Abstract
Thermal stability of the Nd12.5Fe80.6B6.4Ga0.3Nb0.2 hydrogenation, disproportionation, desorption and recombination (HDDR)-treated powder was studied, and it was correlated to the residual hydrogen in the powder. Presence of the residual hydrogen in the HDDR-treated powder was investigated by X-ray diffraction (XRD), thermopiezic analyser (TPA) and hydrogen analysis. The HDDR-treated material contained a significant amount of hydrogen, and it influenced the thermal stability of the material. Coercivity of the HDDR-treated powder was markedly reduced by heating above 600 °C, and it was related to the residual hydrogen. The residual hydrogen existed in the form of Nd2Fe14BHx hydride, and it was disproportionated into α-Fe, Fe2B and NdH2 phases at an elevated temperature. The coercivity reduction was attributed to the magnetically soft α-Fe and Fe2B phases formed by the disproportionation.
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