The first-principles study on the mechanical and electronic properties about rim phase and hard phase of Ti(C,N) based cermets

The first-principle total energy calculations based on density functional theory and ultrasoft pseudopotentials were carried out, within the generalized gradient approximation (GGA) for the exchange and correlation potential, to investigate the mechanical and electronic properties of hard phase (TiC, TiN and TiC0.75N0.25), inner rim phase (Ti0.75Mo0.25C and Ti0.75W0.25C) and outer rim phase (Ti0.75Mo0.25C0.75N0.25 and Ti0.75W0.25C0.75N0.25). According to the formation energy, all the compounds are stable and hard phase possesses the best stability with the largest formation energy and the minimum lattice parameters. Molybdenum and tungsten are observed significantly to increase the bulk modulus B, Young's modulus E, Poisson's ratio υ and B/G, namely, the rim phase has the better above properties than those of hard phase. From the analysis of B/G, Poisson's ratio and calculated hardness, comparing with hard phase, the rim phase possesses the better ductility and lower hardness. Based on the electronic properties of these compounds, the higher hardness for hard phase may attribute to the interactions between Ti-3d and non-metal (C or N) 2p electrons, meanwhile, the relatively low hardness of rim phase may be the results of some metallic d-d interactions near the Fermi level.