Phase Distribution and Coercivity Enhancement in (MM,Nd)-Fe-B Magnets with Dual-main-phase

Abstract

The mischmetal-based sintered magnets were prepared by mixing MMSUB8.8/SUBNdSUB3.4/SUBFeSUB81.8/SUBBSUB6/SUB (MM denotes mischmetal) with NdSUB15/SUBFeSUB79/SUBBSUB6/SUB alloys. The magnet consist of two main phases i.e., (La,Ce)-rich main phase and Nd-rich main phase. For the mass ratio of 8:2 of MMSUB8.8/SUBNdSUB3.4/SUBFeSUB81.8/SUBBSUB6/SUB and NdSUB15/SUBFeSUB79/SUBBSUB6/SUB, many grains of La-Ce-rich main phase are interconnected and the effect of enhancing the coercivity is weak in the sintered magnets. While for the mass ratio of 6:4 most grains of (La,Ce)-rich main phase are nearly separated and covered by the Nd-rich main phase and intergranular phase, and the coercivity increases significantly to 7.70 kOe. Compared with (MMSUB0.3/SUBNdSUB0.7/SUB)SUB30.3/SUBFebalBSUB0.96/SUBCuSUB0.1/SUBAlSUB0.11/SUB magnets prepared by the conventional method, the coercivity doesn’t decrease in the sintered composite magnets of MMSUB8.8/SUBNdSUB3.4/SUBFeSUB81.8/SUBBSUB6/SUB/NdSUB15/SUBFeSUB79/SUBBSUB6/SUB though the MM content of 40 wt.% is higher. The optimization of Nd-rich-main-phase distribution as well as Nd substitution for La-Ce should be responsible for the significant increase of coercivity.