Oxidation-resistant aluminide coatings on γ-TiAl

The long-term application of TiAl alloys based on the gamma-phase at temperatures above 750-800degreesC requires suitable surface coatings to provide the needed oxidation resistance. Without a coating, these alloys, containing large amounts of titanium, suffer from rapid oxidation attack at elevated temperatures. The pack-cementation coating process was used to aluminize the surface region of a Ti-50 at. % Al alloy to TiAl3, the most promising, oxidation-resistant phase in the Ti-Al system. The isothermal oxidation behavior of the coated alloy was studied in the temperature range 800-1000degreesC in air for up to 300 hr. The aluminide coating greatly improves the oxidation resistance of gamma-TiAl, forming a protective alumina scale. The rapid aluminum interdiffusion between the TiAl3 coating and the gamma-TiAl substrate determined the effective life of the coating. In addition, the oxidation behavior of the TiAl2 phase formed by interdiffusion of the coating system was studied by oxidation of cross sections.