Effect of pseudoelastic cycling on the Clausius–Clapeyron relation for stress-induced martensitic transformation in NiTi

This study evaluates the strain-dependence of Clausius–Clapeyron relation of the stress-induced martensitic transformation in a Ti–50.8 at.% Ni. The transformation strain is altered by means of pseudoelastic cycling. It is found that the σ–T linearity coefficient of the relation is greater for the reverse transformation than for the forward transformation, consistent with the smaller transformation strain of the reverse transformation, and that the coefficient increases with mechanical cycling, resulting from decreases of the transformation strains caused by the mechanical cycling. The thermodynamic analysis indicates that the reduction in transformation strain with cycling is caused partially by a reduction in the transformation volume and partially by a reduction in the degree of orientation of the martensite variant.