Development of perfect shape memory effect in sputter-deposited Ti-Ni thin films

Ti-Ni shape memory alloy thin films were deposited using an RF magnetron sputtering method. These films showed a perfect shape memory effect which is the same as that of bulk shape memory alloys. The shape recovery stress and strain measured in the thin films were large enough for fabricating microactuators to power micromachines. The shape recovery stress was more than 400 MPa. The maximum shape recovery strain amounted to 3%. The thin film showed a two-stage deformation upon cooling; the strain induced in each stage recovered perfectly upon heating. The first stage corresponds to the R-phase transformation, while the second the martensitic transformation. The transformation temperatures and shape memory characteristics were strongly affected by heat-treatment and alloy composition. In the present paper, development and characterization of a perfect shape memory effect in sputter-deposited Ti-Ni thin films are presented specially stressing the materials science approaches.