Quantum Chemistry Calculation On Cermet Of Fe_xAl_y System

Metals and ceramic materials are two important ingredients in the developmentof materials. However, the performance of a single material can not meet the demandof properties. Composite materials is one of the major directions of research materials,cermets have received increasing attention because they have a high-intensity, highhardness, wear resistance, resistance to high temperature, and antioxidant properties,as well as chemical stability, plastic and metal toughness.We can understand the nature of various physical properties of solids bystudying their electronic structures. Solids are composed of numerous atoms and eachatom has a nucleus and some electrons. If we write the Schrodinger equation of thismany-particle system and solve it, we can understand many properties of solid. But itis not practical to solve the Schrodinger equation of a many-particle system like thisdirectly and we must make some simplifications and approximations. We can separatethe electronic motion and the nuclear motion by the adiabatic approximation(Born-Oppenheimer approximation) and simplify the many-electron equation toone-electron equation by Hartree-Fock method. But the correlation interactionbetween electrons is not included in this method. The more strict description to thesimplification from many-electron equation to one-electron is the density functionaltheory (DFT). In the framework of DFT, we can get the detail expressions of thefunctional of the exchange-correlation interaction by local density approximation(LDA), local spin density approximation (LSDA), generalized gradientapproximation (GGA) and so on. The wave function of the electron is usuallyexpanded by one set of basis. Solving the coefficients of the expansion, we can getthe solution of the one-electron Schrodinger equation.The relations between composition, structure, chemical bond and property ofTiC,Al₂O₃,Fe_xAl_y,TiC/Fe_xAl_y and Al₂O₃/Fe_xAl_y are studied using density functiontheory and discrete variation method (DFT-DVM). In the figure of TiC DOS, Ti 3dmainly contributes to the conduction band. C 2p peak is in the valence band, but moreintensive peak is in the conduction band. In Al₂O₃, the valence band is mainlycontributed by O 2p, and the conduction band is mainly contributed by Al 3p. InFe_xAl_y, Fe 3d contributions are in the vicinity of the Fermi level within -4 to 2eV, Al3p peak is in the valence band in Fe₃Al, but in the conduction band in FeAl.The ionic bonds become weak, and the covalent is strong gradually from the single phase of TiC, FeAl or Fe₃Al, to composite TiC/FeAl or TiC/Fe₃Al. Theinteraction of the orbital and the covalent bond of TiC/Fe₃Al are stronger than thoseof TiC/FeAl. The results are consistent with the experiment of bending strength andet al when the content or Al increases in the TiC/Fe-Al system.TiC/Fe_xAl_y doped by M atoms(M=Mo, Ni) are studied using DFT-DVM. Thecorrelation among composition, electronic structure, chemical bond and property hasalso been studied. All the atoms charge has been reduced in the TiC compositedoping series. The strengths of covalent bonds mainly decrease in TiC doped by Matoms from Mo to Ni, and the results are consistent with the experiment of hardnessand et al in the TiC doped series.