Strain-hardening resilience via the cooperation of geometrically necessary dislocations and deformation twins in a strong and ductile lightweight high-entropy steel

[Display omitted] •A high-entropy steel with duplex microstructure of compositionally complex austenite and D03 intermetallic compounds is developed.•A resilient strain hardening is achieved by the cooperation of geometrically necessary dislocations and deformation twins.•A very high dislocation density of 6.62 × 1015 m−2 is obtained in common tensile test.•This newly-developed duplex high-entropy steel is strong, ductile and lightweight. In the net-zero era, the burgeoning demands within engineering applications require materials that are not only lighter and stronger but also ductile. A robust strain hardening, crucial for achieving high strength and ductility, is challenging due to limited dislocation density evolution. This study discovers a cooperative strain-hardening strategy in a newly designed high-entropy steel (HES) with a density of 6.82 g/cm3. In this lightweight HES, the duplex microstructure of compositionally complex austenite and D03 intermetallic compounds facilitates the interplay between geometrically necessary dislocations (GNDs) and deformation twins (DTs) during plastic deformation. It generates a strain-hardening resilience during deformation and yields a very high dislocation density of 6.62 × 1015 m-2, contributing to strain hardening of over 900 MPa and a large elongation of 47 %. The resilient strain hardening achieved by the GND-DT cooperative strategy can be applied to various heterostructured alloys, offering a pathway for strong and ductile lightweight materials.