Influence of milling temperature and atmosphere on the synthesis of iron nitrides by ball milling

Fe 3 N, γ′-Fe 4 N and a supersaturated solid solution of N in Fe have been formed by ball milling of pure iron powder in a nitriding atmosphere. The structural development was monitored by X-ray diffractometry and the chemical composition of the end milling product was determined using Rutherford backscattering spectroscopy. The influence of milling temperature and atmosphere on nitriding reactions was investigated by milling Fe powder at three different temperatures (room temperature, 200°C and liquid-nitrogen temperature) and in two nitriding atmospheres (nitrogen and ammonia). A high nitrogen concentration and a large quantity of nitride (Fe 3 N) were obtained at low milling temperatures (room temperature and below). Ammonia gas is a more efficient nitriding gas for the formation of iron nitride, presumably as a result of the catalytic effect of hydrogen.