Numerical Study On Tgo Undulation Of Thermal Barrier Coating Under Fast Cyclic Thermo-Mechanical Fatigue Loading

Thermal barrier coating (TBC) systems have been widely used to protect metallic components exposed to extreme temperatures in gas turbines. They offer potential for increasing the inlet temperature and improving the service life of metallic components. A typical TBC system consists of a thermal barrier coating (TBC), a thermally-grown oxide (TGO), a bond coat (BC) and a superalloy substrate (SUB). In service, the TBC systems experience severe environments, such as high temperature, centrifugal load, vibration load and corrosive combustion gas. Partial delamination of TBC is strongly affected by TGO layer growth and rumpling (evolution of periodic undulations). Based on finite element software ABAQUS, the user subroutines which can simulate the TGO growth in thermal barrier coating system under thermo-mechanical fatigue are developed. Effect of SUB and BC creep, mechanical load, the load changing rates and different phase shift between temperature and mechanical load on the TGO undulation are studied. The main results are as follows:(1) Necessary verifications of TGO growth subroutine have been conducted to assure the validity of those subroutines which are used in the subsequent analysis.(2)When SUB and BC experienced creep only at peak temperature, the evolution of TGO undulation are as follows:under in-phase thermo-mechanical fatigue conditions, with the increasing of mechanical load, the amplitude of TGO is gradually reduced; under out of phase thermo-mechanical fatigue conditions, the amplitude of TGO is gradually increased; when the thermal and mechanical load have phase shift, the amplitude of TGO increased under both positive and negative deviation when subject to tensile load; while the mechanical load is compression, the amplitude of TGO reduced slightly and increased rapidly when thermal load had a positive and negative deviation of 10° compared to mechanical load, respectively.(3) When SUB and BC experienced creep throughout the thermal history, the evolution of TGO undulation are as follows:under in-phase and out of phase thermo-mechanical fatigue condition, the amplitude of TGO is increased rapidly; When accelerating the thermal and mechanical load changing rates, the amplitude shows a steady growth.