Co掺杂对γ′-Ni3Al相稳定性影响的第一性原理研究

The Effect of Co-doping on the Stability of γ′-Ni3Al: A First-principles Study

摘要:

基于密度泛函理论的平面波赝势方法,从原子尺度研究了Co原子掺杂对γ′-Ni3Al晶体结构稳定性的影响。首先通过数值优化与实验结果对比选取了最佳工艺参数,计算了Co原子掺杂前后晶胞的晶体结构、体系的总能量、形成热、结合能及电子态密度和电荷密度,进而分析了体系结构的成键特性和稳定性。计算结果表明：Co原子取代Al原子位置后晶胞结构更稳定；掺杂前后在-10 eV到费米能级的低能级区域,Co、Ni原子的3d轨道与Al原子的s、p轨道发生了强烈的轨道杂化,且原子间的电荷转移量明显增加,使得掺杂后化合物的共价键性增强；与取代Ni原子相比,在费米能级低能级处Co原子取代Al原子时成键电子数增加,其周围价电子相互作用增强,形成的合金体系稳定性提高。最后采用高温长时时效实验对计算结果进行了验证。

Abstract:

In this work, first-principles density functional theory was applied to investigate the effect of Co-doping on the stability of γ′ -Ni3Al. The optimal parameters were determined by comparing the simulations and experimental results. Based on the plane wave pseudopotential method, the crystal structure, total energy, formation enthalpy, cohesive energy, electronic density of states and electron density difference of γ′-Ni3Al phases were calculated, which was used to analyze the stability and bonding characteristics of the crystal structure. The calculation results indicate that the structure of unit cell is more stable after the Al atom is replaced by Co atom. In the range from -10 eV to Fermi energy, the orbital hybridization among Co (Ni) 3d electrons and Al s, p electrons occurs, and the charge transfer among atoms increases obviously, which enhances the covalent bonding in doped γ′ phases. When the Co atom replaces the Al atom instead of the Ni atom, the number of bonding electrons increases at low Fermi energy, and surrounding valence electron interactions are enhanced, so the stability γ′ -Ni3Al phase will be improved. Finally, the simulation results were confirmed by long time aging heat treatment experiments of Inconel 718 alloy.