Region-function-matching design for YSZ-based thermal barrier coatings enables long thermal cyclic lifespan

Abstract

Thermal barrier coatings (TBCs) require both a porous structure to effectively prevent heat flux and a considerably dense structure to resist cracking for long-term protection. These opposite requirements are difficult to achieve in conventional TBCs, which often exhibit uniform structures across their thickness. In fact, the main requirements of a coating vary with thickness owing to differential service conditions. In this study, the structure of a TBC is locally tailored to meet regional performance requirements. First, the load-bearing conditions across the thickness are investigated in a simulation study. Resulting from multiple causes, the bottom region must bear a larger stress than the top region, which is directly exposed to heat flux. Therefore, the structure should be crack-resistant in its bottom region and thermally insulating in its top region. Second, region-function-matching TBCs were prepared, and their performances were evaluated through isothermal cycling and thermal exposure tests. Results show that the TBCs with matching design exhibited double the lifespan of the conventional samples, whereas the thermal insulation was comparable. Finally, the structural evolutions were examined in different regions to analyze the failure behaviors of the TBCs. Healing of the intrinsic two-dimensional pores and formation of the new large pores mainly account for the changes in thermal and mechanical properties of the TBCs. Overall, this region-function-matching design is expected to balance the tradeoff between high thermal insulation and long lifespan.