A method to enhance cyclic reversibility of NiTiHf high temperature shape memory alloys

The effect of severe plastic deformation via equal channel angular extrusion (ECAE) at 650 °C on the thermal cyclic response of the 49.8Ni–42.2Ti–8Hf (in at.%) high temperature shape memory alloy was investigated. The improved thermal cyclic stability under constant tensile stresses in the ECAEd samples was attributed to the increase in critical shear stress levels for dislocation slip, which would accompany the martensitic phase transformation, due to the microstructural refinement and increase in favorable dislocation density.