微量添加晶界合金对烧结Nd-Fe-B力学性能及微观结构的影响

采用双合金法制备系列烧结Nd—Fe—B磁体(保持其主合金成分不变：Ndl4．1Dy0．5Fe79.0B6.4(原子分数)，所添加的晶界合金中的B含量从0．95％(原子分数)逐步增加到6．95％(原子分数))，研究了微量添加晶界合金对烧结Nd—Fe—B力学性能及微观结构的影响。研究结果表明：微量添加晶界合金所制备的磁体，其抗弯强度值普遍高于单合金法制得的磁体；前者的抗弯强度最高可达397MPa，高于铸造，热压磁体的抗弯值，而后者的抗弯强度仅为309MPa。由相结构分析可知，当添加的晶界合金中的B含量为O．95(原子分数)，主相晶格的四方度减小，这时磁体具有最高的抗弯强度。另外，微量添加晶界合金，可使磁体中晶界相的分布更加均匀，从而基本上消除了主相晶粒直接接触的现象，使晶粒的不规则长大得到抑制。这也是微量添加晶界合金后磁体具有较高抗弯强度的原因之一。对磁性能的研究结果表明，微量添加晶界合金几乎不影响烧结Nd—Fe—B磁体的磁性能。

Effect of Minor Grain-Boundary Alloy Addition on Mechanical Properties and Microstructure of Sintered Nd-Fe-B Magnets

The Nd Fe B magnets were prepared by the dual alloy sintered process, in which the main alloy composition of Nd 14.1 Dy 0.5 Fe 79.0 B 6.4 (atom fraction) was invariable and the boron content in the minor addition of grain boundary phase alloys gradually varied from 0.95%(atom fraction) to 6.95%(atom fraction). The effects of the minor addition of grain boundary alloys on the mechanical properties and microstructure of sintered Nd Fe B magnets were studied. It shows that the bending strength of most magnets with minor grain boundary alloy additions is much higher than that of the magnet prepared by the single alloy. The maximum of the former reached 397 MPa, which is higher than the bending strength of cast/hot rolled magnets. The latter is only 309 MPa. The phase analyses indicate that as the boron content in the grain boundary alloys is B=0.95% (atom fraction), the c/a ratio of the main phase lattice reduces, and in the case the magnets has the maximum of bending strength. In addition, minor additions of the grain boundary alloys make the distribution of grain boundary phase more uniform so that the phenomena of the direct contact between main phase grains nearly disappear. The irregular grain growth is restrained. This is also one of the reasons that the magnets with minor grain boundary alloy additions have higher bending strength. The study results also show that minor additions of the grain boundary alloys almost do not affect the magnetic properties of sintered Nd Fe B magnets.