A strategy for improving inherent brittleness without significantly sacrificing the magnetocaloric effect in a Ni-Mn-Sn Heusler alloy

The eutectic design, a prevalent strategy for enhancing mechanical properties, aims to address the poor workability caused by the high brittleness of L2₁ intermetallic phase in Ni-Mn-Sn Heusler alloy as a promising material for solid-state refrigeration. In this study, a eutectic composition of Ni₄₈Co₁₀Mn₃₂Sn₁₀ with a fully L2₁/γ lamellar structure significantly improves mechanical properties, reaching 1950 MPa fracture strength and 20.5 % ductility. However, the desired magnetocaloric effect (MCE) is completely inhibited due to a strong Kurdyumov and Sachs orientation relationship (K-S OR) between eutectic phases. To overcome these challenges, a solution to precipitate primary L2₁ phase is proposed. This approach breaks the K-S OR by promoting epitaxial growth of the L2₁ eutectic phase on the primary L2₁ phase. Consequently, the hypoeutectic Ni₄₈Co₈Mn₃₄Sn₁₀ composition achieves an excellent balance between MCE and mechanical properties, with a maximum magnetic entropy change of 10.13 J kg⁻¹ K⁻¹ under 5 T magnetic field, 1894 MPa fracture strength, and 18.4 % ductility. Our strategy overcomes inherent brittleness without significantly sacrificing the magnetocaloric effect within Ni-Mn-Sn alloys. This study is pivotal for optimizing the structural design and properties of Ni-Mn based Heusler alloys.