Thermal Analysis and Failure Behavior of 8YSZ Thermal Barrier Coatings under Thermal Cycling Tests

In this study, thermal analysis and thermal shock test of 8wt.% yttria stablized zirconia (8YSZ) thermal barrier coatings(TBCs) on low heat rejection(LHR) diesel engine have been conducted. The influence of TBCs on temperature distribution of piston was discussed by employing ANSYS codes. The thermal shock resistance test was carried out by placing the samples under flame jet heating and compressed air cooling in turn. Two kinds of thermal cycling modes with different periods were used to investigate the role of cycling frequency in coatings failure. As the frequency rose, the service life of coatings significantly decreased. The spallation of coatings happened at the interface between bond coat and substrate. The stress calculation results indicated that considerable stress caused by thermal mismatch was one of the main reasons for TBCs failure. The heat affected zone(HAZ) under the bond coat inhibited the diffusion between the bond coat and substrate. The oxide layer consisting of Mg and Al oxides under the HAZ was harmful to the bond between bond coat and substrate, which was another main reason for the spallation of coatings.