Cemented Carbide Wear in Rock Drilling

Cemented Carbide Wear in Rock Drilling
WC/Co cemented carbide is a composite material for highly demanding wearing applications. The unique combination of high hardness (from hard phase WC) and toughness (from the binder, Co) gives a material especially suitable for rock drilling. This thesis investigates the deterioration and wear of these cemented carbide buttons and the correlation to different rock types, see Figs. 1. and 2. The work has been performed at the Tribomaterials Group by Ulrik Beste during 1999-2004, and has been financially supported by AB Sandvik.
To better understand the nature of the wear of the cemented carbide buttons, the counter surface -the rock- has also been studied. A range of important rock types has been investigated with respect to hardness distribution and scratch response in a micro scale and friction properties when slid against cemented carbides. An example of scratch response could be seen in Fig. 3.
The cemented carbide may deteriorate due to a number of mechanisms. The effect of fatigue in the structure was studied in TEM and particle erosion response was used to probe the corresponding mechanical degradation.
Further, homing cross sectioning has been developed and used as a new technique to investigate the presence of weak zones in the surface layer of a drill button, see Fig. 4. It was found that rock penetration into this layer is a very common deterioration mechanism, with profound implications for the nature of the wear.
Figure 4. 
By using the newly developed technique ”Homing cross sectioning” on a cemented carbide rock drill button, it becomes obvious that the surface in a rock drill button has a completely new composition by intermixture of rock.
High resolution scanning electron microscopy has been extensively used to map the deterioration and wear of numerous drill buttons, worn against different rock types in different kinds of drilling applications. Finally, the collected data on the surface damage, the reptile skin formation, the rock penetration and the properties of the rock are assembled into a new view of the deterioration and wear of cemented carbide in rock drilling. The new view includes life limiting factors, five classes of material deterioration and five classes of material removal.