Influence of sulphur on component mixing during laser additive manufacturing process: From single-track to multi-track

In multi-track laser additive manufacturing (MLAM), sulphur plays a critical role in modifying heat and mass transfer within the melt pool, thereby influencing element distribution and the uniformity of the deposited layer. However, experimentally predicting the effect of sulphur on the dynamic evolution of elemental content remains challenging. This study develops a finite element model for MLAM that incorporates the influence of sulphur on melt pool mass transfer, including its effect on the temperature coefficient of surface tension. The model successfully predicts the content distribution of Ni, Fe, and S in both lap and non-lap zones, as well as the geometric profile of the deposited layer, under sulphur-containing and sulphur-free substrate conditions. Results show that sulphur alters the melt pool flow pattern from a center-outward convection to a periphery-driven motion while reducing overall flow velocity. The presence of sulphur decreases the average Ni content in the deposited layer from 7.2 wt% to 6.9 wt% and increases its spatial heterogeneity. Regardless of sulphur content, Ni content rises progressively from the first to the fourth track. After sulphur addition, the content disparity between peripheral regions and other areas of the deposit further widens. Experimental validation confirms good agreement with numerical predictions, with errors below 5.78% for geometric dimensions and up to 9% for Fe contents due to powder stream fluctuations and compositional inhomogeneities. This study provides a robust numerical approach to understanding sulphur-driven compositional evolution in MLAM, offering guidance for improving elemental uniformity and process control.