Formation and evolution mechanisms of pores in Inconel 718 during selective laser melting: Meso-scale modeling and experimental investigations

The forming quality of selective laser melting (SLM) components largely depends on defects such as pore, which seriously deteriorates the mechanical properties. In this study, a meso-scale numerical model based on discrete element method (DEM) and computational fluid dynamics (CFD) has been proposed to simulate the major physical phenomenon during SLM-fabricated Inconel 718 (IN718) superalloy. The model is applicable to the calculation of transient temperature field, molten pool flow behavior and pore evolution (lack of fusion pore and keyhole-induced pore) considering the Marangoni effect and the recoil pressure, which is validated by experiments in terms of the dimension of the track. The numerical results indicated that the lack of fusion pore mainly occurred at inter-track with partially melted powder. It was observed that the morphology of lack of fusion pore gradually changed from small round to elongated irregular shape with decreasing energy density. The keyhole-induced pore appeared below the melt pool and came from the bubbles trapped in the keyhole under violent molten pool flow. Furthermore, bubble coalescence was found to be the main formation mechanism of large keyhole-induced pore. The simulated pore morphology and dimension were in good agreement with those found in bulk samples.