Round Robin into Best Practices for the Determination of Indentation Size Effects

Abstract

The paper presents a statistical study of nanoindentation results obtained in seven European laboratories that 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.

Depth-Sensing Hardness Measurements to Probe Hardening Behaviour and Dynamic Strain Ageing Effects of Iron during Tensile Pre-Deformation

“…This has been confirmed by AFM ( Figure 5 and Figure 6 ). The mismatch between observed and predicted strength data can largely be reconciled by the application of an elastic modulus correction (EMC) procedure [ 24 ].…”

“…This has been accomplished by applying an elastic modulus correction (EMC). While in recent previous work the EMC served the correction of various sources of biases of data from multiple sources (round robin testing) [ 24 ], here it was specifically performed to account for changes in pile-up height induced by pre-deformation.…”

Remarks on Wear Transitions Related to Hardness and Size of Abrasive Particles

“…A question arises from this issue: if the wear rate changes for smaller particles, would there be a suitable hardness to express the worn surface? The answer is not simple once the size effect is present in the indentation event, called the indentation size effect (ISE) [41][42][43][44][45][46][47]. For example, Pintaude et al [48] showed that the indentation size observed in steel could change the (Hi/Hw) CRIT value.…”

Nanoindentation Response of Ion-Irradiated Fe, Fe-Cr Alloys and Ferritic-Martensitic Steel Eurofer 97: The Effect of Ion Energy

“…In the reported studies, the materials were typically exposed to self-ion irradiations using a single ion energy varying from study to study from below 1 MeV (Clozel et al, 2020) to above 10 MeV (Song et al, 2020). As reported by Ruiz-Moreno et al (2020) in conclusion for a Round Robin test, simple comparison of NI results from different laboratories is, however, still problematic. Saleh et al (2016) studied the effect of energy variations of He ions (including ion energies of 1, 2 and 3 MeV) on the NI response of an austenitic stainless steel.…”