Thermally-stable high coercivity Ce-substituted hot-deformed magnets with 20% Nd reduction
We demonstrate a 20% Ce-substituted Nd-Fe-B hot-deformed magnet with a large coercivity (µ0Hc) of 1.69 T and a remanent magnetization of 1.32 T, which are comparable to those for Nd-Fe-B sintered magnets. The temperature coefficient of coercivity (β) of the Ce-substituted magnet was -0.593%/°C in the range of 27–127°C, which is superior to that of a Nd-Fe-B sintered magnet (β = -0.669%/°C) with a comparable coercivity at room temperature. Furthermore, the coercivity and its thermal stability can be increased to µ0Hc =1.83 T and β = -0.51 %/°C by applying the Nd80Cu20 eutectic grain boundary diffusion process to an optimized (Nd0.75Ce0.25)-Fe-B hot-deformed sample. A coercivity of 0.74 T was achieved at 150°C in the Nd-Cu diffusion processed hot-deformed magnets, which is much higher than that of sintered magnets. Microstructure investigations and micromagnetic simulations indicate that the modification of grain boundary phase and formation of a Nd-rich shell near the grain boundaries of the developed (Nd,Ce)-Fe-B hot-deformed magnet is the cause of the improved coercivity at room temperature. Thus, in this work, we realize a microstructure-optimized low-cost (Nd0.8Ce0.2)-Fe-B hot-deformed magnet that can outperform Nd-Fe-B sintered magnets.