Characterization of hydrogen-induced defects in iron by positron annihilation

Abstract

Lattice defects in hydrogen-charged iron have been characterized by the positron annihilation technique (PAT). In annealed and hydrogen-charged specimens, the mean positron lifetime τ¯ and the Doppler broadening lineshape parameter S increased with an increase in the charging time and charging current density. Both saturated, however, at τ¯s = 172 ps, which was larger than the saturation lifetime τ¯s = 166 ps of cold-worked specimens. For all the cold-worked and hydrogen-charged specimens, τmacr; and S were increased by hydrogen charging even in heavily cold-worked specimens, τmacr; and S were increased by hydrogen charging even in heavily cold-worked specimens, where the two PAT parameters were saturated. These suggest that vacancy clusters are introduced during hydrogen charging. According to the PAT results, the vacancy cluster should contain 50 or more vacancies. The estimated concentration of the vacancy clusters in the 10 % cold-rolled and hydrogen-charged specimens was of the order of 1016 cm-3.