Nanocomposite powders of Fe-C system produced by the flowing gas plasma processing

Nanometer-sized alpha-Fe particles formed by the gas evaporation method wer e transferred into the microwave plasma region with a carrier gas of Ar inc luding a small amount of CH, Particles collected after the plasma region we re found to show a composite phase of Fe-C system that consisted of alpha-F e and gamma-Fe (Austenite) and Fe3C. Moessbauer spectroscopy was used to es timate the relative yield of these three phases. An increase of gamma-Fe is followed by the decrease of alpha-Fe with increasing CH4 content. Formatio n of Fe3C was recognized at 0.5vol% of CH4 in Ar gas and became more remark able when the CH4 content was increased. HRTEM observation revealed the ind ividual particles to be a concentric shell structure composed of the Fe-C s ystem. (C) 1999 Acta Metallurgica Inc.