The effect of intermetallic nanoparticles like Ni3Al and nanoparticles of an Fe-rich body-centred cubic phase on the evolution of vacancy defects in an face-centred cubic Fe-34.2Ni-5.4wt%Al model alloy under electron irradiation at 423 and 573K was investigated by using positron annihilation spectroscopy. Nanosized (1 to 8nm) particles, which were 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 depended upon the size and the type of nanoparticles. The effect of the nanoparticles increased when the irradiation temperature increases. The irradiation-induced nucleation and the growth of intermetallic nanoparticles were also observed in an alloy pre-aged at 1023K under irradiation at 573K. Thus, a quantum-dot-like positron state within ultrafine intermetallic particles permitted control of the evolution of coherent precipitates like Ni3Al, along with vacancy defects, during irradiation and subsequent annealing. Possible mechanisms for the absorption of point defects by nanoparticles were considered.

Positron Annihilation Spectroscopy Characterization of Effect of Intermetallic Nanoparticles on Accumulation and Annealing of Vacancy Defects in Electron-Irradiated Fe-Ni-Al Alloy. A.P.Druzhkov, D.A.Perminov, N.L.Pecherkina: Philosophical Magazine, 2008, 88[6], 959-76