## 3 Results and Discussion
### Tribological Properties
[42], abrasive wear was the only main failure mode for this coating. The reason for the latter observation was attributed to the accumulation of the highest proportion of amorphous Si\({}_{3}\)N\({}_{4}\) hard phase in the microstructure [42]. The CrN/CrCN coating was worn in a slight abrasive manner in the centre of the wear track, whereas at the edges, the coating experienced mild abrasion. The wear debris or weakly bounded droplets were drawn from the surface of the sliding track to its edges by the counterpart body, leading to mild abrasion in those areas. Furthermore, the presence of aluminum from the counter body within the wear track of CrN/CrCN coating confirmed the activation of adhesive wear. [PERSON] and [PERSON] [33] reported the same wear mechanisms. The tribofilm was observed on the worn surface of the uncoated WC-Co, as shown in Figure 15e. The detection of Al via EDS analysis (Figure 16d) indicates the transfer of material from the alumina counter body to the surface of the WC-Co substrate during the test. Additionally, cobalt binder extrusion took place on the worn surface (Figure 15f). This condition leads to the relaxation of the internal compressive stresses in WC grains, thus initiating crack formation [43]. Transgranular cracks occurred within most WC grains, as seen in Figure 15f. Figure 17 shows SEM micrographs of typical worn surfaces of different coatings and uncoated WC-Co substrates at the sliding speed of 100 mm/s. The dominant wear mechanisms for CrN/CrCN/DLC coating were delamination and abrasive wear. As seen in Figure 17a, the coating is rubbed off from the surface, mostly in the middle section of the wear track. The detached coating particles may also serve as abrasive particles increasing the wear rate through the development of three-body abrasion mechanism. Mild adhesive wear was also observed. Oxide layers formed during the test were present within the wear track (Figure 17a). Figure 9.0 EDS analysis of zones A-D in Figure 15 for different coatings at the sliding speed of 50 mm/s (**a**) CrN/CrCN/DLC, **(b**)** CrN/ATTiN, **(c)** CrCN/TiSiCN, and **(d**)** uncoated WC-Co substrate. The analysis of the wear track of CrN/AITiN coating (Figure 17b) indicates abrasive wear as a principal wear mechanism. The accumulation of wear debris at the edge of the wear track was responsible for constituting the grooves at those locations. Those particles which were detached from the coating via a brittle failure mechanism, played the role of a third body in the tribological system. A similar finding was reported by [PERSON] et al. (2018). The CrN/CrCN coating presents a smooth worn surface with shallow grooves indicating slight abrasive wear (Figure 17c). The formation of the smooth surface is related to the easy removal of debris particles from the contact surface ([PERSON] and [PERSON], 2017). [PERSON] and [PERSON] (2017) found the same wear mechanism because of the good tribo-mechanical properties of CrN/CrCN coatings. As shown in Figure 17d, the wear track of the CrCN/TiSiCN coating  
Figure 9.1 SEM micrographs of the wear track surface of different coatings at the sliding speed of 100 mm/s (**a**) CrN/CrCN/DLC, (**b**) CrN/AITiN, (**c**) CrN/CrCN, (**d**) CrCN/TiSiCN, and (**e**) uncoated WC-Co substrate. is covered with oxide films and adhesive layers. The elements detected by EDS analysis of these layers (zone 1 in Figure 17d) are shown in Figure 9.2 The presence of W reveals that the coating was removed from the surface of the substrate. In addition, slight abrasive wear at the edges of the wear track of CrCN/TiSiCN coating was observed. [PERSON] et al. [38] confirmed the evidence of ploughing due to abrasion damage of loose wear debris on TiSiCN coating at a medium sliding speed of 150 mm/s. Additionally, the presence of microcracks perpendicular to the sliding direction attests that fatigue wear is taking place on the worn surface of the CrCN/TiSiCN coating.