Coercivity and corrosion resistance enhancement of multi-main-phase Nd-Ce-Fe-B sintered magnets by the grain boundary diffusion process using Pr81.5Ga19.5 and Pr81.5Ga14.5Cu5 alloys

Abstract

In this paper, grain boundary diffusion was performed on multi-main-phase Nd-Ce-Fe-B sintered magnets using two different diffusion sources. The coercivity of the magnet was increased from 928 kA/m to 1036 kA/m and 1174 kA/m by diffusing Pr81.5Ga19.5 (PG) and Pr81.5Ga14.5Cu5 (PGC5), respectively, and the corrosion resistance of the magnet was also improved after the above diffusion process. Two kinds of continuous grain boundaries with different contrast were observed after the PG and PGC5 alloy diffusion process, and the results of line scan and quantitative analysis indicate that they originate from different intergranular phases that have been melted during the heat treatment. The distribution of Ga element after grain boundary diffusion and its effects on the coercivity of the magnet were especially investigated. It was found that the coercivity enhancement of these diffused magnets is mainly attributed to the formation of continuous grain boundary and non-ferromagnetic grain boundary phase to weaken the magnetic exchange coupling between the 2:14:1 grains, as well as the formation of the Pr-rich shell with slightly higher magnetocrystalline anisotropy due to the partial substitution of the Nd atoms by the Pr atoms, which compensates for the coercivity drop by chemical homogenization due to the heat treatment.