Creep strength of Al2O3 + ZrO2·5CaO subjected to thermal cyclic test

The present paper examines the failure mechanism of the coating system of Al2O3–ZrO2·5CaO applied on a Cast iron substrate. The atmospheric plasma spray coating technique was used for coating. A muffle furnace was used to heat the sample to 600 ± 2 °C followed by ambient cooling. Both the heating and cooling cycles were maintained for 30 min. Results were compared between the as-sprayed coated specimen and the post thermal cyclic test specimen. It has been noticed that normal stresses developed due to the formation of thermally grown oxide at the interface of the top/bond coat and constitutes the weakest link in the coating system. Also, differential porosity at the interface led the moisture to penetrate from the top coat to the bottom coat. Thus, a thermochemical process occurred below the bond coat, leading to the formation of oxides and made the top coat gradually more brittle during the thermal cyclic process.