Effect of Al-Y gradient coating on hot corrosion resistance of γ-TiAl alloy at different temperatures

It is generally accepted that the crack is appeared when the thermal stress is accumulated which caused by the mismatch of coefficient of thermal expansion, through which oxygen will severely destroy the substrate at high temperature environments. Therefore, the coatings with gradient structure to reduce thermal expansion mismatch should greatly improve their service stability. Here AleY gradient coating is prepared on gamma-TiAl alloy by magnetron sputtering. The results show that the hot corrosion resistance of gamma-TiAl alloy could be greatly improved, and the activation energy at (750 degrees C-950 degrees C) can be calculated to be 126.88 KJ/mol for the coating. The Al2O3 and Y3Al5O12 (YAG) are the primary phases after hot corrosion, thus providing efficient protection at 750, 850 degrees C. At 950 degrees C, the consumption of oxide layers is accelerated due to the increased temperature so that some corrosive elements (such as S and Na) unavoidably invade into the scale. The improvement of hot corrosion resistance primarily owes to the existence of Y preferentially oxidizes Al to form alpha-Al2O3, and the effect of grain refinement of YAG phases.