Thermographic analysis and modelling of the delamination crack growth in a thermal barrier coating on Fecralloy substrate

The delamination crack growth in a plasma sprayed ZrO2 thermal barrier coating system during thermal cycling was analysed by thermography. A simplified model system was used where a Fe–Cr–Al–Y alloy (Fecralloy Eisen-Chrom™) substrate with relative low yield stress and creep strength simulates the bond coat. The delamination crack area was measured as a function of cycle number and the growth mechanisms were observed and quantified by infrared pulse thermography. Based on this, an empirical model was created to describe the delamination crack growth. In contrast to most of the usual models, the present model calculates delamination crack area (instead of length), accounts for formation of multiple cracks (instead of one), for crack initiation at different times (instead simultaneous initiation), for the positions of the cracks on the sample and to each other as well as for the statistic spatial distribution of the crack initiation sites. The key features of delamination crack growth are met properly by the model approach. Although only one set of parameters was used, the model captures temporal discontinuities of the crack area increase and therefore scatter of delaminated area at a given time.