Fermi energy engineering of enhanced plasticity in high-entropy carbides

Abstract

Mechanical properties of a range of high-entropy rocksalt carbides are investigated via ab-initio modeling and experimental verification. It is found that elastic constants, hardness, and fracture resistance depend on the electronic structure of the system, which is parameterized through two descriptors: the valence electron concentration (VEC) and the integrated density of states from the pseudo-gap energy to the Fermi energy (iDOS(Epg,EF)). Compositions incorporating more electrons (increasing VEC) shift EF further above Epg, filling more deformable metal d-derived t2g bonding orbitals. MoNbTiVWC5, MoNbTaVWC5, CrMoNbVWC5, and CrMoTaVWC5, – stabilizing as a single-phase rocksalt solid solution – each have a VEC ≥ 9.0, an iDOS(Epg, EF) > 5.75 states/cell, and a higher electron abundance than any of the rocksalt binary and ternary carbides. The materials approach the ductility range, achieving an attractive combination of fracture resistance (i.e. enhanced plasticity) and hardness rarely found in ceramic materials. Entropy, allowing high VEC values to be reached within cubic structures, enables a new path for tailoring mechanical properties.