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

Abstract

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 (σTest) were made on these aged specimens. Specimens aged under an appropriate tensile-stress shrink in association with the B2→R transformation and the total shrinkage decreases with increasing σTest. Due to this shrinkage, the specimens do work on the outside: this work is the largest when σTest is between 50 and 100 MPa. The B2→R transformation start temperature of these specimens decreases as σTest increases. In association with the later R→B19′ transformation, the aged specimens shrink when σTest 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.