Temperature Field Numerical Simulation And Experimental Research Of Laser Carburizing Surface Modification On Zirconium Alloy

In view of the problems of poor bio-tribological properties and short service time of zirconium alloys as human implants,the laser carburizing method was used to prepare a composite coating containing carbides and oxides on the surface of zirconium alloy,in order to improve its wear resistance and corrosion resistance.In this paper,the method of combining numerical simulation analysis and experimental research is used.Firstly,the distribution and change law of the sample's temperature field in the process of laser irradiation are obtained by ANSYS software,and then the laser process parameters are pre-optimized.Finally,the macro-morphology,microstructure,surface phase composition,micro-hardness,wear resistance and corrosion resistance of the carburized samples are observed and analyzed.The research contents and research results are as follows:(1)Based on the principle of heat transfer and the interaction between laser and matter,the mathematical model for the analysis of temperature field of laser carburization is established.The thermal physical parameters of substrate and coating,latent heat of phase transformation,thermal radiation,natural convection of air and other factors are considered.Besides,the continuous moving loading of laser heat source is realized.(2)Through the CFD-Post software,the temperature distribution and change law of the sample in the process of laser irradiation are analyzed.The influence of laser power and laser scanning speed on the temperature distribution of the sample is discussed.Based on this,the pre-optimization criterion of laser process parameters is established,and the exploration range of laser process parameters of the sample coated with graphite slurry is obtained.(3)After laser carburizing of the zirconium substrate,due to the significant decomposition and dissolution of graphite powder in the molten pool,the carbide phase of zirconium appeared in the surface of the zirconium substrate.By adjusting the laser process parameters,a carburized layer with good surface smoothness,uniform thickness,and no defects such as holes and cracks was obtained.(4)For the samples with powder thickness of 50?m,the laser energy deposition density has an important influence on the microstructure of the samples.When the density of laser energy deposition is 10 J/mm~2,the near surface area is composed of granular and cellular structures,the middle area is composed of irregular island-like and strip-like structures,and the bonding area is composed of planar and rod-like structures;When the density of laser energy deposition is 8.33J/mm~2,the boundary between the carburized zone,the heat affected zone and the substrate zone is obvious,and the thickness of carburized layer is25?m;When the density of laser energy deposition is 5.71 J/mm~2,the microstructure of carburized area is refined,and the ZrC particles with different sizes are dispersed around the irregular dendritic structure.For the sample with a powder thickness of 100?m,when the density of laser energy deposition is 22 J/mm~2,the carburized area is mainly composed of thin strip-like,needle-like and irregular island-like structure.(5)The hardness of carburized area is improved obviously,and the maximum hardness is about 3.5 times of that of substrate.Compared with the wear quality of the substrate,the wear quality of the laser carburized sample is reduced a lot.The wear mechanism of it is mainly abrasive wear,accompanied with a small amount of adhesive wear.To the samples processed with the appropriate laser process parameters,the corrosion current density of it is lower than that of the substrate,and the corrosion resistance of the carburized layer is improved.