Revealing the deformation mechanisms of an additively manufactured medium entropy alloy with extended dislocation-dominated cellular structures

Rapid solidification cellular structures in additively manufactured metallic materials have attracted considerable interest for their contribution to enhanced mechanical properties. In low-stacking fault energy (SFE) alloys, however, where extended dislocations dominate the cellular structure, the underlying formation mechanism and its influence on deformation behavior remain unclear. Here, we report a dislocation configuration, characterized by spatially dispersed stacking fault networks in a medium entropy alloy fabricated by laser powder bed fusion (LPBF), that enables a high strength-ductility synergy. The deformation mechanisms are investigated via weak-beam dark-field transmission electron microscopy. Our results demonstrate that the low SFE (∼21 mJ/m²) promotes the development of cellular structures dominated by extended dislocations, with their spatial distribution controlled by dislocation dynamics. Cellular structures act as preferential nucleation and extension sites for deformation faults, facilitating the formation of stacking fault ribbons (SFRs) and promoting faulting-induced plasticity. These cellular structures also facilitate the early activation of deformation twins (DTs). The high frequency of stacking fault interactions produces multiple types of stacking fault structures enriched with sessile stair-rod dislocations, thereby effectively enhancing dislocation storage and strain hardening capacity. The contributions of SFRs, DTs, and dislocation distribution to the strain hardening are also discussed. These findings provide fundamental insights into the role of dislocation configurations in the deformation mechanisms of additively manufactured alloys and offer a pathway for optimizing mechanical properties through dislocation engineering.