Structure and resistance to oxidation of an Al-Si diffusion coating deposited by Arc-PVD on a TiAlCrNb alloy

This article presents research results of isothermal and cyclic oxidation of TiAlNbCr intermetallic with and without an Al-Si coating. The coating was deposited by the arc-PVD method in two steps. Firstly, the AlSi layer was deposited then the samples were heated in a vacuum chamber to form a diffusion TiAlSi coating. After coating deposition the samples were heat-treated in vacuum at a temperature of 950 8°C for a period of 2 h. Cyclic oxidation tests were carried out at 950 8°C. The heating and cooling time was 5 min (3 °C/s). Mass changes of the specimen were recorded every 100 cycles. A total of 2400 cycles were performed. An analysis of the results obtained from cyclic oxidation was performed. The analysis of the Si effect on the structure of the layers and on the oxidation mechanism of the TiAlNbCr alloy was performed. Phase composition, morphology and the distribution of elements were defined by EDX, XRD and SEM in AlSi layers as well as in the scale. The results showed that Al-Si coatings (thickness approx. 40 μm) were effective in reducing the oxidation rate of γ-TiAl. The oxide formed on the surface of the Ti- 48Al-2Cr-2Nb coating after oxidation is composed of a mixture of a large portion of Al₂O₃ and a small portion of TiO₂.