Elastocaloric effects in polycrystalline Ni-Fe-Ga foams with hierarchical pore architecture

Abstract

Ni-Fe-Ga foam with hierarchical pore architecture was created by replication casting. The annealed foam had an open porosity 53% and reversible superelasticity with recoverable strain 4.9%. An adiabatic temperature change of 4.1 K with low hysteresis and coefficient of performance 22 were obtained under an external stress 70 MPa. The foam showed improved cyclic stability ($\ensuremath{\sim}2.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in 194 cycles) because of low hysteresis loss under small stress and high crack initiation/propagation resistance in small size nodes and struts, which demonstrated a feasible strategy to enhance the mechanical and functional stabilities of ferromagnetic shape memory alloys via tailoring the material architectures. Nevertheless, the achieved elastocaloric cooling stability still cannot satisfy (${10}^{7}$ cycles) the commercial application, therefore, it should be further explored to become a promising candidate for elastocaloric material.