Two-way shape memory properties of a Ni-rich Ti-Ni alloy aged under tensile-stress

The strength of the ''all-round (two-way) shape memory effect'' and the work we can gain by using this effect were investigated. The alloy used was a Ti-51 (at%)Ni alloy. In order to align particles of Ti3Ni4 precipitate, plate-shaped specimens were aged at 773 K for 6 ks under several different tensile-stresses. Thermal cycling tests under several different tensile-stresses (sigma(Test)) were made on these aged specimens. Specimens aged under an appropriate tensile-stress shrink in association with the B2-->23R transformation and the total shrinkage decreases with increasing sigma(Test). Due to this shrinkage, the specimens do work on the outside: this work is the largest when sigma(Test) is between 50 and 100 MPa. The B2--B19' transformation start temperature of these specimens decreases as sigma(Test) increases. In association with the later R-->Br19' transformation, the aged specimens shrink when sigma(Test) is below 50 MPa, and elongate when it is above. Unrecoverable strain does not remain in the specimen as long as the B2<->R transformation is repeated, but it does when the B2<->R<->B19' transformations are repeated.