Complete ductility in NdFeB-type alloys using the Hydrogen Ductilisation Process (HyDP)

Abstract The work outlined in this paper demonstrates significant improvements in ductility during the Hydrogen Ductilisation Process (HyDP) [1] of a Neomax-type alloy and, for the first time, complete ductility of a sub-stoichiometric alloy. In previous studies, the uniformity of the ductilisation transformation was limited by the presence of the NdFe 4 B 4 phase not undergoing complete disproportionation, which left extremely brittle, micron-scale islands in a highly ductile disproportionated matrix. The present works investigated the influence of a significantly longer (18 h) hydrogen treatment of the Neomax-type alloy to observe whether the completely disproportionated NdFe 4 B 4 phase is as ductile as the disproportionated matrix. It has been observed that, when the NdFe 4 B 4 phase is completely disproportionated, it exhibits similar ductility to that of the disproportionated matrix, showing no sign of cracking under a compressive load. However, inhomogeneity in the book mould material leads to varying quantities of NdFe 4 B 4 phase and thus, varying levels of disproportionation. Despite this, significant improvements were observed in the mechanical behaviour of the Neomax-type alloy. The longer disproportionation treatment also results in larger grains and thus, a lower final coercivity in the recombined state than that of the previous 5 h treatment. For comparison, the mechanical behaviour of a sub-stoichiometric alloy, which did not contain any NdFe 4 B 4 phase, has also been studied. The compression behaviour of this sub-stoichiometric alloy in the disproportionated state was found to be completely ductile. It is clear from this work that it is possible to create a completely ductile NdFeB material directly from the solid cast alloy which, in the future, could have significant implications for NdFeB magnet production.