Erosion Testing of Thermal Barrier Coatings in a High Enthalpy Wind Tunnel

One of the major problems facing the users of aircraft engines and stationary gas turbines in dusty and dirty environments is erosion, causing engine performance deterioration. Thermal barrier coatings (TBCs) are often applied on metal engine components as combustor heat shields or tiles as well as turbine blades allowing enhanced operating temperatures and resulting in increased thermal efficiency of the turbine and also reduced fuel consumption and gaseous emission. Erosive attack by airborne dust or fly ash, coarse particles causes coating degradation resulting in lifting issues of engine components. In the present study, an erosion test facility was used to simulate the mechanisms of coating degradation expected in gas turbines in a more realistic way closer to real engine conditions. A loading situation combining thermal gradient cycling and erosive media was used. The experiments have been performed with an arc heated plasma wind tunnel (PWT total enthalpy up to 20 MJ/kg), which is available at the Institute for Thermodynamics at the University of the Federal Armed Forces in Munich, Germany. The experimental setup and the integration of the air jet erosion test rig into the existing PWT will be elucidated. Different plasma sprayed TBC materials, including the standard TBC material yttria-stabilized zirconia (YSZ), were investigated regarding their erosion resistance. For validation and verification, samples of nickel-based Mar-M 247 and INCO 718 alloys have been used.