High Temperature Deformation and Coercivity of R_2Fe_<14>B compound

主要采用烧结和快速凝固工艺制备了具有高磁饱和度和晶磁各向异性的Nd_2Fe_<14>B稀土磁体。1988年Shimoda等人发现Pr_2Fe_<14 b> B具有热变形性，利用磁各向异性与铸造和变形之间的关系，引入了一种新型磁子。因此稀土磁体经铸造、热变形和热处理等常见金属加工路线有望发展。在这项研究中，我们研究了每一种加工方式所决定的磁性能和微观结构。热压过程分为三个变形阶段。在初始阶段，应力随变形迅速增加，试样内部产生细小裂纹，引起严重的应力松弛。在第二阶段，晶界内存在液体，裂纹愈合，晶粒向流动应力方向重新取向，导致各向异性。在最后阶段，试样受到较大变形的破坏。在600°C的退火过程中，形成了具有高矫顽力的精细结构，并形成了高矫顽力的能量生成物。由包晶反应生成的Pr_6Fe_<13>Cu具有四方反铁磁性。材料设计要求考虑铁磁相和反铁磁相之间的耦合。其它新边界相Nd(Pr)_<11> _ Fe_<87>B_2。

Rare earth magnets of Nd_2Fe_<14>B that has high magnetic saturation and crystal magnetic anisotropy have been made mainly by the sintering and the rapid solidification processing. In 1988 Shimoda et al. showed that Pr_2Fe_<14>B has a hot deformability and a new type of magnetos was inroduced by utilizing the relation between the magnetic anisotropy and casting and deformation ones. Therefore rare earth magnets by a common metals processing route of casting, hot deformation and heat-treatment are expected to develop. In this research we investigated magnetic properties and micro structures determined by each processing. Hot pressing was divided into three deformation stages. At initial stage a rapid increase in stress with deformation resulted in fine cracks inside the sample that induced heavily stress relaxation. At second stage liquid existed in the boundary healed cracks and crystal grains were reoriented to the direction of flow stress that caused the anisotropy. At final stage the samples were damaged by a heavier deformation. Primary Fe particles disappeared by the soaking process and a lower temperature soaking brought about fine structures that resulted in high coercivity and energy product was formed during the annealing of 600ﾟC and its formation caused high coercivity. Pr_6Fe_<13>Cu that is formed by peritectic reaction is tetragonal and antiferromagnetic. Materials design is requested with consideration to the coupling between ferromagnetic and antiferromagnetic phases. Other new boundary phase Nd(Pr)_<11>Fe_<87>B_2.