| Thermal barrier coatings (TBCs) can reduce the metal surface temperature andresult in a significant enhancement of performance and efficiency of gas turbineengines. Consequently, TBCs have been a key technique for heat protection ofaeroengines. However, Calcium-Magnesium-Alumina-Silicate (CMAS) particles suchas sands and volcanic ashes in the air are unavoidablely taken into aeroengines duringservice, which results in significant corrosion and degradation of TBCs. The corrosionof TBCs becomes more serious as increase of the temperature of the combustionchamber threshold due to further elevation of the efficiency of aeroenginges. Toprohibit degradation of TBCs due to corrosion of CMAS, complete understanding ofthe corrosion mechanism is the key point at present. As the components of CMASvary with the change of geographical environment, the relationship of the differentcomponents of the CMAS on failure mechanism of thermal barrier coatings has notyet been fully studied. SEM, XRD, Raman Spectrum, EDS and TEM were used toanalyze the failure of EBPVD-TBCs caused by CMAS corrosion. The main contentsare stated as fallowing:Firstly, the thermal physical properties of artificial CMAS were prepared andanalyzed. It was found that the grain sizes of CMAS basically vary continuouslybetween0.2and45micron; XRD analysis showed the amorphous feature of CMASand no chemical reaction was found between the four components. The meltingtemperature of CMAS raised with the increase of CaO.Secondly, the corrosion microstructure of the ceramic coating and the interfaceof TBCs after exposed to33CaO-9MgO-13Al2O3-45SiO2at1250oC for different timewas explored in depth. Two models of CMAS infiltration along the ceramic coatingwere found. The melt infiltrates via either the columnar gaps or new channels createdby corrosion. The damage behavior of the interface between YSZ and Al2O3thermallycorroded by Calcium-Magnesium-Alumina-Silicate (CMAS) powder at the1250oCfor the time ranging from4to48hours were carefully characterized and analyzedrespectively. Chemical reaction happened during the corrosion process since theCaAl2Si2O8and MgAl2O4were identified at the interface. The growth stain and thethermal strain of CaAl2Si2O8and MgAl2O4easily leaded to appearing crack at thisinterface. Finally, a series of comparison on the effects of TBCs corroded by CMAS withdifferent components was made. The microstructure evolution of TBCs varied withthe component of CMAS and the corrosion temperature. ZrSiO4was found when thecontent of Si reached60%; while the structure of ceramic layer was completelydestroyed when the content of CaO reached50%and the temperature raised up to1400oC. |
PDF Full Text Request