In-Situ Tailoring Microstructures to Promote Strength-Ductility Synergy in Laser Powder Bed Fusion of Nicocr Medium-Entropy Alloy

Abstract

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. For as-deposited geometrically-complex metal components, post-treatments such as hot isostatic pressing (HIP) and heat treatments are commonly applied to further regulate microstructure and performance while preserving the component integrity. However, completely eliminating internal deposition defects is still a challenge for these post-treatments. Meanwhile, post-treated metal components suffer the strength-ductility tradeoff, especially treated at high temperatures, which may cancel the advantages of LPBF owing to the elimination of unique hierarchical microstructures. In this work, we demonstrate a novel in-situ remelting strategy to effectively enhance the strength without sacrificing the ductility of LPBF-fabricated NiCoCr alloy by in-process tailoring microstructures during printing. The obtained microstructures not only achieve densification and grain refinement without sacrificing heterogeneous microstructures but also possess unique crystallographic lamellar textures (CLM) and increased dislocation density. In-depth analyses revealed the formation mechanism of the tailored microstructures by focusing on the changes in the melt pool geometry, inherent thermal history and thermal distortions owing to the in-situ remelting. The present work paves a new way in additively manufacturing metal materials to tailoring microstructures for enhanced mechanical performance without additional treatments.

Keywords: Laser powder bed fusion, medium-entropy alloy, laser remelting, in-situ tailoring microstructures, strength-ductility synergy