Elastocaloric Effect in Aged Single Crystals of Ni54Fe19Ga27 Ferromagnetic Shape Memory Alloy

In the present study, the effect of gamma '-phase dispersed particles on both the L2(1)(B2)-10M/14M-L1(0) martensitic transformations and the elastocaloric effect in aged Ni54Fe19Ga27 single crystals oriented along the [001]-direction was investigated. It was experimentally shown that aging strongly affects the elastocaloric properties of these crystals. The precipitation of semi-coherent gamma '-phase particles up to 500 nm in size in the crystals aged at 773 K for 1 h leads to a 1.4 times increase in the operating temperature range of the elastocaloric effect up to Delta T-SE = 270 K as compared with the initial as-grown crystals (Delta T-SE = 197 K). The adiabatic cooling values Delta T-ad are similar for the as-grown crystals Delta T-ad = 10.9 (+/- 0.5) K and crystals aged at 773 K Delta T-ad = 11.1 (+/- 0.5) K. The crystals containing incoherent gamma '-phase particles sized 5-35 mu m (after aging at 1373 K for 0.5 h) possess an operating temperature range of Delta T-SE = 255 K with slightly smaller adiabatic cooling Delta T-ad below 9.7 (+/- 0.5) K. The aged [001]-oriented Ni54Fe19Ga27 single crystals demonstrate high cyclic stability: the number of cycles does not influence the adiabatic cooling values and parameters of loading/unloading curves regardless of the particle size. The ways to improve the elastocaloric cooling parameters and stability of the elastocaloric effect by means of dispersed particles in the NiFeGa ferromagnetic shape memory alloy were discussed.