Elastocaloric and Magnetocaloric Effects Linked to the Martensitic Transformation in Bulk Ni55Fe11Mn7Ga27 Alloys Produced by Arc Melting and Spark Plasma Sintering

Abstract

The investigation of caloric effects linked to first-order structural transitions in Heusler-type alloys has become a subject of considerable current interest due to their potential utilization as refrigerants in solid-state cooling devices. This study is mainly motivated by the possibility of developing refrigeration devices of improved energy efficiency with a reduced environmental impact. We produced partially textured and isotropic bulk samples of the Heusler-type magnetic shape memory alloy Ni55Fe11Mn7Ga27 by arc melting and spark plasma sintering (SPS), respectively. Their structural, microstructural, and phase transition characteristics and magnetocaloric and elastocaloric effects, associated with first-order martensitic transformation (MT), were studied. The elemental chemical compositions of both samples were close to nominal, and a martensitic-like structural transformation appeared around room temperature with similar starting and finishing structural transition temperatures. At room temperature, austenite exhibited a highly ordered L21-type crystal structure. The partial grain orientation and isotropic nature of the arc-melted and SPS samples, respectively, were revealed by X-ray diffraction and SEM observations of the microstructure. For the arc-melted sample, austenite grains preferentially grew in the (100) direction parallel to the thermal gradient during solidification. The favorable effect of the texture on the elastocaloric response was demonstrated. Finally, due to its partial grain orientation, the arc-melted bulk sample showed superior values of maximum magnetic entropy change (|ΔSM|max = 18.6 Jkg−1K−1 at 5 T) and elastocaloric adiabatic temperature change (|ΔTadme|max = 2.4 K at 120 MPa) to those measured for the SPS sample (|ΔSM|max = 8.5 Jkg−1K−1 and (|ΔTadme|max = 0.8 K).