Ultrastrong Medium‐Entropy Single‐Phase Alloys Designed via Severe Lattice Distortion

• Published in: Advanced materials (Weinheim) Vol. 31; no. 8; pp. e1807142 - n/a
• Main Authors: Sohn, Seok Su, Kwiatkowski da Silva, Alisson, Ikeda, Yuji, Körmann, Fritz, Lu, Wenjun, Choi, Won Seok, Gault, Baptiste, Ponge, Dirk, Neugebauer, Jörg, Raabe, Dierk
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 22.02.2019
• Subjects: ab initio calculation; Alloying elements; atomic bond distances; Chemical bonds; Dislocation pinning; Distortion; Ductility; Entropy; High entropy alloys; lattice distortion; Materials science; medium‐entropy alloys; Structural engineering; Substructures; tensile properties; Variation; Yield strength; Yield stress; ab initio calculation; lattice distortion; tensile properties; medium-entropy alloys; atomic bond distances
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201807142

Severe lattice distortion is a core effect in the design of multiprincipal element alloys with the aim to enhance yield strength, a key indicator in structural engineering. Yet, the yield strength values of medium‐ and high‐entropy alloys investigated so far do not substantially exceed those of conventional alloys owing to the insufficient utilization of lattice distortion. Here it is shown that a simple VCoNi equiatomic medium‐entropy alloy exhibits a near 1 GPa yield strength and good ductility, outperforming conventional solid‐solution alloys. It is demonstrated that a wide fluctuation of the atomic bond distances in such alloys, i.e., severe lattice distortion, improves both yield stress and its sensitivity to grain size. In addition, the dislocation‐mediated plasticity effectively enhances the strength–ductility relationship by generating nanosized dislocation substructures due to massive pinning. The results demonstrate that severe lattice distortion is a key property for identifying extra‐strong materials for structural engineering applications. Ultrastrong VCoNi equiatomic medium‐entropy alloys are developed via severe lattice distortion. The distortion enhances the lattice friction stress and also increases the sensitivity of the yield stress on grain size changes. These design ideas lead to a new alloy with near 1 GPa yield strength despite its precipitation‐free and fully recrystallized fcc structure.