Coupled Chemo-Mechanical Modeling Of Interface Oxidation Of Thermal Barrier Coatings Based On Small Deformation

Thermal barrier coatings(TBCs)have been widely used in aircraft turbine engines,due to the remarkable performances of heat protection,abrasion and anti-corrosion.However,because of the complexity of thermal barrier coatings in geometry,microstructure and operation circumstance,the fracture and spallation of coatings cannot be predicted,and resulting in spalling failure at last.The thermally grown oxide will gradually grow when it subject to complex multiple factors such as thermal,stress and chemistry,which greatly restrict the application of thermal barrier coatings to aircraft engine.This paper mainly considers the growth of TGO under the coupling effects of stress and chemistry on high temperature.Finally,we simulate and analyze the growth of TGO using the finite element software,the main research contents and results are as follows:First,we establish a simple oxidation model under high temperature to research the growth rules of the oxide,obtain the relationship between TGO thickness and temperature,oxygen partial pressure,surface roughness.Furthermore,we analyze how the external environment factors affect the growth of TGO in thermal barrier coatings,such as temperature,oxygen partial pressure,surface roughness.The results show that the TGO grows so fast at first,with the time goes by,the reaction rate decreases,finally stay steady.The influence of temperature and surface roughness on the thickness of the oxidation layer is great,however the oxygen partial pressure has less effect on it;the thickness of the oxide layer increases as temperatures rising and surface roughness increasing,and the degree of oxidation become higher.Second,we have built up the relationship of concentration on force field in the process of high temperature oxidation about TBCs based growth strain under the condition of small deformation assumption,where the total strain can be divided into elastic strain and growth strain.Next we establish the constitutive relation of the force field of the TGO growth process;the average stress is added in the chemical potential,and the influence of force on the chemical field is established through the law of Fick,so the constitutive relation of the chemical field is obtained.In the process of high temperature oxidation of TBCs,a variable n is introduced to represent the growth of the TGO,when it takes 1,which represents TGO,while the zero represents the bonding layer,then we get the evolution equation of TGO.Finally,TBCs coupling model is obtained through equilibrium equation,diffusion equation,TGO evolution equation and constitutive equations during high temperature oxidation process.Third,with the help of software COMSOL,the finite element model of TGO's growth is built by setting the force field,chemical boundary conditions and initial conditions.The control equation of chemo-mechanical coupling theory was written to COMSOL weak form to research the growth law of TGO and the stress of coatings.The results show that the thickness of TGO oxide growth in peak was faster than valley,and the thickness of TGO increases with the increasing of the surface roughness.The interface roughness of TBCs is an important factor which affect the internal stress distribution of the coating,when the interface roughness increases,the stress value will also increase;the compressive stress in the coating has negative effect on the TGO's growth,while the tensile stress has positive effect on the growth of TGO.