion irradiated TiNi SMA thin films

The aim of this project has been the study of the ion irradiation damage in TiNi thin films and the influence of the damage on the martensitic transformation in order to develop high performance shape memory materials which can be used in micro-electro-mechanical system (MEMS) applications. In these studies, we have irradiated pre-deformed TiNi thin films with 5 MeV Ni ions to suppress the martensitic transformation in a thin layer (1/2 to 1/3 of the film’s thickness) and to develop a two-way cyclic motion with thermal cycling. The film motion behaved as predicted at higher doses and showed a reversible two-way strains of 0.5%, and the irradiated microstructure of these consisted of nanocrystalline phases embedded in an amorphous matrix. The amount of curling was sensitive to dose and temperature range of thermal cycling. In order to investigate the stability of these damaged microstructures with temperature, in situ annealing in the TEM and calorimetric (DSC) measurements were performed. The results will be discussed in terms of the microstructural evolution that occurred after annealing.