中文摘要：

运用基于密度泛函理论的第一性原理方法计算了Nb掺杂γ-TiAl金属间化合物的结构参数、能带结构、电子态密度及弹性常数.结果表明：Nb替代Ti掺杂相比Nb替代Al掺杂的形成能低,Nb在替位掺杂时更倾向于取代Ti原子形成稳定的结构,Nb替代Ti掺杂能够提高γ-TiAl金属间化合物的抵御塑性变形能力、断裂强度和延展性;与Nb替代Ti掺杂相比,Nb替代Al掺杂同样增强γ-TiAl金属间化合物的断裂强度且其增强延展性的效果更好,但抵御塑性变形的能力有所削弱.

英文摘要：

This investigation aims at an Nb-doped γ-TiAl intermetallic compound system in which part of Ti or Al atoms are substituted by Nb atoms. The structural parameters, the energy band structures, the electronic densities of states and the elastic constants of Nb-doped γ-TiAl intermetallic compound are calculated and studied by using the first-principles method based on the density functional theory and other physical theory. The first-principle calculations presented here are based on electronic density-functional theory framework. The ultrasoft pseudopotentials and a plane-wave basis set with a cut-off energy of 320 eV are used. The generalized gradient approximation refined by Perdew and Zunger is employed for determining the exchange-correlation energy. Brillouin zone is set to be within 3 × 3 × 3 k point mesh generated by the Monkhorst-Pack scheme. The self-consistent convergence of total energy is at 1.0 × 10~（-6） eV/atom.In view of geometry optimization, it is shown that doping with Nb can change the structural symmetry of the γ-TiAl intermetallic compound. The calculated formation energies indicate that the formation energy of the system in which Ti atom is replaced by Nb atom is smaller than that of Al atom replaced by Nb atom. Accordingly, they tend to substitute Ti atom when Nb atoms are introduced into the γ-TiAl system. The calculated band structures of Nb-dopedγ-TiAl system show that they all have metallic conductivities, which implies that the brittleness of γ-TiAl intermetallic compound could be tailored by Nb-doping. The partial densities of states of the Nb-doped and pure γ-TiAl systems indicate that the intensity of covalent bond between Ti atom and Nb atom is weaker than covalent bond between Ti atom and Al atom while the Ti atoms are replaced by Nb atoms in the γ-TiAl system. What is more, the density of states near Fermi energy increases after Al atoms has been replaced by Nb atoms in the γ-TiAl system. This is an important factor for improving the ductility of γ-TiAl intermetall