Effect of Grain Boundary Modification on the Microstructure and Magnetic Properties of HDDR-treated Nd-Fe-B Powders

The microstructure and magnetic properties of HDDR–treated powders after grain boundary diffusion process (GBDP) with Nd–Cu alloy at different temperatures have been studied. The variation of GBDP temperature had multifaceted influences on the HDDR–treated powders involving the microstructure, phase composition and magnetic performance. An enhanced coercivity of 16.9 kOe was obtained after GBDP at 700 ℃, due to the modified grain boundary with fine and continuous Nd–rich phase. However, GBDP at lower or higher temperature resulted in poor magnetic properties because of insufficient microstructural modification. Especially, the residual hydrogen induced phenomenon during GBDP strongly depended on the GBDP temperature.