Low-temperature diffusion process for hot-deformed bulk permanent magnet using RE-Cu eutectic alloy

This paper reviews recent progresses in coercivity improvement of hot-deformed anisotropic Nd-Fe-B magnets by the low temperature grain boundary diffusion process using RE₇₀Cu₃₀ (RE = Pr, Nd) eutectic alloys. Using Pr₇₀Cu₃₀ alloy, the coercivity was enhanced from 1.60 T to 2.56 T. The hot-deformed samples are expanded along only c-axis direction after the diffusion process by the formation of thick Nd-rich grain boundary phase parallel to the c-planes of platelet shaped Nd₂Fe₁₄B grains. To suppress the reduction in remanence caused by the excess expansion during the diffusion process, we developed an expansion constraint eutectic diffusion process. We demonstrated high performance Dy-free anisotropy magnet with coercivity, μ₀H_c = 1.94 T, and remanence, B_r = 1.35 T, by the expansion constraint diffusion process using a Nd-Cu alloy as a diffusion source.