无重稀土烧结钕铁硼磁体的晶粒细化研究

Study of grain refinement in Dy-free Nd-Fe-B sintered magnet

在无重稀土、同成分条件下,通过调整铸片冷却辊速与气流磨分级轮转速制备出了不同晶粒尺寸的烧结钕铁硼磁体,并分析了铸片柱状晶宽度、粉末粒度、磁体晶粒尺寸及矫顽力之间的对应关系。研究结果表明,铸片柱状晶的细化、均匀化是气流磨粉末细化、均匀化的基础,而铸片细化配合较高的分级轮转速才能细化最终烧结后晶粒尺寸。对应晶粒平均尺寸最小达到3.76μm,对应矫顽力达到1339kA/m。晶粒尺寸细化促使各晶粒表面缺陷面积减少而轮廓更为平滑,降低反磁化形核几率并降低了微观散磁场,从而提高矫顽力。

Various types of Nd-Fe-B sintered magnets were prepared by adjusting wheel speed of strip casting and rotation speed of filter wheel in jet-milling machine on the condition of Dy-free and uniform composition and the relationship between critical parameters including columnar grain width,powder size,ultimate grain size and coercivity was investigated.It was discovered that refinement and homogenization of the casted strips are the critical precondition for those of jet-milled powder,and ideal grain refinement of the magnet was possible only when refinement of strips were combined with high rotation filtering jet-milling.Corresponding average grain diameter was 3.76μm low and the coercivity was 1339 kA/m high.Grain refinement possibly reduces the superficial defect area and smoothen the boundary of the grain,and that decreases the possibility of anti-magnetization and local magnetostatic interaction field,increasing the coercivity ultimately.