Phase transformation within dynamically refined microbands inducing ultrahigh and sustained strain hardening in high-entropy alloys containing L1₂ precipitates

Metallic materials exhibiting ultrahigh strength coupled with exceptional ductility play a pivotal role in advanced industries, yet enhancing strength typically sacrifices strain hardening and ductility. This study presents a strategy that activated an innovative deformation mechanism to overcome the long-standing trade-off between strength and ductility in an L1 ₂-strengthened Al ₅Ti ₈(FeCoNi) _86.9B _0.1 high-entropy alloy. After aging at 765 °C for 4 hours, the alloy achieved a yield strength of 1227 MPa, an ultimate tensile strength of 1742 MPa, and an elongation of 39.9%, attributed to the ultrahigh and sustained strain hardening induced by phase transformation within dynamically refined microbands during deformation. Our findings indicated that FCC→BCC transformation within the microbands was more favorable in an FCC matrix with a larger width. Furthermore, a high density of superlattice intrinsic stacking faults and Lomer-Cottrell locks in L1 ₂ phase were formed, leading to additional strain hardening of the alloy. The synergistic interaction between phase transformation and microband formation offers a promising approach for designing novel high-performance alloys with exceptional strength and ductility.