Testing method to assess lifetime of EB-PVD thermal barrier coatings on tubular specimens in static and cyclic oxidation tests

A testing methodology is presented to assess the delamination failure of an yttria stabilized zirconia electron beam physical vapor deposited (EB-PVD) top-coat as studied for tubular specimens applying short thermal cycles with high heating and cooling rates as well as for oxidation tests at constant temperature. The influence of maximum temperature and specimen diameter were investigated. Higher maximum temperatures as well as a smaller specimen diameter resulted in shorter lifetimes. No significant difference was observed between the static and cyclic oxidation tests. The failure relevant time at elevated temperatures is correlated with the thickness of the thermally growing oxide (TGO) scale developing on the bond coat. The experimental results can be described using a residual stress based analytical approach. In the model the lifetime is assumed to be terminated when a critical stress is reached.