Computational analysis of fracture and healing in thermal barrier coatings

Abstract

Thermal Barrier Coating (TBC) systems are protective layers applied to critical structural components of gas turbines operating at high-temperature. A typical TBC system consists of three different layers, namely a ceramic Top Coat (TC), an active Thermally Grown Oxide (TGO) layer and a metallic Bond Coat (BC). The outer ceramic TC that protects the substrate from high temperature gases and an intermediate BC acts as a bonding layer and also provides oxidation resistance to the underlying components by acting as a sacrificial layer. As a result of the oxidation process, TGO layer is formed at the interface between the TC and BC layer. Lifetime of a typical system lies around several hundred cycles after which, a cost and time intensive maintenance operation is necessary to replace the coating in order to continue safe operation of the engine. Earlier research on TBC micromechanical studies have been focussed on evaluating the influence ofmicrostructure on thermomechanical properties or stress distribution in the TBC system. Numerical efforts on TBC failure such asmodelling the different coating composition, TGOgrowth process and interface irregularities have been made in the past to predict its influence on lifetime of the TBC system. In this research, microstructural features and a novel self healing TBCs are explored through numerical simulations to predict its lifetime enhancement. The overall objective of this research is to develop a modelling and analysis tool capable of simulating fracture and healing processes in the TBC system. The resulting numerical tool aids in setting up design guidelines for the successful development of the proposed self healing TBC system.