Intermediate hydrogenation phase in the hydrogenation-disproportionation-desorption-recombination process of Nd2Fe14B-based anisotropic magnets

To understand the disproportionation and anisotropy-inducing mechanism of t he hydrogenation-disproportionation-desorption-recombination process of Nd2 Fe14B-based anisotropic magnets, the disproportionated structure of Nd13.0F e65.9Co11.0B7.0Ga1.0Zr0.1 alloys has been investigated via transmission ele ctron microscopy. An intermediate hydrogenation phase of the tetragonal Fe3 B (t-Fe3B) has been revealed to appear in the early stage of disproportiona tion. The t-Fe3B possesses lattice coherency and an associated "one-to-one" orientation relationship with the parent Nd2Fe14B phase. Within the t-Fe3B grain, fine Nd2Fe14B particles exist along with NdH2 particles. The diamet er of the Nd2Fe14B particles is around 50 nm, and they have close orientati on to that of original Nd2Fe14B. An anisotropy-mediating disproportionation scheme with the intermediate hydrogenation phase is proposed. (C) 1999 Acm Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.