Effect of niobium on the HDDR behaviour of near-stoichiometric NdFeB alloys

The HDDR behaviours of Nd11.8Fe81.3Nb1B5.9, Nd11.8Fe80.3Nb2B5.9 (at%) alloys were studied using a high resolution scanning electron microscope (HRSEM) in order to relate the initial, intermediate and final microstructures, to that of NdFeB-type alloys without additions. The disproportionation of the Nd2Fe14B (phi) matrix phase starts at the grain boundary and at the interface of the Nb26Fe32B42/phi phases, resulting in the formation of a submicron structure consisting of Fe, Fe2B and Nd-hydride. The HDDR process proved to be a very rapid and efficient method of homogenising the as-cast alloys. Promising magnetic properties have been obtained for bonded magnets using the HDDR powder.