Mechanically Activated Disproportionation and Microstructure Nanocrystallization of a Nd<SUB>14</SUB>Fe<SUB>66.9</SUB>Co<SUB>11</SUB>B<SUB>7</SUB>Zr<SUB>0.1</SUB>Ga<SUB>1.0</SUB> Permanent Magnetic Alloy

Abstract

In order to obtain nano-structured as-disproportionated microstructure in partially Co-substituted NdFeB-type alloys, the Nd14Fe66.9GCo11B7Zr0.1Ga1.0 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), Mössbauer spectrometry, and transmission electron microscopy (TEM), respectively. The results show that the Nd2(Fe, Co)14B matrix phase in the alloy can be mechanically disproportionated by a two-stage reaction. Firstly, the Nd2(Fe, Co)14B matrix phase in the alloy is hydrogenated into Nd2(Fe, Co)14BH(x), until the value of x achieves about 2.9 when a full hydrogenation is achieved. After that, the Nd2(Fe, Co)14BH(x) phase is gradually disproportionated into alpha-Fe(Co), NdH2.7, and (Fe, Co)2B phases upon further milling in hydrogen. The as-disproportionated phases NdH2.7, (Fe, Co)2B, and alpha-Fe(Co), are typically nano-structured, with an average grain size of about 10 nm, which lays the basis for synthesizing nanocrystalline Nd2(Fe, Co)14B grains via a subsequent desorption-recombination treatment.