Toward Maximum Utilization of Heavy Rare Earths in Sintered Nd–Fe–B Magnets by Grain Boundary Diffusion Source and Application Area Optimization

Abstract

Reduction in the utilization of resource critical heavy rare earth (HRE) elements such as Dy and Tb in NdFeB-based magnets is crucial for cost-effective coercivity enhancement at the high operating temperature in E-motors. The grain boundary diffusion process (GBDP) is optimized and aim to maximize HRE utilization by selective magnetic hardening of areas in the magnet such as corners or edges that are highly susceptible to demagnetization, as demonstrated by finite element magnetostatics simulation on an internal permanent magnet synchronous traction motor for electric vehicles. This becomes especially important considering the advent of additive manufacturing, which has the potential to realize such tailored approaches with local magnetic hardening based on specific application requirements. Commonly industrially used HRE source TbHx, as well as complex multicomponent Tb-containing alloys such as Tb10Pr60(Cu,Al,Ga)30 are investigated on commercial grade NdFeB-based sintered magnets. Highly efficient Tb utilization with a normalized coercivity increase of 3866 kA/m/wt% Tb (4.86 T/wt% Tb) is achieved with only a minor reduction in remanence from around 1.45 T in the initial magnet to 1.43 T after GBDP, paving the way toward HRE-balanced high-performance magnets for sustainable electric motor applications.