Coercivity Enhancement of Nd-Fe-B Powders via Grain Boundary Diffusion with a Tb/Cu Mixture

We investigated the changes in the microstructures and magnetic properties of a grain boundary diffusion-processed (GBDP) anisotropic Nd-Fe-B powder. The powder was obtained via hydrogenation decomposition desorption recombination (HDDR) and diffused with heavy rare-earth elements (HREs), such as Dy and Tb fluorides, as well as metallic powders. The HREs diffused through the grain boundaries into the HDDR powder and were found primarily in the RE-rich triple junction regions. The HREs in the RE-rich regions formed the main phase (Nd2Fe14B), followed by a high-coercivity (Nd+Tb)(2)Fe14B shell. We also studied the GBDP powder with Tb and low-melting temperature elements such as Cu and Al. The addition of Cu to the GBDP source effectively improved the grain boundary structure and diffusion depth. The magnetic properties changed from remanence and coercivity of 12.5 kG and 15.7 kOe to 12.3 kG and 23.9 kOe, respectively, for GBD by Tb and Cu mixtures.