Effects of Oxygen Content in Fe Powder and NH<SUB>3</SUB> Pressure on Preparation of Fe Nitrides by MA

Mechanical alloying (MA) in NH3 has been applied to prepare Fe16N2 powder where two different kinds of iron powders, i.e., elctrolytic Fe powder and carbonyl Fe powder were used as the starting materials.Nitriding has proceeded better in the electrolytic Fe powder than in the carbonyl Fe powder. On the other hand, oxidation has proceeded further in the latter than in the former. For example, after mechanical alloying in NH3 for 160 h 12 at%N and 2.0 at%O were contained in the specimen of the electrolytic Fe iron powder, and 11.5 at%N and 2.7 at%O in the specimen of the carbonyl Fe powder. The MA process under higher pressure of NH3 has an effect on preventing oxidation.The specimen obtained by the MA process showed a super-saturated bcc structure below 14-15 at%N, and Fe3N structure above 18-19 at%N. Fe16N2 could not be obtained by the MG process for the 11.1 at%N and Fe-13.3 at%N specimens prepared by the MA process.