Hot-pressed Sm2Fe17Nx∕Fe–Co composites: Factors controlling densification and in situ nitrogenization of Sm2Fe17 phase

The effects of powder preparation and conditions of hot pressing on the structure and density of consolidated Sm2Fe17Nx and Sm2Fe17Nx∕Fe–Co magnets have been studied. Densities achieved in the case of Sm2Fe17Nx powders prepared through a low-energy milling were higher than after a high-energy milling. The difference is mostly caused by the different particle size, and it can be eliminated by an additional low-energy milling of the coarse high-energy milled powder. The presence of a ductile soft magnetic phase greatly facilitates densification, leading to considerably higher absolute and relative densities in hot-pressed Sm2Fe17Nx∕Fe0.65Co0.35 composites. We have found that during hot pressing, nitrogenization of the Sm2Fe17 phase may occur in situ if pressed together with Fe–Co–N powders. Because Fe–Co–N releases nitrogen below the decomposition temperature of Sm2Fe17Nx, we were able to fabricate the Sm2Fe17Nx∕Fe0.65Co0.35 composite with the density up to 7.6g∕cm3 by hot-pressing mixtures of Sm2Fe17 and (Fe0.65Co0.35)89N11 powders.