Correlations between nano twins–dislocation cells and strength in a severely rolled Fe-based FeMnNiCr high-entropy alloy

This study investigates the formation of nano twins and dislocation cells at grain boundaries, enhancing tensile strength. After vacuum melting and microstructural optimization, the cost-effective FeMnNiCr high-entropy alloy was severely cold-rolled by 62% and 75%, reaching an ultimate strength of 1198 MPa. Fracture analysis from tensile tests showed both ductile and brittle features, with flat areas and dimples of various sizes and shapes. The alloy’s stacking fault energy was estimated to be 35 mJ·m⁻², allowing multiple deformation mechanisms. Microstructural analysis indicated that dense dislocation walls and twins mainly interact through three processes: partial dislocation accumulation promotes twin formation and the creation of the 9R structure (comprised of partials on every third (111) plane); twins on alternating planes generate new dislocation pathways or form Lomer-Cottrell locks; primary stacking faults at boundaries are constrained by 9R and twin structures as they pass through dislocation walls. Overall, the alloy exhibits synergistic microstructures that enhance the strength through unique dislocation–twinning interactions.