Helium and hydrogen irradiation induced hardening in CLAM steel

• The bulk-equivalent hardness H0irr of the ion irradiated region was discussed by nano-indentation measurement.
• In order to explain the synergistic effects of hydrogen and helium, single-(He+) and sequential-(He+ plus H+ subsequently) irradiation experiments were designed.
• The synergistic effects of hydrogen and helium were analyzed by microstructure investigation.
• The irradiation induced hardening behavior in the steels can be explained by the dispersed barrier hardening model which was consistent with the nano-indentation hardness results.

The irradiation hardening behavior of low activation martensitic steel was investigated by nano-indentation measurements combined with transmission electron microscopy analysis. The steel was irradiated by single-(He+) and sequential-(He+ plus H+ subsequently) ions at 773 K respectively. The continuous hardness (H) vs. depth (h) profiles at shallow depths were given by the continuous stiffness measurement (CSM) which can be analyzed according to Nix–Gao model and film/substrate system hardness model. The nano-indentation hardness results showed that both single-(He+) and sequential-(He+ plus H+ subsequently) irradiated steel exhibited obvious hardening and the hardening level of single-(He+) was higher than that of sequential-(He+ plus H+ subsequently) one. The bulk-equivalent hardness H0irr of the ion irradiated region was obtained by fitting the nano-indentation data using Kasada method. The microstructure analysis indicates that sequential-ion irradiation induced dislocation loops with larger size and smaller number density compared to single-ion irradiation at 773 K. The irradiation induced hardening behavior in the steels subjected to different ion irradiations can be explained by the dispersed barrier hardening model which was consistent with the nano-indentation hardness results.