Open Access to JRC Research Infrastructures Project – Tymofii Khvan
Atomic force microscopy analysis of nanoindents in ion-irradiated Eurofer97
The Open Access project is a supportive investigation under the POLONEZ BIS 3 research. The ultimate goal of the latter is to develop a self-sufficient experimentally computational protocol based on nanoindentation testing, which must combine a set of techniques to qualitatively characterize the effect of ion damage on metallic materials as a surrogate for neutron irradiation.
Steels used in constructing structural components for nuclear reactors exhibit indentation pile-ups during the indentation process. It refers to the phenomenon when a certain amount of material’s volume is pushed out of the indented area. This leads to a distorted imprint shape and an inadequate measure of the mechanical properties. Even though it is possible to apply mathematical corrections to the wrong measurements, detailed inspection of the pile-up shapes can give a deeper insight into the material’s behavior.
Information about the pile-up shapes may serve as a validation resource for computational simulations of the nanoindentation process. The crystal plasticity finite element method (CPFEM), mainly applied in the related research, can imitate the pile-up formation process as it depends on crystal orientations or phases present in the microstructure. Validation of the results of molecular dynamics simulations, also used in the research, is commonly based on the pile-up shapes obtained from microscopy. Both computational approaches are extensively applied at NOMATEN and will benefit from this data, as it can additionally verify the correctness of constitutive parameters. Moreover, an extension of the CPFEM model with strain gradient theory to account for indentation size effects (ISE) (planned in collaboration with the MLC lab at JRC-Petten as a PhD project) can also use the obtained data as an input. ISE directly contributes to the eventual shape and height of a pile-up. It is also known to change with irradiation. Thus, the pile-up formation will be affected as well.
In this Open Access call, we propose to use a combined approach of nanoindentation (performed at NCBJ) and the atomic force microscope (AFM) (available at the MLC lab of JRC) to investigate the nanoindentation imprints on reduced activation ferritic/martensitic steel 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 structural features responsible for radiation hardening. Both materials were irradiated with ions to different damage levels. The shapes of the imprints and their dependence on the irradiation dose, indentation depth or material microstructure are essential in understanding the small scale plasticity properties of metallic materials. This information will be eventually used in development and validation of computational models commonly applied in the research carried at NOMATEN.
