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

Failure is a main headache for thermal barrier coatings (TBCs). Typically, whether failure occurs depends on a competition between cracking driving force (negatively related to strain tolerance) and cracking resistance. However, it is difficult to simultaneously enhance these two properties in conventional mono-structures, 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 tri-modal features. The macro-columnar structure was tailored to enhance the strain tolerance, the meso-gradient structure in individual columns was porosity-distributed from bottom to top to enhance the cracking resistance, and the micro-lamellar structure was deposited to further tolerate strain and to prevent heat flux. Firstly, the tri-modal-featured structure was tailored in 2000 μm thick TBCs. Thermal cyclic test showed that the life span was nearly 4 times and 9 times that of the conventional one-way designs of columnar and gradient TBCs, respectively. Secondly, a finite element model was developed to investigate the mechanism responsible for the long life span. Co-operation in lowering driving force and increasing cracking resistance significantly retards the cracking behavior in thick coatings. Finally, dominant factors for the tri-featured structures were discussed and optimized to further extend the life span of thick TBCs. Overall, the matching design between strain tolerance and cracking resistance provides a fundamental way for durable protection in thick TBCs.