Magnetic and microstructural modification of the Dy-free HDDR Nd-Fe-B powders with micron BN addition by the grain boundary diffusion engineering

Abstract

The micron BN powders were studied as diffusion sources for the grain boundary diffusion process to HDDR (hydrogenation-disproportionation-desorption-recombination) Nd-Fe-B powders. The coercivity of HDDR powders was enhanced by about 52.1 %. The only downside is that the remanence was slightly reduced because BN powders were a non-magnetic additive. Microstructural investigations showed that the nonferromagnetic Nd-rich grain boundary phases envelop the Nd2Fe14B grains because the wettability of the interface between the matrix and the grain boundary phases was improved by diffusing BN powders. The preferred residence of BN in the intergranular phases and their reaction with the grain boundary phases might both contribute to the enhancement of the coercivity. As a result, the research and development of the grain boundary diffusion process with non-rare earth materials have significance in further minimizing the use of rare earth (RE).