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.

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 multi-physical 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.

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 counter-clockwise 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.

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.