Improvement of Magnetic Properties of Zn-bonded Sm-Fe-N Magnets and Investigation of Microstructural Changes at Sm2Fe17–Zn Interface

This paper reviewed development of Zn-bonded Sm-Fe-N magnets in our group, and reported interfacial diffusion and phase changes at the Sm2Fe17–Zn interface during annealing. For increasing magnetic properties of Zn-bonded Sm-Fe-N magnets, decreasing oxygen content, improving dispersibility of Zn, and increasing relative density are necessary, therefore we prepared low oxygen content Sm-Fe-N and fine Zn powders. The powders were sintered by spark plasma sintering process for increasing density under low oxygen atmosphere resulting in obtaining high (BH)max of 200 kJm-3 with relatively high coercivity of 1.28 MAm-1 and β(HcJ) of –0.34%C-1. In order to further improve the (BH)max, it is necessary to control interfacial diffusion and reaction between Sm2Fe17N3 and Zn phases. Thus, as a first step, microstructural changes and interdiffusion coefficient at the Sm2Fe17–Zn interface were investigated using Sm2Fe17–Zn diffusion couples, in this study. It was clear that interdiffusion of Zn, Fe and Sm occurred during annealing below melting temperature of Zn, and the diffusion rate of Zn was faster than those of Fe and Sm. Furthermore, with Zn diffusing into Sm2Fe17 phase, the Sm2Fe17 decompose to ThMn12Sm(Zn,Fe)12 and α-FeZn phases with specific crystal orientation relationship. ©2023 Japan Society of Powder and Powder Metallurgy.