Quantitative Characterization Of Infiltration Depth And Distribution Of Y Elements In Thermal Barrier Coatings With CMAS Corrosion

Thermal barrier coatings(TBCs)have become a key thermal protection technology for aero-engines because of their high-temperature and high-insulation material properties,which can effectively reduce the operating temperature of the substrate and improve engine performance and thermal efficiency.During the service process of aero-engines,it is always inevitable to ingest sand,dust,volcanic ash and other calcium,magnesium,aluminum and silicon particles(CMAS),which causes CMAS corrosion failure.This failure has become a key issue that restricts the serviceability of TBCs and their safety applications.At present,with the increase of the engine's thrust ratio,the temperature at the inlet side of the gas continues to rise and the high-temperature corrosion of CMAS has become the most dangerous and complex service environment for TBCs.In this paper,the study of the penetration depth and microstructure of CMAS after high temperature corrosion of thermal barrier coatings can provide a reliable reference for CMAS corrosion.The depth of penetration of thermal barrier coating at different exposure temperature and time was detected by Impedance Spectroscopy.In addition,SEM,XRD,Raman spectroscopy,and electron probes were used to systematically study the microstructural changes of APS-TBCs and the content of Y in different corrosion temperatures and times.The main research content is as follows:Firstly,the Impedance Spectroscopy method was used to detect the changes of the impedance values of the CMAS high-temperature corrosion thermal barrier coatings at different temperatures and times.The equivalent circuit of the CMAS high-temperature corrosion thermal barrier coating was proposed and the circuit was performed using Z-View.Furthermore,the curve of the Impedance Spectroscopy of different corrosion temperature and times was obtained and the penetration depth of CMAS could be calculated according to the formula.It laid a good foundation for the following research.Secondly,SEM is used to investigate the penetration depth and microstructure of CMAS high-temperature corrosion samples at different temperatures and at different temperatures.It is concluded that the corrosion depth of CMAS during the thermal barrier coating process increases with the increase of corrosion time.After 1h of corrosion time at 1250?,the ceramic layer still has a lamellar structure and most of the regions still show a columnar structure.Columnar crystal degradation occurs in some regions and the edges and corners begin to round;After 4 hours of corrosion,the degree of spheroidization of the surface grains increased.After 8 hours of corrosion,a large area of spheroidization occurred and large flakes began to appear on the surface.In addition,sample was analyzed by Raman and XRD.The high temperature corrosion of CMAS in the thermal barrier coating resulted in the precipitation of Y in YSZ,which led to the transformation of t phase to m phase with obvious structural changes.Thirdly,the electronic probes are used to test the Y element content in the ceramic layer.The change law of Y element content in ceramic layer and CMAS layer was analyzed and studied after CMAS etching at different times and different temperatures.According to the experimental results,during the process of the CMAS etching of the thermal barrier coating,the Y element in the infiltration direction of the CMAS tends to gradually increase until the final Y element content tends to remain stable.At the same temperature,the content of Y in the CMAS layer of the CMAS high-temperature corrosion thermal barrier coating increases with the increase of corrosion time,and the effect of the corrosion temperature on the loss of the Y element of the CMAS high temperature corrosion thermal barrier coating is more affected by the corrosion temperature.