TGO growth behavior in refurbished thermal barrier coating system after creep: The critical role of γ-channel width in dd6 superalloys

Secondary service of single crystal superalloys after refurbishment has great significance for the engineering application of thermal barrier coating (TBC) and prolong the service lifetime of high-temperature components. This study focused on the thermally grown oxide (TGO) growth mechanism of TBCs samples that have been refurbished following creep loading with varying stresses. Results indicate that the creep stress before refurbishment leads to an increase in the γ-channel width in DD6 superalloys, and the width is positively proportional to the initial creep stress. The increased γ-channel width in the DD6 substrate induced an increase in the content of θ-Al₂O₃ in TGO at the early stage of secondary oxidation. The TGO rate constant (k_p) of refurbished samples exhibit an exponential relationship with the width of γ-channel in DD6 substrate. Therefore, at the same secondary oxidation time, a larger γ-channel width in the DD6 substrate leads to a thicker TGO thickness, which in turn leads to faster failure due to more micro-defects.