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• A new Ni 35 (CoFe) 55 V 5 Nb 5 (at.%) high entropy alloy was developed with an excellent strength and ductility synergy. • A novel L1 2 -Ni 3 Nb nano-precipitate is introduced, which is completely different from the conventional L1 2 -Ni 3 Al and D0 22 -Ni 3 Nb. • First-principles calculations show that some ni and nb atoms are substituted by Co, Fe, and V, and the formation energy of L1 2 -Ni 3 Nb is lower than D0 22 -Ni 3 Nb, forming (Ni 24 Co 18 Fe 6) 3 (Nb 10 V 4 Fe 2) nano-precipitates with an L1 2 crystal structure. • The novel bifunctional nano-precipitates, not only improve the strength by hindering dislocation slip, but also reduce the stacking fault energy of the matrix, changing the deformation mode of the alloy. High-entropy alloys (HEAs) with a single-phased face-centered-cubic structure possess excellent plasticity but generally low strength. Precipitation strengthening is one of the most promising methods to improve the strength of alloys. However, plagued by a nerve-wracking fact that strength-ductility trade-off frequently limits the improvement of alloy properties. To overcome this problem, a new Ni 35 (CoFe) 55 V 5 Nb 5 HEA with an excellent strength and ductility synergy was developed by introducing a novel bifunctional L1 2 -Ni 3 Nb nano-precipitate. This HEA exhibits a high yield strength of 855 MPa, ultimate tensile strength of 1,302 MPa and marvelous elongation of ∼ 50%. First-principles calculations show that the (Ni 24 Co 18 Fe 6) 3 (Nb 10 V 4 Fe 2) nano-precipitate with a L1 2 structure possesses lower formation energy than that with D0 22 structure. The novel nano-precipitates provide two-fold functions. On the one hand, L1 2 -(Ni 24 Co 18 Fe 6) 3 (Nb 10 V 4 Fe 2) nano-precipitates have a high anti-phase boundary energy, contributing to a significant increment in the yield strength through precipitation strengthening. More importantly, the precipitation of the precipitates lowers the stacking fault energy (SFE) of the alloy matrix, contributing to the excellent work-hardening ability and large plasticity through activating the continuous formation of SF networks and Lomer-Cottrell locks during deformation. The strategy to introduce the novel bifunctional nano-precipitates paves a new way to enhance the strength-ductility synergy of alloys. [Display omitted]. [ABSTRACT FROM AUTHOR]

• At a strain rate 3800 s−1, the dual-phase steel shows a high flow strength of 4067 MPa. • The framework structure weakens the local strain within the sample. • High-strain-rate deformation promotes the structure transformation of nanoprecipitates, alleviating strain concentration. High–strain–rate deformation of steels is prone to generating localized adiabatic shear bands (ASB) due to strain localization, leading to plastic instability and fracture. Nanoprecipitate–strengthened austenite–martensite dual–phase (DP) steel is a kind of promising impact–resistant materials due to their high strength and excellent plasticity. In this study, the effects of a combination of nanoprecipitates and the frame structure of DP steels with the hard martensite as the support framework on the dynamic mechanical properties were systematically investigated. The nanoprecipitate–strengthened DP steel exhibited excellent dynamic performance. At a strain rate of 3800 s−1, the maximum flow stress of the DP steel with nanoprecipitates reached ∼ 4067 MPa, which was 1146 MPa higher than its counterpart without nanoprecipitates. High–strain–rate deformation induced the transformation of Cu–rich nanoprecipitates from body–centered cubic (B2) to 9R twin structure, alleviating the stress concentration. Upon high–strain–rate deformation, the high strength of nanoprecipitate–strengthened DP steel induced the formation of a narrow shear band with sever–deformed microstructure. The frame–structure of DP steel restrained the transformation of deformed shear bands (DSB) to transformed shear bands (TSB) due to the deformation–induced martensitic transformation of austenite, delaying the crack formation and propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new Al 16 Fe 10 Cr 20 Ni 24 Co 30 (at. %) HEA has been developed. • The low ductility of the as-cast AC HEA is due to the stress localization. • The partly recrystallized R800 HEA possesses multi-scale heterogeneous two-phase lamellar structure. • B2 nanoprecipitates share the stress and promotes the formation of SFs. Two-phase high-entropy alloys (HEAs) have high strength due to the contribution of interface-dependent strengthening, but the deformation incompatibility between the two phases causes instability. The initiation of cracks occurs at the two-phase interfaces, which ultimately leads to low ductility. To overcome this problem, the strategy proposed in this work is to introduce nanoprecipitates as a buffer zone and simultaneously promote stress release caused by the formation of stacking faults (SFs) at the two-phase interfaces, reducing the stress localization at the two-phase interface, thus improving the ductility. The Al 16 Cr 20 Fe 10 Co 30 Ni 24 HEA was chosen as the model material to evaluate this approach. After rolling at 800 °C, the HEA had a two-phase lamellar structure consisting of a face-centered cubic (FCC) phase and an ordered body-centered cubic BCC (B2) phase. Recrystallization occurred within the FCC phase, and precipitates were present in both the FCC and B2 lamellae. The B2 nanoprecipitates in the FCC phase play the most important role, contributing to the improvement of yield strength and buffering the direct contact between gliding dislocations and the two-phase interface. In addition, the B2 nanoprecipitates also promote the widespread formation of SFs at the two-phase interfaces, leading to stress release. More importantly, nanoprecipitates are nucleation sites for SFs. The formation of an SF network improves the strain-hardening ability. The HEA shows a yield strength of 1,120 MPa and an ultimate tensile strength of 1,540 MPa while still exhibiting an elongation to fracture of ∼25 %. [ABSTRACT FROM AUTHOR]