Aluminum grain boundary decohesion by dense sodium segregation

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

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Abstract

Despite numerous investigations, grain boundary (GB) embrittlement of metallic structural materials is a poorly understood fundamental phenomenon in materials science. One of the well-known examples is that minute traces of sodium induce an embrittlement in aluminum alloys that results in drastic failure and limits their applications. From first-principles density function theory calculations, we found that sodium atoms densely segregate and neighbor into the 5(012)[100] GB in aluminum with large segregation energies and that the GB strength drops to only one fifth of the strength of the clean Al GB. Gradual sodium segregation leads to not only a large GB expansion but also to the replacement of stronger Al-Al metallic bonds with the weaker Al-Na mixed ionic-metallic bonds and Na-Na metallic bonds. This result in a drastic GB decohesion that reduces the GB tensile strength dramatically until it approaches the strength of bulk sodium. Dense segregation of sodium forms a Na film along the GB and opens an easy channel for oxidation and corrosion along the GB, which further accelerates the intergranular embrittlement.

Original languageEnglish
Article number214109
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume85
Issue number21
DOIs
Publication statusPublished - Jun 8 2012

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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