CMAS infiltration and mitigation strategies for minimizing premature degradation failure of high temperature ceramic coatings in turbine engines

Sand and volcanic ash may be ingested into an aircraft engine during operation in regions where these materials are abundant. These calcium-magnesium-aluminosilicate (CMAS) compositions infiltrate into high temperature electron-beam physical vapor deposited (EBPVD) ceramic thermal barrier coatings (TBCs). CMAS interacts both thermochemically and thermomechanically with the ceramic coating. Of the possible phases that originate from transformations that take place during the interaction, the monoclinic phase is associated with a volumetric expansion, introducing additional stresses to the coating system and promoting micro-crack initiation. It is therefore vital to elucidate the complementary nature between the thermochemical and thermomechanical mechanisms influencing the residual stress for better coating and CMAS-related degradation monitoring. This work compares results and draws connections from outcomes of previous efforts using 3D confocal Raman spectroscopy to non-destructively evaluate localized, microscale, coating degradation of standard EB-PVD 7YSZ TBCs due to CMAS attack. Preliminary CFD simulations also provide the opportunity to evaluate microstructural effects on CMAS infiltration and infiltration rate. The larger picture of coating degradation monitoring is used to suggest mitigation strategies to prevent premature coating failure with a future outlook toward CFD simulation studies. The ability to non-destructively capture this degradation and represent the associated probed volume will lead towards better damage monitoring as well as aid in the development and implementation of more CMAS-resistant coatings and additional mitigation strategies.