Phase-field Simulation And Experiment Of Element Interdiffusion Behavior Between The Bond Coating And Substrate Of Thermal Barrier Coatings

As an advanced thermal insulation ceramic coating,thermal barrier coatings(TBCs)greatly increase the working temperature of aero-engine,and then improve the functions and thermal efficiency of aero-engine.However,when the coatings work at high temperatures,the harsh environment will cause oxidation,erosion,and corrosion of the TBCs.What's worse,it would induce the elements interdiffusion between the bond coat and substrate,which can eventually lead to the spalling of the coat.The element interdiffusion between the bond coat and the substrate will lead to the formation of Kirkendall pores and interdiffusion zone at the interface,and the topologically close-packed(TCP)generated in the substrate will induce the secondary reaction zone,resulting in a significantly decline on the mechanical properties of both the interface and substrate.However,the element interdiffusion between the bond coating and the substrate of thermal barrier coatings hasn't been thoroughly studied.In this work,based on the thermodynamics and kinetics of materials,the interdiffusion model between the bond coating and the substrate is established to simulate the diffusion of elements by the phase field method,and the corresponding experimental study is carried out through microstructure characterization.The main research is listed as follows:(1)According to the CALPHAD phase diagram thermodynamics,the Gibbs free energy of ? phase and ? phase of Ni-Al-Cr ternary alloy and its isothermal cross-section phase diagram at 1100oC are calculated.Further,the initial diffusion couple of the phase is determined by isothermal section phase diagram and the initial composition of the bond coating and substrate.The atomic mobility of each element in the ? phase and the ? phase is calculated based on the atomic dynamics theory and then convert into the chemical mobility in the phase field model,which provides parameters for the phase field model of element interdiffusion.(2)Based on the phase diagram thermodynamics and atomic dynamics,the element interdiffusion model of the bond coating and substrate of the thermal barrier coatings is established by phase field theory.The model parameters are selected according to the relevant literature,and the element interdiffusion and phase evolution control equations are derived.The distribution of Al and Cr at 1100°C with time and the evolution of microscopic phase structure are obtained.The simulation resultsshow that both Al and Cr elements diffuse from the bond coating to substrate,but the change of content of Al is not as obvious as that of Cr.And as the diffusion time prolonged,the element diffusion rate is gradually reduced.In addition,the bond coating underwent ??? phase transition due to a decrease in the Al content.(3)An experimental study on the interdiffusion of elements between the NiCrAlY bond coating and DD6 high temperature single crystal substrate of thermal barrier coatings is carried out.The distribution of elements and the microstructure evolution of the bond coating and substrate are studied by means of microscopic characterization methods such as SEM,DES and XRD.The experimental results show that the Al and Cr elements diffuse from the bond coating to the substrate,and an interdiffusion zone are formed at the interface between the bond coating and substrate,accompanied by a large number of topologically close-packed phase,which induce the secondary reaction zone together with matrix phase.