## 3 Results and Discussion
### Mechanical and Tribological Properties  
The results obtained from the hardness tests (Figure 9) also revealed some differences between the two types of coatings that can be correlated with their microstructure and  
Figure 8: XRD diffractograms of the reference coating WC-Co-Cr and the GC coating.  
Figure 7: EDX mapping of the GC coating in cross-section (**a**) and the corresponding EDX analysis (**b**).  
the tendency to crack formation. The reference coating is significantly harder than the GC coating. This is due, on the one hand, to the higher WC content in the reference coating, and, on the other hand, to the heterogeneous particle size and composition of the GC coating. This also led to a larger variation in hardness.  
The WC-Co-Cr coating exhibits significantly better resistance to crack formation and propagation under similar loading conditions to those of the GC coating (see Figure 10). As indicated by the red markings around the indentation region in Figure 10a, the crack development can be classified as non-critical. In contrast, the crack propagation in the GC coating must be considered critical. The cracks originate within the coating (cohesive failure) and extend beyond the indentation area.  
Figure 10: Representative CLSM image at 50\(\times\) magnification of the crack propagation test (HB; \(\mathcal{O}\) 2.5 mm; test load = 62.5 kg) of (**a**) the WC-Co-Cr coating and (**b**) the GC coating.  
Figure 9: Bar chart showing the mean values and standard deviations for the HV1 hardness measurement of the investigated coatings.  
A comparison of the values for the evolution of the coefficient of friction during the tribological tests (see Figure 11) shows that the GC coating has a significantly longer run-in phase than that of the reference coating (approximately 7500 laps compared to 2500 laps). Furthermore, the coefficient of friction curve of the GC coating consistently displays significantly higher values than that of the reference coating. The steady-state friction coefficient of the GC coating is over twice that of the reference coating. The increased friction resistance is due to the larger metal components in the GC coating. The cleaning coefficient between the ball and the metal components is significantly higher than, for example, with carbides.  
The sliding wear behavior of the GC coating can be explained by its diverse chemical composition, which creates varying local conditions for the WC ball during testing. As a result, the green curve exhibits significantly more fluctuation compared to the red one.  
Regardless of the measured values for the coefficient of friction, what is particularly noteworthy is that neither the WC-Co-Cr nor the GC coating exhibits any significant material loss. Figure 12 clearly shows that there is no notable difference in surface topography between the unexposed area and the wear track exposed to the test conditions in the yellow-marked measurement area.  
As a result, it was not possible to determine the wear volume for either of the tested coating types, as no wear track depth was generated. Considering their mechanical and tribological properties, the GC coatings are significantly less hard and have poorer resistance to crack formation. Despite this, the GC coatings demonstrate similar resistance to sliding wear tests under the same conditions.  
Figure 11: Coefficient of friction curves of the GC (green) and WC-Co-Cr (red) coatings using WC as the counter body.