METASTABLE IRON NITRIDES BY MECHANICAL ALLOYING

Mechanical alloying of iron nitrides, epsilon-Fe3N and gamma'-Fe4N tog ether with alpha-Fe has been carried out in an attempt to produce the metastable alpha ''-Fe16N2, phase. The distribution of nitrogen in as- milled and annealed materials is determined by Mossbauer spectroscopy. The distinctive feature in the Mossbauer spectrum of alpha ''-Fe16N2, the hyperfine component with B-hf = 40 T attributed to Fe in 4d sites which are furthermost from nitrogen is not seen in any of the Mossbau er spectra. The as-milled product is nanocrystalline alpha-Fe with an amorphous intergranular phase of approximate composition Fe80N20. The magnetization of samples decreased on milling and returned to the star ting values after annealing which recovers the equilibrium starting mi xtures. In the case of the Fe3N + Fe experiments, annealing produced s ome Fe4N together with Fe3N and Fe.