EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The shape of the indenter at its tip can significantly affect the results of indentation measurements especially for indentations at low depths. Indenters are inevitably blunted during their use, namely when indenting hard materials. Although some bluntness can be corrected by the calibration of the indenter area function, it is advantageous to know the tip radius since that will tell the user if the indenter has to be replaced. The method proposed in this work is based on a description of the Berkovich indenter by a spheroconical model where the tip radius is considered to be a measure of the bluntness. In our work we used several new indenters and we monitored the evolution of their tip radius after series of wear tests on fused silica and sapphire. After each wear test the tip radius was calculated from low load indentations (5 µN to 1000 µN). The low load indentations should reflect the tip blunting by the change of the indentation depth. This study was completed by evaluation of the tip radius of several tens of new and used indenters.
The results of the low load indentations showed that the indenter tip radius increased only by ~7% after 10k indentations on sapphire at 400 mN load. Similar result was found for the wear tests on fused silica. The indentation depth and the ratio of elastic to total work of indentation (nIT) at 1 mN of this indenter wear study were compared with the values obtained on the new and used indenters. A simple relation between the estimated tip radius from the spheroconical model and the indentation depth at 1 mN was found: this relation can be used to relatively easily estimate the indenter tip radius from the depth value that is defined by the ISO 14577 standard.