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

作者：Udagawa Yutaka^*; Yamaguchi Masatake; Abe Hiroaki; Sekimura Naoto; Fuketa Toyoshi

来源：Acta Materialia, 2010, 58(11): 3927-3938.

DOI：10.1016/j.actamat.2010.03.034

• Cladding
• Zircaloy
• Zirconium
• Hydride
• Ab initio

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 gamma(S) and unstable stacking energy gamma(US) of Zr-H systems by using ab initio calculations. The ductile/brittle behavior of the hydride is discussed based on the difference between gamma(S) and gamma(US) 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 gamma(S) and gamma(US), 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 gamma(S) and a 200-300% larger gamma(US) than those in pure zirconium. This indicates that zirconium hydride has an extremely brittle nature due to the synergistic effect of a small gamma(S), implying easy generation of a fracture surface, and large gamma(US), implying a difficulty in dislocation motion, compared with pure zirconium. Furthermore, Rice's ductile/brittle parameter D was 1.4 in the delta-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.

• 出版日期2010-6