The Research On High Temperature Oxidation Resistance Of Thermal Barrier Coating Prepared By Pack Cementation Process And Plasma Spraying

Thermal Barrier coatings(TBCs)are mainly used in aviation aircraft engine turbine blades.The typical structure of thermal barrier coatings is mainly composed of ceramic top coat(TC)and metallic bond coat(BC).TC with high temperature resistance,low thermal conductivity and other properties.It can reduce the actual surface temperature of the metal substrate during the serving and improve the using temperature of the metal parts.The BC mainly has the high temperature oxidation resistance and improve the physical compatibility between the substrate material and ceramic material,reduce the oxidation rate of coating and avoid disbonding of the thermal barrier coating system caused by thermal expansion coefficient mismatch.Taking GH586 nickel-based high-temperature alloy as substrate material,Co-CrY-modified aluminide coating as the BC of thermal barrier coatings prepared by pack cementation proceeding.Ceramic layer chooses 8%Y2O3 stabilized zirconia(YSZ),fabricated by plasma spraying.The organization and structure of the pack cementation coating was analyzed;isothermal oxidation and cyclic oxidation of the BC and TBCs after plasma spraying under the 1000? were analyzed respectively.The oxidation mechanism and failure process of the BC and TBCs failure process were studied.The main results are as follows:(1)Co-Cr-Y modified aluminum coating was prepared by pack cementation proceeding,and the process parameters were optimized.Based on the coating thickness and the high temperature oxidation rate,one coating was selected.Composition proportion is 10Co-20Cr-7Al-4Y(wt.%).After cementation proceeding,the coating structure has two main components,outer layer and diffusion layer.Coating surface are mainly Al0.96Ni1.04 and AlNi phase.(2)The pack cementation coating has a mass gain of only 0.36 mg/cm2 after isothermal oxidation at 1000 ? for 100 h,the coating has good high temperature oxidation resistance.The surface are mainly composed of Al2O3 after isothermal oxidation 100 h.Cyclic oxidation 100 times,the oxide coating on the surface of a flat,surface oxide reunion and miscibility.Except Cr2O3 and Al2O3,the coating surface also appeared some CoAl2O4,NiCr2O4 spinel phase.Along with the cyclic oxidation continues,Al content of the outer coating reduce continuously,lead to coating inside occur the ?-NiAl???-Ni3Al??-Ni+Al transformation,makes the coating degradation.(3)Plasma spraying TC surface is uneven,TC/BC interface distribution is obvious.The BC layer surface appear uneven condition on the microstructure,BC and TC show hook or state.The porosity of plasma spraying TC was analyzed with the method of image analysis,the final measured ceramic coating porosity of 9.0% on average.Thermal barrier effect of Plasma sprayed TBCs under the 700?,800? and 900? are: 64??72?and 83? respectively.(4)When thermal barrier coating system isothermal oxidation 100 h,large holes and cracks appeares on the TC/TGO interface.When Cyclic oxidation 100 times,TGO is divided into two layers.The lower color is deeper,mainly composed of Al2O3.The upper shows a shallow color,in addition to the Al2O3 generation,also generates a large random block oxide spinel structure.Cavity and the separation of local area formed in TGO/TC interface.The main reasons for the failure of thermal barrier coating system are TGO layer thickening and the formation of cavities and cracks at the TC/TGO interface.the increase of holes and cracks extension makes the ceramic layer stripping from the TC/TGO interface.