Features of the Electronic Structure of TiC and VN Phases of the Mechanically Alloyed Equimolar TiC-VN Blend

Abstract

The electronic structure of TiC and VN phases, which undergo gradual structural transformations under impact stress at mechanical alloying of the equimolar TiC-VN blend in a high-energy planetary mill, has been studied. Based on the experimental results of the study of the kinetics of phase transformations, three structural models characterizing the flow of this process were proposed and considered. Namely, Ti4C4 and V4N4 phases (TiC and VN) in the initial state; Ti3C4 and V3N4 phases, existing when the maximum fraction of structural vacancies accumulates at the second stage of mechanical alloying; solid solutions of Ti3VC4 and V3TiN4 formed in the final synthesis products. Based on the results of theoretical calculations performed using the linearized muffin-tin orbitals in the plane wave approximation (LMTO PLW) calculations of the density of electronic states (DOS) spectrum were performed and the main parameters of the electronic structure of phases were determined for each of the model proposed. It is shown that near the Fermi level, the total DOS for TiC and VN mainly consists of hybridized 3d states of metals (Ti or V) and 2p states of nonmetals (C or N), which leads to the formation of covalent bonds in the compounds. DOS profiles of the TiC and VN phases, which contain many structural vacancies, are significantly blurred (both the valence and conductivity bands) and contain additional peaks near the Fermi level. These factors indicate a high degree of structural instability, which creates preconditions for further formation of solid solutions. Density of electronic states of (Ti, V) C and (V, Ti) N solid solutions formed are somehow similar to the DOS of the initial compounds. Based on the results of theoretical calculations of the electronic structure parameters and on the data of other authors, it is shown that alloying of TiC with V generally improves its mechanical characteristics. The impact of mechanical alloying is higher on VN phase in the TiC-VN blend than on TiC phase.