Ab initio study on plane defects in zirconium-hydrogen solid solution and zirconium hydride

Yutaka Udagawa, Masatake Yamaguchi, Hiroaki Abe, Naoto Sekimura, Toyoshi Fuketa

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)

Abstract

Hydrogen embrittlement of zirconium alloys is one of the main causes of the mechanical degradation of the fuel cladding in light water reactors, and has therefore been extensively studied. Although various conjectures have been proposed as the origin of such embrittlement, it is not known which one plays the most important role: the brittle nature of the hydride, micro-crack nucleation by interaction of hydride precipitates with dislocations or void nucleation at the interface between hydride precipitates and zirconium matrix. The purpose of the present study was to elucidate the origin of the embrittlement by investigating the fracture properties of the hydride. We have evaluated the surface energy γS and unstable stacking energy γUS of Zr-H systems by using ab initio calculations. The ductile/brittle behavior of the hydride is discussed based on the difference between γS and γUS among the hydride, pure zirconium and hydrogen solid solution. For the solid solution at a H/Zr ratio less than 0.5 we obtained a monotonous decrease by 15-34% and 50-100% in γS and γUS, respectively, from those in pure zirconium, indicating a reduction in both brittleness and ductility. Thus, hydrogen-induced embrittlement of the hcp Zr matrix was not confirmed. On the other hand, for the hydride we obtained a 25% smaller γS and a 200-300% larger γUS than those in pure zirconium. This indicates that zirconium hydride has an extremely brittle nature due to the synergistic effect of a small cS, implying easy generation of a fracture surface, and large γUS, implying a difficulty in dislocation motion, compared with pure zirconium. Furthermore, Rice's ductile/brittle parameter D was 1.4 in the d-hydride, indicating that it undergoes brittle fracture more easily than iridium, known as an extremely brittle material. These results seem sufficient to attribute hydrogen embrittlement of zirconium alloys substantially to the brittle nature of the hydride.

Original languageEnglish
Pages (from-to)3927-3938
Number of pages12
JournalActa Materialia
Volume58
Issue number11
DOIs
Publication statusPublished - 2010 Jun

Keywords

  • Ab initio
  • Cladding
  • Hydride
  • Zircaloy
  • Zirconium

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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