Significant enhancement in the coercivity and thermal stability of bulk hot-deformed Nd-Fe-B magnets by intergranular addition of Nd-Dy/Tb-Cu-Ga alloys

High coercivities of 2.6 T and 2.7 T were achieved in 6-mm-thick hot-deformed Nd-Fe-B magnets through the intergranular addition of Nd ₃₅Dy ₃₅Cu ₁₅Ga ₁₅ and Nd ₃₅Tb ₃₅Cu ₁₅Ga ₁₅ alloy powders, respectively, consuming only 2.2 wt.% heavy rare-earth elements (HREs). These coercivities are similar to those attained in previous works in which approximately 4.5 wt.% HREs were consumed. The temperature coefficients of coercivity at 20−200 °C were improved from −0.45 %/°C to −0.39 %/°C and −0.38 %/°C for the two doped magnets, respectively, showing the excellent thermal stability of coercivity of the bulk hot-deformed magnets. Microstructure observations revealed that the Dy/Tb-containing nonferromagnetic intergranular phase was formed, the grain size and aspect ratio were decreased, and the high-anisotropy (Nd,Dy/Tb) ₂Fe ₁₄ B matrix phase was formed after the doping process, which were responsible for the enhancement in coercivity. Micromagnetic simulations were performed to facilitate discussions of the importance and priority of these factors with regard to their effects on coercivity.