New insights into the creep degradation mechanisms in thermal barrier coating/single-crystal superalloy system with temperature and stress dependency

Abstract

Thermal barrier coating (TBC) is crucial for the performance of turbine blades at high temperatures; however, it degrades the microstructure of single-crystal superalloy (SX), thereby reducing creep life. Despite this, the degradation mechanisms associated with the complex multi-layer damage and inter-layer diffusion behavior for TBC/SX systems have not yet been fully elucidated. In this study, using integrated experimental efforts and multiscale characterization techniques, the creep degradation mechanisms of TBC/SX systems at 900°C/500 MPa, 980°C/300 MPa, and 1050°C/160 MPa are systematically investigated. Results demonstrate that the creep degradation from TBC intensifies with increasing temperature (T) and stress (σ) ratio (T/σ), exhibiting significant dependency on these two factors, and primarily reduces lifespan of the steady-state stage, with minimal effects on the accelerating stage. During creep deformation, the cracking behavior caused by thermally grown oxide (TGO) beneath the top coat (TC) layer, voids resulting from internal oxidation and interdiffusion in the bond coat (BC) layer, and the recrystallization growth driven by the sandblasting process in the secondary reaction zone (SRZ) are temperature-sensitive damages. In contrast, the initiation and propagation of cracks associated with the topologically close-packed (TCP) phases in the SRZ exhibit pronounced stress sensitivity. Furthermore, the formation of the substrate diffusion zone (SDZ) and the decomposition of γ/γ′ interfacial dislocation networks driven by the Cr–Ru diffusion, as well as the increased stacking fault energy in the γ′ phase due to Co loss, are responsible for the acceleration of steady-state creep rate at 1050°C /160 MPa. This work provides a comprehensive and in-depth understanding of the degradation mechanisms under thermal–mechanical coupling in TBC/SX systems, offering new insights into targeted design optimization for multilayered coatings.