Thermal fracture of zirconia–mullite composite thermal barrier coatings under thermal shock: A numerical study

Thermal barrier coatings (TBCs) are used in many high temperature applications to allow components to sustain high temperatures and severe temperature gradients while improving performance. However, TBCs have a limited life due to crack nucleation and propagation, which leads to coating delamination and loss of thermal protection. Thermally activated time-dependent behavior of the coating is a major cause of surface and interface fracture in thick TBCs. This study investigates the reduction of time-dependent deformation through the addition of mullite to YSZ based TBCs. Fracture mechanics analyses were performed for three coating architectures: monolithic YSZ, monolithic mullite and a mullite-YSZ composite. The effect of coating architecture and surface crack morphology on interface fracture was investigated. It was found that mullite and YSZ combined to influence the thermal shock behavior of the composite coatings which experienced a reduced driving force for interface fracture compared to monolithic YSZ coatings while having a higher thermal resistance compared to monolithic mullite coatings.