Thermal cycling behaviour of plasma-sprayed thermal barrier coatings with pre-oxidized NiCrAlY and NiCoCrAlY bond-coats

This contribution deals with thermal cycling of thermal barrier coatings (TBCs) with NiCrAlY and NiCoCrAlY bond-coats, and yttria stabilized zirconia (YSZ) top-coat that were prepared by atmospheric plasma spraying from commercial powders. The samples were pre-oxidized, based on isothermal oxidation of the two bond-coats, in order to diminish the influence of residual stresses after spraying on thermal cycling experiments. Surface topographies of both bond-coats were measured using optical profilometry and several surface parameters were evaluated to characterize them. Microstructural degradation caused by thermal cycling was examined by scanning electron microscopy with an emphasis on the role of bond-coat surface features on local damage mechanisms. An important micromechanism for TBCs with the NiCoCrAlY bond-coat was multiple parallel cracking of the TGO layer that was likely also responsible for lower endurance of these coatings.