Mechanisms of rapid magnetocaloric enhancement of La–Fe–Co–Si alloy by high-temperature hot compression with large deformation

Abstract

In this study, the microstructure, phase composition, magnetic transition, and magnetocaloric effect of the LaFe10.6Co0.9Si1.5 alloy hot compressed at high temperatures over 1173 K with a strain rate 0.005 s−1 and reduction ratio 50%–70 % are studied. No La(Fe, Si, Co)13 phase is formed until the hot-compression temperature is elevated to 1273 K and the reduction ratio is increased to 70 %. As a result, 86.8 ± 2 wt% 1:13 phases are rapidly obtained in the LaFe10.6Co0.9Si1.5 ingot. The whole process can be completed within only 10 min and no post-annealing process is needed. This fast formation of the La(Fe, Si, Co)13 phases is possibly induced by the directional atomic diffusion, accelerated atomic diffusion, and the stability of the La(Fe, Si, Co)13 phase and structural relaxation caused by the sufficiently restored elastic energy during the hot compression. The LaFe10.6Co0.9Si1.5 ingot hot compressed at 1273 K with a reduction ratio 70 % at a strain rate 0.005/s exhibits a second-order phase transition and negligible magnetic hysteresis. A large magnetic entropy change of 4.4 J/kg.K and a wide working temperature range of 57 K under 2 T are acquired near room temperature. This study proposes a new efficient hot compression route for processing the La–Fe–Co–Si alloy and enhancing the magnetocaloric effect.