Application of NDE to Thermal Barrier Coatings

摘要

Thermal barrier coatings (TBC) are applied to the hot-section components of turbine engines in order to protect the base metallic parts from high temperature degradation. TBC is a composite system consisting of a porous ceramic topcoat, an intermediate metallic layer of bond-coat and a metallic substrate. The durability of a TBC is dependent on the choice of the initial materials and processing techniques as well as on the TBC thickness, porosity content and its resistance to high temperature degradation due to oxidation and erosion. In this paper, the application of non-destructive evaluation (NDE) to TBC systems representative of those used in the critical components of aircraft engines is presented. An eddy current technique is used to measure the thickness of thermal-sprayed TBC, and knowing the thickness, electrical capacitance measurement is carried out to estimate the porosity. The porosity values estimated by NDE are compared with those obtained by the conventional optical microscopy at two different laboratories and by vacuum volumetric measurements. Also, oxidation of the bond-coat at elevated temperatures is examined by eddy current method and the results are correlated with micrographs of the TBC cross-sections.