Assessment of stress characteristic and interfacial delamination in thermal barrier coatings considering the connected crack network

The coalescence induced by the propagation of inter-lamella and intra-lamellar cracks in thermal barrier coatings (TBCs) by atmospheric plasma spraying (APS) is the root cause of coating spallation. To clarify the influence of defects such as cracks on the coating failure, a real TBC model including the connected crack networks, spherical pores, and unmelted particles is developed. A defect-free equivalent model is also established for comparison. The through-thickness thermal conductivity and elastic modulus of the ceramic layer are determined by experiments and simulations. The stress state and damage evolution of the TC/TGO interface under these two models are evaluated. The results show that the thermal insulation of APS TBC is mainly dominated by the inter-lamella crack. The defects in the coating cause a great increase of stresses in the ceramic layer and at the TC/TGO interface. The TBC lifetime by an equivalent model will be higher than the experimental value. The TGO creep can delay the damage of the TC/TGO interface. The results of this study can provide significant theory guidance for designing advanced TBCs toward high insulation and long life.