Recombination of the Nd2Fe14B phase after reactive milling under hydrogen of a Nd-Fe-B powder

Mechanical milling under reactive hydrogen atmosphere of a Nd-Fe-B powder, followed by vacuum annealing up to 600 deg. C, was achieved. Both as-milled and annealed powders were investigated by X-ray diffraction and Moessbauer spectrometry. During reactive milling, the Nd2Fe14B phase disproportionates into neodymium hydrides (NdH2±x) poorly crystallized α-Fe and an amorphous Fe-B phase. Upon annealing, hydrogen desorbs from the neodymium hydride and this is followed by the recombination of the Nd2Fe14B phase. The recombination temperature was found to be 520 deg. C. The recombination reaction is incomplete, likely due to oxygen contamination, as neodymium oxides, α-Fe and Nd1.1Fe4B4 phases are detected in the powder annealed at 600 deg. C