Effect of surface roughness in the determination of the mechanical properties of material using nanoindentation test

Abstract

A quantitative model is proposed for the estimation of macro-hardness using nanoindentation tests. It decreases the effect of errors related to the non-reproducibility of the nanoindentation test on calculations of macro-hardness by taking into account the indentation size effect and the surface roughness. The most innovative feature of this model is the simultaneous statistical treatment of all the nanoindentation loading curves. The curve treatment mainly corrects errors in the zero depth determination by correlating their positions through the use of a relative reference. First, the experimental loading curves are described using the Bernhardt law. The fitted curves are then shifted, in order to simultaneously reduce the gaps between them that result from the scatter in the experimental curves. A set of shift depths, Δhc , is therefore identified. The proposed approach is applied to a large set of TiAl6V4 titanium-based samples with different roughness levels, polished by eleven silicon carbide sandpapers from grit paper 80 to 4,000. The result reveals that the scatter degree of the indentation curves is higher when the surface is rougher. The standard deviation of the shift Δhc is linearly connected to the standard deviation of the surface roughness, if the roughness is high-pass filtered in the scale of the indenter (15 µm). Using the proposed method, the estimated macro-hardness for eleven studied TiAl6V4 samples is in the range of 3.5-4.1 GPa, with the smallest deviation around 0.01 GPa, which is more accurate than the one given by the Nanoindentation MTS™ system, which uses an average value (around 4.3 ± 0.5 GPa). Moreover, the calculated Young's modulus of the material is around 136 ± 20 GPa, which is similar to the modulus in literature.

Influence of roughness and tilt on nanoindentation measurements: A quantitative model

“…With this procedure, the roughness is deconvoluted from the tilt. It has to be underlined that, as already mentioned in (Xia et al ., ), the roughness depends on the scan size. Thus the given values are not absolute but still they are comparable.…”

“…Xia et al. ()registered a high number of load‐displacement curves using the continuous stiffness measurement (CSM). The proposed statistical treatment of all those curves allows taking into account both the indentation size effect and the surface roughness, i.e., the obtained hardness for a given material does not depend either on the contact depth or on the surface roughness.…”

Mechanical properties of orthodontic wires derived by instrumented indentation testing (IIT) according to ISO 14577

“…This finding can be attributed to two major reasons: (a) the results of nano-indentation are dependent on the loading conditions, tending to increase from lower (2 mN) to higher loading conditions (100 mN), possibly attributed to the contribution of the native oxide film as the indentation depth is superficial, within a few hundreds of nanometer from the outer surface [8]. Such shallow indentation depths characterize more the surface and near surface properties rather than the bulk ones [7]; (b) the shallow indentation depths are strongly affected by specimen roughness, and thus, the accuracy of experimental results are sensitive to the specimen roughness state [10]. …”

Importance of age on the dynamic mechanical behavior of intertubular and peritubular dentin

“…A concern in most applications involving nanoindentation is the contribution of surface topography to the evaluated properties [e.g. 77,78]. Special precaution was taken during the discrete indentation mode of evaluation to avoid regions near the interface between the peritbular cuff and intertubular matrix and the edge of the lumens.…”