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

Khvan Tymofii


Noels Ludovic, (ULg),

SCK•CEN Mentor

Terentyev Dmitry
+32 14 33 31 97

SCK•CEN Co-mentor

Bonny Giovanni
+32 14 33 31 98

Expert group

Structural Materials

PhD started


Short project description

Nano-indentation has been used since 1970th to investigate the fundamental aspects of mechanical behavior because of its ability to probe at the nanometer scale, thus avoiding impact of natural defects present in real-life crystals and delivering their true properties. Nowadays, the application of nano-indentation in nuclear materials science rapidly emerges because: (i) it is non-destructive method allowing to deduce important mechanical characteristics; (ii) it utilizes extremely small volume of probing material; (iii) such compact setup is capable to perform variety of mechanical loads including high temperature testing. Thus, the nano-indentation techniques is proposed to characterize the impact of neutron irradiation on mechanical properties of materials, and in particular to be applied for primary candidates structural materials for future nuclear applications where neutron loads are especially high.

Design and construction of future reactors like ITER or MYRRHA are extremely ambitious projects which have huge impact on engineering science development, industrial engagement and social perception of energy extracted by efficient and safe nuclear operation. Development and qualification of structural materials for these future nuclear systems require one to demonstrate that after neutron irradiation the material mechanical properties sustain at the acceptable safety limit. That's why R&D to design new materials with dedicated microstructure to resist neutron damage are ongoing. Down selection of these innovative materials requires fast, efficient, accurate and financially competitive testing procedures. This is where the nano-indentation techniques (NIT) can play its role.

Thanks to a possibility to probe a volume in a range of one to several micrometers, the NIT enables the usage of accelerated heavy ion irradiation which can be applied to surrogate the neutron damage. Given appropriate irradiation conditions and proven NIT procedure it is possible to speed up the design of new materials tremendously.

The present project concerns with the application of NIT for mechanical testing of structural materials for future fusion and fission applications. It is well known that nano-indentation process involves generation of dislocations from the indenter tip which "probe" the response of a material, expressed through the interaction of those indent-induced dislocations with the actual material microstructure. Thus deducing the "true" properties of the material requires subtracting the deformation induced by indent itself. In each material and depending on test temperature, the indent-induced deformation has a unique pattern. Correspondingly, the process of nano-indentation should be modelled by appropriate tools and which should account for the presence of both original and irradiation induced microstructural defects. This project is dedicated to the development of the expertise on modelling and experimental testing by means of nano-indentation.

The computational model will be developed in collaboration with University of Liege (leading university), whereas experimental NIT measurements will be performed at UCL (partner university). To provide data for validation, SCK-CEN will utilize mechanical/microstructural facilities and computational expertise to assess the impact of irradiation on mechanical properties.


The ultimate scientific objective of the project is to develop and validate the full-scale model for the nano-indentation process of neutron and ion irradiated steels. The relevant irradiation conditions would correspond to the irradiation temperature of 300-550°C and the dose in the range of 1-20 dpa. These conditions correspond to the well-known problem of low-temperature embrittlement (plastic flow instability) and irradiation creep. Currently, SCK-CEN together with OCAS struggle to improve the steels by dedicated thermo-mechanical treatment. Investigation of those steels, including irradiation, will provide valuable contribution to the project.

The computational model is to be developed on the basis of Finite Element (FE) code, in which the crystal plasticity will be used to describe the deformation mechanisms, including the impact of irradiation defects. The model for technologically relevant steels is to be constructed in several steps, starting from pure BCC Fe, moving to Fe-Cr-Carbon system and finally ferritic-martensitic steel. Dedicated tensile tests, assisted by camera recording, will be performed to deduce the true properties of these materials, which will be used as input for the FE model of nano-indentation. Supporting atomistic calculations will be performed to understand the generation of plastic deformation under the indenter tip, where the elasticity theory breaks down. Also, atomistic calculations will be used to assess local rules for the interaction of dislocations with radiation defects and thermal activation.

The validity of the model will be tested using ion irradiated samples (already planned in the R&D programme of SCK-CEN), as well as high temperature NIT (available through collaboration with H2020 M4F project partners). Post-deformation microstructure will also be explored by at SCK-CEN, thanks to the availability of FIB and TEM techniques.

Depending on the success of the model, the prediction of the impact of neutron damage on the mechanical properties and effect of test temperature will be assessed in collaboration with other partners (JRC and CVR) who have access to perform NIT in Hot Cells on neutron irradiated materials. This project will therefore help to clarify up to which extend NIT can support testing of neutron irradiated materials and extracting engineering relevant properties by nano-scale operations.