AES characterization of oxide grains formed on ductile cast irons in exhaust environments

Abstract

AbstractCast alloys (SiMo and Ni‐resist) were oxidized at 850°C for 50 h in dry air and synthetic diesel exhaust gases. High‐resolution AES analysis and SEM studies on sections of the inner oxides showed that, for both alloys, thicker silicon‐containing oxides layers were formed at metal/oxide interfaces in diesel than in air. For SiMo, fayalite appeared to precipitate within this layer in diesel gases, thus lowering its protectiveness. Further out, silica may reprecipitate. Where the austenitic Ni‐resist failed to maintain a protective interfacial oxide, a highly irregular oxide/metal interface led to metallic Ni‐rich particles becoming trapped in the oxide. Copyright © 2002 John Wiley & Sons, Ltd.