Modeling and simulation of 3D geometry prediction and dynamic solidification behavior of Fe-based coatings by laser cladding

To accurately predict the three-dimensional (3D) characteristics of the coating and dynamic solidification process during coaxial powder-fed laser cladding, an improved 3D multi-physics finite element model including heat transfer, fluid flow, shielding gas pressure, powder temperature-rise, surface tension, and free surface movement is proposed. The input parameters of the model only depend on the thermophysical properties of the deposited material and the process parameters. Therefore, the model has good universality, and can be flexibly applied in other laser cladding systems or deposited materials. The average width and height error for the experimental and simulated is 6.05% and 4.15%, respectively. The numerical model has good abilities to predict the 3D geometry of the coating. The accuracy of the model can be indeed improved by considering the powder temperature-rise and shielding gas pressure during the modeling process. The dynamic growth process of the coating, spatiotemporal variations of the temperature and temperature gradient were discussed in detail to reveal the solidification mechanism. Finally, the relationship between the crystal characteristic (planar, cellular, columnar, and equiaxed grains) and thermal parameters (the temperature, the temperature gradient, and the solidification rate) was established. The results show that the temperature gradient and undercooling at the solidification interface are significantly responsible for the crystal characteristic, while the grain size is mainly governed by the solidification rate.