A matching design between strain tolerance and cracking resistance for a long lifespan in thick thermal barrier coatings

Failure is a main disadvantage of thermal barrier coatings (TBCs). Typically, whether failure occurs depends on competition between the cracking driving force (negatively related to strain tolerance) and cracking resistance. However, it is difficult to simultaneously enhance these two properties in conventional monostructures since they often need totally opposite structures. In this work, a novel structure was designed to co-enhance strain tolerance and cracking resistance in thick TBCs. The novel structure appears to have trimodal features. The macro-columnar structure was tailored to enhance the strain tolerance, the mesogradient structure in individual columns was porosity-distributed from bottom to top to enhance the cracking resistance, and the microlamellar structure was deposited to further tolerate strain and to prevent heat flux. First, the trimodal-featured structure was tailored in 2000-μm-thick TBCs. Thermal cyclic tests showed that the lifespan was nearly 4 and 9 times that of the conventional one-way designs of columnar and gradient TBCs, respectively. Second, a finite element model was developed to investigate the mechanism responsible for the long lifespan. Cooperation in lowering the driving force and increasing the cracking resistance significantly retards the cracking behavior in thick coatings. Finally, dominant factors of trimodal-featured structures were discussed and optimized to further extend the lifespan of thick TBCs. Overall, the matching design between strain tolerance and cracking resistance provides a fundamental method for durable protection in thick TBCs.