Ab initio study on plane defects in zirconium-hydrogen solid solution and zirconium hydride
Ab initio study on plane defects in zirconium-hydrogen solid solution and zirconium hydride
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DOI：
10.1016/j.actamat.2010.03.034
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发表时间：
2010-06-01
期刊：
影响因子：
9.4
通讯作者：
Fuketa, Toyoshi
中科院分区：
文献类型：
--
作者：
Udagawa, Yutaka;Yamaguchi, Masatake;Fuketa, Toyoshi
锆合金的氢脆是导致轻水反应堆燃料包壳机械性能退化的主要原因之一，因此得到了广泛的研究。虽然人们对这种脆化的起源提出了各种猜测，但究竟是氢化物的脆性、氢化物析出物与位错相互作用产生的微裂纹形核，还是氢化物析出物与锆基界面处的空洞形核，目前还不清楚。本研究的目的是通过研究氢化物的断裂性能来阐明脆化的原因。用从头算方法计算了Zr-H体系的表面能伽马(S)和不稳定堆积能伽马(US)。根据氢化物、纯锆固溶体和氢固溶体在伽马(S)和伽马(US)之间的不同，讨论了氢化物的塑性/脆性行为。对于H/Zr比小于0.5时的固溶体，我们得到了单调下降的伽马(S)和伽马(US)，分别比纯锆单调下降了15-34%和50-100%，这表明脆性和塑性都降低了。因此，氢致脆化没有得到证实。另一方面，对于氢化物，我们得到的伽马比纯锆的伽马小25%(S)和大200-300%(US)。这表明，与纯锆相比，由于小伽马(S)和大伽马(US)的协同作用，氢化锆具有极高的脆性，前者意味着容易产生断口，后者意味着位错运动困难。此外，赖斯的延性/脆性参数D在三角洲氢化物中为1.4，表明它比Ir更容易发生脆性断裂，Ir是一种极脆的材料。这些结果似乎足以将锆合金的氢脆本质归因于氢化物的脆性。(C)2010年Acta Materialia Inc.由爱思唯尔有限公司出版。版权所有。
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. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.