Enhanced Cyclability of Superelasticity and Elastocaloric Effect in Cu and B Co-Doped Co-Ni-Ga Shape Memory Alloys

We developed a [001] B2 preferentially oriented Co-Ni-Ga alloy with Cu and B co-alloying, which 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 behaviors with a high yield strength of ~1300 MPa and an appreciable failure strain of ~8.8%. An exceptional superelasticity combined with fully reversible strain of 2.5%, low driving force of 99 MPa, narrow stress hysteresis of 33.5 MPa and extraordinary mechanical cyclic stability for 20,000 cycles was also successfully achieved in the studied alloy. By virtue of its superior mechanical responses, an excellent room-temperature elastocaloric effect showing a moderate adiabatic temperature change of -3.2 K at a small transformation strain of 1.5% was observed over 20,000 cycles without any apparent degradation. More importantly, the fatigue resistance of superelasticity and elastocaloric effect is extremely enhanced relative to the reported single-crystal counterparts. The great performances of superelasticity and elastocaloric effect of the optimized Co-Ni-Ga alloy imply a promising future for advanced superelastic and solid-state refrigeration applications, and the collaborative design approach may be exploited to other intermetallic-type shape memory alloys