Fine-grain-embedded dislocation-cell structures for high strength and ductility in additively manufactured steels

Abstract

Metals manufactured with either a fine-grained structure or a nano-grained structure possess the ultrahigh strength at the expense of ductility. Therefore, materials that combine high strength and ductility should be immediately manufactured for a wide variety of practical applications. In this study, we report a bulk stainless steel with fine grains embedded by dislocation cells using additive manufacturing (AM) methods, which can efficiently and economically manufacture complex structures to achieve the desired mechanical properties. Compared with conventionally cast and forged 316L steels, the average yield strength and tensile elongation of AM 316L steels are 170% and 45% higher, respectively, attributed to a synergistic deformation of the fine-grain-embedded dislocation-cell structures. High strength is expected from a block of dislocation cells and solute atoms to the planar slip of dislocations, whereas high ductility depends upon the slip of fine-grain boundaries associated with the altered shape of an embedded dislocation cell. Moreover, as deformation proceeds, the complex interlaced dislocation cell network structure and deformation twinning can further enhance work hardening as well as tensile elongation. This study proposes a fine-grain-embedded dislocation-cell structure to achieve high-strength-and-ductility materials.