Study on sintering mechanism for extrusion-based additive manufacturing of stainless steel through molecular dynamics simulation

Abstract

Unlike conventional metal powder based additive manufacturing (AM) technology, a Printing-Debinding-Sintering (PDS) process that adopts polymer-based filaments with highly filled metal particles can be employed as an economical approach to create metal parts at high fabrication rate and a low manufacturing cost. To achieve dense metal parts, the underlying sintering mechanism should be well understood, which has not yet been documented. In this study, molecular dynamics (MD) simulation was conducted to comprehensively unveil the sintering mechanisms during PDS of stainless steel 316L using a novel Fe-Ni-Cr three-element, three-particle sintering configuration. The mechanism of Cr element aggregation at the grain boundaries was revealed by analyzing the evolution of particle structure, diffusion activation energy, and interactions among solute elements during the unique heating process of PDS. In addition, the microstructure of the PDS-built 316L samples was characterized to verify such an aggregation phenomenon. It was found that the self-diffusion coefficient of Cr element increased substantially at the 1600 K holding stage. Meanwhile, Cr element was diffused to grain boundary and formed severe grain boundary aggregation due to its lower diffusion activation energy and stronger interactions between atoms. Moreover, the extra energy released due to this aggregation phenomenon promoted a further coalescence of particles. This study provides an atomic-scale understanding of sintering behavior of PDS-built Fe-based alloys, which paves a way for the multiscale modeling of the sintering process in PDS of other alloy systems.