Research On Processing And High Temperature Resistance Of Sputtering Al/Al₂O₃Gradual Coating On γ-TiAl Alloy

γ-TiAl alloy is a new type of lightweight high temperature structural materials, its density is onlyabout half of the nickel-base high temperature alloy, while they have similar mechanical behaviorunder high temperature, so γ-TiAl alloy is a promising high temperature structural materials in thefuture. However, the insufficient high-temperature corrosion resistance of γ-TiAl alloy after700℃limits its practical application.The issue proposed to form Al/Al2O3coatings on the surface of γ-TiAl alloy by using themagnetron sputtering technique, and form a gradual diffusion layer between the aluminium layer andthe substrate by using diffusion technique, in order to improve its high-temperature corrosionresistance properties. The main research topics include:Researching on the process of aluminum on γ-TiAl alloy, investigating the effects of majorparameters on the forming of aluminium and aluminium oxide layers by using the magnetronsputtering technique. Evaluating of the diffusion process of Al layer at different temperature and time.Analyzing of the layers, including morphology, composition distribution by SEM, EDS to obtain anoptimum process. Characterizing of the layers, including morphology, composition distribution andphase composition by SEM, EDS and XRD. Investigating of the basic mechanical properties byscratch testing and measuring of micro-hardness. Keeping the coated and uncoated specimens in thechamber electric furnace at different temperature to conduct the oxidation expiment, thermal shockexperiment, molten salt corrosion experiment. After all tests, analyzing phases of the coatings byXRD, observing the surface and cross-section microscopic morphology of the coating by SEM,studying element distribution of the coating through EDS.Through systematical experiments and verification, firstly, the optimum process parameters ofaluminum on γ-TiAl intermetallic alloy as below: Ar gas flow rate30sccm, sputtering power capacity130W, distance between source cathode and work-piece40mm, working pressure0.5Pa,5hours.Secondly, the optimal diffusion parametre was5hours at600℃, the diffusionlayer is uniform anddense. Thirdly, the optimum process parameters of reaction magnetron sputtering aluminum oxide asfollows: the ratio of Ar gas and oxygen gas flow rate7:1, distance between source cathode andwork-piece40mm, working pressure0.5Pa, half past two hours. Fourthly, the surface hardness onlayer is750HV0.1, which higher than the surface hardness of the substrate350HV0.1. The adhesionstrength beteew deposited layer and substrate is about40N. Lastly, after oxidation, the uncoat specimen is a layered scale structure, the microstructure of the oxide layer appeared loose. The denseAl/Al2O3gradual coatings block the invasion of oxygen atom effectively, which showing excellenthigh temperature oxidation resistance. And at high temperature molten salt corrosion of850℃or900℃, the high temperature corrosion resistance of the coated and uncoated specimens. Mechanismsof hot corrosion of the coating is discussed. It revealed that the fused salt accelerated the corrosionprocess of the coated and uncoated specimens at850℃, theoxidation reaction and the vulcanizationreaction between molten salt and the coated and uncoated specimens were occured at900℃.