High-performance lightweight materials are urgently needed because of energy savings and emission reduction. Here, we design a new steel with a low density of 6.41 g/cm³, which is a 20% weight reduction compared to the conventional steel. The mechanical properties and microstructures of the steels prepared with different routes are systematically explored by utilizing uniaxial tensile testing and transmission electron microscopy. The steel processed by cold rolling and recrystallization annealing at 950 °C for 15 min shows an ultra-high yield strength of 1241 ± 10 MPa, while retaining a good ductility of 38 ± 1%. The high yield strength is mainly related to the synergistic precipitation strengthening introduced by nanoscale B2 and κ′-carbides. It is encouraging to notice that the yield strength increased without scarifying ductility, compared to the ST steel. The key reason is that the high strain hardening rate is activated by combined factors, including the blockage of numerous twins and nanoscale B2 to the dislocation movements, and dynamic slip band refinement. This study is instructive for concurrently enhancing the strength and ductility of austenitic lightweight steels with fully recrystallized grains and dual nano-precipitates.

The addition of Co to Ni-based alloys can reduce the stacking fault energy. In this study, a novel Ni-26.6Co-18.4Cr-4.1Mo-2.3Al-0.3Ti-5.4Nb alloy was developed by increasing the Co addition to 26.6 wt.%. A new strategy to break the trade-off between strength and ductility is proposed by introducing dense nanosized precipitations, stacking faults, and nanoscale twins in the as-prepared alloys. The typical characteristics of the deformed alloy include dense dislocations tangles, nanotwins, stacking faults, and Lomer–Cottrell locks. In addition to the pinning effect of the bulky δ precipitates to the grain boundaries, the nanosized γ′ particles with a coherent interface with the matrix show significant precipitation strengthening. As a result, the alloy exhibits a superior combination of yield strength of 1093 MPa and ductility of 29%. At 700 °C, the alloy has a high yield strength of 833 MPa and an ultimate tensile strength of 1024 MPa, while retaining a ductility of 6.3%.

Polycrystalline copper samples were deformed in the range of strain rate between ~10⁻³ and 10⁷ s⁻¹ using a material testing machine, split Hopkinson pressure bar and electric gun. The quasi-static and Hopkinson bar samples were compressed at the strains of 0.1 and 0.4, and the electric gun samples were compressed at the shock pressures of 19, 25, 35 and 49 GPa. The dislocation structure in the recovered samples was determined using high-resolution X-ray line profile analysis. Compared to the quasi-static and Hopkinson bar tests, different characteristics of the evolution of dislocation density and arrangement were found in the planar plate impacts of the electric gun. The correlation between the flow stresses and the dislocation densities in the samples was discussed using the Taylor equation.

In this study, we report a strategy to suppress the formation of large Cu-rich particles by adding excessive interstitial carbon into CuFeMnNi high-entropy alloys. With the increase in C contents in the CuFeMnNi HEAs annealed at 1000 °C, the size and area fraction of the submicron Cu-rich particles markedly decreased. Of note, the CuFeMnNi 1.5 at. %C alloy containing nanosized Cu-rich particles (13 nm) displayed excellent strength–ductility synergy, with yield strength of 695 ± 10 MPa, ultimate tensile strength of 925 ± 20 MPa, and ductility of 21.5%. This is because the addition of carbon significantly increases the diffusion speed of Cu atoms, thereby restraining the growth of Cu-rich nanoparticles. As a result, the comprehensive mechanical properties of the prepared HEAs were significantly enhanced. Additionally, the active diffusion channels induced by high-temperature short-time annealing significantly inhibited the grain growth, which improved the ductility. This work creates a new strategy for solving the dilemma caused by the large Cu-rich particles in the Cu-containing HEAs.