Optimisation of HDDR processing parameters of sintered NDFEB magnets

摘要

In recent years rare earth metals have hit the headlines due to supply restrictions of neodymium and dysprosium from the main supplier China. The work in this thesis investigates the possibility of recycling sintered NdFeB-type magnets using a combination of hydrogen decrepitation (HD) and the HDDR process (Hydrogenation Disproportionation Desorption and Recombination).ududIn this work the development of microstructure during the HDDR process has been identified and the route taken by hydrogen during absorption and desorption. The microstructure and magnetic properties have been shown to be affected by the process temperature, disproportionation pressure and recombination pressure and time. Sample batches up to 100g exhibit little variation in magnetic properties however 400g batches result in large variations partially due to incomplete recombination. By increasing the disproportionation pressure it was possible to simultaneously process mixed scrap feeds with different Dy and Co levels, however a large variation in magnetic properties was also observed.ududOptimal processing of sintered Nd(_{13.4})Dy(_{0.7})Fe(_{78.6})Al(_{0.7})Nb(_{0.4})B(_{6.3}) was performed by in-situ HD followed by HDDR at 880(^o)C with a disproportionation pressure of 1500mbar and recombination under vacuum. The resultant powder exhibited a remanence of 1.08 T, coercivity of 840 kAm(^{-1}) and maximum energy product of 178 kJm(^{-3}).