Surface Wettability of Volcanic ash on APS and EB-PVD Thermal Barrier Coatings

The ingestion of volcanic ash into the combustion chamber of a jet engine is widely recognized as a potential threat to the ceramic thermal barrier coatings (TBCs) of turbine blades. Incessant efforts to increase output efficiency have led to jet engine turbine operating temperatures that increasingly exceed 1200°C. This increase in operating temperatures exacerbates detrimental effects of volcanic ash on the TBCs. TBCs are produced primarily by either air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD). Here,the damage generated by ash from Eyjafjallajokull volcano, on APS and EB-PVD yttria-stabilized zirconia (YSZ) TBC material was studied by quantifying the spreading characteristics of pellets of volcanic ash on this TBC material at heating rates of 5Kmin^-1 and 10Kmin^-1. Spreading experiments were conducted using an optical dilatometer, operating at temperatures equivalent to those encountered in operational combustion chambers. A comparative analysis of APS and EB-PVD coatings was performed whereby the wettability of the ash on the surface parameters of the TBCs have been investigated in detail. It was observed that there was a significant difference in the infiltration depth and the columnar microstructure of the EB-PVD coatings was responsible for faster spreading of the ash on its surface: