Wetting and spreading behaviour of molten CMAS towards thermal barrier coatings and its influencing factors

Abstract

Thermal barrier coatings (TBCs) are inevitably subject to corrosion caused by molten calcium-magnesium-alumino-silicate (CMAS), which leads to severe degradation in the properties of the coatings. In this study, a novel device for evaluating the wetting performance of molten CMAS was developed, which solved the challenging problem of measuring the contact angle of CMAS on TBCs at high temperatures. The wetting and spreading behaviour of CMAS under various conditions was studied, and the effect of various factors such as temperature, surface roughness, and the coating preparation process on the wetting behaviour was systematically analysed using this new method. The results demonstrate that the spreading distance can decrease and the contact angle can increase on rough surfaces, and the contact angle is proportional to the square of the roughness at the stable stage. The wettability is also determined by the viscosity, which in turn is governed by the temperature and the reactive production of CMAS and the coatings.

Keywords

• Thermal barrier coatings
• CMAS wetting
• Contact angle