Latent strain in titanium–nickel thin films modified by irradiation of the plastically-deformed martensite phase with 5 MeV Ni2+ Original Research Article

Lattice damage brought on by heavy ion irradiation is able to alter the displacive transformation characteristics of near equiatomic titanium–nickel. Irradiation of sputtered TiNi thin films can modify thermomechanical response to a depth of more than a micron, and may thus be used to create a perfectly bonded heterophase that deploys materials of sharply differing latent thermal strain on opposite sides of a thin sheet. If the alloy film is first martensitized, and then deformed in tension prior to partial-depth exposure to ion beam damage at temperatures well below As, a novel active-passive bilayer results that expresses pronounced bending displacements on subsequent heating. In the present paper, describing experiments on stretched 6-μm thick sputtered Ti50.2Ni49.7 films irradiated with 5 MeV Ni2+, we show that ion-induced latent bending can be cyclically reversed in temperature-displacement space, and that appreciable mechanical work can be extracted. Marked effects are observed at doses as low as 5×1013 Ni2+ cm−2. The approach, in which nominally planar processing is used, derives mechanical robustness from a naturally diffuse interface between the beam-damaged stratum and the adjacent unmodified shape-memory layer.