Mechanically activated disproportionation and microstructure nanocrystallization of a Nd ₁₄Fe _66.9Co ₁₁B ₇Zr _O.1Ga _1.O permanent magnetic alloy

In order to obtain nano-structured as-disproportionated microstructure in partially Co-substituted NdFeB-type alloys, the Nd ₁₄Fe _66.9Co ₁₁B ₇Zr _O.1Ga _1.O alloy was disproportionated by room-temperature reactive ball milling in hydrogen, with the mechanical energy serving as the driving force. The reaction progress during milling was examined by hydrogen absorption measurement, and the corresponding microstructure change was characterized by X-ray diffraction (XRD), Mossbauer spectrometry, and transmission electron microscopy (TEM), respectively. The results show that the Nd ₂(Fe, Co) ₁₄B matrix phase in the alloy can be mechanically disproportionated by a two-stage reaction. Firstly, the Nd ₂(Fe, Co) ₁₄B matrix phase in the alloy is hydrogenated into Nd ₂(Fe, Co) ₁₄BH _x until the value of x achieves about 2.9 when a full hydrogenation is achieved. After that, the Nd ₂(Fe, Co) ₁₄BH _x phase is gradually disproportionated into α-Fe(Co), NdH ₂₇, and (Fe, Co) ₂B phases upon further milling in hydrogen. The as-disproportionated phases NdH ₂₇, (Fe, Co) ₂B, and ₁₄-Fe(Co), are typically nano-structured, with an average grain size of about 10 nm, which lays the basis for synthesizing nanocrystalline Nd ₂(Fe, Co) ₁₄B grains via a subsequent desorption- recombination treatment.