Comparative Study on the Thermal Performance of Cr-Cr_xO_y and YSZ-CoNiCrAlY Coatings Exposed at 900 °C

Yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) deposited on CoNiCrAlY oxidation protective bond coats are commonly required in temperature regimes up to 1200 °C (e.g., hot gas turbine regions) due to their superior thermal behavior and mechanical properties. For temperatures up to around 900 °C, oxidation protection can be alternatively provided by metallic-ceramic Cr-Cr_xO_y coatings. For the present research, Cr-Cr_xO_y atmospheric plasma sprayed (APS) and YSZ-CoNiCrAlY APS-high velocity oxy-fuel TBC coatings were deposited on a NiCr20Co18Ti substrate. The samples were isothermally heat treated at 900 °C for 10 h in an environmental atmosphere and subsequently isothermally oxidized at the same temperature for 1200 h. Investigations of the physical, chemical, and mechanical properties were performed on the as-sprayed, heat-treated, and oxidized samples. The oxidation behavior, microhardness, cohesion, and adhesion of the samples were correlated with the microstructural investigations and compared to the conventional TBC system. It could be shown that heat treating decreased the Cr-Cr_xO_y coatings crack susceptibility and led to the formation of a protective thermally grown Cr oxide layer. The experimental work on the YSZ-CoNiCrAlY system revealed that the phase composition of the bond coat has a direct influence on the oxidation protection of the coating system.