Vickers Hardness Indentations Measured with Atomic Force Microscopy

Vickers hardness indentations on a steel gage block (∼900 HV) with diagonals between 3.4 and 44 μm have been measured with a calibrated atomic force microscope (AFM) and with an optical-based method. From the AFM images the diagonals were measured from hard copies of diagonal profiles and automatically by image analysis. The combined standard uncertainty for the 3.4-μm diagonals was 10% for the optical-based and only 2.4% for the profile-based measurements (68% confidence level). Indentations with diagonals between 10 and 44 μm had concave shapes, in contrast to the 3.4-μm indentations. We show that optical-based measurements were not made at the level of the background plane, but higher on the indentation ridges.