Kinetic Monte Carlo Simulation Of ZrO₂ Coating Deposited By EB-PVD

In engineering applications,thermal barrier coating?TBC?has been applied to aeroengine and gas turbine,where YSZ coatings,ZrO₂ as the main component,are widely used.Electron beam physical vapor deposition?EB-PVD?technology is one of the main methods to prepare TBC,whose columnar crystal structure effectively reduces the thermal stress of the coating in the service process,resulting in an ultra-long life.The traditional experimental methods have the disadvantages of long cycle,high cost,and are unable to reveal the internal physical mechanism.Therefore,the numerical simulation,represented by the kinetic Monte Carlo?KMC?,is widely used in the theoretical research of EB-PVD deposition process to reveal the deposition process and improve the production process.However,lack of potential function for KMC simulation is one of the main obstacles in the simulation of ZrO₂ deposition process.In this paper,after the first principle and molecular dynamics methods are firstly employed to fit the ZrO₂ potential function,the theoretical model of ZrO₂ coating deposited by EB-PVD based on KMC is established,which is used to investigate the effect of EB-PVD processing parameters on microstructures and morphology of fabricated coating.In this paper,the first principle is employed to optimize the structure of ZrO₂ supercell.The coarse-grain approximation is used to reduce the dimension of supercell model,as a result of ZrO₂ coarse-grain models.In order to obtain a wider range of potential function,different strains are applied to optimize the structure by use of first principle for the robust ZrO₂ structure under various strains.Becasue fitting the potential function is based on the model structure,high temperature will disturb ZrO₂ supercell,and cause some changes in the potential function.Therefore,the ab initio molecular dynamics?AIMD?method is used to optimize the structure at high temperature.It follows that the radial distribution function of ZrO₂ is calculated.Then,according to the calculated radial distribution function in the unstrained state,the initial input value of potential function in multi-state iterative Boltzmann inversion is estimated by Boltzmann inversion.Combining molecular dynamics calculation and structure adjustment,the final potential function discrete table is obtained.To verify the correctness of the potential function,the initial structure is relaxed by using the fitted initial potential function,where the structure is compared before and after relaxation to ensure that the potential function is correct.The diffusion activation energy of coarse-grain ZrO₂ particles,with the direction of minimum energy path,is calculated by using the nudged elastic band?NEB?,which reveals the possible particle diffusion path and energy variation characteristics during ZrO₂ coatings deposited by EB-PVD.The internal diffusion needs overcome higher energy barrier than surface diffusion,which indicates that the latter is the main hop mode of ZrO₂ particles during EB-PVD deposition.This is attribute to the fact that the internal particles are limited by the more surrounding particles,leading to more diffusion energy.Moreover,the interlayer diffusion needs overcome larger energy barrier,because the path across the layer is longer than that in the layer.By comparing the matrix coordinates and the stacking sequence of the model,the conversion formula between matrix coordinates and the actual coordinates is established.Finally,the theoretical model of ZrO₂ coating deposited by EB-PVD is proposed in framework of KMC,considering the shadow effect and momentum mechanism model.By the proposed theoretical model,the effect and physical mechanism of the temperature,initial kinetic energy and deposition rate on the microstructure and morphology of ZrO₂ coatings deposited by EB-PVD are investigated.The simulated coating morphology is consistent with the experimental results in most cases.It is found that the porosity decreases with the increase of the temperature and initial kinetic energy or the decrease of deposition rate.Additionally,increasing the temperature and initial kinetic energy can effectively promote the growth of columnar crystal size.At last,the reason for the differences between the simulation results and experimental results is analyzed.