Microstructural Changes with N Content in Sm-Fe-N Alloys

Abstract

The microstructures of Sm ₂ Fe ₁₇ N _x (0≪x≪6) powders were observed by transmission electron microscopy (TEM). Sm ₂ Fe ₁₇ N ₂₃ powders nitrided in N ₂ gas have high dislocation densities due to lattice expansion. Sm ₂ Fe ₁₇ N _x powders nitrided in a mixture of NH ₃ and H ₂ gases (3≪x≪6) have cell-like structures. The dislocation density increases and the cell diameter decreases with increasing N content, and Sm ₂ Fe ₁₇ N _5.9 powders consist of 30 to 50 nm in diameter Sm ₂ Fe ₁₇ N _x microcrystalline grains surrounded by an amorphous phase. Sm ₂ Fe ₁₇ powders nitrided above 600°C dissociate into SmN and α-Fe phases with characteristic sizes of 10 to 20 nm.