Metastable iron nitrides by mechanical alloying

Abstract

Mechanical alloying of iron nitrides, ε-Fe3N and γ′-Fe4N together with α-Fe has been carried out in an attempt to produce the metastable α″-Fe16N2 phase. The distribution of nitrogen in as-milled and annealed materials is determined by Mössbauer spectroscopy. The distinctive feature in the Mössbaur spectrum of α″-Fe16N2, the hyperfine component with Bhf = 40 T attributed to Fe in 4d sites which are furthermost from nitrogen is not seen in any of the Mössbauer spectra. The as-milled product is nanocrystalline α-Fe with an amorphous intergranular phase of approximate composition Fe80N20. The magnetization of samples decreased on milling and returned to the starting values after annealing which recovers the equilibrium starting mixtures. In the case of the Fe3N + Fe experiments, annealing produced some Fe4N together with Fe3N and Fe.