Phase-field simulation of particles rigid body motion at the early stage of sintering in powder bed fusion with electron beam: A proposal for computational efficiency

The sintering of powder particles prior to full melting is a defining feature of the powder bed fusion with electron beam (PBF-EB) process, distinguishing it from other metal additive manufacturing techniques. Sintering involves the movement of atoms toward contact points between adjacent particles, leading to neck formation and growth. This atomic movement is driven by the high working temperatures of PBF-EB, which activate diffusion mechanisms and induce rigid body motion (RBM) of particles. While research on the numerical analysis of diffusion is growing, the motion of the particles occurring during the PBF-EB and its relevance are still unexplored. This work uses a phase field model to capture the physics of early-stage sintering in PBF-EB, incorporating both diffusion and RBM driven by vacancy migration. The influence of RBM parameters on neck formation and growth during the sintering of Ti6Al4V particles under PBF-EB conditions is investigated. Simulations encompass different process phases and durations (from seconds to hours), including the preheating of the layer and the cooling of the build. In addition, this work addresses the computational challenges of modelling RBM and proposes a novel approach to enhancing diffusion coefficients to emulate RBM effects, significantly reducing simulation times. Results indicate that incorporating RBM accelerates sintering and leads to larger neck formation compared to diffusion alone, although computational time increases by 30 %. Consequently, RBM should be prioritised in scenarios where its impact is critical, such as the preheating phase of PBF-EB. In contrast, during the process, the neck growth can be analysed by the novel proposed approach which significantly enhances computational efficiency while effectively capturing the influence of RBM on neck growth.