| 研究実績の概要 |
The primary scope of this research is to determine the lattice defects responsible for hydrogen embrittlement in metallic materials, that are relevant in the hydrogen infrastructure, by in-situ measurements in a hydrogen environment and under application of tensile stress using newly developed experimental methods based on positron annihilation spectroscopy.
An experimental system was developed using a specific electrolytic cell that allows in-situ positron annihilation measurements under stress loading while charging hydrogen. Hydrogen-induced defects in pure iron strained under constant stress were successfully identified and their changes over time were tracked. In pure iron under conditions of high hydrogen susceptibility, the formation of vacancy-hydrogen complexes and their growth process into vacancy clusters by aging in air was observed for the first time.
In addition, using a high-intensity positron beam, the formation and time dynamics of hydrogen-induced defects in pure nickel was measured by high-speed positron lifetime measurements. Monovacancy-size defects were detected immediately after hydrogen charge, which indicates that vacancy-hydrogen complexes were formed just by hydrogen addition. Upon room temperature aging, the complexes gradually disappeared and vacancy clusters were formed, which increased in size. Hydrogen desorption from the complexes leads to mobile vacancies which agglomerate into increasingly larger clusters. These vacancies are thought to play an important role in the hydrogen embrittlement of nickel.
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