On the microstructural evolution and accelerated magnetocaloric phase formation in La-Fe-Si alloys by hot forging deformation

To solve the difficulty in forming magnetocaloric phase in La-Fe-Si alloys due to intrinsic incompleteness of peritectic reaction and slow diffusion rate, we proposed here a new approach of hot forging deformation to accelerate the phase formation. The evolution of phase constitution, grain structure and magnetocaloric effect has been systematically investigated, and the underlying mechanism was revealed. It was found that a novel microstructure, consisting of refined layer phases and high-density grain boundaries, formed during the forging deformation and played a key role in promoting the phase formation process. As a result, a dominant La(Fe, Si)13 phase with a volume fraction of 82.2% was obtained in the 84.4% deformed sample after annealing at 1323 K for only 1 h. This led to a large magnetic entropy change of 14.6 J/kg K at 2 T compared with 1.3 J/kg K for the non-deformed sample. A prominent magnetic entropy change of 19.4 J/kg K at 2 T was obtained after annealing for 12 h and hydrogenating, and the integrity of the sample was maintained. The current results suggest that the hot forging deformation effectively facilitates the magnetocaloric phase formation in La-Fe-Si alloys, and becomes a promising route for mass production of near-net-shape magnetic refrigerants.