45钢基体激光熔覆316L粉末搭接过程中Cr元素分布机制研究

Distribution Mechanism of Cr Element During Laser Cladding Overlapping Process of 316L Powder on 45 Steel Substrate

为了探究激光熔覆搭接过程中元素分布的演化机制,建立了基于体积平均法的Eulerian-Eulerian多相流三维熔化凝固模型,模拟了45钢基体激光熔覆316L粉末的过程,获得了搭接过程中第一、二道熔覆层之间温度场、流场及溶质场的相互作用机制。对比分析了搭接过程中第一、二道熔覆层模拟与试验的熔池形貌结果,熔深误差分别为1.96%和5.39%,熔高误差分别为0.97%和2.62%,熔宽误差分别为7.27%和6.70%,验证了模型的可靠性。Cr元素分布结果表明:在第一道熔覆层的影响下,第二道熔覆层Cr元素的平均含量略高于第一道熔覆层Cr元素的平均含量。搭接区域Cr元素的平均含量略高于两道熔覆层Cr元素的平均含量。这是由于第一道熔覆层影响第二道熔覆层的熔池尺寸、横截面左右温度梯度分布及基体热量吸收,因此两道熔覆层的元素分布有着显著差异。

Objective The composition distribution of the deposited layer in the laser cladding overlapping process is investigated numerically and experimentally.To achieve large-scale remanufacturing,an overlapping method is often implemented.The current results indicate that the characteristics of the second-track molten pool,including its size and flow state,will be changed,or even deformed,under the influence of the first track and gravity during overlapping cladding,and the final distribution of components will be affected by the change in molten pool flow,which directly affects the molding quality.Additionally,the laser overlapping cladding process exhibits highly complex heat transfer and thermo-elastic-plastic-flow multi-physics field coupling changes,which are accompanied by physical phenomena,such as melting,solidification,and phase transitions in the metal powder that cannot be directly observed through experiments.The fluid flow and heat transfer in the molten pool during the overlapping cladding process are presented in a 3D view in this study;this is done to deeply analyze the composition distribution characteristics in the two tracks and the interaction mechanism of the first and second tracks.Methods First,a 3D Eulerian-Eulerian multiphase flow model based on the volume averaging approach is developed in this study to investigate the laser cladding overlapping process with 316L steel powder on a 45 steel substrate,which is coupled with multiphysical phenomena of molten flow,heat transfer,and mass transfer.Appropriate process parameters(molten height,molten width,and molten depth)are obtained through the previous orthogonal test to obtain the appropriate powder utilization and laser absorption rates by adjusting the model.Finally,the model is solved,and the distribution states and evolution laws for the temperature,velocity,and solute fields in the laser cladding overlapping process are obtained.The composition distribution mechanism in the overlapping process is analyzed by comparing the temperature,flow,solute fields,and experimental results of the two track cladding layers.Results and Discussions By comparing the simulation results of two tracks during the overlapping process,the geometric morphology of the cladding layers is observed to have a better consistency(Figs.6 and 7).The temperature field of the second track is slightly higher than that of the first track(Figs.4 and 5)for the same process parameters.The cross-sectional temperature field of the second track is asymmetric.Similar to the flow field evolution of the first track,the second track exhibits clockwise and counterclockwise vortices in the longitudinal section of the molten pool[Figs.8(b)and 9(b)].Unsimilar to the first track,the cross-section of the molten pool of the second track is asymmetric,owing to the inconsistency of the temperature gradient[Fig.9(c)].In addition,the element distribution in the deposition layer obtained by the two-track cladding layer simulation is compared with the experimental data,and the results show that the chromium content in both tracks is nearly the same from above to below(Figs.12 and 13).The overlapping area of the first track is partially remelted by the second track.Some elements of the first track will enter the molten pool of the second track,and the content of the powder metal will be increased,which results in the Cr content of the overlapping region being slightly higher than those of the two tracks.Conclusions In this study,the effects of the first track on the morphology,temperature field,flow field,and solute field of the second track,during the laser cladding overlap process,are investigated.Comparing the simulation results for the two tracks reveals that the temperature field evolution of the two tracks is exceedingly similar.However,the evolutions of the flow fields and distributions of the solute fields of the two tracks are vastly different owing to the influence of the first track cladding layer in the overlapping cladding process.Our study shows that the evolution of the molten pool and element distribution in the deposition layer of the second track are greatly influenced by the first track.To achieve better repair of high-end parts with the lower defect tendency,a better overlapping rate should be considered in the laser cladding overlapping process.