Stage-sensitive microstructural evolution of nanostructured TBCs during thermal exposure

Nanostructured thermal barrier coatings (TBCs) often exhibit bimodal structure comprised of both nanozones and lamellar zones, and therefore, their sintering behaviour can be different from that of conventional coatings. In this study, changes in the microstructure and properties of nanostructured TBCs were investigated. The results show that their microstructural evolution is highly time-sensitive during long thermal exposure at 1150 °C. In stage I (0-20 h), changes in mechanical properties were significant. The dominant microstructural change was faster healing of flat pores, whereas the macroscopic structure seemed less affected. In stage II (20-500 h), the changes in properties were much slighter and some large macroscopic voids appeared. In brief, the microscopic healing of pores in lamellar zones leads to a significant change in mechanical properties in stage I, whereas sintering of the nanozones leads to macroscopic voids in stage II.