Abstract:Mechanically activated disproportionation of Nd₁₂Fe₈₂B₆ alloy by ball milling in hydrogen atmosphere was experimentally investigated. The aspects of thermodynamics and kinetics for the mechanically activated disproportionation of the NdFeB alloy were discussed. Both the evolution of the disproportionation reaction and the corresponding microstructure change of the alloy during milling were characterized by X-ray diffraction (XRD) analysis. The results show that the matrix phase Nd₂Fe₁₄B of the as-cast Nd₁₂Fe₈₂B₆ alloy can be disproportionated into a mixture of Nd-hydride (H₅Nd₂), FeB/Fe₂B, and α-Fe, by ball milling under hydrogen pressure of 0.2MPa. The as-disproportionated phases are of the size about 20nm, suggesting that ball milling in hydrogen is an effective route for low-temperature disproportionation processing of the NdFeB alloy to ensure a full nano-structured as-disproportionated microstructure. This is the basis for synthesizing Nd₂Fe₁₄B/α-Fe nano-composites with magnetic exchange coupling effect by subsequent desorption-recombination processing.

Key words: mechanically activated disproportionation; NdFeB alloy; nano-structured phases; ball milling