Strain-induced multiscale structural changes in lamellar thermal barrier coatings

Abstract The thermal mismatch stress, as well as residual stress, in coating/substrate systems often leads to structural changes and subsequent coating debonding in the systems. This study focused on the changes induced in the microstructure and properties of lamellar yttria-stabilized zirconia coatings upon heating, with the aim of elucidating their starting microstructure prior to sintering. The results showed that the combined effect of the residual stress and the thermal mismatch stress results in scale-sensitive changes in the properties of the coatings. The macroscale properties changed significantly, while the microscale properties changed only slightly. Structural characterization revealed that a certain degree of expansion at the tips of both the intersplat pores and the intrasplat cracks occurs, contributing to the microscale structural changes observed in most regions. Moreover, a few mesoscale cracks covering several layers were also observed. A lamellar structural model was developed to correlate the multiscale structural changes observed with those in the properties. Finally, this study revealed that the actual starting structure of plasma-sprayed thermal barrier coatings prior to sintering is different from that in the as-deposited state. This should aid in obtaining an in-depth understanding on the microstructural and properties evolution of the constrained coatings under actual service conditions.