Some observations on scratch and indentation hardness measurements

Abstract

Measurements have been made in order to compare the scratch hardness with the corresponding indentation hardness of lead, copper and mild steel at room temperature. Both types of measurement were made using the same conical indenter, and the effects of lubrication, normal load and apical angle were investigated. It is shown that the scratch hardness values were most reproducible when measured with conical indenters of apical angles in the range 120°-170°. However, these values were rarely the same as the indentation hardness for a given cone. The hardness characteristics of lead, at room temperature, differed from those of the other metals in that the scratch hardness was generally 1·6 times greater than the indentation hardness, and both kinds of measurement were independent of cone angle. It was concluded that this was due to ideal plasticity in a metal deformed at, or above, half the melting point, and that this type of behaviour would be anticipated in other metals indented at sufficiently high homologous temperatures. Finally, the scratch hardness measurement was used to demonstrate the greater degree of anisotropy observed in single crystals, under these experimental conditions, compared with the identation technique.