Considering the influence of non-equibiaxial stress state and initial residual strain on the compressive buckling of the ceramic layer, a quantitative characterization method of the damage generated at the interface between the top coat and bond coat in thermal barrier coating based on uniaxial compression was developed. It was verified by the axial compression tests of the single crystal specimens with EB-PVD thermal barrier coating after undergoing various isothermal oxidation times and thermal cycles. On this basis, the correlations between the measured interfacial damage and the thermal loads experienced as well as the thickness of thermally grown oxide (TGO) were analyzed. The results show that the critical compressive strain inducing the spallation of thermal barrier coating at room temperature can effectively characterize the accumulation of interfacial damage caused by isothermal oxidation and thermal fatigue. Under the same TGO thickness, the damage caused by thermal fatigue is greater than that caused by isothermal oxidation. The total damage generated in thermal barrier coating can be divided into three parts: oxidatively driven damage related to TGO thickness, mechanically driven damage related to stress–strain cycles in the coating, and their interaction, where the interaction term is negative.

Thermally grown oxide (TGO) is a critical factor for the service life of thermal barrier coatings (TBC). Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system. At present, technologies of numerical simulation to TGO growth include two categories: coupled chemical-mechanical methods and mechanical equivalent methods. The former is based on the diffusion analysis of oxidizing elements, which can describe the influence of bond coat (BC) consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC, and has high accuracy for the thickness evolution of TGO, but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced. The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO. Based on the measured TGO thickness growth curve, simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.

The mechanical behavior of case-carburized 18Cr2Ni4WA steel is investigated by an optimization method combined with finite-element simulation based on indentation tests. For a measured load-displacement curve, the uniqueness of the combination of the strain hardening exponent and yield stress of a material is discussed by analyzing their effects on the maximum reaction force and residual displacement. The result shows that the effects of yield stress on the load-displacement curve are more pronounced than those of the strain hardening exponent when the elastic modulus is prior known. An optimization model containing an equality constraint is constructed and carried out in every indentation location, and its results indicate that the strain hardening exponent may be constant with depth in the case-carburized steel. The conclusion is further verified through a modified optimization model proposed herein. Therefore, the gradient in the mechanical behavior for the carburized material is primarily reflected by the variation in yield stress with depth. The correlation between hardness and yield stress is established through the least squares method according to the results of the modified optimization model and should help predict the mechanical behavior of parts in the carburized material.

Thermal-mechanical fatigue (TMF) tests and isothermal fatigue (IF) tests were conducted using thin-walled tubular specimens under strain-controlled conditions. The results of TMF tests showed a strong correlation between mechanical behavior and temperature cycling. Under different phases of temperature and mechanical loading, the hysteresis loop and mean stress of the single crystal superalloy showed noticeable variations between the stress-controlled and strain-controlled conditions. In the strain-controlled TMF test, temperature cycling led to stress asymmetry and additional damage, resulting in a significantly lower TMF life compared to IF life at the maximum temperature. Moreover, the OP TMF life is generally lower than that of the IP TMF at the same strain amplitude. The Walker viscoplastic constitutive model based on slip systems was used to analyze the TMF mechanical behavior of the single crystal superalloy, and the change trends of the maximum Schmid stress, the maximum slip shear strain rate, and the slip shear strain range were analyzed, and their relationship with the TMF life was investigated. Finally, a TMF life prediction model independent of the loading mode and phase was constructed based on meso-mechanical damage parameters. The predicted TMF lives for different load control modes and phases fell within the twofold dispersion band.