Mechanistic understanding of microstructure evolution in extrusion-based additive manufacturing of stainless steel using modeling, simulation, and experimental analysis

Extrusion-based additive manufacturing (AM) has been widely adopted as a cost-effective approach to building metal materials for engineering applications. The final microstructure and properties are strongly dependent on the post-processing, e.g., debinding and sintering, of the as-printed part. In this study, the structure evolution at a microscopic length scale during this extrusion-based AM process was understood by discrete element modeling, simulation, and experimental validation. In the simulation three groups of stainless-steel particles were placed with different distribution patterns by imposing different packing strategies. By considering both surface and grain boundary diffusion mechanisms during modeling and simulation, the microstructural evolution, including pore size reduction and grain growth were revealed. Effects of particle distribution patterns on the grain and pore morphology during sintering have also been uncovered. The simulation results were experimentally validated by characterizing stainless steel specimens at different sintering stages through X-ray computed tomography and microscopies, indicating their good alignment with the realistic microstructure evolution. The research findings from this study provide valuable insights into unique sintering behaviors affected by AM and guide the process optimization for metal alloys fabricated through the extrusion-based sintering-assisted AM process.