Comparison of nanoindentation results obtained with Berkovich and cube-corner indenters

There is increasing interest in using sharp cube corner indenters in nanoindentation
experiments to study plastic properties. In combination with finite element methods it is for
instance possible to extract stress-strain curves from load-displacement curves measured with
differently shaped pyramidal indenters. Another example is the fracture toughness of
coatings, which can be studied using cracks produced during indentation with cube corner
tips. We have carried out indentation experiments with Berkovich and cube corner indenters
on eight different materials with different mechanical properties. To gain information about
the formation of pile-up and cracks, indentation experiments with cube corner indenter were
performed inside a Scanning Electron Microscope (SEM) using a custom-built SEMMicroindenter.
The results show that reliable hardness and modulus values can be measured
using cube corner indenters. However, the fit range of the unloading curve has a much bigger
influence on the results for the cube corner than for the Berkovich tip. The unloading curves
of a cube corner measurement should therefore be carefully inspected to determine the region
of smooth curvature and the unloading fit range chosen warily. Comparison of the modulus
results shows that there is no significant difference between cube corner and Berkovich
measurements. Also for hardness, no fundamental difference is observed for most of the
investigated materials. Exceptions are materials like silicon nitride, cemented carbide or
glassy carbon, where a clear difference to the hardness reference value has been observed
although the modulus difference is not pronounced.