Influence of deformation and heat treatment on the transformation temperatures of TiNi alloys

The transformation temperatures of TiNi shape memory alloys can be influenced by the appropriate combination of deformation processes and of heat treatment. The increased dislocation density and the residual stresses cause the decrease of the phase transformation temperatures M, and M(f) and assit in the formation of the rhombohedral phase in the alloys with higher Ti content. The formation of the rhombohedral phase usually found in alloys enriched with Ni or with some transitive metal, is in the investigated alloy influenced by the residual stresses induced in the matrix. The rhombohedral phase is formed after the cold rolling and after the subsequent annealing up to the temperature of 500°C/1 h. The transformation temperatures determined on the basis of functio­nal dependence ρ=ρ(T) agree good with the results of X-rays analysis