Molten pool flow and microstructure evolution in laser cladding of SiC/Mo-based coating

The influence of melt pool flow and microstructure on coating morphology and performance is of significant research value. However, there is currently a lack of systematic research on the multi-scale coupling mechanism between heat transfer, flow behavior, and grain evolution during the laser cladding process, especially the insufficient understanding of the synergistic effect under non-isothermal conditions. In this study, a multiphase coupled numerical model combined with a cellular automaton (CA) model is employed to investigate the mechanisms underlying non-isothermal flow and microstructural evolution during the laser cladding process. Experimental results validate the effectiveness of the developed multiphase model that couples macroscopic heat transfer and flow in laser cladding. Based on the multiphase coupled model, the heat transfer and flow behavior within the melt pool were analyzed, revealing the interaction mechanisms between temperature and flow velocity. The evolution of cellular, columnar, and equiaxed crystals during the solidification of the molten pool was further investigated, and the solidification parameters (G, R), as well as the composite parameters (G*R, G/R) were quantitatively analyzed. Dendritic growth results indicate that during columnar crystal growth, the solute concentration between adjacent grains continuously increases, leading to microsegregation; whereas at the top of the melt pool, the overlapping solute accumulation zones associated with equiaxed crystal growth inhibit dendritic growth. The study identified that the primary cause of the undercooling nucleation phenomenon is the increased growth rate during solidification, which alters the temperature gradient at the solid-liquid interface. This change leads to the undercooling of the composition and ultimately results in the transformation from columnar to equiaxed crystals (CET). The SiC/Mo-based coating significantly enhances the microhardness and wear resistance of IN718 alloy. This study provides a theoretical foundation for predicting microstructural evolution in carbide-coated laser cladding processes.