Oxidation behavior of titanium aluminides

Results from an ongoing study of the high temperature oxidation of intermetallic compounds in the Ti-Al system are presented. The oxidation behavior of alloys based on TiAl (y) has been found to be extremely complex depending on temperature and atmosphere composition. Protective alumina scales are formed in pure O2 up to a critical temperature above which a mixed Ti02/A1203 scale forms and grows at rates which are orders-of-magnitude faster than that of alumina. This phenomenon is believed to result from the formation of Al-containing internal oxides which coupled with the closeness in stability of alumina and the titanium oxides, prevents the alumina from becoming continuous. Continuous alumina scales were not observed, even at temperatures below 1000 OC, when N2 was present in the oxidizing gas. The effect of the N2 has been shown to be involved with the initial development of the reaction products.