Enhancement of coercivity and thermal stability of Pr85Al15 doped NdFeB sintered magnets followed with grain boundary diffusion

Magnetic-property modification and thermal stability improvement for high-performance NdFeB magnets by dual-alloy (DA) sintering with Pr85Al15 (PrAl) together with grain boundary diffusion (GBD) with Tb55Pr20Cu25 (TbPrCu) is demonstrated. The coercivity is increased from 14.9 to 16.4–18.0 kOe for the magnet DA sintering with 2–4 % PrAl. Pr and Al at grain boundary strengthens magnetic decoupling effect. In addition, a thin layer of (Nd, Pr)2Fe14B with higher magnetocrystalline anisotropy field (HA) is formed at grain surface. Both effects contribute to the coercivity enhancement for the magnets prepared by DA sintering with PrAl. Furthermore, remarkable coercivity enhancement, from 14.9 to 18.0 kOe to 22.7–27.1 kOe, with improved thermal stability is attained for the above magnets after GBD with Tb55Pr20Cu25 alloy. Besides, the increased Curie temperature of 2:14:1 phase indicates the entrance of Tb into 2:14:1 phase and helps to improve thermal stability. Most importantly, various magnetic levels of high-performance NdFeB magnets, including 48–52 M, 45H, 50SH and 40-45UH, can be easily attained by modifying the amount of PrAl for DA sintered magnets and/or GBD with TbPrCu alloys.