Suppression of radiation damage microstructure in aluminum by trace impurities

Abstract

The elements Ag, Ca, Fe, In, Mg, Ni, Si, Sn, and Zn at a concentration of 100 at ppm have little or no effects on damage microstructure in aluminum irradiated with neutrons to doses up to 2.6 dpa at 0.37 T m . The elements Cr, Cu, Mn, Ti, V, and Zr at the 100 at ppm level retard formation of voids and dislocations; Mg and Si suppress damage at higher concentrations. The effective elements reduce the concentrations of voids rather than the void sizes. Fine precipitates occur in all damage structures, some of which are probably transmutation-produced Si of which up to 1000 at ppm was created. In some alloys where voids are suppressed the precipitates are of a plate-like form on a scale and distribution similar to those of earlier loops. Copious, bulky precipitation occurs in Al-Zn alloys with no correlated suppression of voids. There is no correlation of damage suppression with atomic size or with abnormal thermal diffusion coefficients. All elements that retard void formation have solid solubility limits close to 100 at ppm at the irradiation temperature, and for the most part are known to decrease the lattice parameter of aluminum and to have much larger binding energies with interstitial atoms than with vacancies. These conditions are consistent with damage suppression models involving trapping of interstitial atoms by elements with negative lattice misfit.