Hygrothermal Coupling and Cracking Mechanisms of Thermal Barrier Coatings under Extreme Humid-Hot Environments

Engineering

Thermal barrier coatings are widely used to protect metallic hot-section components in aero-engines, gas turbines, energy equipment and other high-temperature systems. Their durability, however, is strongly affected by humid-hot service environments in which temperature gradients, moisture diffusion, oxidation, salt-containing deposits and thermo-mechanical cycling act simultaneously. This paper presents a project-oriented theoretical study on the hygrothermal coupling and cracking mechanisms of thermal barrier coating systems under extreme humid-hot conditions. Based on the research objectives of establishing generalized moisture-heat coupling models, clarifying interface damage mechanisms and supporting reliability evaluation, a multi-field framework is discussed for the ceramic top coat, thermally grown oxide, bond coat and substrate. The model concept considers non-Fourier heat conduction, non-Fickian moisture diffusion, phase-lag behavior, internal heat and moisture sources, and scale-dependent interface effects. The paper further analyzes how transient temperature and humidity fields generate mismatch stresses, promote oxidation and pore coalescence, change fracture toughness near interfaces, and accelerate crack initiation, propagation and spallation. Unlike purely empirical discussions, the proposed interpretation links material parameters, environmental loads and failure modes through a mechanics-based route suitable for numerical simulation and semi-analytical solution. The results indicate that moisture is not only an environmental boundary condition but also an active participant in thermal stress redistribution and interface degradation. The analysis is therefore useful for comparing coating architectures before costly validation tests are arranged. The study provides a structured basis for lifetime prediction, coating design, and future experimental validation of thermal barrier coatings in complex humid-hot service conditions.

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