Mobility of lattice vacancies in iron

Abstract

Abstract Three series of experiments to measure the mobility of vacancies in iron have been performed with a high-voltage electron microscope. The temperature dependence of the growth speed of interstitial-type dislocation loops during electron irradiation between 400°C and 860°C indicates an energy of 0·62 ±0·07 eV, and this is assigned to one half of the migration activation energy of a single vacancy, namely 1·24·0·14 eV. The annihilation of electron–radiation–induced vacancies U detected by the shrinkage and disappearance of interstitial clusters during post–irradiation annealing at temperatures between 270°C and 350°C. The temperature dependence of the process yields the energy of 1–47 ± 0·05 eV. The extent of the annihilation of deformation-induced vacancies is detected by the variation of interstitial cluster formation by electron irradiation. This annihilation process gives the same energy, 1·50 ±0·08 eV, and the same annealing half–time as those in the annihilation process of the radiation–induced vacancies. The energy is assigned to the dissociation prooess of divacancies. The difficulty for migration of divacancies in iron is deduced during the analysis of the above three experiments. The temperature dependenoe of vacancy cluster formation by the electron–radiation–induced motion of single vacancies indicates this difficult motion of divacancies.