High Temperature Oxidation Performance Of Microcrystal Repair Coatings For Single Crystal Superalloy

In order to satisfy the high temperature oxidation resistance of the hot end components of the weapon system under high temperature conditions and the reutilization of the hot end components after surface corrosion failure,a kind of microcrystalline coating with the same composition as the DD6 Nickel-based single crystal superalloy was prepared on the DD6 Nickel-based single crystal superalloy matrix by electric discharge deposition technology.The oxidation kinetics curves of DD6 alloy and microcrystalline coating at 950℃,1050℃and 1150℃were obtained by automatic circulating oxidation furnace and high precision balance.The morphology,composition and phase composition of DD6 alloy and microcrystalline coating before and after oxidation were characterized by scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）and X-ray diffraction（XRD）.The high temperature oxidation behavior of alloys and coatings was systematically studied.The results are as follows:（1）The surface of the prepared microcrystalline coating is spatter,and there is an obvious boundary between the coating and the substrate surface,showing a good metallurgical bonding.（2）After cyclic oxidation of DD6 alloy and microcrystalline coating for 100h,the weight gain of DD6 alloy and microcrystalline coating occurred at the initial stage of oxidation at three different temperatures.The difference is that the surface oxide film of DD6 alloy was spalled after cyclic oxidation for 50h at 950℃,and there was no obvious curve decline of the microcrystalline coating.After cyclic oxidation of DD6 alloy at1050℃for 20h,the oxide film falls off,and the oxidation curve of microcrystalline coating for 100h does not decrease.At 1150℃,the surface oxide film of DD6 alloy will flake off after oxidation for only 10h,and the surface oxide film of microcrystalline coating will flake off after oxidation for 20h.After oxidation for 70h,the surface oxide film of microcrystalline coating will flake off faster than that of DD6 alloy.（3）The oxide film of DD6 alloy and microcrystalline coating can be divided into three layers at three different temperatures.The upper layer is Ni O,the lower layer is Al₂O₃,and the middle layer is different.The middle layer of DD6 alloy at 950℃is Ni Ta₂O₆,Ni Cr₂O₄and Ta OX.The intermediate layers of the microcrystalline coating are Ni Ta₂O₆,Ni Cr₂O₄,Ni Al₂O₄and Ta O_X.At 1050℃,the intermediate layers of DD6alloy and microcrystalline coating oxide film are Ni Al₂O₄,Ni Cr₂O₄,Ni Ta₂O₆and Ta O_X.At 1150℃,the intermediate layers of DD6 alloy and microcrystalline coating oxide film are Ni Al₂O₆,Ni Cr₂O₄and Ta O_X.The oxide film of the coating was denser at all the three temperatures.The oxide film of DD6 alloy was cyclically oxidized for 100h,and shedding areas were found at all the three temperatures.No obvious shedding areas were found on the surface of the coating at 950℃and 1050℃,and the oxide film was partially shed at 1150℃,but it was still relatively dense.