Intermetallic compounds, usually hard and brittle in nature, have long been an important constituent phase in various metallic materials. Their sizes play the pivotal role in work hardening for ductility. Fine precipitates can induce high ductility, while their large-sized counterparts are just the opposite, inevitably decreasing ductility susceptible to breakage. Here, we propose to deploy a heterogeneous grain structure (HGS) with large-sized intermetallic compounds to overcome the bottleneck of low ductility. We work with an equiatomic multi-principal element VCoNi alloy of low stacking fault energy, with the face-centered cubic (FCC)-structured grains as the matrix and the large-sized kappa (κ) intermetallic compounds of volume fraction of 26 % as the second phase. The FCC grains are designed as a two-level HGS through an incomplete grain growth during recrystallization annealing, spanning ultrafine-grains (size <1 μm) and fine grains (1–5 μm). Upon tensile straining, the HGS is dynamically reinforced by the evolution of ultrafine grains due to the change of twin boundaries into high-angle boundaries. Furthermore, the HGS produces the geometrically-necessary dislocations especially for the hetero-deformation-induced work hardening. The synergistic work hardening is obtained by forest dislocation-mediated hardening and geometrically-necessary dislocations-based hardening, along with strain partitioning between FCC phase and κ phase. As such, the HGS achieves a respectable ductility of 21% at an ultrahigh yield strength of 1.8 GPa that would normally require the nano-precipitation. Our results offer a feasible solution to a superior synergy of high ductility and high strength by means of the HGS strategy in a microstructure typically containing large-sized intermetallic compounds.

Intermetallic compounds, usually hard and brittle in nature, have long been an important constituent phase in various metallic materials. Their sizes play the pivotal role in work hardening for ductility. Fine precipitates can induce high ductility, while their large-sized counterparts are just the opposite, inevitably decreasing ductility susceptible to breakage. Here, we propose to deploy a heterogeneous grain structure (HGS) with large-sized intermetallic compounds to overcome the bottleneck of low ductility. We work with an equiatomic multi-principal element VCoNi alloy of low stacking fault energy, with the face-centered cubic (FCC)-structured grains as the matrix and the large-sized kappa (κ) intermetallic compounds of volume fraction of 26 % as the second phase. The FCC grains are designed as a two-level HGS through an incomplete grain growth during recrystallization annealing, spanning ultrafine-grains (size <1 μm) and fine grains (1–5 μm). Upon tensile straining, the HGS is dynamically reinforced by the evolution of ultrafine grains due to the change of twin boundaries into high-angle boundaries. Furthermore, the HGS produces the geometrically-necessary dislocations especially for the hetero-deformation-induced work hardening. The synergistic work hardening is obtained by forest dislocation-mediated hardening and geometrically-necessary dislocations-based hardening, along with strain partitioning between FCC phase and κ phase. As such, the HGS achieves a respectable ductility of 21% at an ultrahigh yield strength of 1.8 GPa that would normally require the nano-precipitation. Our results offer a feasible solution to a superior synergy of high ductility and high strength by means of the HGS strategy in a microstructure typically containing large-sized intermetallic compounds.