空孔型欠陥のin situおよび二次元分布計測による金属水素脆化支配欠陥

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The main purpose of this research is to improve the positron annihilation spectroscopy technique, which is the only method for detecting atomic vacancies and to obtain confirmation of the defects thought to be responsible of the hydrogen embrittlement in common metals used in the hydrogen energy infrastructure, that is the vacancy-hydrogen complexes. An in-situ positron annihilation lifetime measurement method in a hydrogen environment, as well as in a hydrogen environment and under tensile stress, was developed and the existence of the vacancy-hydrogen complex, which becomes unstable by room temperature aging due to the hydrogen desorption after unloading, was proved in pure bcc-iron, which has a very large hydrogen diffusion coefficient.A Teflon electrolytic cell was devised for in-situ positron annihilation measurements under electrolytic hydrogen addition and stress loading. Positron lifetime measurements were carried out while charging charging the samples that were strained at fast or slow strain rate up to 25% in a hydrogen environment. The results for the sample strained at fast strain rate showed the formation of vacancy clusters irrespective of the measurements during in-situ hydrogen charge or in air, in accordance with previous studies. On the other hand, in the sample strained at slow strain rate the formation of vacancy-hydrogen complexes was detected during the hydrogen charge. Subsequently, these defects grew into increasingly larger vacancy clusters as a function of aging time in air due to the hydrogen desorption from the sample.