Research On High Temperature Properties Of Laser Remelting Plasma Sprayed ZrO₂-8%Y₂O₃ Thermal Barrier Coatings On GH4169 Alloy

GH4169 alloy is nickel-based age-hardening superalloy,which has good mechanical properties,thermal processing and welding properties at high temperature,used in Aero-engine turbine disks,blades and other structural parts at present.The thermal barrier coating plays an important role in further improving the working temperature of the superalloy material.It can increase the service temperature by 100 ~ 150 ?,reduce the fuel consumption and improve the service life of the aviation engine.The thermal barrier coating prepared by the plasma spraying technology has many porosity and cracks,and bonding force between the coating and the substrate is poor.Furthermore,the ability of resisting to thermal fatigue and crack propagation is poor too.In order to solve these problems,CO2 laser is used to remelting the plasma sprayed thermal barrier coating in this paper to reduce the porosity and crack of the coating and improve the high temperature performance of the thermal barrier coatings.The surface morphology,cross-sectional morphology,phase composition and elemental distribution of the two thermal barrier coatings have been analyzed by SEM,EDS and XRD.It turned out that the surface of the plasma sprayed thermal barrier coatings is composed of molten and semimolten particles,resulting in rugged,porous,and a lot of pores and micro-cracks in the coating.After laser remelting,the structure is homogeneous and dense,forming a remelting layer of 120?m thick,and the pores and cracks are greatly reduced.The two kinds of thermal barrier coatings of main phases are t-ZrO2 and c-ZrO2.Meanwhile,the thickness of the adhesive layer is about 100?m and the thickness of the ceramic layer is about 180?m.High temperature oxidation experiments on the substrate and thermal barrier coatings have been conducted.The results show that the oxidation products on the surface of the matrix alloy are Cr2O3 and Fe2O3,which can protect the substrate.With the increase of the temperature,the spinel phase in the oxide film increases,resulting in the peeling of the oxide film.After a high temperature treatment on oxidation of the thermal barrier coating,the Al2O3-based TGO layer was formed at the interface of the bond layer and ceramic layer.The dense remelting layer of the laser remelting thermal barrier coatings hindered the diffusion rate of oxygen in the ceramic layer,leading to a higher resistance to high temperature oxidation.The hot corrosion experiments on the substrate and thermal barrier coatings have been conducted.The results show that the matrix alloy forms a loose porous oxide film at the initial stage of hot corrosion,which has a certain hot corrosion resistance.With the increase of hot corrosion time,the amount of sulfide in the oxide film increases,resulting in the increase of internal stress between the oxide film and the substrate,At the same time,the oxide film peels and,hot corrosion accelerates.The hot corrosion failure behavior of the thermal barrier coatings is mainly caused by the reaction of Y2O3 and Na2SO4,which leads to the transition from t-phase ZrO2 to m-phase ZrO2.The ceramic layer produces volume change and increases the internal stress,leading to crack initiation and propagation.After laser remelting,the plasma sprayed TBCs removes most of the cracks and pores in the coating layer,forming a homogeneous and dense remelting layer,which prevented the diffusion of molten salt and greatly enhanced the thermal corrosion resistance.