3-dimensional Numerical Study On TGO Undulation Of Thermal Barrier Coatings Under Thermo-mechanical Fatigue Loading

Thermal barrier coatings have been widely used to provide thennal insulation in gas turbines,thus increasing the inlet temperature and service life of metallic components.Thermally grown oxide is formed during the high temperature dwell in service of TBCs,whose growth and rumpling are of great importance to partial delamination of TBCs.In this dissertation,3D models are created by SolidWorks and the influence of initial TGO amplitude?mechanical loading magnitude and lateral growth strain in TGO on TGO rumpling behavior are studied using finite element software ABAQUS and its internal user subroutine UEXPAN which is verified to be correct before it is used in the subsequent studies.The main results are as follows:(1)Necessary verifications of TGO growth subroutine UEXPAN have been conducted to assure the validity of it which are used in the subsequent studies.(2)When only cyclic thermal loading is applied,TGO amplitude is gradually increased with cycling but final undulation magnitudes varies with different models.The amplitude increasements are 0.07?m?0.52?m and 0.74?m for initial amplitude of 2?m?4?m and 12?m after 20 cycles respectively.The change of TGO amplitude is influenced by plastic strain of BC in cooling and reheating but by plastic strain of TGO in high temperature dwell period.(3)When thermo-mechanical loading is applied,TGO rumpling behavior is subject to joint influence of mechanical loading and lateral growth strain in TGO.Anisotropic TGO rumpling will occur when lateral growth strain is small and mechanical loading is big enough at the same time.Namely,tensile mechanical loading makes undulation flatten in the direction parallel to mechanical loading and rough in the direction perpendicular to mechanical loading while compressive mechanical loading have opposite effects.Anisotropic TGO rumpling will disappear when lateral growth strain is big enough whatever the mechanical loading is,while undulations in both direction are even more rough with the increase of cycling number.