CMAS corrosion behavior and failure analysis of APS-SPS double-ceramic-layer thermal barrier coatings

Calcium-magnesium-alumina-silicate (CMAS) corrosion is a critical bottleneck restricting the reliable service of thermal barrier coatings (TBCs) at high temperatures. To develop high-performance CMAS-resistant TBCs, this study investigates the corrosion behavior, mechanical property evolution, and failure mechanisms of APS-SPS double-ceramic-layer TBCs (APS-SPS DCL TBCs). Microstructure, mechanical properties, and failure characteristics were analyzed using corrosion tests, electron microscopy, nanoindentation, and finite element (FE) stress analysis. Single-ceramic-layer SPS and single-ceramic-layer APS coatings were constructed in FE models for comparative analysis. Results show the coatings exhibit excellent CMAS resistance, with the infiltration depth less than half the SPS layer thickness after 20 hours of corrosion. CMAS corrosion causes coating failure at the SPS/APS interface, distinct from APS/TGO interface failure under high temperature oxidation. CMAS infiltration increases the elastic modulus and hardness of the SPS layer, and the equivalent modulus increases approximately linearly with corrosion time. Stress analysis reveals that tensile stress concentrates at the valleys and compressive stress dominates at the peaks for the APS/TGO interface, while an opposite distribution appears at the BC/TGO interface. Comparative simulations verify that single-layer coatings suffer severe interfacial stress concentration after CMAS attack, whereas the bilayer structure effectively mitigates thermal mismatch stress. The vertically cracked SPS layer relieves stress and slows infiltration, while the lamellar APS layer acts as a physical barrier; their synergistic effect contributes to the outstanding CMAS resistance. This work provides theoretical support for the design and optimization of novel CMAS-resistant DCL TBCs.