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

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/m(3)). These values result in H-cj (kOe)+(BH)(max) (MGOe) > 75. Between 293K (20 degrees C) and 473 K(200 degrees C), the temperature coefficients of remanence and intrinsic coercivity are alpha(Br) = -0.122%/degrees C and alpha H-cj = -0.403%/degrees C, respectively. A maximum operating temperature of 503 K (230 degrees C) 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. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4803657]