Fe content influence on the microstructure of solution-treated Sm-Co-Fe-Cu-Zr alloys

Abstract

There is a great interest towards further enhancing the energy product of the most prominent high temperature permanent magnets Sm-Co-Fe-Cu-Zr by raising Fe content. Here we investigated the Fe content influence on microstructure of the solution-treated precursors, which is essential for designing subsequent aging conditions to develop desired cellular nanostructure. The combined X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations reveal that raising Fe content from 16.2 to 23.5 wt% in the solution-treated Sm25CobalFexCu5.6Zr3.0 (wt.%) alloys increases the 2:17R ordering degree (or its fraction) and decreases the density of stacking faults (SFs). In comparison with the Fe-16.2 wt% sample without cellular structure, the Fe-19.5 and Fe-23.5 wt% samples exhibit fine cellular nanostructure, the higher the Fe content, the larger the nanocells. Unlike the Fe-16.2 and Fe-19.5 wt% samples with homogeneous elemental distributions in the matrix, the Fe-23.5 wt% sample shows elemental segregations, thus leading to localized cellular nanostructures. Further comparative investigations show that raising Fe content has a similar influence on the microstructure to that by extending aging time on the Fe-16.2 wt% alloy, which indicates that the alloys with higher Fe content are easier to form equilibrium phases. These findings may provide important information to design proper aging condition for achieving desired cellular nanostructure in the Fe-rich Sm-Co-Fe-Cu-Zr permanent magnets.