Study On Foreign Partocles Erosion/hot Corrosion Performance Of Al₂O₃-modified 7YSZ Thermal Barrier Coatings

The feather-like columnar crystal prepared by PS-PVD has the characteristics of high porosity and high strain tolerance.Compared with the traditional TBCs of APS coatings with layered structure and EB-PVD coatings with fine columnar structure,PS-PVD 7YSZ thermal barrier coating（TBC）has higher thermal insulation and thermal cycling performance,which is expected to replace the traditional thermal barrier coatings for aeroengine.However,due to the loose structure of PS-PVD 7YSZ TBC,it is faced with potential failure problems such as erosion and hot corrosion,which greatly limits the application of PS-PVD 7YSZ thermal barrier coating.In this paper,the erosion and hot corrosion properties of PS-PVD 7YSZ thermal barrier coatings are studied.By comparing with traditional coatings,the influence of coating structure on the erosion failure forms of coatings is explored,and the erosion failure mechanism of coatings is analyzed.The corrosion mechanism of 7YSZ TBC in CMAS molten salt and Na Cl was discussed.On this basis,the improvement methods of spraying process control and Al-modification are proposed to improve the erosion and hot corrosion resistance of the coating.Then the erosion and hot corrosion properties of the modified PS-PVD 7YSZ TBCs were studied.The main conclusions are as follows:（1）Among the three kinds of TBCs with different structures,EB-PVD TBCs with fine columnar structure have the best erosion resistance,and the erosion weight loss rate is 112μg/g.APS coating with layered structure has the lowest erosion resistance,and the erosion weight loss rate is 248μg/g.PS-PVD coating with feather columnar structure has the lowest erosion resistance,and the erosion weight loss rate reaches 360μg/g.（2）The hardness of APS coating is the highest,and brittle fracture and spalling mainly occur in the layer structure unit of the coating during erosion.The hardness of EB-PVD coating is the lowest,but the fracture toughness of fine columnar crystal is higher,and the material is mainly removed in the form of cutting during erosion.PS-PVD coating feather columnar crystal fracture toughness is low,and the diameter（about 20-30μm）is large,single columnar crystal is subject to greater impact load when erosion,coating erosed in two forms of cutting and columnar crystal fracture to remove material（3）In 800-1200 mm spray distance,the coating erosed rate increases with the increase of coating spray distance;in the hydrogen addition of 0/5/10 slpm,the coating erosed rate increases first and then decreases with the hydrogen content.The erosion failure of coating under different spraying parameters is mainly cutting and columnar crystal fracture.The main reason for the increase of erosed rate is the increase of the failure mode of columnar crystal during scour.（4）After the Al-modification of PS-PVD 7YSZ thermal barrier coating,a denseα-Al₂O₃overlay was formed on the surface of the coating to plug the micro-nano pores on the"cauliflower head"grains and open columnar crystal gaps.The effect of Al-modification technology on the thermal cycling performance of the coating is small,and the water quenching life of 4 h Al-modified sample is higher than that of sprayed sample.The main mechanism is to reduce the weight of the cutting failure mode of the coating.However,due to the thin size of the overlay,the improvement of the columnar fracture failure mode of the coating is not significant.（5）PS-PVD 7YSZ thermal barrier coating is vulnerable to CMAS and Na Cl hot corrosion due to its open pores and material properties.Al-modification technology can provide good protection for PS-PVD 7YSZ thermal barrier coating.By forming a dense overlay on the surface of the coating,it can effectively reduce the penetration of corrosive substances into the coating and improve the hot corrosion resistance.（6）α-Al₂O₃overlay is formed on the surface of the coating after Al-modification,which can not only prevent the penetration of CMAS molten salt,but also affect the thermochemical effect of CMAS.Theα-Al₂O₃overlay making the production of anorthite and other high melting point spinel in the process of hot corrosion,stabilizing the molten salt in the upper part of the coating to reducing the penetration of molten salt.Na Cl has little harm to the YSZ ceramic layer,but it has strong attack to metal bond.The Na Cl electrochemical corrosion model greatly accelerated the growth rate of TGO between the ceramic layer and the metal bonding layer,and led to the catastrophic oxidation of the metal layer.