Mesoscopic evolution of molten pool during selective laser melting of superalloy Inconel 738 at elevating preheating temperature

Due to the poor weldability of Inconel 738 alloy, defects (cracks, pores) always exist in the selective laser melting(SLM) process. In this paper, the molten pool evolution of the single track, including the morphology, porosity and crack formation, was systematically investigated by numerical simulation, and the effects of different preheating temperature and process parameters were verified by experimental analysis. The detailed temperature-dependent thermal physical properties were applied into the Volume of Fluid (VOF) method to simulate a powder bed computational domain which was established by Discrete Element Model (DEM). The simulation results show that the change of molten pool width by different laser power and preheating was not as significant as that of depth. The results also demonstrate that higher energy density and preheating temperature induced the generation of pores at the bottom of molten pool, which can be explained by the variation in cooling rates . Moreover, the change of temperature gradients in three-dimensional directions with the increase of preheating temperature was also investigated, which explained the reason for crack forming and extending through the center line. Finally, the evolution of molten pool at a higher preheating temperature 1000℃ was simulated to further underpin the positive effect of preheating on preventing cracks formation.