Influence of chlorine on the oxidation behavior of TiAl-Mn intermetallic compound

Excellent oxidation resistance of reactive-sintered titanium aluminides was reviewed and the mechanism of forming protective Al2O3 film was studied. TiAl-Mn containing more than 200 mass ppm chlorine from raw titanium powder showed very little mass gain after oxidation from 1173 to 1398 K in air. The chlorine effect was found obviously in composition of alpha(2) + gamma and gamma regions in the Ti-Al phase diagram. The chlorine effect was found even in a plasma are melted TiAl-Mn alloy with chloride covering or oxidized in air containing a small amount of chlorine gas. Also, other halogen elements as fluorine and bromine had the same effect as chlorine. It was clear. in particular by surface analyses that chlorine existed in TiO2 near the oxide/metal interface in the early stage of oxidation and decreased oxygen ion vacancies in TiO2. Then TiO2 growth was interrupted and protective Al2O3 scale was formed on the titanium aluminide. Copyright (C) 1996 Elsevier Science Limited