2021 Fiscal Year Research-status Report
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
| Project/Area Number |
21K04627
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| Research Institution | Chiba University |
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Principal Investigator |
Chiari Luca 千葉大学, 大学院工学研究院, 助教 (20794572)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | 水素脆化 / 空孔型欠陥 / 金属 / その場測定 |
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| Outline of Annual Research Achievements |
The main objective of this research is to detect the dominant lattice defects of the hydrogen embrittlement mechanism in the common structural materials used in the hydrogen infrastructure by advancing the current empirical techniques that make use of positron annihilation spectroscopy.
Using a high-speed positron lifetime measuring device, changes over time in the hydrogen-induced defects in hydrogen-charged pure Fe and Ni were measured to track the growth behavior of atomic vacancies. The generation of a large concentration of hydrogen-induced vacancies immediately after hydrogen charge was confirmed. These defects are thought to originate from the trapping and binding of hydrogen atoms with atomic vacancies during the hydrogen charging process, that is the formation of vacancy-hydrogen complexes. The time dynamics during aging at room temperature was recorded on the order of minutes and the agglomeration process of those vacancies into increasingly larger vacancy clusters with time was observed to last for up to several hours. This clustering process is attributed to the gradual desorption of hydrogen from the vacancy-hydrogen complexes, which leave unstable monovacancies that eventually cluster into large vacancies.
These results proved experimentally the formation of vacancy-hydrogen complexes during the hydrogen charge of pure metals. These results represent a significant step forward in the understanding of the role of the vacancy-hydrogen complexes as the dominant lattice defects of the hydrogen embrittlement mechanism in structural metals.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Overall, the current status of this research is evaluated to be progressing rather smoothly. The implementation of the research plan for the first year is considered to have been carried out on time and according to the originally planned schedule, as described in the project research proposal.
The interaction of hydrogen with lattice defects was elucidated in pure metals, that make up the structural materials of the hydrogen infrastructure, after addition of hydrogen by cathodic electrolysis. The formation of vacancy-hydrogen complexes in these materials upon hydrogen charge was demonstrated empirically for the first time. Subsequently, the role of these vacancy-hydrogen complexes in the formation of hydrogen-induced vacancies in pure materials was investigated during aging at room temperature. The crucial importance of the vacancy-hydrogen complexes as the precursors of the vacancy clusters was confirmed. The results of these experiments are very important in terms of the understanding of the generation and behavior of vacancies in hydrogen-charged metals.
The measurements followed in detail the original plan described in the research proposal. The results obtained so far are very satisfactory and overall confirm the outcomes anticipated in the research proposal.
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| Strategy for Future Research Activity |
The plan for the remaining two years of the research project is anticipated to continue as scheduled and outlined in the research proposal. In particular, the plan of the second stage of the project is progressing according to the schedule and we are planning to conduct it out as detailed in the research project description.
In the remainder of this project, we aim to empirically prove that the accumulation of the vacancy-hydrogen complexes in high-strain regions, such as grain boundaries, are the defects responsible for the hydrogen embrittlement in structural materials, such as iron-based alloys. With that purpose in mind, we are planning to further advance the current empirical techniques for the detection of atomic defects by in-situ measurements using positron annihilation spectroscopy.
The vacancy-hydrogen complex is considered to be a hydrogen/stress-induced defect, but becomes unstable due to hydrogen desorption after unloading or in a hydrogen-free environment. Therefore, to prevent the defect species from changing during the measurement time, we will develop a positron lifetime measurement set-up in a hydrogen + stress environment to directly tackle the vacancy-hydrogen complex.
In addition, we will demonstrate the local accumulation of atomic vacancies in a hydrogen-embrittled material using a positron probe microanalyzer by obtaining a two-dimensional defect mapping. By varying the chemical composition and structure of the samples and the experimental conditions, we will elucidate the causal relationship between the defect behavior and the hydrogen embrittlement.
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| Causes of Carryover |
In the first fiscal year of the research project, high-speed measurements of the change over time in the hydrogen-induced defects were conducted. Because of the current restrictions on the implementation of international joint research, the measurements could be mainly accomplished without great expenditures in the purchase of new equipment. In addition, the direct costs that had been planned to cover the travel expenses for joint research and the attendance of academic conferences could not be used because of the current overseas travel restrictions due to the ongoing pandemic and the holding of academic conferences online.
The incurring amount will be fully used in the remaining fiscal years of the project, by purchasing the new equipment needed to carry out the in-situ measurements under hydrogen + stress loading environment and the two-dimensional mapping of defects, as detailed at points (1) and (3) of the description of the research proposal. In addition, should the conditions for travel improve, part of the incurring amount will be used to attend international and domestic conferences, and/or international joint research.
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Research Products
(10 results)
