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

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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.