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The effects of Re, W and Co on dislocation nucleation at the crack tip in Ni have been studied by the molecular dynamics method. The results show that the activation energy of dislocation nucleation is lowered by the addition of Re, W and Co; moreover, the activation energy decreases when the alloying element increases from 1 at.% to 2 at.%. The energy landscapes of the atoms are studied to elucidate these effects. Quantification analyses of the bonding strength between Ni and X (X = Re, W or Co) reveal that strong bonding between Ni and X (X = Re, W or Co) in the dislocation nucleation process can suppress the cleavage process and enhance the ability of dislocation nucleation. The surface energy and unstable stacking fault energy are also calculated to understand the alloying effects on the dislocation nucleation process. The results imply that interaction between alloying elements and Ni atoms plays a role in promoting the dislocation nucleation process at the crack tip. The ability of Re, W and Co in improving the ductility of the Ni crack system is in the order W > Re > Co. The results could provide useful information in the design of Ni-based superalloys.

A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ'+2γ to 10γ'+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer's thickness. A Ni/Ni3Al multilayer with 10γ'+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young's modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ' phase volume fraction are calculated by varying the proportion of the γ and γ' phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt–Reuss–Hill rule of mixtures.

Local density functional is investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method for ScN in the hexagonal structure and the rocksalt structure and for hexagonal structures linking a layered hexagonal phase with wurtzite structure along a homogeneous strain transition path. It is found that the wurtzite ScN is unstable and the layered hexagonal phase, labelled as ho, in which atoms are approximately fivefold coordinated, is metastable, and the rocksalt ScN is stable. The electronic structure, the physical properties of the intermediate structures and the energy band structure along the transition are presented. It is found that the band gaps change from 4.0 to 1.0 eV continuously when c/a value varies from 1.68 to 1.26. It is noticeable that the study of ScN provides an opportunity to apply this kind of material (in wurtzite[h]-derived phase).

Based on our structural model and a tight-binding Hamiltonian the electronic structure of the superconductor YBa{sub 2}Cu{sub 3}O{sub 7} has been calculated by the use of a recursion method. Compared with the single crystal, we mainly analyzed the feature of the electronic structure showing the twin boundary and evaluated the probability of various configurations of Cu and O ions, the type of the hybridization bonds, and various (Cu-O){sup +} complexes in superconducting ceramics. Meanwhile, we indicate that the twin boundary may be closely related to an electron deficiency.

CO adsorption on small Aun (n = 1 — 7) clusters which are supported by a partially reduced rutile TiO2(110) surface has been investigated by the first-principles method. The low coordinated sites of Au clusters are favorable for CO adsorption. CO—Aun—TiO2 system displays surface magnetism. There is a strong interaction between the adsorbed CO molecule and the supported Au clusters.

Based on the tight-binding bond recursion method, the energetics parameters of ∑3[111] grain boundary in nickel are investigated. The theoretical results indicate that the boron enhances interatomic energy between the host atoms, and between impurity and nickel atoms. Calculations of the energy of the grain boundary segregation show that boron, nitrogen, and phosphorus have the tendency to segregate onto the grain boundary and segregation property of boron is stronger than that of nitrogen and phosphorus.

Based on Gauss’ principle of least constraint and Nosé-Hoover thermostat formulation, the numerical algorithms for molecular dynamics simulation are developed to investigate the properties of grain boundary in transition metals Fe and Ni at finite temperature. By the appropriate choice of heat bath parameter, a constant temperature version can be realized. A series of parameters are introduced to describe quantitatively the crystallographic characteristic and the distortion of structure unit. The results indicate the applicability of the calculation mode developed by us and reveal the feature of the atomic structure of grain boundary at finite temperature.

Based on related experiments, in this paper a model is presented to study the electronic structure of an impurity--stacking-fault complex. Using the tight-binding Hamiltonian and recursion method, we have calculated the electronic structure of systems containing an impurity--stacking-fault complex. Based on the calculation of the structural energy, the relation between impurity and stacking-fault energy was given. It found that impurity oxygen increased the stacking-fault energy of the Ni system, whereas impurity Fe decreased it markedly, which has been proved by our electron-microscope experiments. Calculations of the partial-wave integral local density of states for atoms give information on the local charge transfer and hybridized orbital.

The electronic structure of a boron-iron alloy was investigated theoretically by the self-consistent-field X\ensuremath{\alpha} scattered-wave method. A model cluster containing the light-impurity\char21{}vacancy complex B-V-B was presented for consideration of the effect of size, the character of the chemical bond, and other related experimental facts. Energy levels, density of states, partial-wave local density of states, transition states, and one-electron properties such as charge distribution and the Hellmann-Feynman force have been obtained. Based on the calculation, the concept of the ``efficient neighbor'' as a result of local structure was introduced. The calculation shows that the B-V-B model reflects the effect of the light impurity boron in the B-Fe alloy system, explains the mechanism of the B-V-B complex in the host, and indicates that the effect of the B-V-B complex is very localized.