Long-term cyclic oxidation of Al–Si diffusion coatings deposited by Arc-PVD on TiAlCrNb alloy

This article presents research results of long-time cyclic oxidation of TiAlCrNb intermetallic alloy with and without an Al–Si coating. The coating was deposited by the Arc-PVD method in two steps. First the AlSi layer was deposited, and 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 950 °C for 2 h. Cyclic oxidation tests were carried out at 950 °C. Heating time was 23 h and cooling was made in static air. Mass changes of the specimens were recorded after each cycle. A total of 60 cycles were performed. An analysis of the results achieved during cyclic oxidation was performed. Phase composition, morphology and distribution of elements in AlSi layers as well as in the scale were investigated using EDX, XRD and SEM. The results showed that Al–Si coatings were very effective in reducing the oxidation rate of γ-TiAl especially during the first 40 cycles. The oxide formed on the coating after oxidation is composed of a mixture of a large portion of Al2O3 and a small portion of TiO2. After 40 cycles of oxidation the main component of the scale was rutile. Kirkendall voids were found in the coating.