Effect of phosphorus on vacancy-type defect behaviour in electron-irradiated Ni studied by positron annihilation

Abstract

Very dilute Ni–P system (containing 50–240appm phosphorus) irradiated by 5MeV electrons at various temperatures (270–543K) was studied by positron annihilation spectroscopy (PAS) and the electrical resistivity measurements. Under irradiation at 270K (below stage III in Ni), the accumulation of the monovacancies in the Ni–P system is 1.5–2.0 times greater than that in pure Ni irradiated in the same conditions. This fact attests to the strong interaction between P atoms and self-interstitial atoms (SIAs). As a result of the non-mobile SIA–P complexes formation, the mutual recombination of point defects is suppressed and the vacancy accumulation is, respectively, enhanced. During post-irradiation annealing, the vacancy migration induces the transport process of the phosphorus atoms and leads to the formation of the vacancy clusters decorated with P atoms. The annealing behaviour of the defect structures in Ni–P systems after irradiation at enhanced temperatures was also studied. The influence of phosphorus on the formation and further evolution of the vacancy aggregates decrease with increasing of the irradiation temperature.