5d过渡金属在Ni_3Al中掺杂效应的第一性原理研究

First-Principles Study of Doping Effects of 5d Transition Metal in Ni_3Al

5d过渡金属Hf、Ta、W、Re、Ir被广泛地应用于第4、5代镍基单晶高温合金中,但对于其机理却没有系统的理论研究。采用基于密度泛函理论(density functional theory)的第一性原理平面波超软赝势方法研究5d过渡金属Hf、Ta、W、Re、Ir掺杂镍基单晶高温合金γ′-Ni3Al相前后系统的晶格常数、形成热、结合能、态密度、差分电荷密度及电荷布局。计算结果表明:5d过渡金属Hf、Ta、W、Re、Ir掺杂Ni3Al系统后有优先占据Al原子位置的倾向,且与周围的Ni 3d电子和Al 3p电子发生强烈的轨道杂化,使电子被束缚,离域性变小,峰变窄;掺杂前系统中主要是Ni原子与最近的Al原子之间的共价键作用,掺杂后系统中主要是Ni原子与最近的X原子(Hf、Ta、W、Re、Ir)之间的共价键作用,且随原子序数的增大共价键逐渐增强。

5d transition metal Hf, Ta, W, Re and Ir is widely used in Ni-based single-crystal （SC） superalloys of the fourth and fifth generation, but for the mechanism, there is no theoretical and comprehensive research. Equilibrium lattice constant, formation enthalpy, cohesive energy, density of states, electron density difference and electronic populations of the pure and the 5d transition metals Hf, Ta, W, Re and Ir doped Ni3Al were studied by the plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculations show that the occupational site of 5d transition metals Hf, Ta, W, R and Ir are of the AI site after doping; strongly orbital hybridization between the orbital electron of Ni 3d and Al 3p occur after Hf, Ta, W, Re, Ir doping, which lead to the bound electrons, smaller delocalization and narrower peak; Ni atoms and the first nearest neighbor AI atoms are covalent bonds in pure Ni3Al; however, Ni atoms and the first nearest neighbor X（Hf, Ta, W, Re, Ir） atoms are covalent bonds, which are gradually increased with the enlargement of atomic number of 5d transition metals.