Microstructural evolution and thermo-mechanical response of Ni ion irradiated TiNi SMA thin films

The present study focuses on the effect of 5 MeV Ni ion irradiation of plastically strained (*e #~ 4%) martensitic TiNi thin films, which is used as a processing technique for a novel out of plane bending actuator. Conceptually, the frustration of the martensitic transformation due to ion beam damage in a 2 *mm surface layer of a 6 *mm thick film will create a sharp differential latent strain on reverse transformation. This latent strain causes a two-way bending motion during cyclic heating and cooling, and in addition, this thermal actuator can be used to do useful mechanical work on both heating and cooling. To better understand the behaviour of these ion irradiated thin films, TEM observations and motion experiments were conducted. Results are presented and discussed as they relate to the ion induced microstructure and its influence on the martensitic transformation and the shape memory effect.