Multi-scaled heterostructure enables superior strength–ductility combination of a CoCrFeMnN compositionally-complex alloy

Abstract

Compositionally-complex alloys (CCAs) with the face-centered cubic (fcc) structure exhibit excellent fracture toughness and stable mechanical property across a broad temperature range from cryogenic to room temperatures. However, yield strength of those alloys is usually low, making them difficult to meet the demands of practical engineering application. In a prototype CCA with the nominal chemical composition of Co₁₀Cr₁₀Fe₄₉Mn₃₀N₁ (atom percent), a multi-scaled heterostructure from sample to atomic scales was obtained by performing triaxial cyclic compression and short-term annealing on the blocky alloy. The material exhibits a heterogeneous distribution of strain at the sample scale. At the grain scale, dense twins and twin–twin network, laths featured with local chemical order as well as dislocation cells jointly hinder plastic deformation. At the nanoscale, the chemical order within grains also impedes dislocation motion. During plastic deformation, different sample positions within the heterogeneous material and various regions at each position undergo coordinated deformation, resulting in significant hetero-deformation induced strengthening. Simultaneously, the continuously activated dislocations, stacking faults and nano-twins lead to a high yield strength of 1020 MPa in the material while maintaining a fracture elongation of 30%. This study provides new insights for the design and development of high-performance metallic materials.