In-situ tailoring microstructures to promote strength-ductility synergy in laser powder bed fusion of NiCoCr medium-entropy alloy

Laser powder bed fusion (LPBF) has received widespread attention owing to its digital, flexible, and controllable fabrication process, which opens new possibilities for the direct and fast production of metal components with extremely complex geometries and good performance. Generally, post-treatments are conducted to further regulate the microstructure and performance of as-deposited geometrically-complex metal components. In this work, instead of applying post-treatments, we demonstrate a novel in-situ remelting strategy to effectively enhance the strength without sacrificing the ductility of LPBF-fabricated NiCoCr medium-entropy alloy by in-process tailoring microstructures. We find that in-situ remelting processing not only changes the melt pool ge-ometry in favor of optimizing densification and developing unique crystallographic lamellar microstructures, but also promotes inherent thermal distortions and heat treatments during manufacturing resulting in increased dislocation density and grain refinement in the LPBF-remelted specimen. The present work paves a new way in additively manufacturing metal materials to tailor microstructures for enhanced mechanical performance without additional treatments.