Oxidation protection behaviour of titanium aluminide coatings developed by TIG technique

Titanium alloys are attractive in aerospace applications for low density and good mechanical properties, but they have poor oxidation and wear resistance. A coating layer of titanium aluminide can mitigate these problems to some extent and make the alloys suitable for hot structure applications. This paper discusses the formation of titanium aluminide coatings on commercial purity titanium (CPTi) surfaces by melting a preplaced aluminium and titanium powder mixture, using a tungsten inert gas welding torch. Depending on powder composition and energy input, the resolidified melt layer produced a single-phase α2–Ti3Al or a dual-phase α2 and γ–TiAl microstructures of lamellar or columnar dendritic types. The microhardness varied from 400 to 600 Hv based on the microstructure variation within the coating. Testing the resistance to oxidation, by heating and cooling through 9 cycles at 750 °C for a total of 100 h in air, gave a weight gain of 1.00 mg cm−2 for the α2–Ti3Al coating compared to 2.60 mg cm−2 for the CPTi specimen. The dual-phase coating showed much improved oxidation resistance with a weight gain of 0.35 mg cm−2 after exposure under similar conditions.