Ferromagnetic shape memory Ni-Fe-Ga alloy foams for elastocaloric cooling

Abstract

An efficient and clean solid-state cooling technique based on elastocaloric effect (eCE) has received great interests as a promising refrigeration technology for the last decade. The eCE materials release and absorb heat under the application/removal of uniaxial stress due to the stress-induced martensite transformation (MT). Ferromagnetic shape memory alloys have great potential to produce large eCE because they require low stress to drive the stress-induced MT. In this report, we employed replication casting technique to fabricate Ni-Fe-Ga alloy foams with NaAlO2 as space holder. The martensite transformation, superelasticity and compressive elastocaloric properties of the annealed foam were investigated. A completely reversible superelastic behavior with a total recovery strain of 3.3% was found at temperatures slightly higher than austenite finishing temperature. As a result, the foam exhibited an adiabatic temperature change (ΔTad) 3.4 K and large specific eCE strength |ΔT/Δσ| = 56.7 K GPa−1 under an external stress 60 MPa. The enhanced eCE properties of the foam over bulk alloys, and the large specific surface area for better heat exchange, imply that the present Ni-Fe-Ga foam has great application potential for room-temperature cooling.