Ageing in Parent Phase and Martensite Stabilization in a Ni₅₀Ti₃₀Hf₂₀ Alloy

Abstract

The effect of ageing in parent phase and martensite stabilization on melt spun Ni₅₀Ti₃₀Hf₂₀ ribbons were investigated by Differential Scanning Calorimetry and X Ray Diffraction. Thermal treatments in parent phase generally shift the martensitic transformation range as far as an equilibrium state is reached. The equilibrium state, here found for a thermal treatment at 450^°C (723 K), was adopted as start state to investigate ageing in martensite (commonly indicated as martensite stabilization). Martensite stabilization involves diffusion processes with an activation energy in the order of 1.2 eV: results add a piece of evidence to the general principle of Symmetry-Conforming Short-Range Order advanced by Ren and Otsuka.