Investigation of the effects of He bubbles on the nucleation, growth and thermal stability of Al–Cu nanoprecipitates in ion implanted Al foils

Abstract

The effects of He bubbles on the thermal evolution of θ ′ Al 2Cu precipitates in Al matrix are investigated. The Al–Cu precipitates and the He bubbles were produced at the same depth region (≈200 nm below the sample surface) by Cu + and He + ion implantation followed by furnace annealing in vacuum at temperatures of 200, 250 and 280 °C for 2–5 h. The Cu and He concentration–depth profiles were determined by Rutherford backscattering and elastic recoil detection analysis, respectively. The precipitates and bubbles morphologies were examined by means of transmission electron microscopy. It is demonstrated that the presence of He bubbles reduces the nucleation and the growth rate of the precipitates. Both effects are discussed taking into account that the processes of (a) precipitate nucleation, (b) diffusion interaction between precipitates and (c) precipitate growth/dissolution are affected by the decrease of the local vacancy concentration in the matrix, which is caused by the formation and the thermal relaxation of the bubble system. Based on the above results He implantation is proposed as an alternative tool to control the mean sizes of precipitate systems.