Coercivity enhancement of hot-deformed NdFeB magnet by doping R80Al20 (R = La, Ce, Dy, Tb) alloy powders

Significant enhancement in coercivity for hot deformed (HD) NdFeB magnets is achieved by doping R80Al20 (R= La, Ce, Dy, Tb) alloy powders. All studied samples exhibit fine microstructure with good (00L) texture. By doping R80Al20 powders, the coercivity of HD NdFeB magnets is significantly increased from 16.0 kOe to 19.4 kOe, 20.0 kOe, 21.8 kOe, and 23.8 kOe for R = La, Ce, Dy, and Tb, respectively, while (BH)max is decreased from 41.5 MGOe to 39.3-40.8 MGOe slightly. Microstructure analysis shows that Ce or La prefers to distribute mostly at grain boundary, while Dy or Tb and Al locate at grain boundary and surface. The magnetic isolation due to R-rich phase containing Nd, Ce or La, Al at the grain boundary contributes to coercivity enhancement with the samples with R = La and Ce. In additional to magnetic isolation, the strengthened magnetic anisotropy field of 2:14:1 phase due to Tb or Dy, and slight Al substitutions gives rise to the significant enhancement of coercivity for those with R80Al20 (R = Dy and Tb).