含Nb或Ge的锆合金表面氧吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 研究了纯锆表面和含Nb或Ge锆合金表面上氧的吸附性质. 结果表明, Nb和Ge对Zr(0001), (1120)和(1010)表面吸附性质的影响各不相同. 根据计算得到的偏聚能结果, Nb和Ge迁移到Zr(0001)表面比迁移到其他两个表面更容易, 而Nb和Ge 都可以降低Zr(0001)表面对氧原子的吸附能力, 因此这两种元素都能抑制锆合金的初始氧化. 进一步的电子结构分析发现, Nb和Ge改变表面对氧原子的吸附能力是通过改变表面d能带的分布来实现的.     

Effect of Ni and vacancy concentration on initial formation of Cu precipitate in Fe–Cu–Ni ternary alloys by molecular dynamics simulation

In the present work, the effects of Ni atoms and vacancy concentrations(0.1%, 0.5%, 1.0%) on the formation process of Cu solute clusters are investigated for Fe–1.24%Cu–0.62%Ni alloys by molecular dynamics(MD) simulations. The presence of Ni is beneficial to the nucleation of Cu precipitates and has little effect on coarsening rate in the later stage of aging. This result is caused by reducing the diffusion coefficient of Cu clusters and the dynamic migration of Ni atoms. Additionally, there are little effects of Ni on Cu precipitates as the vacancy concentration reaches up to 1.0%,thereby explaining the embrittlement for reactor pressure vessel(RPV) steel. As a result, the findings can hopefully provide the important information about the essential mechanism of Cu cluster formation and a better understanding of ageing phenomenon of RPV steel. Furthermore, these original results are analyzed with a simple model of Cu diffusion, which suggests that the same behavior could be observed in Cu-containing alloys.     

First principles calculations of relationship between the Cu surface states and relaxations

In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu(100), Cu(110), and Cu(111) surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.