Characterization of iron nitride powders formed by mechanical alloying and atmospheric heat treatment techniques

Iron nitrides were manufactured by mechanical alloying of Fe2.33N and Fe powder mixtures at starting compositions of Fe12N2 and Fe16N2 and annealed in air at 200 and 240°C. It was found that the supersaturated nanocrystalline α-Fe solid solution phase was produced after MA, and iron nitrides were formed after heat treatment. The saturation magnetization (σ) of the heat-treated powders is higher than those of the as-milled powders. The σ values for the specimens heat treated at 200°C are higher than those heat treated at 240°C, and the highest value among all of the samples is 218 e.m.u./g which is obtained by annealing of as-milled Fe12N2 powders in air at 200°C for 6 hours. The possible existence of the α"-Fe16N2 phase is responsible for the high saturation magnetization in mechanically alloyed Fe16N2 and Fe12N2 powders.