Optimized coating procedure for the protection of TiAl intermetallic alloy against high temperature oxidation

The interest for TiAl intermetallic alloys is growing in the last years because of their excellent ratio between mechanical properties and density. However, the application is restricted at temperatures up to 873–973 K by the resistance to oxidation. For this reason it is of great importance to study protective coatings able to raise its temperature of performance above 1073 K. 3 layer was obtained on the surface of Ti–Al intermetallic samples, depositing an Al coating by arc Physical Vapour Deposition, followed by a thermal treatment. The microstructure and the composition of the coating were characterised before and after the thermal treatment by Scanning Electron Microscopy, X-Ray Diffraction, Focused Ion Beam and Glow Discharge Optical Emission Spectroscopy. The mechanical behaviour of the thermal treated layer was investigated by means of scratch tests and nano-indentation. ions at 1123 K were carried out on coated and uncoated samples, in order to study the effect of the coating on the oxidation resistance of the samples. The aluminide coating provides a protection against oxidation in air at the considered temperatures due to its ability to form a continuous Al2O3 scale on the surface. The TiAl3 layer phase transformations occurring during high temperature exposition were also investigated.