The paper presents a statistical study of nanoindentation results obtained in seven European laboratories which have joined a round robin exercise to assess methods for the evaluation of indentation size effects. The study focuses on the characterization of ferritic/martensitic steels T91 and Eurofer97, envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various final indentation depths, force-controlled single cycle and force-controlled progressive multi-cycle measurements using Berkovich indenters at room temperature have been combined to calculate the indentation hardness and the elastic modulus as a function of depth applying the Oliver and Pharr method. Intra- and inter-laboratory variabilities have been evaluated. Elastic modulus corrections have been applied to the hardness data to compensate for materials related systematic errors, like pile-up behaviour, which is not accounted for by the Oliver and Pharr theory, and other sources of instrumental or methodological bias. The correction modifies the statistical hardness profiles and allows determining more reliable indentation size effects.
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This research also contributes to the Joint Programme on Nuclear Materials (JPNM) of the European Energy Research Alliance (EERA), in particular to the EERA JPNM pilot project NINA – NanoIndentation for Nuclear Applications.This work has received funding from the Euratom research and training programme 2014–2018 under grant agreement No. 755039 (M4F project) and has been supported by the EURATOM Direct Actions.
- small scale testing
- indentation size effect
- ferritic/martensitic steel