Nanostructured TiNi-based shape memory alloys processed by severe plastic deformation

We present the processing, microstructure and properties of nanostructured TiNi-based shape-memory alloys synthesized by severe plastic deformation (SPD), including high-pressure torsion, equal-channel angular pressing, and multi-step SPD deformation (SPD plus cold rolling or drawing). It was found that the SPD processing did not alter the phase transformation sequence of the alloys but changed the morphology of the martensite. Also, we found that the mechanical and shape memory properties were improved by forming nanostructures in these alloys; SPD processing rendered a higher recovery stress (up to 1.5 GPa) and a higher maximum reverse strain (up to 10%) of shape memory, which are desirable in various practical applications.