First-principles study on a new type of quaternary carbonitride VWCN with outstanding mechanical properties

Abstract

Ceramics with outstanding mechanical properties have great potential applications in industrial fields ranging from cutting tools to scratch and wear resistant films. Here, a new type of transition-metal carbonitride VWCN is proposed by introducing the fourth element W into the ternary V2CN system. The value of valence electron concentration (VEC) per two atoms was tuned to enhance the hardness and the corresponding ideal strengths as well as the electronic stability. By an improved structure searching method, an orthorhombic Pmm2 structure of VWCN was firstly uncovered and verified as its ground-state phase. The relative formation enthalpy calculations show that it is the most energetically favorable phase in the pressure range of 0–300 GPa. The lattice dynamical stability was also checked by the phonon spectrum calculations. The systematic study of mechanical property showed this Pmm2-VWCN not only has a great improvement of hardness value from 23 GPa for V2CN to 35 GPa, but also has a large pure shear strength of 31 GPa. Meanwhile, it also exhibited surprisingly high ductility and toughness relative to V2CN. Electronic analysis revealed that the mechanical enhancement induced by the introduction of the element W mainly stems from the variation of structure and the consequent presence of hybridizations between TM-d and LE-p orbitals, which is also responsible for the minimized EF DOS by exactly separating the bonding and antibonding states.