LATENT STRAIN IN TITANIUM-NICKEL THIN FILMS MODIFIED BY IRRADIATION OF THE PLASTICALLY- DEFORMED MARTENSITE PHASE WITH 5 MeV Ni~(2+)

摘要

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 ther- momechanical 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 A_s, a novel active-passive bilayer results that expresses pronounced bending displacements on subsequent heating. In the present paper, describing exper- iments on stretched 6-μm thick sputtered Ti_50.2Ni_49.7 films irradiated with 5 MeV Ni~(2+), 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 ×10~13 Ni~(2+) 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.