Open Access to JRC Research Infrastructures Project – Tymofii Khvan

Nanoindentation Testing of Ion-Irradiated Eurofer97: Supportive Microstructural Analysis Using Atomic Force Microscopy

Ion irradiation may serve as a tool for mimicking the impact of neutron irradiation on the mechanical properties of materials. However, the limited penetrating ability of ions requires sophisticated methods to correctly test the modified properties. Commonly applied nanoindentation testing is an informative method, however, highly sensitive to a variety of conditions. Reduced activation ferritic/martensitic (RAFM) steels chosen to construct structural components of nuclear reactors exhibit indentation pile-ups during the indentation process. It refers to the phenomenon in which a certain amount of material volume is displaced out of the indented area. This leads to a distorted imprint shape and an inadequate measure of mechanical properties. Although mathematical corrections can be applied to wrong measurements, detailed inspection of pile-up shapes can give a deeper insight into the behavior of the material during the microscale deformation process. It is known that the effect of irradiation additionally affects pile-up formation and may reveal certain trends in the performance of the irradiated material. Moreover, the knowledge about the piling-up process can serve as a validation resource for computational simulations of the nanoindentation process. The crystal plasticity finite element method (CPFEM), widely applied in related research, can mimic the pile-up formation process because it depends on the crystal orientations or phases present in the microstructure. Furthermore, the validation of the results of molecular dynamics simulations is commonly based on pile-up shapes obtained from microscopy. Both computational approaches are widely applied at NOMATEN and will benefit from these data.

This project is to be held as a collaboration between NOMATEN and Joint Research Center of the European Commission in Petten, the Netherlands (JRC-Petten), under the Open Access call. It is planned to observe the nanoindentation imprints using an atomic force microscope in ion-irradiated Eurofer97. Since Eurofer97 has a complex microstructure, we plan to additionally investigate a model material serving as a basis for Eurofer97: Fe9Cr. This approach will allow us to progress with the microstructural complexity; hence, we will isolate the structural features responsible for the irradiation hardening. Nanoindentation testing was applied under a set of conditions, using different forces and indented shapes. This information will eventually be used in the development and validation of computational models commonly applied in the research carried out at NOMATEN.