Impact of the microstructure on the swelling of aluminum alloys: characterization and modelling bases

International audienceSwelling of metals under irradiation is largely studied in the nuclear industry for its impact on the safe and efficient operation of reactors. However, the case of aluminum alloys remains poorly documented as they are exclusively used in nuclear research reactors which operate at lower temperatures than nuclear power plants. Void swelling in aluminum alloys, which results from the cavities induced by the fast neutron flux in reactor, is measurable only at high fluences, for which few measurement points are available. In this study, samples with various quenching rates were used in order to simulate the variations obtainable during the fabrication of large reactor components. A first series of samples were irradiated with heavy ions in single beam (Au$^4+$) to understand the impact of the quenched microstructure on the voids swelling. A second series of samples were irradiated in a triple beam (W$^9+$, He$^+$ and Si$^+$) to simulate the aluminum transmutation occurring inside reactors. Samples were investigated at very fine scale and characterized to understand the key mechanisms of swelling. Then, quantitative measurements of the swelling were performed in each sample. A high dispersion of the swelling values and a higher value are observed after ion irradiation compared to neutron irradiation for a similar irradiation dose, which seems to be related to the very high damage rate created by ion-irradiation. The high dispersion of published swelling values measured after neutron irradiation is interpreted as due to different neutron spectrum conditions because of different positions of the samples in the reactors. Therefore, it appears relevant to complement the description of swelling in aluminum alloys with a modeling approach. Swelling values from the literature were incorporated into a Brailsford & Bullough swelling model for two different damage rates, after estimating the parameters of the model from the literature. This work aims at a better comprehension of the swelling of aluminum alloys both from a quantitative and qualitative point of view and draws the basics requirements for future swelling models