Electro-thermomechanical behaviour of a Ti-45.0Ni-5.0Cu (at.%) alloy during shape memory cycling

In the present paper, electrical resistance (ER) changes are measured simultaneously with the stress-assisted two-way memory effect (SATWME) in Ti-45.0Ni-5.0Cu (at.%) wires during thermal cycling (max. 15 cycles) for several different stress levels. Interesting qualitative evolutions of the ε-ER-T loops during cycling are observed as a function of the applied stress. On cooling, for stresses higher than 175 MPa, a clear deviation of the ε-T curves is verified and the reversion of this anomaly is not observed during heating. After some cycles, serrations are frequently observed on the ER-T loops essentially below Mf and above Af, indicating an interaction between the formation and reversion of oriented martensite variants with the defects introduced during the thermomechanical cycling. A linear relationship is observed between ER and ε for the direct and reverse transformation ranges. The characteristic slope d(ΔR/R)/dε is slightly dependent on the applied stress and on the number of thermal cycles.