Micro–Meso–Macro Modelling of Thermal-Shock Failure in CVD-SiC Coatings on 2.5D C/SiC Composites

Chemical-vapor-deposited SiC coatings on 2.5D woven C/SiC composites exhibit a statistical dispersion of approximately one order of magnitude in thermal-shock lifetime, which empirical design rules cannot predict. We present a micro–meso–macro integrated computational materials engineering (ICME) framework that couples atomistic grain-boundary (GB) degradation, phase-field-generated polycrystalline representative volume elements (RVEs), and a global–local mesoscale model with dual cohesive zones (intra-coating and coating/substrate interface) to quantitatively predict thermal-shock delamination under a single thermal-shock cycle. A two-tier scale-bridging strategy decomposes cohesive properties into a defect-controlled absolute baseline (anchored by pull-off experiments) and a bond-controlled normalised temperature trend (transferred from molecular dynamics), enabling a physically rigorous and experimentally calibratable mapping. Key findings: (i) MD predicts GB cohesive-strength retention of only 32–38 % at 1573 K versus ∼65 % for grain interiors; (ii) the 2.5D RVE reveals ∼1.5× in-plane stress amplification at fiber-bundle crests; (iii) a temperature-driven failure-mode bifurcation occurs between 1400 °C and 1500 °C, mechanistically consistent with the He–Hutchinson crack-deflection criterion; (iv) SEM–EDS fractography of 30 specimens confirms mixed-mode failure in 93.3 % of cases, cross-validating the predicted regime at Γ≈0.25–0.5. The framework predicts non-monotonic design windows for interface roughness (Ra≈6–10 μm), grain size (d g ≈1–10 μm), and a minimum coating thickness (∼70 μm), with thermal-shock experiments (one cycle) at 1300 °C corroborating the ascending roughness branch (Ra≈11.6 μm retaining 82 % versus 47 % for near-polished). The framework provides transferable design maps for CVD-SiC and analogous heterogeneous coating systems.