Protection from oxidation of second and third generation TiAl intermetallic alloys by magnetron sputtering deposition of a TiAl/TiAlN coating

A two-layer TiAl/TiAlN coating was deposited by High Power Impulse Magnetron Sputtering on the surface of three TiAl intermetallic alloys for improving their oxidation resistance. The effectiveness of the surface coatings was tested in a facility designed for simulating the service conditions of turbine engines components. The response of uncoated and coated samples was compared during thermal cycling up to 1000 °C under oxidizing environment. The growth of oxide layers and the degradation of the coatings were investigated by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and X-ray Photoelectron Spectroscopy. The surface coating was found to greatly improve the oxidation resistance of Ti-47Al-2Cr-8Nb and Ti-43.5Al-4Nb-1Mo alloys, while more limited benefits were observed for the Ti-48Al-2Nb-0.7Cr-0.3Si alloy. The different performance of the same coating deposited on different substrates has been tentatively attributed to the different alloying elements present in the intermetallic substrate, and that can diffuse towards the protective coating and the growing oxide layer.