Residual Hydrogen in Nd-Fe-B HDDR Powder and Its Effect on Coercivity of Hot-Pressed Compact

Residual hydrogen in the HDDR-treated Nd_12.5Fe_80.6B_6.4Ga_0.3Nb_0.2 powder and its effect on the coercivity of consolidated compact of the powder were investigated. Hydrogen desorption of the HDDR powder was studied by vacuum gauge and TPA. Compaction of the HDDR powder was performed by hot-pressing technique. The Nd_12.5Fe_80.6B_6.4Ga_0.3Nb_0.2 HDDR powder contained significant amount of residual hydrogen (approximately 1520 ppm). Coercivity of the hot-pressed compact was radically reduced when the compaction was performed at the temperature above 650 °C. The radical coercivity reduction in the compact hot-pressed above 650 °C was attributed to the presence of the soft magnetic phases, α-Fe and Fe₂B formed via disproportionation of the Nd₂Fe₁₄BH_x. The residual hydrogen may have contributed for the formation of Nd₂Fe₁₄BH_x.