Nb掺杂对Ni基合金中γ′→γ″相转变影响的第一原理研究

First-Principle Investigation on Nb Doping Promoting γ′ → γ″ Phase Transformation in Ni-Based Superalloy

摘要:

通过第一原理计算Nb掺杂对γ′-Ni3Al和γ″-Ni3Nb两相形成热、结合能及态密度的影响，研究了Nb掺杂量γ′-Ni3Al和γ″-Ni3Nb两相的合金化行为。结果表明，在γ′-Ni3Al和γ″-Ni3Nb两相共存的熔体中，在Nb掺杂量小于15.625(at%)范围内，与γ″-Ni3Nb相比，γ′-Ni3Al相有较好的稳定性；而Nb掺杂量大于18.75(at%)时，γ″-Ni3Nb相有更大的稳定性。其中，在Nb掺杂15.452--16.34 (at%)范围内，γ′-Ni3Al和γ″-Ni3Nb两相有相近的晶格常数，是使其发生γ′-Ni3Al → γ″-Ni3Nb共格相转变的必要条件。Nb掺杂量大于18.75(at%)后，γ′-Ni3Al和γ″-Ni3Nb两相费米能级处态密度的差值明显增大，γ″-Ni3Nb相稳定性增强。此外，在γ″-Ni3Nb相长大的同时，可发生γ′-Ni3Al相的分解而消失。

Abstract:

By means of first-principles calculating the formation enthalpy, binding energy and states density of γ′-Ni3Al and γ″-Ni3Nb phases, the influence of Nb doping on alloying behaviors of γ′-Ni3Al and γ″-Ni3Nb phases is investigated. Results showed that, in the molten of the γ′-Ni3Al and γ″-Ni3Nb phases, compared to γ″-Ni3Nb phase, the γ′-Ni3Al phase has a lower stability in the range of Nb doping quantity being less than 15.625(at%), but the γ″-Ni3Nb phase has a bigger stability in the range of the Nb doping quantity being more than 18.75(at%). Wherein, the γ′-Ni3Al and γ″-Ni3Nb phases have the close lattice parameters in the range of 15.452-16.34 (at%) of Nb doping, which is thought to be an essential condition of promoting γ′-Ni3Al → γ″-Ni3Nb coherent phases transformation. The difference of the states density in the Femi-level location increases obvious as the quantity of Nb doping is more than 18.75(at%), which enhances the stability of γ″-Ni3Nb phase. Moreover, the decomposition of the γ′-Ni3Al phase occurs at the same time the γ″-Ni3Nb phase growing, which may result in the disappearing of γ′-Ni3Al phase.