Modulating liquid metal flow by IN718 addition to improve surface quality in laser direct metal deposition of SS 316L

The surface quality of cladding layer (CL) in laser direct metal deposition (LDMD) is strongly related to liquid metal flow. Improving the surface quality by modulating liquid metal flow is an effective strategy. Hence, a three-dimensional thermo-fluid dynamic model is established to investigate the influence of IN718 addition rate on the liquid metal flow and morphology evolution process of the formation of SS 316L CL during LDMD. The standard deviation and fluctuation amplitude of surface height of CL in central longitudinal section (LS) are defined to analyze the two-dimensional surface quality. The three-dimensional surface deviation of CL is calculated to discuss the three-dimensional surface quality. With the IN718 addition rate increasing, the temperature coefficient of surface tension is reduced and the surface tension gradient is decreased, which leads to the weakened Marangoni flow. The height of molten bulge is reduced due to the weakened Marangoni flow and then the difference between the heights of the solidified bulge and depression on the CL surface is decreased. As a result, the standard deviation and fluctuation amplitude of surface height of CL in central LS are reduced significantly and the three-dimensional surface deviation of CL is decreased greatly. The results can provide valuable reference for improving the surface quality in LDMD of SS 316L.