Role of severe plastic deformation on the cyclic reversibility of a Ti _50.3Ni_33.7Pd₁₆ high temperature shape memory alloy

The present work focuses on the effect of microstructural refinement on the thermo-mechanical cyclic stability of a Ti_50.3Ni _33.7Pd₁₆ high temperature shape memory alloy (HTSMA) which was severe plastically deformed using equal channel angular extrusion (ECAE). The grain/subgrain size of the high temperature austenite phase was refined down to about 100 nm, the lowest reported to date in HTSMAs. The increase in strength differential between the onset of transformation and the macroscopic plastic yielding after ECAE led to a notable enhancement in the cyclic stability during isobaric cooling-heating experiments. The reduction in irrecoverable strain levels was attributed to the increase in critical stress for dislocation slip due to the microstructural refinement during the ECAE process.