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, which enhance tensile properties. Following vacuum melting and microstructural optimization, the cost-effective FeMnNiCr high-entropy alloy underwent severe cold rolling with reductions of 62% and 75%, achieving a maximum ultimate strength of 1198 MPa. Microstructural analysis of fracture surfaces 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 also estimated to be approximately 35 mJ/m², enabling multiple deformation mechanisms. Microstructural evaluation revealed that dense dislocation walls and twins mainly interact through three processes: partial dislocation accumulation promotes twin formation and the development of the 9R structure; twins on alternating planes create new dislocation paths 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 displays synergistic microstructural features that strengthen it via unique dislocation-twinning interactions.