On the shrinkage of neutron irradiation-induced cavities in Eurofer97 steel upon heating

ABSTRACT

By employing in situ transmission electron microscopy (TEM) observation and cluster dynamics (CD) simulations, we studied the annealing behaviours of neutron irradiation-induced cavities in reduced activation ferritic/martensitic (RAFM) steel Eurofer97 subjected to heating up to 550 °C. Experimental results showed that the cavities behaved differently from the general coarsening behaviours of cavities formed by ion implantations. Rapid shrinkage of some cavities was observed when heating temperatures exceeded 500 °C. Three types of cavity annealing behaviours were identified: (i) cavity remained stable; (ii) cavity shrank to a smaller size and then kept stable; (iii) cavity shrank and eventually disappeared. The CD simulations, which were based on the rate theory, well reproduced these experimental observations. It was revealed that the shrinkage course can be terminated by the dramatic rise of helium density (helium/vacancy ratio) inside the shrinking cavity. Cavity stopping shrinkage and being stable at high temperatures, without being annealed out, potentially suggests the modification in cavity coarsening kinetics driven by the conventional Ostwald ripening mechanism.

KEYWORDS:

• Neutron irradiation
• cavity shrinkage
• heating
• in situ TEM
• CD simulation

Acknowledgments

The authors would like to thank all the members of the fusion materials laboratory (FML) of the Karlsruhe Institute of Technology (KIT), Germany for their help in handling irradiated materials. This work is supported by the Helmholtz Association of German Research Centers (HGF) and has been carried out within the framework of Nuclear Fusion Programme at KIT. Also, this work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme under grant agreement No. 101052200.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Euratom Research and Training Programme [grant number 101052200]; Helmholtz Association of German Research Centers (HGF).