Effect of Top coat Spraying Condition on CMAS Damage Kinetics in Air Plasma Sprayed Thermal Barrier Coatings

Abstract

One of new material issues of thermal barrier coatings (TBCs) on hot section components in gas turbine engines is the attack by molten calcium-magnesium-alumino-silicates (CMAS). In this work the influence of the top coat spraying condition on the CMAS damage kinetics in air plasma sprayed (APSed) TBC specimens was investigated by employing a synthetic CMAS product. Experimental works were carried out with three different top coats prepared from powders with different particle sizes and shapes. It was found that the depth of CMAS infiltration increased proportionally to the square root of exposure time in all specimens. The infiltration rate was analyzed based on a mercury porosimetry measurement, which suggested that the physical CMAS infiltration into the APSed top coat by the virtue of capillary action may play an intrinsic role in the CMAS damage. The reaction rate between the CMAS and the ceramic top coat was also influenced by the spraying condition.