Effects of Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings at 1100 °C

Highlights: • Nanostructured YSZ top coat slightly reduced double layered TGO growth rate and weight gain of TBCs. • Y was slightly incorporated in the Al₂O₃ (TGO) layer of HVOF NiCoCrAlTaY coating as Y containing small oxide precipitates. • The segregation of Ta-enriched oxides (TaO_x) at the middle of TGO layer led to the formation of some cavities. • TaO_x formation in TBCs including MCrAlTaY bond coats can be prevented by presence of Al₂O₃ film including fine Al-Y oxides. - Abstract: In this research, the effects of thin Al₂O₃ diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al₂O₃ diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al₂O₃/nanostructured YSZ coating at 1100 °C.