A Fundamental Analysis of Factors Affecting Chemical Homogeneity in the Laser Powder Bed Fusion Process

In this work a novel mathematical framework, that fully describes the fusion and vapourisation state transitions in multi-component systems, has been applied to assist in understanding the fundamental mechanisms of defect formation and chemical homogenisation in the laser powder bed fusion process (L-PBF). Specifically, the role of vapourisation and condensation of the multi-component metallic substrate is investigated to determine the importance of properly capturing the state transitions when understanding the substrate evolution. The framework is applied to a ternary metallic system; it is revealed that entrained vapour bubbles in chemically dissimilar flows promote greater homogenisation during the condensation and collapse of these bubbles when compared to non-condensing phases. It is further shown that as the laser power density is increased, there is a greater tendency for preferential element evaporation of the lighter elements; this preferential element evaporation is quantified numerically for the first time, and shown to be a non-linear function of power density.