Copper and graphene oxide co-doping in Ni-Mn-Sn alloys: A pathway to superior mechanical properties and elastocaloric effect

This study investigates the optimization of the martensitic transformation and mechanical properties of Ni-Mn-Sn alloys through the co-doping of Cu and graphene oxide. Firstly, the research examines the effect of Cu doping, which significantly enhances the entropy change (ΔS_tr) during the martensitic transformation. First-principles calculations predict that co-doping with Cu and graphene oxide reduces the martensitic transformation temperature, increases the Curie temperature, and decreases the magnetization difference between austenite and martensite (ΔM). These theoretical predictions are corroborated by experimental results. The impact of graphene oxide doping on the microstructure was analyzed, showing that it induced secondary phase reinforcement and grain refinement. The precipitates in the graphene oxide-doped alloy significantly impeded the martensitic transformation. However, the compressive strength increased from 267 MPa in the undoped state to 1041 MPa, and the fracture strain improved from 3.6 % to 6.84 % at a graphene oxide content of 3 at%. The Ni₅₀(Mn_31.9C_0.6Cu_3.5)Sn₁₄ alloy with minor precipitates along grain boundaries demonstrating a ΔT_ad of −4.05 K under a 3 % strain at room temperature. These findings indicate that the synergistic effect of Cu and graphene oxide co-doping offers a promising strategy for developing high-performance elastocaloric materials for solid-state refrigeration applications.