Mesoscopic study of thermal behavior, fluid dynamics and surface morphology during selective laser melting of Ti-based composites

Abstract A mesoscopic simulation based on the randomly packed powder bed model was developed to study the thermal behaviors during selective laser melting (SLM) of Ti-based composites. Effects of processing parameters on the thermal behavior, fluid dynamics and surface morphology evolution within the molten pool were investigated. The obtained results revealed that the operating temperature, cooling rate and melt lifetime were highly enhanced as the laser power was increased. Meanwhile, the increased molten pool dimensions, the turbulent fluid flows, the improved escaping rate of the entrapped gas and the efficient rearrangement of reinforcing particles within the molten pool appeared at the application of the high laser power. At the optimized processing parameters, the peak of the operating temperature profile located in the laser and powder interaction area was apparently disappeared with the formation of the maximum temperature of 3300 K and, the mean operating temperature of the platform caused by the heat accumulation was as high as 1300 K. Moreover, the surface morphology of the molten pool predicted by the simulation showed a variation from continuous pores to fragments, then to the typical and regular liquid front, and finally to the turbulent liquid front and spatter and balling phenomenon as the laser power increased. At the laser power of 200 W and laser energy density of 140 J/m, the maximum velocity was located in the front and rear region and, the velocity vector located in the melt advanced front pointed to the rear region of the molten pool, indicating that the melt from the irradiation region would complete the efficient melt supplement and avoid the formation of residual pores and therefore, a good and flat surface with few spatters was obtained with the clear liquid front. The simulated surface morphology was found to be consistent with the experimental measurements.