Mastering a 1.2 K hysteresis for martensitic para-ferromagnetic partial transformation in Ni-Mn(Cu)-Ga magnetocaloric material via binder jet 3D printing

Abstract Magnetocaloric (MC) materials have gained traction in the research and industry communities for their prospects in solid state magnetic refrigeration. Important to the commercialization of MC materials are: (1) establishment of a fabrication method that can combine high surface area for heat transfer and geometric freedom for designing an efficient heat exchanger which has low pressure drop for the coolant and (2) advancement of low cost alloys with appropriate MC properties. In this regard, additive manufacturing may provide the geometric freedom necessary for adapting designs to solid state cooling, and the Ni-Mn(Cu)-Ga Heusler ferromagnetic shape memory alloys (FSMAs), exhibiting a martensitic para-ferromagnetic transformation at Tms=304 K, can provide a low-cost MC material, very promising for magnetic cooling. In this study, a Ni49.5Mn19.1Cu6.6Ga24.8 (at.%) alloy is additively manufactured using powder bed binder jet 3D printing with subsequent sintering. This printed and sintered material enabled a large change of magnetization during partial transformation cycles with the smallest temperature hysteresis recorded for FSMAs, equal to about 1.2 K, regardless the value of magnetic field applied. Under 2 T and at 304 K it exhibits an adiabatic temperature change (ΔTad) of 2 K and a stable cycling behavior of ΔTad = │1.7│ K for 100 cycles. The maximum of magnetic field-induced entropy change |ΔSm, 2T| ≈ 12.0 J/kg·K was estimated at 304 K. These results demonstrate the viability of powder bed binder jet 3D printing as an effective fabrication method for functional magnetocalorics, as well as the outstanding MC characteristics of a low-cost Ni-Mn(Cu)-Ga Heusler-type FSMA.