Integrated testing approach using a customized micro turbine for a volcanic ash and CMAS related degradation study of thermal barrier coatings

Abstract

A volcanic ash (VA) test stand has been built with a precise particle feeder, concentration measuring unit and a mini turbine with an integrated thermal barrier coating (TBC) system on the blisk for the first time in a laboratory scale. This setup has allowed the testing of melting, sticking, corrosion and erosion behaviour of volcanic ash in-situ at high temperature in a realistic manner in a gas turbine. Moreover, this mini engine runs with kerosene which could also bring all the impurities such as sulphur in to system which might change the reaction mechanisms of TBC and VA. The particle size influence on the sticking/escape behaviour in the engine components was tested but a clear statement on the particle size versus its sticking behaviour could not be made, although the particles in the size range of 1–10 μm are more susceptible to melting in the given conditions. The blisks were coated with two different TBC materials such as 7 wt% yttria stabilised zirconia (7YSZ) and gadolinium zirconate (GZO) using electron beam physical vapour deposition (EB-PVD) technique. Both coatings were tested in corrosion-erosion regime under VA at high temperature and it was found out that the coating with higher toughness (7YSZ) has performed better than the other coating under the used testing conditions.