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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.

First-principles calculations based on the total-energy, all-electron, full-potential linear muffin-tin orbitals method within the local-density approximation have been employed to study the ground-state properties of the ternary intermetallic Ti2AlNb (O phase). The equilibrium volume, cohesive energy, formation energy, and bulk modulus are obtained. The results calculated compare well with the available experimental results. The densities of states and charge-density plots show that the bonding in Ti2AlNb is metallic in nature and has a more covalent bond than in Ti3Al. It is found that Nb atoms decrease the covalent bonding around themselves locally and increase the degree of directional bonding between Ti and Al, which may explain why Ti2AlNb (O phase) enjoys better ductility and fracture toughness than Ti3Al.

The discrete variational method within the framework of density functional theory is used to study the effect of zirconium on the electronic structure of the grain boundary in . The results for the interatomic energies show that the strength of the grain boundary is increased by the substitution of Zr for Al. The calculation of the charge distribution indicates that the directionality of the bonds in the grain boundary region is weakened by the addition of Zr. These results show that the alloying effect of Zr introduced into can significantly improve the ductility of , while strengthening the grain boundary.

The electronic structure of and grain boundaries in containing B are investigated by the use of the discrete variational method. The effects of B on grain boundaries are discussed. The results show that B forms stronger bonding states with its neighbouring host atoms, and it can be expected that the cohesive strength of the grain boundaries will be increased.

Based on our structural model and a tight-binding Hamiltonian the electronic structure has been calculated by use of a recursion method (RM) for two models of the tetragonal DO 22 and the cubic Ll 2 crystal structure in Al 3 Ti + X ( X = Mn , Fe or Cu ) for contrast. The results show that the binary Al 3 Ti is stabilized in the DO 22 structure, and the alloying element (AE) X is found to strongly favor Al site and to promote the stability of the Ll 2 structure, in agreement with the experiment. The transform of the crystal structure from the DO 22 to the Ll 2 may be induced by the constriction of the lattice constant c and the elongation of the lattice constant a after the AE X replaces Al for the DO 22 . The result also shows that the Ll 2 structure in the Al 3 Ti + X alloys has the strong directional bonds which may cause the material to be brittle.

The electronic structure of γ′ phase in nickel-base superalloy containing impurity Zr is studied in the paper. Based on the model presented, we calculated the energy levels, the density of states, the partial-wave local density of states and the charge transfer of the system by use of the SCF-Xα-SW method. We compared the properties of Ni6AlZr with those of Ni6Al2. The result shows that the nonbonding peaks decrease evidently, some new stable bonding orbitals appear in the lower energy region, the unoccupied orbitals move towards high energy region and the energy gap increases, which all indicate that the γ′ phase is intensified and is more stable after Zr instead of Al in the system. The result of charge transfer shows that the Zr atom loses outer electrons, which is of benefit for the Zr atom to dissolve in the γ′ phase.

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.