Abstract
The paper presents the application of Closed Hollow Cathode Physical Vapor Deposition (CHC-PVD) method for the depostion of Ti-Al-Cr-Y-Si coatings on γ-TiAl 48-2-2 alloy for high temperature oxidation protection. The study concerned the analysis of the coating’s growth mechanism, initial microstructure as well as phase transformations investigations using high resolution Scanning Transmission Electron Microscopy (STEM) and high temperature X-ray diffraction (HT-XRD). The coated alloy was subjected to high temperature oxidation test at 850 °C where a fivefold lower mass gain compared to bare 48-2-2 alloy was observed. Detailed microstructural investigations allowed to characterize the thermally grown oxide scale, which was found to be composed of nanometric layers of titania, equiaxed (Al,Cr)2O3 and columnar alumina. These investigations provided microstructural evidence for the Cr effect on the formation of Al2O3, which was postulated previously. Yttrium was found to segregate to the grain boundaries of alumina oxide scale during high temperature oxidation, indicating the occurence of the reactive element effect.
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