On the measurement of recovery strains of thermo-mechanically cycled Ni-Ti memory alloy

This paper includes an experimental study of strains variation (recovery and permanent strains) in a Ni-Ti alloy due to thermo-mechanical cycling. The shape memory effect (SME) was evaluated in strip-shaped specimens using a special bending apparatus and discussed with respect to different thermo-mechanical loading paths. The definite transformation temperatures of the studied alloy were achieved by applying several heat-treatments at various temperatures and for different times, and observing the phase transformation behaviour using DSC analysis. To identify the phases present after annealing the specimens were subjected to XRD measurements. It was found that the nature of transformation cycle during the two applied thermo-mechanical loading paths (especially a stress during reverse transformation) and the changes developed in microstructure of the cycled material can both affect the strains behaviour.