Study On Corrosion Resistance Of Thermal Barrier Coating By EB-PVD Exposed To NaCl

With the changing and deteriorating service environment of aeroengines and gas turbines,the stability of thermal barrier coating materials on the surface of hot end components is put forward more stringent requirements.Foreign matter erosion is an important factor that destroys the stability of thermal barrier coating materials,such as molten salt corrosion（Na₂SO₄+V₂O₅）,environmental sediment（CMAS）and marine atmospheric corrosion.At present,the corrosion mechanism of molten salt and CMAS of thermal barrier coating has been relatively clear,and some progress has been made in the research of corrosion protection.However,the blade thermal barrier coating in marine environment bears multiple and complex corrosion,which has received little attention.With the proposal of the"dark blue strategy"and the emergence of the South China Sea issue,the corrosion resistance of thermal barrier coatings to the marine environment has gradually become a hot issue,and the deposited ions in the marine atmosphere are mainly Na⁺,Cl^-.In this thesis,the most widely used YSZ and La Zr Ce O（LZC）/YSZ double-layer thermal barrier coatings with good application prospects were prepared by electron beam physical vapor deposition（EB-PVD）.Taking them as the research object,the Na Cl corrosion resistance of EB-PVD YSZ and LZC/YSZ thermal barrier coatings were systematically investigated.The main results show that:（1）Thermal corrosion resistance of YSZ thermal barrier coating in Na Cl molten saltIn the presence of Na Cl molten salt,the ceramic layer and bonding layer of YSZ coating are separated and fall off,which can not play the role of thermal protection,and the thermal cycle lifetime is obviously shortened.The failure of the coating in Na Cl molten salt mainly occurs at the edge of the coating,and then gradually develops into the interior of the coating.Na Cl molten salt spilled to the coating edge,which further accelerated the formation of thermal growth oxide（TGO）at the coating edge and the degradation of the bond coating.The thickening of TGO leads to the thermal growth stress of the coating in the circulating cooling stage,and the bond coating is gradually degraded at the same time,which leads to the separation and falling off of the ceramic coating and the bond coating.Therefore,the shortening of the service life of YSZ coating should be attributed to the joint action of the thickening of TGO layer and the degradation of the bond coating.（2）Resistance of LZC/YSZ thermal barrier coatings to Na Cl molten salt hot corrosionIn the presence of Na Cl molten salt,the double-layer ceramic layers of LZC/YSZ coatings are seriously damaged,the bond coating is seriously degraded,and the thermal cycle lifetime of the coating is greatly shortened.Compared with YSZ coating,the damage of LZC/YSZ coatings is more serious.Na Cl molten salt spilled to the coating edge,accelerated the formation of TGO at the coating edge,and further degraded the bond coating at the coating edge.In addition,during the thermal cycle,due to the mismatch of thermal expansion,thermal mismatch stress will be generated between the two ceramic layers.The influence of thermal cycle leads to the generation of cracks,which further promotes the corrosion of Na Cl molten salt.With the deepening of corrosion,it leads to the thickening of TGO and the degradation of the bond coating,which in turn promotes the generation of cracks.Therefore,the failure of the coating should be attributed to the synergistic effect of thermal growth stress caused by TGO thickening,thermal mismatch stress caused by thermal expansion mismatch between double-layer ceramic layers and degradation of the bond coating.The thermal mismatch stress between the double-layer ceramic layers and the poor mechanical properties of LZC ceramic layer are considered to be the reasons for the more serious damage of LZC/YSZ coatings than YSZ coating.