Formation of 1:13 Phase in La(Fe,Si) -Based Compounds by Diffusion of LaFe,Si Fe(Si) Couple

摘要

Formation mechanism of the 1:13 phase in ${hbox {La}}({hbox {Fe}},{hbox {Si}})_{13}$ compounds has been investigated by the diffusion of ${hbox {LaFeSi}}/alpha-{hbox {Fe}}({hbox {Si}})$ couple at 1353 K and 1443 K. After annealing at 1353 K for 12 days, 0.8 mm thick 1:13 phase was obtained between LaFeSi and $alpha-{hbox {Fe}}({hbox {Si}})$ sheets. A layer of ${hbox {La}}_{5}{hbox {Si}}_{3}$ phase determined by EDS appeared all along the interface of LaFeSi and 1:13 phase. In addition, ${hbox {La}}_{5}{hbox {Si}}_{3}$ phase was also found in grain boundary of 1:13 phase grains and La-rich phase was found in grain boundary of $alpha-{hbox {Fe}}({hbox {Si}})$ sheet. It is believed that ${hbox {La}}_{5}{hbox {Si}}_{3}$ phase and grain boundaries working as rapid diffusion paths were important for the formation of 1:13 phase in ${hbox {La}}({hbox {Fe}},{hbox {Si}})_{13}$ compounds. 1:13 phase mainly formed in the $alpha-{hbox {Fe}}({hbox {Si}})$ master alloy sheet. In addition, large grains of 1:13 phase were close to the LaFeSi sheet and small grains of 1:13 phase were close to $alpha-{hbox {Fe}}({hbox {Si}})$ layer. It indicated that La and Si elements diffused from LaFeSi sheet to $alpha-{hbox {Fe}}({hbox {Si}})$ sheet- in the formation process of 1:13 phase. There was an endothermic peak at 207 K in the DSC curve of the 1:13 phase obtained from diffusion couple annealed at 1353K. It indicated the occurrence of magnetic phase transition.