Residual Stress And The Stability Of Thermal Barrier Coatings Under Thermal Cycling

With the development of aeronautic technology, Thermal Barrier Coatings (TBCs) is used widely. Residual stress near the interface because of interfacial topography, thermal expansion misfit and serve condition is a major factor of spallation, and the residual stress accumulation during thermal cyclings induces instability of TBCs. In this paper, taking TBCs which is made by Plasma-Spraying as the object, based on the thermal elastic- plastic and statical shakedown theory, the residual stress and instability are studied.Firstly, based on Melan's theory and Mises' yield theorem, the model of shakedown is established in the conditions of strain hardening and temperature field, the criterion and cyclic load steps of shakedown are analyzed, and the finite element method(FEM) for calculating shakedown limit with the thermal loadings is discussed. Secondly, based on heat exchange and thermal-elastic theory, the temperature grads for 3-layer TBCs is obtained, the reasons and characteristics of thermal stress of TBCs during thermal cycling are analyzed. Thirdly, the models of flat and cylinder are established for different interfacial topographies. The residual stress has been simulated by thermal elastic-plastic FEM, considering the factors of thermal grads, thermal expansion misfit and geometrical. The effects of material properties and interfacial topography on residual stress are analyzed. Finally, based on the instability of TBCs during thermal cyclings, the relation of the residual stress/strain cumulation is discussed. The residual stress cumulate process during thermal cyclings is simulated, taking the temperature-dependent material properties into account. The effect of the interfacial topography on stability process and the shakedown of the most dangerous point are analyzed.The results show that the relation of temperature field and the thickness of TBCs of flat model is linear and that of cylinder model is logarithm. The maximal residual stress located on the interface. The greater is the difference between material properties, the greater is the residual stress, and the residual stress of BC increases more fleetly than that of top coat. The residual stress is affected obviously by interfacial topography between top coat and bond coat. The residual stress will be...