Physics

Grain size

Strengthening mechanisms of materials

Grain boundary strengthening

Ultimate tensile strength

Creep

Strain hardening exponent

Dislocation

Composite material

Flow stress

Metallurgy

Materials science

Slip (aerodynamics)

Ductility (Earth science)

Alloy

Grain boundary

Plasticity

Microstructure

Thermodynamics

Materials Research Letters

An equiatomic VCoNi medium-entropy alloy possesses high sensitivity to grain-boundary strengthening, achieved by severe lattice distortions. Its ultrafine-grain structure enables 1.5 Gigapascal yield strength even for the fully recrystallized alloy with a single face-centered cubic structure. The high density of grain boundaries also generates high back stresses via piling up of massive dislocations, and the low cross-slip probabilities produce not only robust dislocation-mediated plasticity but also high back stress contribution to flow stress, which affords high strain-hardening capability to ultrafine-grain alloys, with 1.7 Gigapascal ultimate tensile strength with remarkable ductility. Our approach provides a new method for developing ultrastrong metallic materials.

Ultra-strong and strain-hardenable ultrafine-grained medium-entropy alloy via enhanced grain-boundary strengthening