Positron annihilation spectroscopy characterization of effect of intermetallic nanoparticles on accumulation and annealing of vacancy defects in electron-irradiated Fe–Ni–Al alloy

Abstract

The effect of intermetallic nanoparticles like Ni3Al and nanoparticles of an Fe-rich bcc phase on the evolution of vacancy defects in an fcc Fe–34.2 wt% Ni–5.4 wt% Al model alloy under electron irradiation at elevated temperatures (423 and 573 K) was investigated using positron annihilation spectroscopy. Nanosized (1–8 nm) particles, which are homogeneously distributed in the alloy matrix, cause a several-fold decrease in the accumulation of vacancies as compared to their accumulation in a quenched alloy. This effect depends on the size and the type of nanoparticles. The effect of the nanoparticles increases when the irradiation temperature increases. The irradiation-induced nucleation and the growth of intermetallic nanoparticles were also observed in an alloy pre-aged at 1023 K under irradiation at 573 K. Thus, a quantum-dot-like positron state within ultrafine intermetallic particles, which we revealed earlier, allows control of the evolution of coherent precipitates like Ni3Al, along with vacancy defects, during irradiation and subsequent annealing. Possible mechanisms of the absorption of point defects by nanoparticles are discussed.