Unveiling the enhancing mechanism of cyclic stability in Tb doped Ni-Mn-Sn Heusler alloys

Abstract

Rare-earth (RE) doping has been demonstrated as a feasible approach to improve the cyclic performance of Ni-Mn-based Heusler alloys, but the current demonstration of underlying mechanism is simply ascribed to strengthening of the grain boundary cohesion. In this work, the effects brought by RE doping on microstructure, stress induced martensitic transformation behavior and cyclic stability of Ni-Mn-based alloys were systematically investigated. By Tb doping, a stable adiabatic temperature change (|ΔTad|) of ∼ 5.5 K over 1000 cycles with no significant degradation was obtained in (Ni43Mn47Sn10)99.5Tb0.5. (1) Through the in-situ digital image correlation strain measurement and in-situ SEM observation upon loading process, it revealed a multipoint nucleation of the martensitic transformation across the specimen arising from the intergranular NiSnTb secondary phase as nucleate sites, which weakens the strain concentration and suppresses the crack tendency. (2) The multipoint nucleation promotes the transformation volume fraction, making the large |ΔTad| could be driven by a small transformation strain (Δεtr) and (Ni43Mn47Sn10)99.5Tb0.5 yields a |ΔTad/Δεtr| up to 8.7 K %−1. Such reduction in applied strain further alleviates the extension of the cracks. Both the two factors brought by Tb doping in (Ni43Mn47Sn10)99.5Tb0.5 give rise to the enhancement in cyclic stability of the large elastocaloric effect.

Keywords

• Heusler alloys
• Martensitic Transformation
• Solid-state refrigeration
• Elastocaloric effect
• Rare-earth doping
• Cyclic stability