Effects of bond coat and top coat (including nano zones) structures on morphology and type of formed transient stage oxides at pre-heat treated nano NiCrAlY/nano ZrO2-8%Y2O3 interface during oxidation

Bond coat geometry is able to significantly influence thermally grown oxide (TGO) layer formation and growth in thermal barrier coating systems at the onset of oxidation. Moreover, nanostructured yttria stabilized zirconia coating with three model structure (including nano zones) could reduce oxygen partial pressure to the formation pressure of continues alumina oxide scale which was able to protect the substrate from extra oxidation and corrosion. Thus, nano NiCrAlY/nano YSZ and normal NiCrAlY/nano YSZ coatings were prepared by air plasma spray method and then evaluated by high temperature oxidation test at 1000 °C for 160 h. As-sprayed samples were also pre-oxidized at 1000 °C for 48 h and then examined by electrochemical polarization test. The corrosion rate of the pre-oxidized nano NiCrAlY/nano YSZ coating was estimated to be the lowest compared to that of the other samples. It might be related to the formation of continues alumina layer on the nano NiCrAlY at the onset of oxidation. This continuous layer could reduce the penetration of the aggressive solution into the NiCrAlY coating and acted as a protective layer (with the lowest anodic current density). This layer also lessened TGO growth rate at the stages II and III of the growth.

Graphical AbstractThinner TGO layer with lowest spinels (a) and thicker TGO layer with more spinels (b)Figure optionsDownload as PowerPoint slide