Shape memory properties of Ni-Ti based melt-spun ribbons

Recoverable strains above 4 pct can be obtained under similar to100 MPa loads for the NiTi and Ni45Ti50CU5 ribbons, transforming to B19' martensite. The B19 martensite is formed in the Ni25Ti50CU25 ribbon after crystallization, and according to the lowering in transformation strain as Cu content increases, the recoverable strain is close to 2.5 pct for similar to150 MPa load. The transformation temperatures exhibit a linear dependence on the applied stress, which can be quantitatively described by means of a Clausius-Clapeyron type equation. The NiTi and Ni45Ti50CU5 ribbons exhibited some degree of two-way shape-memory effect (TWSME) after thermomechanical cycling. Texture analyses performed on the different ribbons allow us to better understand the transformation strains obtained in each ribbon. The amounts of shape-memory effect (SME) and nonrecoverable strain shown by the studied ribbons are of the same order as those already observed in bulk materials, which makes melt spinning an ideal substitute to complicated manufacturing processes if really thin samples are needed. However, applicable stresses in melt-spun ribbons are limited by a relatively premature brittle fracture caused by irregularities in ribbon thickness.