Investigations on the oxidation behaviour of MAX-phase based Ti₂AlC coatings on gamma-TiAl

Kurzfassung

In this study the oxidation resistant and MAX-phase based material Ti₂AlC was investigated as coating material on the γ-TiAl based high temperature alloy Ti-45Al-8Nb regarding the improvement of the oxidation behaviour. The 10 µm thick layer was deposited by low temperature magnetron sputtering. Phase formation was enhanced after the deposition process by heat treatment at 1000°C under high vacuum conditions (10^-6 mbar). The Ti₂AlC MAX-phase should intend the formation of a slow growing and protective Al₂O₃ scale when exposed to air at 950°C as well known for the base material. But the results show that the pre-treated coating system oxidized as fast as the non-pre-treated system. The coatings failed after 40 and 60 1h-cycles by spallation. SEM and EDS analysis after exposure exhibited the growth of a thick mixed oxide scale on top of the annealed MAX-phase coating. Additionally, zones of enrichment as well as depletion of Al, Ti and Nb formed at the substrate/coating interface indicating enhanced diffusion processes within the Ti₂AlC layer, presumably leading to fast oxidation.