Systems-Based Approach to Predicting Thermal Barrier Coating Delamination Due to CMAS Infiltration

Abstract

Calcium-magnesium alumino-silicate (CMAS) infiltration and attack are difficult to simulate at real-world rates. To better understand the sensitivity of the process to engine operating parameters and CMAS chemical composition, a systems-based reduced order infiltration model that incorporates combustion gas properties, TBC microstructural properties, thermal barrier coating (TBC) heat transfer properties, and CMAS physical properties was developed. The aim was to predict the time to delamination for aircraft engines operating in non-benign environments. The penetration depths reached by a synthetic four-element CMAS mixture within a clean TBC were calculated by finite difference method. Engine operating conditions and TBC top coat types were varied to study the effects on the penetration depths and times. A larger difference between operating temperature and cold shock temperature was found to increase the risk of Mode I delamination. An increase in engine operating temperature had little effect on the critical penetration depth, but significantly influenced the actual penetration depth and time. An increase in electron beam - physical vapor deposition (EB-PVD) TBC taper angle resulted in a decrease in the critical penetration depths, suggesting a greater risk of Mode I delamination. The time taken to reach the actual penetration depth increased with operating time, until the TBC was consumed, at which point penetration time decreased with operating temperature due to lower melt viscosity.