Elastocaloric effect in Ti-Ni shape-memory wires associated with the B2 ↔ B19' and B2 ↔ R structural transitions

We have studied the elastocaloric properties of Ti-Ni shape-memory wires subjected to specific heat treatments to decouple the B2 ↔ R transition from the B2 ↔ B19' one. The entropy values at moderate stresses (∼170 MPa) for the B2 ↔ B19' transition are remarkably high (in the range 60–80 J/kg K). However, in spite of the B2 ↔ R transition exhibits significantly lower entropy changes (∼12 J/kg K), the much smaller hysteresis of this transition gives rise to a larger reversible elastocaloric effect for low applied stresses. Therefore, the reversible elastocaloric strength associated with the B2 ↔ R is larger than the elastocaloric strength associated with the B2 ↔ B19' transition.