Studies on Martensitic Transformation and Pseudoelasticity of Ti50Ni25Cu25 Ribbons

Ti50Ni25Cu25 ribbons prepared by rapid solidification process (RSP) at 4000 rpm are studied to investigate the transformation behavior, microstructure and mechanical properties. As-spun Ti50Ni25Cu25 ribbons are nearly fully amorphous with a lower wavenumber Qp than the amorphous Ti-Ni alloys and the partially amorphous Ti50Ni40Cu10 ribbons owing to its high Cu content. Both crystallization activation energy Ea and onset temperature Tx for Ti50Ni25Cu25 ribbons are lower than those for Ti50Ni50 and Ti50Ni40Cu10 ribbons/thin films, which also indicate a worse thermal stability exhibited in amorphous Ti50Ni50-xCux alloys with high Cu content. Texture of {100}B2 orientation is discovered on the contact side of the ribbons, due to that the heat flow associated with ribbon processing is normal to the spin wheel during RSP. Nanoindentation tests show that proper annealing process is required to obtain well crystallized ribbons with promising pseudoelasticity (PE). The PE property of these annealed ribbons is found to be related to two factors: the transformation latent heat and the precipitation behavior. The PE recovery ratio of nanoindentation tests can reach > 80% in these ribbons, indicating quite good PE property exhibited in annealed Ti50Ni25Cu25 ribbons.