Excellent mechanical properties and giant room-temperature elastocaloric effect in spark plasma sintered Ni-Co-Mn-Ti shape memory alloy

All-d-metal Heusler-type Ni-Mn-Ti alloys have emerged as a research focus in the field of elastocaloric refrigeration due to their remarkable elastocaloric effect. However, the mechanical properties of these materials present a challenge for their engineering applications. In this work, Ni₃₇Co₁₃Mn_33.5Ti_16.5 alloys with varying particle sizes were successfully prepared under different conditions using spark plasma sintering. The influence of particle size on the microstructure, mechanical properties and the elastocaloric effect were systematically explored. The results indicate that smaller particle sizes can significantly enhance mechanical properties during the SPS process, primarily due to grain refinement and the presence of Ti-rich second phases within the grains. Notably, compressive strength and fracture strain reached as high as 2225 MPa and 33 %, respectively, marking an increase of 145.9 % and 312.5 % over the as-cast alloy. Additionally, an unprecedently adiabatic temperature variation of 31.2 K was obtained upon loading in the sintered Ni-(Co)-Mn-Ti shape memory alloys.