Reduced Annealing Time and Enhanced Magnetocaloric Effect of La(Fe,Al)13 Alloy by La-nonstoichiometry and Si-doping

摘要

LaFe13-x Mx(M=Si,Al)alloys are promising for use in magnetic refrigeration.However,they require long annealing time(30 days)in order to optimize the magnetocaloric properties.Research has shown that the addition of extra La in off-stoichiometric alloys can greatly shorten the annealing time.Therefore,the purpose of this study is to investigate the influence of the extra addition of La on the annealing properties of a new off-stoichiometric La1.7Fe11.6Al1.4-xSix(x=0,0.1,0.4)alloys.It was demonstrated that after a 36 h annealing time,a large volume fraction of 1:13 magnetocaloric phase was obtained for all alloys.Further microstructural analysis of the off-stoichiometric La1.7Fe11.6Al1.4-xSix alloys revealed a facet-like grain morphology.The La1.7Fe11.6Al1.4 and La1.7Fe11.6Al1Si0.4 alloys were shown to contain large 1:13 phase precipitates separated in a La-rich matrix,while the La1.7Fe11.6Al1.3Si0.1 alloy had a continuous 1:13 phase matrix with a fine dispersion of La-rich precipitates throughout.When the magnetic field varied between 0 and 2 T,the corresponding magnetic entropy change and relative cooling capacity for the La1.7Fe11.6Al1.3Si0.1 specimen were determined as 4.58 J/kg K and 173.6 J/kg,respectively.More importantly,the La1.7Fe11.6Al1.3Si0.1 alloy displayed only a slight volume change when the meta-magnetic phase transition occurred,which is promising for cyclic use.