Rock adhering to cemented carbide surfaces – The role of image acquisition

In rock drilling, cemented carbide rock drill buttons are rotating and impacting the rock to crush it, and water or air is used to flush away the debris. The wear of the buttons is influenced by many factors, of which the type of rock being drilled is a major one, e.g. drilling sandstone is more severe than granite. A notable mechanism in the contact between rock and button is the transfer of rock material to the button surface, both replacing the binder in the cemented carbide and covering the surface. Whether this transfer is improving or impairing the wear resistance of the buttons can be debated. At first glance it seems granite is more prone to cover the button surface than sandstone. However, the image acquisition technique and magnification have a great influence on the measured rock coverage, and it is found to be similar between the rock types when investigated in closer detail. The connection between rock transfer and wear resistance must be more complex, if any exists. This investigation highlights the importance of understanding the acquisition technique, particularly regarding the depth sensitivity in relation to what is analysed. The depth sensitivity can be problematic if thin layers are missed. It can also give valuable information regarding the thickness of adhered layers, if different analysis techniques and settings are combined. New and improved instruments for scanning electron microscopy have made it possible to use lower acceleration voltages with high resolution and thus made the technique possible to use in a more surface sensitive mode. Varying the acceleration voltage probes the sample at different depths, thereby revealing the thickness profile of the adhered layer. Together with simulation of electron trajectories, the thickness of the adhered layer can be mapped with a method not exclusive to the samples in this work. •Automated image analysis used to measure rock adhering to cemented carbide.•Scanning electron microscopy correlated to simulation of electron trajectories.•Rock coverage of granite and sandstone very similar at small scale.•Method for thickness mapping, not exclusively for materials in current work.