DESIGN OF THE ND-FE-B-BASED ALLOYS WITH IMPROVED THERMAL-STABILITY OFSTRUCTURAL AND MECHANICAL-PROPERTIES

The permanent magnets produced from the Nd-Fe-B alloys with additions of Dy, Tb. Co. Nb, and Ga are studied. Investigations of the effects o f Nb and Ga on magnetic properties and microstructure of sintered magn ets showed that these additions increase the magnetization coercive fo rce H-lc, up to 2000 kA/m and improves the thermal stability of perman ent magnets. The long-term and short-term service temperatures increas e up to 150 degrees C and 180 - 200 degrees C, respectively. Microstru ctural examinations ai sintered magnets showed the presence of the pre cipitates of Nb-bearing Nd-(Co, Fe)-B-type precipitates (H phase) betw een the grains of the dominant Nd2Fe14B phase (Phi phase). The benefic ial effect of Nb on H-lc is caused by the elimination of chemical inho mogeneity of grain-boundary areas of Phi phase and by the smoothing of the surfaces of the Phi-phase grains. Gallium is dissolved primarily in the Phi phase and in the NdCo-based phase (K-2 phase). The presence of gallium in the K-2 phase weaken its magnetic properties, and this improves the magnetic insulation of the grains of major phase.