Plastically deformable and transformable B2 intermetallic phase enabling extraordinary strength-ductility synergy in eutectic high-entropy alloy

The B2-type intermetallic compound plays a critical role in strengthening the eutectic high-entropy alloys (EHEAs). However, their ductilities are usually sacrificed due to the intrinsic brittleness of the B2 phase. To address this long-standing issue, here we designed a new EHEA strengthened by plastically deformable and transformable B2 intermetallic phase via thermodynamic calculations. This newly designed EHEA exhibits a superior uniform elongation of 24.2±1.6%, while maintaining a high strength of 1,380±30 MPa and an exceptional strain-hardening exponent of 0.56. Such excellent strength-ductility synergy is attributed to the dynamic activations of multiple cooperative deformation behaviors. With the increase of tensile strain, the deformation structure in the FCC phase gradually evolved from dislocations to stacking-fault networks and microbands. More importantly, the B2-intermetallic phase, which is usually considered a brittle intermetallic phase, also underwent distinct plastic deformation stages, including the activation of multiple slip systems, the transformation from B2 to L1 0 phase, and the significant twining behavior inside the L1 0 phase. These unique behaviors collectively contribute to the sustained and steady plastic deformation without early cracking and the achievement of an ultrahigh strain-hardening response. This study not only addresses the intrinsic brittleness issue of the B2 phase but also provides fundamental insights into the innovative design of ultrastrong and ductile EHEAs and other multiphase metallic materials.