| Ti2AlNb alloy is a potential material for aero-industries due to its lightweight, attractive hightemperature mechanical properties. However, insufficient oxidation resistance is the main drawbackwhich restricts the actual application of this alloy in many circumstances. By using magnetronsputtering, Al/Al2O3coating is deposited on the surface of Ti2AlNb to improve its high temperatureoxidation resistance.The process parameters for deposited Al are exhibited as followed. Work voltage is between900～920V, work current is between0.14～0.16A, work pressure is between0.5～0.6Pa, distancebetween poles has a range of35～50mm, time is3h, the flow of Ar is30sccm. The processparameters for deposited Al2O3are also exhibited as followed. Work voltage is between1000～1050V,work current is between0.2～0.3A, work pressure is between0.7～0.9Pa, distance between poleshas a range of35～50mm, time is3hour, the flow of Ar is50sccm, and the flow of O2is5sccm. Theresults show that the composite coating is consist of5μm Al2O3surface layer and10μm Al interlayer,the surface phase structure of the coating are Al2O3and Al.The surface of the composite coating iscompact and no pores and cracks. For enhancing the binding force, the Al/Al2O3coating is heattreated by vacuum annealing furnace.The coating was analysed by SEM, EDS, XRD, Vicker’shardness and scratch tester, the results show that samples display the best comprehensive propertieswhen they are diffused at600℃for10h. The surface of the diffusion coating is uniform and dense,there is an apparent diffusion layer in the coating. The hardness of diffusion coating reaches to1500HV0.1, and the bonding force is38N.The substrates and the coated samples are oxidized at the650℃,750℃,850℃for100h. It turnsout that the weight gain of coated samples are much less than the substrates. SEM was used to thedetected the morphology of the oxidation film, EDS was used to detect the element distribution andXRD was used to identify the phase. After oxidation at650℃,750℃，diffusion coating is coveredwith dense Al2O3film, after850℃oxidation, the diffusion coating surface appears a few cracks,while the subsurface is TiAl3, it also protect the substrate. The experiment results show that diffusioncoating can improve the oxidation resistance of the Ti2AlNb alloy.The thermal shock resistance experiment was conducted on the diffusion coating. After60cycles,the diffusion coating fails.The substrates and the coated samples are respectively immersed at20%(wt) NH4NO3, H2SO4, HCl solution. It turns out that the corrosion resistance of the matrix is better than the diffusioncoating. |
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