Numerical investigation on the cracking behaviors of thermal barrier coating system under different thermal cycle loading waveforms

The influence of a thermal cycle fatigue (TCF) loading waveform on cracking behaviors of an atmospheric plasma-sprayed thermal barrier coating (TBC) system was numerically studied using the commercial software. Results showed that the TCF loading waveform considerably affects stress distributions in the TBCs and is the leading factor for the initiation and propagation of cracks in TBCs samples. Under triangular load waveform, the cracks initiate and grow in top-coat (TC) layers. However, under trapezoidal load waveform, the cracks are likely to initiate at an off-valley location and propagate along the TC/thermally-grown-oxide (TGO) interface, causing the complete spallation of the TC layer. Furthermore, the influences of the prior time and holding time on the crack initiation and propagation under the trapezoidal loading conditions were discussed, respectively. Interfacial cracks are likely to initiate when the prior time is prolonged. Under the trapezoidal loading conditions, the location of crack initiation moves from the peak to the off-valley location of a TC/TGO interface as holding time increases. Under a long holding time of the trapezoidal loading conditions, an improved spray quality of TC/TGO interface can increase the service life of TBCs.