Effects of (Nd, Pr)-Hx addition on the coercivity of Nd-Ce-Y-Fe-B sintered magnet

Abstract

Y-Ce co-substituted RE-Fe-B (RE, rare earth) sintered magnets with good thermal stability have attracted growing attention as low-cost hard magnetic materials. The inferior intrinsic properties of Y2Fe14B and Ce2Fe14B to Nd2Fe14B, however, limit the substitution of Y-Ce for Nd at a low level. In this work, (Nd, Pr)-Hx powders are introduced into (Nd, Pr)22.8(Y, Ce)7.7FebalM1.3B1.0 sintered magnets to further enhance the coercivity. By incorporating 1 wt% (Nd, Pr)-Hx, the coercivity is increased to 9.7 kOe, which is 16.9% higher than that for the starting magnet (8.3 kOe). Continually increasing (Nd, Pr)-Hx addition to 2 and 3 wt% lead to a very limited coercivity increment, i.e. to 10.0 kOe and 10.3 kOe, respectively. The formation of continuous RE-rich intergranular phase by the extra Nd/Pr after (Nd, Pr)-Hx dehydrogenation can enhance the magnetic isolation effect between adjacent matrix phase grains, resulting in coercivity enhancement. However, more Nd atoms exist in the RE-rich phase rather than form the Nd-rich hardening shell, which is distinct from the available Nd-Ce-Fe-B system. The REs distribution within the matrix phase grain is similar before and after (Nd, Pr)-Hx incorporation for the Nd-Ce-Y-Fe-B system. It is deemed that the preferential occupancy of Y in the 2:14:1 matrix phase hinders the diffusion of Nd into the outer layer of Y-Ce enriched regions, being responsible for the limited coercivity increment with higher (Nd, Pr)-Hx addition. The present work suggests that tuning the distribution of Y is of crucial importance to further improve the coercivity of Y-containing permanent magnets.