INVESTIGATION OF THE RESISTANCE TO DEMAGNETIZATION IN BULK RARE-EARTH MAGNETS COMPRISED OF CRYSTALLOGRAPHICALLY-ALIGNED, SINGLE-DOMAIN CRYSTALLITES WITH MODIFIED INTERGRANULAR PHASE

The research presented in this dissertation investigates whether an increased coercivity of Neodymium-Iron-Boron (Nd2Fe14B) based bulk magnets at elevated temperature (160°C), which is now only obtainable by substituting ~7wt% dysprosium (Dy) for a portion of neodymium (Nd), can be achieved through specific microstructural modifications with decreased Dy concentrations. The approach is to reduce the size of individual crystallographically-aligned grains in the magnet so that each grain can only support a single magnetic domain and to simultaneously dilute the Nd-Fe inter-granular phase present in conventional magnets with a non-Fe-containing, Nd-rich phase (Nd-Cu alloy) in an attempt to partially magnetically isolate the individual crystallites. The results of this research show that hot-deformed bulk magnets with the microstructural features described above have similar coercivity to commercially sintered magnets that are used in traction motor of electric and hybrid vehicles. The increase in coercivity due to the modification of intergranular phase is analyzed in the framework of what would be expected from the partially magnetic isolation of the individual grains