Coercivity Enhancement of Nd-Fe-B HDDR Powder by Grain Boundary Diffusion Process with Rare-Earth Hydride

Abstract

The grain boundary diffusion (GBD) process with rare-earth hydride was performed to increase the coercivity of hydrogenation–disproportionation–desorption–recombination (HDDR) powder. Before the GBD process, we investigated the effect of post-annealing of the initial HDDR powder on its magnetic properties. Low-temperature annealing reduced the coercivity of the HDDR powder. However, the coercivity decline decreased with increasing annealing temperature, becoming similar to that of the initial powder at 900°C. After the GBD process at 850°C for 1 h, the coercivity increased by about 4 kOe with 4 wt.% NdH x -Cu, forming a thick and continuous grain boundary phase. In addition, the coercivity and remanence of the HDDR powder produced by the GBD process with NdH x -Cu were higher when using NdH x in spite of the same amount of diffusion as at 2 wt.%.