Effect of processing hydrogen pressure on magnetic properties of HDDR Nd-Fe-B magnet

High coercivity and anisotropic Nd-Fe-B powders for making anisotropic bonded magnets have been prepared by hydrogenation-disproportionation-desorption-recombination (HDDR). We found that the processing hydrogen pressure is intimately correlated with the formation of $c$ -axis crystal texture of Nd2Fe14B phase. There exists a critical hydrogen pressure, $P_{\mathrm {crit}}$ , during hydrogen-disproportionation stage, that promotes the formation of $c$ -axis crystal texture. When processing hydrogen pressure is higher than $P_{\mathrm {crit}}$ , the formation of $c$ -axis texture deteriorates and results in isotropic Nd-Fe-B magnetic powders. The existence of $P_{\mathrm {crit}}$ is ascribed to the thermodynamics and kinetics origin during HDDR process.