Towards full-dense high geometric fidelity parts via binder jetting and controlled sintering

This study challenges the conventional metal binder jetting additive manufacturing (BJAM) approach for high-quality part fabrication, proposing a cost-effective alternative with coarse water-atomized powders. The modified AISI-4340 steel powders, with high carbon and oxygen content, underwent BJAM and a two-stage super-solidus liquid phase sintering (SLPS) process, resulting in near-full density, minimal distortion, and exceptionally low surface roughness. The study revealed for the first time that the improved density and surface finish came at the expense of losing fine features due to grain fragmentation and solution-reprecipitation mechanisms. A processing map based on liquid fraction, surface roughness, and relative density was established. It was demonstrated that the sintering conditions can be fine-tuned to preserve fine geometric features while attaining high relative densities of up to 98 %. These findings highlight the importance of such a map for all material systems requiring SLPS for densification, particularly when employing BJAM for net-shape manufacturing of intricate and fine features.