The formation of bubbles in Zr alloys under Kr ion irradiation

We report here a study of Kr ion implantation and resultant bubble formation in Zr and Zr alloys, including Zircaloy-2 and Zircaloy-4. Implantations into thin foils were performed in-situ in the HVEM/Tandem facility at Argonne National Laboratory at temperatures between 300 to 800°C and to doses up to 2 X 10²⁰ ion m^-2. Bulk specimens were implanted in an ion-beam chamber and then thinned for viewing by TEM. In thin foils, only small bubbles (3-10 nm) were formed at all temperatures with the exception of the Cr-rich Valloy where 13 nm bubbles were formed. Bulk samples implanted at 300°C contained a bubble morphology similar to that observed after implantation into thin foils. However at high temperatures (500-800°C) large faceted bubbles (up to 30 nm) were produced in bulk specimens. The results indicate that bubble formation and evolution below 500°C is controlled by gas concentration, while it is controlled by bubble mobility at high temperatures.