Studies of the sintering kinetics of thick thermal barrier coatings by thermal diffusivity measurements

In order to study the evolution of thermal properties of TBC, as a function of time and temperature, thermal diffusivity evaluation by laser flash method has been performed. The measurements have been performed on freestanding yttria-stabilized zirconium oxide (YPSZ) TBCs. In particular, measurements have been carried out at five different temperatures in the range 900-1300 °C, for different ageing times (from 1 up to 150 h). The data show a significant increase of the thermal diffusivity also after exposures of few hours, especially at the highest testing temperatures. Microstructural analysis carried out by optical and electron microscopy clearly showed that the observed thermal diffusivity variations can be ascribed to sub-micrometric crack healing and sintering neck formation. Mechanical testing confirmed the microhardness increase of TBC as well. Finally the data have been summarised in order to experimentally define a “functional life” curve of the TBC, as a function of ageing time and temperature.