The Effect of Vacuum Heat Treatment on the Oxidation Behavior of APS Thermal Barrier Coating

Thermal barrier coating (TBC), which consisted of a NiCoCrAlY bond coat (BC) and a ZrO₂-8 wt.%Y₂O₃ topcoat (TC), was fabricated on the nickel-base superalloy by air plasma spray (APS). The BC and TBC was treated by vacuum heat treatment (VHT). The oxidation of coating with and without VHT has been performed at 1050℃. Oxidation behavior of coatings and thermally grown oxide(TGO) scale were studied by SEM with EDS. As shown in the results, after treating by VHT, a continuous Al₂O₃ layer formed more rapidly on the VHT coating than that formed on the APS coating, which can act as a diffusion barrier to suppress the formation of other detrimental oxides. The pre-oxidation treatments reduced the growth rate and extend the steady-state growth stage. The TGO in VHT TBC was still a single layer Al₂O₃ oxide after 120h. However, after same oxidation time, the TGO in APS TBC produced a dual-layer oxide consisting of an inner Al₂O₃ layer and outer spinel layer. Therefore the VHT improves the oxidation resistance of APS coating.