Nanoindentation of ion-irradiated reactor pressure vessel steels – model-based interpretation and comparison with neutron irradiation

Abstract

Ion-irradiation-induced hardening is investigated on six selected reactor pressure vessel (RPV) steels. The steels were irradiated with 5 MeV Fe²⁺ ions at fluences ranging from 0.01 to 1.0 displacements per atom (dpa) and the induced hardening of the surface layer was probed with nanoindentation. To separate the indentation size effect and the substrate effect from the irradiation-induced hardness profile, we developed an analytic model with the plastic zone of the indentation approximated as a half sphere. This model allows the actual hardness profile to be retrieved and the measured hardness increase to be assigned to the respective fluence. The obtained values of hardness increase vs. fluence are compared for selected pairs of samples in order to extract effects of the RPV steel composition. We identify hardening effects due to increased levels of copper, manganese-nickel and phosphorous. Further comparison with available neutron-irradiated conditions of the same heats of RPV steels indicates pronounced differences of the considered effects of composition for irradiation with neutrons vs. ions.

Keywords:

• Nanoindentation
• plastic zone
• ion irradiation
• neutron irradiation
• reactor pressure vessel steel
• irradiation hardening

Acknowledgements

The use of HZDR Ion Beam Center facilities and the support by its staff is gratefully acknowledged. We kindly thank H. Hein for supply of unirradiated and neutron-irradiated material ANP-4, F. Gillemot for supply of irradiated material GW8 as well as M. Rossner for sample preparation. The reported research was performed within the EU-project SOTERIA. This project has received funding from the Euratom research and training programme 2014–2018 under Grant Agreement N° 661913.