A method of heat-treatment of near γ-TiAl to enhance oxidation resistance by the formation of a Ti5Si3 layer

It is shown that the heat-treatment of near γ-TiAl in a silica capsule under low oxygen partial pressure at 1283 K for 50 h produces a thin (1–2 μm) Ti5Si3 external film on the near γ-TiAl specimen. This layer confers significant improvements in oxidation resistance for at least 500 h in air at 1173 K. The silicide layer is thought to be produced as the result of gaseous transport of SiO from the walls of the silica vessel to the specimen surface and its reaction there. However, the production of SiO requires that particularly low values of oxygen partial pressure develop within the silica capsule. Mechanisms whereby this can be achieved are discussed but the likely process involves the solution of oxygen within the specimen. The outcome is that the heat-treatment procedure represents a cost-effective CVD-type process for enhancing the oxidation resistance of near γ-TiAl intermetallics.