Thermal-fluid behavior and microstructure morphology during laser melting deposition of TiC/Ti6Al4V functionally graded materials

Laser melting deposition (LMD) is an additive manufacturing technology that involves complex thermodynamic and kinetic characteristics in the molten pool. A perspective on the thermal-fluid dynamic behavior in the molten pool is essential for investigating the microstructure morphology and solidification characterization. In this study, a three-dimensional transient thermal-fluid coupling model is proposed for describing thermal-fluid dynamic behavior within the molten pool during laser melting deposition of TiC/Ti6Al4V functionally graded materials. The simulated temperature distribution and deposition layer morphology agree well with the experimental results. The simulation results indicate that the heat accumulation phenomenon generated during the LMD process can exacerbate the penetration effect of the molten pool. The solidified deposition layer will be remelted to form a large cross-layer molten pool, and the molten metal in the remelted zone will move from the lower layer to the upper layer driven by the Marangoni convection. Furthermore, the unmelted TiC particles and the in-situ generated TiC particles can decrease the free energy of the molten pool, induce heterogeneous nucleation, and promote the growth of equiaxed crystals.