【摘要】 钨作为一种重要的核材料,在辐射环境下的微观演化行为与自间隙原子缺陷的扩散行为密切相关.研究不同构型自间隙原子的扩散行为有助于全面理解材料的微观演化过程.本文采用分子动力学方法重点考察了钨中具有不同构型的双自间隙原子随温度变化的扩散行为.结果表明:彼此互为最近邻的<111>双自间隙原子,随着温度的升高,从一维扩散演变成三维扩散,在<111>方向保持稳定的最近邻结构;次近邻<111>双自间隙原子在一定温度范围内沿<111>方向一维扩散,当温度高于600 K将解离成两个独立运动的自间隙原子;而三近邻结构在温度高于300 K就将解离.非平行结构的双自间隙原子在一定温度范围内形成固着性结构,几乎不移动,但在温度高于1000 K时将转化成移动性缺陷.通过将微动弹性带算法获得的自间隙原子迁移能与阿伦尼乌斯关系拟合的结果进行对比,表明了钨中单自间隙原子和双自间隙原子的扩散系数随温度的变化规律不适于用阿伦尼乌斯关系来描述,而线性关系则能合理地描述这一规律.更多还原

【Abstract】 Tungsten, due to its desirable properties(high melting point, low sputtering coefficient, good irradiation resistance etc.), is considered as a promising candidate for the plasma facing materials in future nuclear fusion reactors. Therefore, it will work in extremely harsh environments because it is subjected to the bombadement of high-flux plasma particles and the irradiation of high energy neutrons, resulting in vacancies and interstitials.The migration behavior of self-interstitial atoms is one of the most important factors determining the microstructure evolution in irradiated metals because it will greatly affect the mechanical properties of materials. The study of the diffusion behavior of di-interstitials with different configurations contributes to a better understanding of the self-interstitial atom behavior in tungsten. Despite the inherent difficulty in experimental approaches, atomistic simulation provides an effective means of investigating the defect evolution in materials. In this paper, based on the newly developed interatomic potential for W-W interaction, the diffusion behavior of self-interstitial atoms in tungsten is studied by molecular dynamics simulation. This work focuses on the investigation of the diffusion behavior of di-interstitials with different configurations at different temperatures. The obtained results show that the di-interstitials with the first nearest neighbor configuration presents the one-dimensional migration in the <111> direction at temperatures below 1400 K. As the temperature increases, it makes rotations from one(111>-to other(111)-directions. Thus migration of diinterstitial atoms with the first nearest neighbor configuration exhibits a change in mechanism from onedimensional to three-dimensional migration, keeping the stable <111> configuration in the whole investigated temperature range. The migration of di-interstitial atoms with the second nearest neighbor configuration is onedimensional along the(111> direction within a certain temperature range. When the temperature is above 600 K,the di-interstitial atoms will dissociate into two individual self-interstitial atoms and move independently.However, the migration of di-interstitial atoms with the third nearest neighbor configuration dissociates at a temperature just above 300 K. The non-parallel self-interstitial atoms form a sessile configuration within a certain temperature range. Once the sessile cluster is formed it can hardly move. Interestingly, it will transform into mobile defect when the temperature is higher than 1000 K. By comparing the migration energy values of these configurations obtained by nudged elastic band method with those of the Arrhenius fits, we find that the diffusivity for each of single-and di-interstitial atoms in tungsten is a linear function of temperature rather than Arrhenius as usually assumed.更多还原