The present work investigates the irradiation hardening of Fe-based model ferritic alloys after Fe-ion irradiation experiments in order to deduce mechanistically based nominal hardness from the nano-indentation tests on the ion-irradiated surface. Ion-irradiation experiments were carried out at 290 °C with 6.4 MeV Fe3+ ions. The constant stiffness measurement (CSM) was used to obtain the depth-profile of hardness. The results has been analyzed and discussed based on the Nix-Gao model and an extended film/substrate system hardness model. The depth-sensing nano-indentation techniques with CSM revealed that the hardness gradient of the unirradiated Fe-based model alloy can be explained through the indentation size effect (ISE). On the other hand, the gradient of ion-irradiated surface of these samples includes not only the ISE but also softer substrate effect (SSE). We propose a new approach to evaluate a nominal hardness, which may connect to the bulk hardness, from experimentally obtained nano-hardness depth profile data.
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