Mechanical and elastocaloric effect of aged Ni-rich TiNi shape memory alloy under load-controlled deformation

Abstract

This study investigated the elastocaloric effect of Ni-rich Ti49.6Ni50.4 shape memory rods under compression. As-received rods, rods aged at 300 °C for 1 h, and rods aged at 275 °C for 125 h were investigated to reveal the effects of aging on the elastocaloric properties. These samples were first trained under constant stress of 1200 MPa or 1500 MPa, which decreased the B19′ transformation temperature and stabilized the R-phase transformation. Associated with the changes in transformation temperatures, the pseudoelasticity performance and elastocaloric effect of the samples decayed with increasing training times and then became stable when the training time exceeded a certain value. The sample aged at 275 °C for 125 h, which was most hardened by the precipitation hardening effect, exhibited better stability during the training process due to less plastic deformation and thus retained an obvious elastocaloric cooling effect. Because the precipitation treatment broadened the transformation range of the sample aged at 275 °C for 125 h by introducing a two-stage B19’→R→B2 reverse transformation, the elastocaloric cooling effect of 7 °C could be utilized at a relatively large temperature range of −20 °C to 100 °C.