Application of thermal gradient and thermal cycling tests to Al₂O₃/CYSZ functionally graded TBC in the presence of simultaneous hot corrosion and CMAS effects

Alternative thermal barrier coating, functionally graded Al₂O₃/CYSZ was investigated for CMAS and hot corrosion melts attack under high temperature. Two different test setups were used to simulate the harsh environment of gas turbine engines. Thermal gradient and thermal cycling tests were carried out by using a static heat source laser. Commercial single-layer CYSZ was used as a comparison. As a result of XRD analysis and with the help of Rietveld refinement, the monoclinic transformation was compared for both TBCs. While there was no tetragonal-monoclinic transformation for a functionally graded coating because of protective inert alumina surface, CYSZ has %12.3 and %66.4 monoclinic transformation after thermal gradient and thermal cycle test at 1200 °C, respectively. The t-m transformation resulted in the failure of TBC because of the volume extension of zirconia and the TBC system. Microstructure, EDS and XRD analysis were performed to determine the failure of TBCs.