PhD Defense | Tymofii Khvan | Nanoindentation for sub-miniaturized testing of irradiated materials: FEM analysis and experiments

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

Materials chosen for constructing 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 undesirably degrades the material mechanical properties 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, the high temperature neutron irradiation for the research purposes is very expensive, long and complicated process, so the possibilities to imitate the damage of neutrons by other types of irradiation are in high interest. In this research we set a goal to substitute the complicated neutron irradiation by relatively cheap, fast and safe (in terms of residual activity) ion irradiation, analyze its impact on the mechanical properties, and to compare with the existing data done with neutrons. We target to establish an experimentally-computational procedure aimed on 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 done on structural materials for nuclear applications. The procedure is based on the nanoindentation testing, as a very informative technique to characterize the mechanical properties of materials on the nano-/microscale levels. It is highly useful in testing of thin sub-surface 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 simulating the nanoindentation deformation process in pure α-iron (as a basic material with “simple” microstructure) and Eurofer97 reduced activation ferritic/martensitic steel (as the reference material for future fusion and Gen IV reactors), whereas the latter is in the as-received and ion-irradiated states.

Within the project, both materials are experimentally characterized with macro-tensile and nano-compressive deformations; their microstructures are excessively studied using a variety of microscopy techniques. The obtained data is used to establish the materials’ constitutive laws to feed the nanoindentation FEM models. The correct set of the constitutive parameters confirmed experimentally allows us to semi-empirically link the nano/micro- 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 on the interconnection of the both types of the radiation-induced damage.

Globally, the execution of the proposed research is driven by the substantial complexities to use neutron irradiation for the research purposes. It is expected, that the outcoming results will pace the delivery of new research data in nuclear materials field, and give a rise of similar studies. The project shall also positively contribute to the stability of the European energy sector and accessibility to the future stable energy sources.

Promotor:

• Ludovic Noels (ULiège)

SCK CEN mentors:

• Dmitry Terentyev (SCK CEN)

• Giovanni Bonny (SCK CEN)

Click here for a list of obtained PhD degrees.