Thermal fracture of zirconia–mullite composite thermal barrier coatings under thermal shock: An experimental study

Thermal barrier coatings (TBCs) are used in applications that involve high temperatures and severe temperature gradients in order to improve product performance. The understanding of the mechanisms resulting in coating delamination allows the development of materials that can prolong component life. The goal of this study was to demonstrate that single layer mullite–YSZ composites resulted in reduced interface fracture under the application of a thermal shock. This was accomplished by comparing the thermal shock behavior of three coating architectures: monolithic YSZ, monolithic mullite and a mullite–YSZ composite. The coating architectures were chosen to optimize material properties to reduce the driving force for coating failure. It was found that under thermal loads that result in similar surface temperatures, the mullite–YSZ composite developed shorter multiple surface cracks along with shorter horizontal cracks compared to the monolithic YSZ. The composite coating was able to combine advantageous material properties from both the constituent ceramics.