Nickel ion irradiation of plasitically deformed martensitic titanium nickel thin films

At present, little is known about the response of the martensitic phase in TiNi alloys to heavy ion irradiation. However, previous studies [2,3] of ion and electron irradiation show that these alloys are highly susceptible to disorder and amorphization at damage levels below 1 dpa. This substantially affects their transformation characteristics and their shape memory effect. The present study focuses on the effect of 5 MeV Ni ion irradiation of plastically strained (epsilon-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 2mum surface layer of a 6mum thick film will create a sharp differential latent strain on reverse transformation. This latent strain causes a two-way bending motion during cycling heating and cooling. This processing technique can be used to do useful mechanical work on both beating and cooling. To better understand the behavior 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.