Investigation of mechanical and electronic properties of a novel quaternary transition-metal nitride Ti0.25W0.25V0.25Ta0.25N

Multi-element transition-metal nitrides possessing combinations of outstanding mechanical and physical properties have attracted increasing attention due to its potential applications. Here, a new transition-metal nitride alloying four metal elements of Ti, W, V and Ta is proposed, in which the doping ratios of these four metal elements are equal. Using an improved structure searching method, the potential structures with low enthalpies were fully explored. An orthorhombic structure was firstly disclosed and verified to be its ground-state phase. It is the most energetically favorable structure in the pressure of 0∼100 GPa. The phonon spectrum calculations demonstrated its lattice dynamical stability. Systematic study of its mechanical properties showed the orthorhombic structure not only possessed a large hardness of 32.4 GPa but also behaved a large indentation shear strength of about 30 GPa, greatly exceeding its well-known fcc-B1 phase (about 15 GPa). Meanwhile, we also compared the orthorhombic phase to its disordered structure within B1 phase by generating special quasirandom structures (SQS) with a 3 × 3 × 3 supercell (216 atoms), which can be viewed as its high-entropy phase. The results displayed this SQS system had comparable hardness and strength but greatly improved ductility and toughness relative to the ordered B1 phase.