Oxidation behaviour of gamma titanium aluminides with or without protective coatings

Abstract

The γ-TiAl alloys are promising high temperature materials for aeroengines due to their low density, high specific strength and low material cost compared with Nickel based superalloys. However, the insufficient ductility at room temperature and the limited oxidation resistance at temperatures above approximately 750°C have limited their applications. Oxidation resistance in the application temperature range of 800 and 1000°C is of particular importance. Remarkable improvement to the environmental resistance by adding ternary and quaternary elements to the γ-TiAl alloys has been reported; however, alloying additions frequently deteriorate their mechanical properties. Surface modifications or coatings, which promote the formation of highly protective alumina scales, are also viable ways to improve the environmental resistance of TiAl alloys. In this article, the research work from the last 30 years on the oxidation behaviour of bare and coated TiAl alloys will be reviewed, with special focus on the γ-TiAl alloys. The review will begin with the oxidation behaviour of TiAl substrate alloys and the oxidation behaviour of γ-TiAl alloys with high temperature coatings such as aluminide, MCrAlY, Ti–Al–X and thermal barrier coating (TBC) system will be followed.