Long lifespan optimized double-layered structural design of thermal barrier coatings with equivalent thermal insulation performance

The thermal insulation performance and lifespan are critical factors for thermal barrier coatings (TBCs) effectiveness in high-temperature applications. This study presents a double-layered structure design that utilizes the concept of equivalent thermal insulation to reduce residual stresses, cracking driving force, and crack propagation, thereby extending the TBCs' lifespan. Three groups of yttria-stabilized zirconia (YSZ)/La2Zr2O7 double-layered structures (D-I, D-II, and D-III) were developed, each providing the same thermal insulation equivalent to 600 μm YSZ as reference coating but with varying initial elastic modulus in top-layers. Simulation results revealed that residual stresses at the crack tip in the top-interface (σ22-top) were 4.3 %, 12 %, and 28 % lower than those in the bottom-interface (σ22-bottom) for specimens D-I, D-II, and D-III, respectively. Furthermore, D-III also exhibited a σ12-top stress that was two times lower than the σ12-bottom stress. The strain energy release rate (SERR) was lowest in D-III, indicating its superior resistance to crack growth compared to D-I and D-II. Importantly, a “switching-region” was identified in D-I and D-II, where the coatings transitioned from partial to total spallation. In contrast, no such transition occurred in D-III, even after prolonged thermal exposure. Further analysis identified three distinct stages of crack development―region-I (05 h), region-II (520 h), and region-III (20100 h)―based on thermal exposure. Specimen D-III demonstrated the lowest crack propagation across all thermal exposure durations, while other specimens experienced early failure, transitioning from partial to total spallation. D-III maintained its resistance to spallation for a longer period, making this design a promising approach for improving the thermal durability and lifespan of TBCs. •Designed double-layer structure with the concept of equivalent thermal insulation•A “switching-region” was identified in D-I and D-II, where the coatings transitioned from partial to total spallation.•Identified three distinct stages of crack development―R-I, R-II, and R-III.•D-III exhibiting a σ12-top stress that was two times lower than the σ12-bottom stress.•D-III maintained its resistance to spallation for a longer period.