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

Abstract

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 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.