Interface Stresses and Morphology Evolution Due to Nonlinear Growth of Thermally Grown Oxides in a 700 °C Coated Steam Dual-Pipe System

In response to the demands for thermal insulation and oxidation resistance in ultra-supercritical unit steam pipes used for power generation, a novel coated steam dual-pipe system incorporating thermal barrier coating technology has been presented. However, the growth stress induced by volume-change growth strain during thermally grown oxide (TGO) growth increases residual stress in coating systems, leading to interfacial rumpling and stress concentration at the interlayer interface. This ultimately triggers interfacial crack growth and interface spalling. Understanding interfacial stress and morphology evolution under the nonlinear growth of the TGO layer, along with quantifying the influence of growth strain parallel and perpendicular to TGO interfaces, is crucial for predicting coating system failure. This study applies an established TGO nonlinear growth simulation method based on element conversion and growth strain application. Investigation into the influence of TGO growth on interface stress distribution and morphology evolution in a coated steam dual-pipe system operating at 700 °C reveals significant increases in tensile and compressive stresses along TGO interfaces under nonlinear TGO growth, accompanied by a small change in interface morphology. Lateral growth strain parallel to the interface primarily governs interfacial stress and morphology evolution, while transverse growth strain has limited contribution due to deformation compatibility. The findings offer a theoretical basis for studying real TGO growth in coatings, elucidating the dynamic process of local stress redistribution and interface movement.