J. Phys. IV France 112 (2003) 841
Super-high strength shape memory thin filmsK. Yamazaki1, S. Kajiwara2, T. Kikuchi2, K. Ogawa2 and S. Miyazaki1
1 Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan
2 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
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.
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