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

• Main Authors: Jeong Min Park, Dae Cheol Yang, Han-Jin Kim, Dong Geun Kim, Sunghak Lee, Hyoung Seop Kim, Seok Su Sohn
• Format: Article
• Language: English
• Published: Taylor & Francis Group 2021-07-01
• Series: Materials Research Letters
• Subjects: medium-entropy alloy; severe plastic deformation; ultrafine grain structure; severe lattice distortion; grain boundary strengthening
• Online Access: http://dx.doi.org/10.1080/21663831.2021.1913768

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.