激光熔覆316L粉末熔池热-流动态演化及微观组织研究OA

Understanding transient thermo-fluid behavior within the molten pool is critical for regulating microstructural evolution and interfacial stability during laser cladding of dissimilar steels.In this study,the dynamic evolution of molten pool flow,thermal transport,and solidification behavior during laser cladding of 316L powder on AISI1045 steel is systematically investigated through an integrated numerical-experimental framework,with emphasis placed on revealing the intrinsic coupling mechanism among laser heat input,molten metal convection,dilution evolution,and microstructure formation under transient solidification conditions. A three-dimensional transient thermal fluid coupled numerical model is established to simultaneously describe laser-material interaction,phase transformation,heat conduction,and non-isothermal molten metal flow during single-track laser cladding.Temperature-dependent thermophysical properties of both the substrate and powder materials are calculated through CALPHAD-based phase diagram analysis and incorporated via an apparent heat capacity formulation to accurately capture latent heat release during melting and solidification.The Arbitrary Lagrangian-Eulerian(ALE)dynamic mesh method is introduced to continuously track gas-liquid free-surface deformation and molten pool boundary migration.The model enables quantitative prediction of molten pool morphology evolution,internal flow structure,and temperature gradient distribution under varying laser power conditions.Numerical results are further validated through cross-sectional morphology characterization and microstructural observations of experimentally fabricated coatings.Simulation results reveal that Marangoni-driven thermo-capillary convection dominates molten pool transport behavior throughout the cladding process.Surface tension gradients induced by temperature variation drive molten metal flow from the high-temperature central region toward the cooler boundary zones,forming stable bidirectional circulation vortices within the molten pool.This convection pattern significantly enhances internal momentum exchange and thermal redistribution compared with purely conductive heat transfer.At a laser power of 800 W,temperature gradients exceedingly approximately 2 000 K are generated near the leading edge of the molten region,while velocity differences reach 0.245 m/s,accelerating localized cooling and producing pronounced spatial heterogeneity in solidification conditions. As laser power increases from 800 W to 1 200 W,the peak temperature is increased by approximately 400 K and the maximum melt flow velocity approached 0.5 m/s,indicating intensified thermo-capillary convection and enhanced mass transport capability.Strengthened convective heat transfer promotes simultaneous expansion of molten pool width,height,and penetration depth,resulting in improved metallurgical bonding and interfacial mixing between coating and substrate.The substrate melting fraction increases monotonically with increasing heat input,producing dilution ratios ranging from 0.35 to 0.50.These quantitative results demonstrate that laser thermal input directly governs interfacial mass transfer behavior and dilution evolution during dissimilar steel cladding. Coupled analysis of temperature gradient(G)and solidification rate(S)further establishes a quantitative relationship between transient molten pool dynamics and dendritic growth behavior.The cooling rate parameter(G·S)gradually increases from the upper region toward the bottom of the cladding layer,leading to continuous refinement of dendrite arm spacing.Experimental characterization confirms a transition from columnar dendritic structures near the clad surface to equiaxed grains close to the substrate interface.The results demonstrate that this morphology transition originates from convection-induced redistribution of thermal gradients rather than conduction-controlled solidification alone,highlighting the dominant role of melt flow in regulating solidification pathways.The proposed thermo-fluid coupling framework provides predictive capability for regional microstructure evolution and offers a physically based strategy for process optimization in laser cladding of dissimilar material systems.