Oxidation-creep damage assessment of Ni-based single-crystal superalloy and coated system

The oxidation-creep behavior and failure mechanisms of Ni-based single-crystal superalloys, both with and without a thermal barrier coating (TBC), were investigated through a combined experimental and theoretical approach. The results indicate that TBC-coated specimens generally exhibit longer creep life. Multi-scale characterization techniques were employed to analyze the failure mechanisms. Both coated and uncoated specimens exhibited varying degrees of oxidation and shear slip. Severe oxidation was observed in uncoated specimens. The oxidation mechanism under creep loading was analyzed in detail, and then the oxidation kinetics and damage models incorporating temperature and stress effects were established. In contrast, coated specimens developed a continuous and dense thermally grown oxide (TGO) layer at the top coat (TC)/bond coat (BC) interface, effectively mitigating substrate oxidation. Based on continuum damage mechanics (CDM) and crystal plasticity (CP) theory, a creep constitutive and damage model was developed for the uncoated alloy, incorporating oxidation, defect evolution and material degradation. For the coated material, an enhanced model was established, accounting for the coordinated deformation between the coating and substrate, as well as the coating's oxidation resistance. The Crystal plasticity finite element method (CPFEM) simulations successfully predicted the creep behavior, with computed creep life and deformation trends showing good agreement with experimental results.