Enhanced elastocaloric effect and mechanical properties of Gd-doped Ni-Co-Mn-Ti-Gd metamagnetic shape memory alloys

Improving elastocaloric effect (eCE) and mechanical properties is the key to developing high-performance eCE cooling materials. In this paper, the metamagnetic shape memory alloys Ni _35.5Co _13.5Mn ₃₅Ti _15-xGd _x ( x = 0–0.9) were successfully prepared by arc melting method, and the effects of Gd substitution for Ti on the martensitic transformation (MT) temperature, phase composition, microstructure, eCE and mechanical properties of the alloys were systematically investigated. With the introduction of Gd elements, the transformation temperature shifts to a low temperature, and the mechanical properties of the alloy are also enhanced. The fracture strength increased from 980 MPa ( x = 0) to 1142 MPa ( x = 0.9). At room temperature (RT), a large adiabatic temperature change of + 13.5 K/− 12.7 K is obtained after loading/unloading, and a constant temperature change of + 5.6 K/− 5.5 K is obtained without apparent degradation under the compressive stress of 400 MPa during 61 cycles for all-d metal Heusler Ni _36.5Co _13.5Mn ₃₅Ti _14.9Gd _0.1 alloy. The adiabatic temperature change of 13.5 K exceeds the elastocaloric temperature change of most NiMn-based alloys available at present, and the mechanical properties of Ni-Co-Mn-Ti-Gd alloy are at a high level among the NiMn-based alloys. The precipitation of the Gd-rich second phase along the grain boundaries is intrinsically responsible for the improved mechanical properties.