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Sodium-induced embrittlement of an aluminum grain boundary

机译：钠诱导的铝晶界脆化

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摘要

Primary aluminum produced industrially by electrolysis inevitably contains some sodium which is an undesired impurity element in aluminum alloys as it promotes intergranular fracture. However, the physical origins of Na-induced intergranular embrittlement in aluminum are still unclear. This work provides a comprehensive investigation of the nature of the Na-induced grain-boundary embrittlement in aluminum by means of first-principles calculations with the highly precise full-potential linearized augmented plane-wave method within the framework of the Rice-Wang thermodynamic model and within the method of ab initio tensile test. We introduce a free-surface slab model and determine the grain-boundary and free-surface energies, the most energetically favorable segregation site of Na along the Al grain boundary, its segregation energy to the Al grain boundary, and the possible fracture modes of the grain boundary with Na in the different sites and their corresponding fracture energies. We establish that Na has a large driving force (-0.84 eV/atom) to segregate from Al bulk to the symmetrical grain-boundary core site, and its segregation significantly reduces grainboundary strength. We show that the method using the Rice-Wang thermodynamic model and the method of ab initio tensile test are essentially equivalent and both confirmed that Na is a strong intergranular embrittler with a potency of +0.62 eV/atom. Na segregation leads to grain-boundary expansion and a significant charge density decrease over the whole grain boundary. Analysis in terms of the relaxed atomic and electronic structures and bonding characters shows that the aluminum-sodium bond has ionic character and is weak in both grain-boundary and free-surface environments.
机译：工业上通过电解生产的原铝不可避免地含有一些钠，这是铝合金中不希望的杂质元素，因为它会促进晶间断裂。但是，Na引起的铝晶间脆化的物理起源仍不清楚。这项工作通过在Rice-Wang热力学模型框架内使用高精度全势线性化增强平面波方法进行第一性原理计算，对铝引起的铝引起的晶界脆化的性质进行了全面研究。并从头开始进行拉伸试验。我们引入一个自由表面平板模型，并确定晶界和自由表面能，Na在Al晶界上能量最有利的偏析位点，其到Al晶界的偏析能以及晶界可能的断裂模式。 Na在不同位置的晶界及其相应的断裂能。我们确定，Na具有很大的驱动力（-0.84 eV /原子）从Al块偏析到对称的晶界核心部位，并且其偏析显着降低了晶界强度。我们表明，使用莱斯-旺热力学模型的方法和从头算拉伸试验的方法基本相同，并且都证实Na是一种强晶间脆化剂，效力为+0.62 eV /原子。 Na偏析导致晶界膨胀，整个晶界上的电荷密度显着降低。根据弛豫的原子和电子结构以及键合特性的分析表明，铝-钠键具有离子性，并且在晶界和自由表面环境中均较弱。

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  • 来源
    《Physical review》 |2010年第22期|p.84-100|共17页
  • 作者

    Shengjun Zhang; Oleg Y. Kontsevoi; Arthur J. Freeman; Gregory B. Olson;

  • 作者单位

    Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA;

    Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA;

    Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA,Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA;

    Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA;

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  • 正文语种 eng
  • 中图分类
  • 关键词

    grain and twin boundaries; composition, segregation; defects and impurities;

    机译：晶界和孪晶界;组成;偏析;缺陷和杂质;

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