Super-high strength shape memory thin films

Abstract
Using a sputter-deposition technique, super-high strength shape memory films have been developed with Ti-Ni-Cu alloys having the composition range of Ti: 51-55, Ni: 40-46, Cu: 4-6 (at. %). The maximum stress applicable without any permanent strain is about 1.5 GPa, being accompanied with a perfectly recoverable strain of about 5% on heating above A . The maximum shape recovery stress measured by thermal cycling test under various constant stresses is 900 MPa with a shape recovery strain of 4.6%. A superelasticity with 850 MPa shape recovery stress and small hysteresis is attained for 53.5Ti-37.0Ni-9.5Cu thin films. These excellent properties are due to two factors; one is the existence of very thin plate bct precipitates with large coherency strains in the B2 parent phase, which are produced by heating the as-sputtered amorphous films with Ti-rich contents (more than 50%), and the other is ternary alloying.