Prediction of bluntness for pyramidal indenters from nanoindentation curves

A blunted height of a sharp indenter can be elucidated by fitting the indentation load versus the indentation depth data into Kickʹs law. Nanoindentations adapting two Berkovich indenters with different bluntnesses were performed on fused silica and then resulting nanoindentation loading curves were analyzed from a linear proportional fitting between the square root of the indentation load and the indentation depth modified with the blunted height; the blunted heights of 4.1 ± 0.5 and 38.4 ± 1.9 nm were estimated for the new and the severely worn indenters, respectively. In addition, the validity of this bluntness prediction was confirmed by a direct observation with an atomic force microscope; the blunted height measured for the indenter B was 45 nm comparable with the predicted value. The bluntness correction applied to the indentation data for a 200 nm-thick SiO2 coating on Si substrate yielded not only roughly overlapped nanoindentation curves but also discrete discrepancies at low and peak load regimes. These phenomena are discussed from a geometrical difference of both indenters within the blunted regime and an extensive deformation of the hard substrate at deep indentations.