Determination of Thermal Barrier Coatings Average Surface Temperature After Engine Operation for Lifetime Validation

Assessment of ex-service parts is important for the power generation industry. It gives us the opportunity to correlate part conditions to specific operating conditions like fuel used, local atmospheric conditions, operating regime, and temperature load. For assessment of thermal barrier coatings, one of the most valuable pieces of information is the local thermal condition. A method has been developed in Alstom, allowing determination of a thermal barrier coating average surface temperature after engine operation. It is based on the analysis of the phase composition of the thermal barrier coating by the acquisition of an X-ray diffraction spectrum of the coating surface, and its analysis using Rietveld refinement. The method has been validated by comparing its outcome to thermal models and base metal temperature mapping data. It is used for assessment of combustor and turbine coatings with various purposes: Determination of remnant coating life, building of lifing models, or determination of the coating degradation mechanisms under some specific operating conditions. Examples will be presented showing applications of this method.