Revealing multiphysics effects on microstructure characteristics in powder-fed laser cladding based on a comprehensive model

To accurately and quantitatively reveal the physical mechanism underlying the formation of microstructure during coaxial powder-fed laser cladding, a three-dimensional comprehensive model, coupling laser-powder interaction, temperature field, and flow field, is developed to identify the effects of multiphysics on microstructure characteristics. The high-speed camera and numerical simulation are employed to characterize the powder distribution, which is converted into the corresponding cladding layer growth rate and applied to solve the temperature rise and flow behavior of the molten pool. The energy conservation equation and the Navier-Stokes equation are applied to describe the physical field government, and the free surface motion of metallic liquid is tracked utilizing the Level Set method. The comprehensive model accurately visualizes the molten pool hydrodynamic behavior and temperature field distribution during laser cladding. In addition, the experimental results are combined to analyze the formation mechanism of microstructure. The direction and magnitude of forces acting on the metallic liquid in the flow field (such as surface tension, Marangoni force, recoil pressure) intuitively explain the formation of circulation in the molten pool, ultimately reflected in the grain growth direction. The evolution of cooling rates in the molten pool indicates that the specific location and varied temperature field dominates the grain type and size of the cladding layer, which contributes to the planar crystal, cellular crystal, columnar dendrite, equiaxed dendrite and equiaxed crystal from bottom to top.