Coercivity enhancement of hot-deformed Nd-Fe-B magnet by grain boundary diffusion process using the reaction of NdHx and Cu nanopowders

In this study, the coercivity enhancement of hot-deformed Nd-Fe-B magnet by grain boundary diffusion process (GBDP) has been studied with a new method. The mixed powders of NdHx and Cu were used as a diffusion source instead of the Nd-Cu eutectic alloy powders in order to simplify the GBDP. Before GBDP, reactions of NdHx and Cu powders were examined by XRD patterns. The Nd-Cu eutectic reaction in the mixed powders was confirmed after heat treatment at temperature higher than 550 °C. In the GBDP, the amount of diffused Nd-Cu alloy increased with increasing heat treatment temperature. However, when the same amount of Nd-Cu is diffused, the coercivity increment of the heat-treated magnet at low temperature is higher than that of the heat-treated magnet at high temperature. It is observed that higher temperature can induce grain growth and composition change of the Nd-rich grain boundary phase. The large coercivity increment of approximately 8 kOe was achieved after GBDP at 600 °C for 1 h, where the diffused Nd-Cu was 5.85 wt%. •The mixture of NdHx powder and Cu nanopowder was employed for GBDP.•The mixed powders were employed as diffusion source instead of Nd-Cu alloy.•The Nd-Cu eutectic reaction in the mixed powders took placed above 550 °C.•The large coercivity increment of 8 kOe was achieved at 6 wt% of NdHx-Cu content.