Hot-pressed Sm_2Fe_(17)N_x/Fe-Co composites: Factors controlling densification and in situ nitrogenization of Sm_2Fe_(17) phase

摘要

The effects of powder preparation and conditions of hot pressing on the structure and density of consolidated Sm_2Fe_(17)N_x and Sm_2Fe_(17)N_x/Fe-Co magnets have been studied. Densities achieved in the case of Sm_2Fe_(17)N_x. 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 Sm_2Fe_(17)N_x/Fe_(0.65)Co_(0.35) composites. We have found that during hot pressing, nitrogenization of the Sm_2Fe_(17) phase may occur in situ if pressed together with Fe-Co-N powders. Because Fe-Co-N releases nitrogen below the decomposition temperature of Sm_2Fe_(17)N_x, we were able to fabricate the Sm_2Fe_(17)N_x/Fe_(0.65)Co_(0.35) composite with the density up to 7.6 g/cm~3 by hot-pressing mixtures of Sm_2Fe_(17) and (Fe_(0.65)Co_(0.35))_(89)N_(11) powders.