Hardness testing has always been an attractive and convenient technique to characterize the mechanical behavior of materials. The documented history of hardness testing dates back more than 250 years but still its potential is far from being entirely exploited. The refinement of hardness testing in terms of nanoindentation, a depth and load sensing indentation technique, with a displacement resolution of less than a nanometer, now allows to study elastic and plastic properties of samples only consuming minimal material volumes and is therefore particularly popular for the local characterization of samples with limited volume, such as modern nano-materials or microelectronic components.
In addition, these days efficient material testing techniques are for instance required to support quality control or to supply data for process simulation. Conventional uniaxial testing is suitable for this request, yet it demands elaborate sample fabrication and is in need of rather large material volumes. Nanoindentation tremendously eases sample preparation and can access a far broader range of materials and structures. Hence, various concepts have been introduced to link hardness values to uniaxial flow curves, but still their feasibility remains an open question.
Therefore, this study aimed to provide evidence that a multiple sharp tip approach can be used to extract the stress/strain behavior of metals independent of their microstructure. By varying the opening angle of the pyramidal indenter tips, a representative strain can be ascribed to each angle for the corresponding indentation stress. Using four different tips, one can construct the flow curve from the obtained data pairs and the measured Young’s modulus. Nevertheless, the success of these experiments depends on careful calibrations and the consideration of length-scale effects, such as the indentation size effect. Our results showed excellent agreement with the literature data from uniaxial tests for eight different samples, comprising different crystal structures and microstructures.
In summary, the presented nanoindentation approach is an outstanding method to extract plastic flow properties of metals, especially when the material is limited, demanding to machine, or high lateral resolution is required, and could therefore potentially become as a standard testing technique in future.