Recent Progress in Local Characterization of Damage Evolution in Thermal Barrier Coating Under Thermal Cycling

Abstract

Thermal barrier coating (TBC) systems are currently often tested by thermal cycling with or without temperature gradient on cylinder coupons. As a major drawback, edge effect associated with this geometry induces large scatter in TBC life at spallation. Thus, we promote the use of a laser shock to induce an artificial defect located at the top-coat/oxide interface. This method enables firstly to monitor damage evolution by means of non-destructive methods from this defect during thermal cycling at homogeneous temperature and for burner rig testing with superposed thermal gradient across the TBC. Secondly, by the knowledge of artificial defect location, an accurate 3D reconstruction of the crack tip was performed based on serial sectioning by focus ion beam and viewing by scanning electron microscopy. Founded on these observations, a sensitivity analysis of the measurement uncertainties with respect to the energy release rate of propagating cracks and to the process zone where damage elaborates is proposed.