Nanoindentation for sub-miniaturized testing of irradiated materials: FEM analysis and experiments

Materials chosen for the construction of structural components in nuclear reactors require careful selection and characterization, as their operational conditions presume the constant influence of harmful neutron irradiation and high temperatures. It inadvertently degrades the mechanical properties of the material and eventually may lead to the failure of the component. Therefore, we need to ensure that the margin of safety of a material is enough to sustain a certain amount of neutron damage. However, high-temperature neutron irradiation for research purposes is a very expensive, long, and complicated process, so the possibilities of imitating the damage of neutrons by other types of irradiation are of high interest. In this research, we set the goal to substitute complicated neutron irradiation with relatively cheap, fast, and safe (in terms of residual activity) ion irradiation, to analyze its impact on the mechanical properties, and to compare it with existing data done with neutrons. We aim to establish an experimentally computational procedure aimed at the effective characterization of the consequences of ion irradiation as a surrogate for neutron irradiation. This may significantly accelerate the delivery of new research data on structural materials for nuclear applications. The procedure is based on nanoindentation testing, as a highly informative technique to characterize the mechanical properties of materials on the nano-/microscale levels. It is highly useful in testing of thin subsurface regions with variative properties, which is the case for ion irradiation. The performed nanoindentation experiments are used to establish and validate the crystal plasticity finite element model that simulates the nanoindentation deformation process in pure α-iron (as a basic material with a “simple” microstructure) and Eurofer97 reduced activation ferritic/martensitic steel (as the reference material for future fusion and Gen IV reactors), while the latter is in the as-received and ion-irradiated states. Within the project, both materials are experimentally characterized with macro-tensile and nanocompressive deformations; their microstructures are studied excessively using a variety of microscopy techniques. The data obtained are used to establish the constitutive laws of the materials to feed the nanoindentation FEM models. The correct set of the constitutive parameters confirmed experimentally allows us to semi-empirically link the nano-/microscale and macroscale deformations. Moreover, the radiation-modified material laws based on the tensile tests of neutron-irradiated Eurofer97 found in literature have shown a high accuracy in simulations of ion-irradiated material, which points to the interconnection of the two types of radiation-induced damage. Globally, the execution of the proposed research is driven by the substantial complexities of using neutron irradiation for research purposes. The outcoming results are expected to pace the delivery of new research data in the field of nuclear materials and give rise to similar studies. The project shall also positively contribute to the stability of the European energy sector and the accessibility to future stable energy sources.