A Morphology Transfer Coefficient for Thermal Stress Design in Dual-Surface CVD Nickel Coatings

Thermal mismatch stresses developed during post-deposition cooling of chemical vapour deposition (CVD) nickel coatings on uranium substrates can trigger interfacial debonding. Existing analyses idealise the coating free surface as either perfectly flat or perfectly conformal to the substrate, an assumption inconsistent with CVD growth physics. This study introduces a morphology transfer coefficient α∈ [0,1] that quantifies roughness transmission from substrate to free surface, and evaluates its effect on residual stresses through parametrised thermo-elastic finite element simulations. The von Mises stress σvM at the interface peak exhibits thickness-dependent competition switching: increasing α reduces it in thin coatings where membrane action dominates, but amplifies it in thick coatings where bending prevails. The interface normal stress, which drives Mode-I debonding, rises monotonically with α for all thicknesses via a valley-shielding mechanism. A critical migration coefficient averaging 0.80 is identified, above which the maximum σvM relocates from the interface peak to the free-surface valley; below 0.5 it remains locked at the interface peak for all geometries. Three transferable design guidelines are derived: minimise α to suppress debonding, select coating thickness in the bending-dominated regime, and adopt α ≤ 0.5 for single-site failure assessment. These findings provide a constraint-driven design framework for dual-surface coating systems.