Fe-Cr-Ni合金中点缺陷形成及相互作用的第一性原理研究

First-principles study of the formation and interaction of point defects in Fe-Ni-Cr alloys

304NG奥氏体不锈钢由于具有良好的力学性能和耐腐蚀性,被广泛应用于核电工业. 304NG奥氏体不锈钢受辐照会产生多种点缺陷,进而影响材料力学性能.为了研究304NG奥氏体不锈钢中点缺陷的产生机理,以面心立方Fe-Cr-Ni合金为模型,利用基于密度泛函理论的第一性原理方法研究了多种点缺陷结构的晶格常数,形成能,结合能,扩散迁移及相互作用,并计算了γ-Fe中相应的的性质作为对照.研究结果表明:Fe空位和Fe-Fe <100>哑铃是Fe-Cr-Ni合金中容易形成的点缺陷.基于对这两种点缺陷的迁移能垒分析,发现Fe-Fe <100>哑铃要比空位更易迁移.相互作用能的计算表明在Fe-Cr-Ni合金中相邻Fe空位存在吸引作用,会促进孔洞的形成;Fe空位-Fe-Fe <100>哑铃及Fe空位-Fe-Cr <100>哑铃均存在较弱的排斥作用,此外,在第一、二近邻位置的八面体间隙Fe原子都会和空位结合,使体系恢复为完整晶胞.

304 NG austenitic stainless steel is widely used in nuclear power industry because of its good mechanical properties and corrosion resistance. 304 NG austenitic stainless steel irradiated will produce many kinds of point defects, which will affect the mechanical properties of the material. In order to study the formation mechanism of point defects in 304 NG austenitic stainless steel, the lattice constants, formation energies, binding energies, migration barriers and interactions of various point defect structures are calculated by the first-principles method based on density functional theory in FCC Fe-Cr-Ni alloys, and the corresponding properties in γ-Fe are calculated as a comparison. The results show that Fe vacancy and Fe-Fe <100> dumbbell are easy to form in Fe-Cr-Ni alloys. Based on the analysis of the migration barriers of the two kinds of point defects, it is learnt that Fe-Fe <100> dumbbell is easier to migrate than the Fe vacancy in Fe-Cr-Ni alloys. The calculation of point defects interaction energies show that there is an attractive interaction between adjacent vacancies in Fe-Cr Ni-alloys, which can promote the formation of voids;there is a weak repulsive interaction between Fe vacancy-Fe-Fe <100> dumbbell and Fe vacancy-Fe-Cr <100> dumbbell, and Fe atoms in the octahedral interstitial sites in both the first-nearest-neighbor shell and the second-nearest-neighbor shell enter into vacancy and let the structure become a complete crystal cells.