Computational analysis for understanding the failure mechanism of APS-TBC

Thermal barrier coatings (TBCs) systems are widely used in gas turbines. However, the potential of thermal barrier coatings cannot be fully exerted due to the lack of a reliable life prediction of the coating, which requires the better understanding of the TBC failure mechanisms. In the present work, the failure mechanism of atmospheric plasma spraying (APS) was studied. The FE simulation was adopted to explore the stress distribution in TBC, and then thermal fatigue experiments were carried out. Two advanced constitutive models have been developed and implemented into ABAQUS through UMAT in order to simulate the mechanical behaviors of TBC system under thermal cyclic load. The constitutive model for ceramic top coat (TC) could model the non-symmetry of tensile and compressive loading, and viscoplastic constitutive model was used for the substrate. The stress distributions along the interfaces between TC and bond coat (BC) were obtained. For as-deposited APS-TBC, the thermally grown oxide (TGO) is very thin, which is less than 0.3 μm, the small cracks only initiate in the ceramic top coat not in TGO. The crack imitates at the off-peak and propagates to the peak in TC. Finally the crack will have tendency to occur in internal top coat and be spallation. Meanwhile, the FE simulation and experiment data can provide a basis to develop a more accurate life prediction model.