Nb在Ni3Al中取代行为及合金化效应的第一性原理研究

摘要

采用基于第一性原理的平面波赝势方法,研究了Nb原子在Ni3Al中的格点取代行为及合金化效应.通过对不同原子被置换后体系的形成热、结合能及电子态密度的计算和比较,发现Nb原子倾向于取代Ni3Al中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Nb原子的取代行为,对Nb原子占据的格点以松散或紧凑分布下体系的总能、形成热、结合能以及电子态密度进行了计算,结果表明Nb原子占据的格点更倾向于紧凑分布.为了研究Nb对Ni3Al的合金化效应,对Nb原子占据体系的结合能,电子态密度和电荷密度进行了计算,结果表明Nb原子的加入能提高Ni3Al的稳定性.研究表明,Nb在Ni3Al中的极限固溶度介于6.25at%-12.5at%之间.%By using the first-principles plane-wave pseudopotential method based on the density functional theory, substitution behavior and alloying effect of Nb in Ni3Al are studied.The analyses of the formation enthalpies, the cohesive energies and the densities of states of systems with different substitution behaviors show that Nb prefers to occupy the Al site.The site preference is determined primarily by the electronic structure, and the calculated result is in good agreement with the experimental result.In order to further study the site preference, the occupied sites are divided into being of relaxed distribution and unrelaxed distribution, which are two different distributions.The calculations of total energy, the formation enthalpy, the cohesive energy and the density of states of system indicate that Nb has a preference for unrelaxed distribution.In order to study the alloying effect of Nb in Ni3Al, the calculations of cohesive energy, density of states of system and electronic charge density indicate that Nb in Ni3Al could increase the stability of the alloy.The study also indicates that the limited solubility of Nb in Ni3Al lie between6.25at ％ and 12.5at ％.