Vacancy migration in α-iron investigated using in situ high-voltage electron microscopy

ABSTRACT

Modeling the microstructural evolution of irradiated materials requires knowledge of the migration energies of point defects, which results from energetic particle radiation. Herein, we measured the growth rate of self-interstitial atom (SIA) clusters in electron-irradiated α-iron at 275–320 K using in situ high-voltage electron microscopy. To improve the statistical accuracy of the measurement, we used photographic films and video data. This enabled analysis of a considerable amount of data by extracting several SIA clusters and tracking their size growth using image processing techniques. By fitting the temperature-dependent cluster growth rate to the Arrhenius relations derived using rate theory analysis, we obtained vacancy migration energy of $0.52\pm 0.03$ eV. The validity of the estimation method was confirmed from the consistency of the dependence of the damage rate on the cluster growth rate using the applied rate theory analysis. We also investigated the possible roles of faster motion of tri-vacancies compared to those of mono- and di-vacancies, as demonstrated by first-principles calculations, on the obtained migration energy using a kinetic analysis model. In addition, the effects of impurities leading to decrease in the cluster growth rate were briefly discussed.

KEYWORDS:

• Migration energy
• vacancy
• interstitial atom cluster
• in situ observation
• high-voltage electron microscopy

Acknowledgments

We are grateful to Messrs. K. Ohkubo, T. Tanioka, R. Oota, and Y. Yamanouchi of the High Voltage Electron Microscopy Center at Hokkaido University for their technical support in the electron irradiation experiments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported in part by the Technology Transfer Initiative (TTI) research project (2016, 2017), Center for Advanced Research of Energy Materials, Faculty of Engineering, Hokkaido University, “Advanced Characterization Nanotechnology Platform, Nanotechnology Platform Program (MEXT)” of the High Voltage Electron Microscope Laboratory at Hokkaido University, “Interorganization Atomic Energy Research Program” of the Universities-Japan Atomic Energy Agency Joint Research Project, and JSPS KAKENHI Grant Numbers 15K06663, 17K07021, 19K05334.