Mechanically activated disproportionation of NdFeB alloy by ball milling in hydrogen

Mechanically activated disproportionation of Nd 12 Fe 82 B 6 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 Nd 2Fe 14 B of the as cast Nd 12 Fe 82 B 6 alloy can be disproportionated into a mixture of Nd hydride (H 5Nd 2), FeB/Fe 2B, and α Fe, by ball milling under hydrogen pressure of 0.2 MPa. The as disproportionated phases are of the size about 20 nm, 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 Nd 2Fe 14 B/ α Fe nano composites with magnetic exchange coupling effect by subsequent desorption recombination processing.