Study of sintered Nd-Fe-B magnet with high performance of Hcj (kOe) + (BH)max (MGOe) > 75

摘要

We have developed a Nd-Fe-B sintered magnet of extremely high performance. The intrinsic coercivity H cj is as high as 35.2 kOe (2803kA/m) together with the maximum energy product (BH)max of 40.4 MGOe (321.6kJ/m3). These values result in H cj (kOe) + (BH)max (MGOe) > 75. Between 293 K (20oC) and 473 K (200oC), the temperature coefficients of remanence and intrinsic coercivity are α B r = ?0.122 %/°C and α H cj = ?0.403%/°C, respectively. A maximum operating temperature of 503 K (230oC) is obtained when permeance coefficient P c = ?B/H = 2. Grain boundary diffusion (GBD) technique on magnet surface has been developed to increase H cj by 3.6 kOe without significantly decrease of B r and (BH)max. The intrinsic coercivity of the GBD treated magnet H cj(C) has a linear relationship with that of the untreated magnet H cj(B) between 200 K and 473 K (in unit of kOe): H cj(C) = 1.03H cj(B) + 2.38. The enhancement of H cj by GBD treatment has contributions not only from the improvement of microstructure but also from the increase of H a in the grain surface layer. It is also found that GBD treatment brings no deterioration in corrosion resistance of untreated magnet.