CFD modelling of the powder segregation in multi-material laser directed energy deposition

Abstract

One of the prevailing challenges in multi-material laser Directed Energy Deposition is the segregation of the constituents during the delivery of the feedstock into the melt pool. This phenomenon is of particular concern when metal-ceramic mixtures are involved, as the differences in the inertial properties of the powders are higher and segregation is aggravated. This issue affects the reliability of the process; indeed, powder segregation can influence the composition of the melt pool and, thus, that of the final part or coating. In this work, Computational Fluid Dynamics modelling is adopted to study this phenomenon and to explore strategies to overcome it. Firstly, a base multi-material CFD model is built. Secondly, a simplified algorithm is proposed to reduce the computational cost of simulating multiple scenarios. This model is first validated numerically against the base model. Then the simplified multi-material CFD model is experimentally validated. Thirdly, the developed tool is implemented to elaborate two strategies to minimise powder segregation in a Co-WC powder mixture. The first one is quite straightforward and little development is necessary to incorporate it to the industry. Conversely, the second one, though promising, needs further development and its practicality needs to be evaluated before being ready for industrial implementation.