Enhanced cyclability of superelasticity and elastocaloric effect in Cu and B co-doped Co-Ni-Ga shape memory alloys

A< 001 >B2 preferentially oriented Co-Ni-Ga alloy with Cu and B co-alloying is synthesized. It contains two kinds of ductile secondary phases precipitated in the columnar grain interior and grain boundaries, respectively. This textured Co-Ni-Ga-Cu-B heterostructural alloy presents remarkable mechanical properties with a high yield strength of ~1203 MPa and an appreciable failure strain of ~8.8%. It also offers exceptional superelasticity with a fully recoverable strain of 2.5%, a low driving force of 99 MPa and narrow stress hysteresis of 33.5 MPa. Excellent mechanical cyclic stability for 20,000 cycles after cyclic training is also successfully achieved. With the advantages of its superior mechanical responses, an excellent room-temperature elastocaloric effect is demonstrated with a moderate adiabatic temperature change of −3.2 K at a small transformation strain of 1.5%, which is observed over 20,000 cycles without any apparent degradation. More importantly, the fatigue resistance of the superelasticity and the elastocaloric effect is much more enhanced relative to the reported single-crystal counterparts. The great performances of the superelasticity and the elastocaloric effect of the optimized Co-Ni-Ga alloy imply a promising candidate for advanced superelastic and solid-state refrigeration applications. The collaborative designing approach may be exploited to other intermetallic-type shape memory alloys.