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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.