# Comprehensive Study of the Mechanical and Tribological Properties of NiCr-Al Detonation Coatings
## 3 Results and Discussion
### Wear Characteristics  
The tribological properties of GC and HC NiCr-Al based on element distribution were determined by the friction coefficient (\(\mu\)) and wear rate (Wv, mm\({}^{3}\)/N \(\times\) m) (Figure 11). Figure 11a shows the results of tribological testing of the GC NiCr-Al. The graph shows that initially the friction coefficient varied somewhat, and then it reached a relatively stable level. This could be attributed to the gradient structural characteristics of the coating. The friction test results between the NiCr-Al GC and 100 Cr6 steel are as follows: \(\mu\) = 0.74 \(\pm\) 0.05; Wv = (3.13 \(\pm\) 0.20) \(\times\) 10\({}^{-3}\) mm\({}^{3}\)/N \(\times\) m. Figure 11b shows the results of tribological testing  
Figure 10: Nanohardness and elastic modulus of NiCr-Al coatings with gradient (**a**) and homogeneous (**b**) structure of element distribution. Figure 9: Microhardness of NiCr-Al coatings obtained by the detonation spraying method. of the HC: \(\mu\) = 0.80 \(\pm\) 0.04; Wv = (5.73 \(\pm\) 0.30) \(\times\) 10\({}^{-3}\) mm\({}^{3}\)/N \(\times\) m. Figure 11c,d show the wear track profiles after tribological testing, and the wear area of the HC is two times higher compared to the GC. Thus, the results of tribological testing of the GC and HC using the \"ball-on-disk\" method, based on element distribution, reveal that the GC has higher wear resistance. Figure 12 shows the SEM images of the wear tracks of the NiCr-Al detonation-sprayed coatings after tribological testing. In the GC coating (Figure 12a), due to the high aluminum content in the surface layer (as shown in Figure 7a), the material demonstrates enhanced plasticity, which reduces the likelihood of brittle fracture. As a result, the GC coating surface undergoes more extensive plastic deformation under frictional load. In contrast, the HC coating (Figure 12b) exhibits visible microcracks and fragmentation, indicating a higher tendency for brittle failure. Based on elemental analysis and SEM observations, the dominant wear mechanism appears to be adhesive in nature. This finding corresponds well with the observations made by [PERSON] et al. [55], where adhesive wear was reported in CGS 316L stainless steel coatings. In that study, plastically deformed debris adhered to the wear track and contributed to the third-body wear mechanism. Although both coatings exhibited similar coefficients of friction, profilometric measurements (Figure 11c,d) revealed that the wear area of the HC coating was approximately twice as large as that of the GC coating. This difference can be attributed to the fragmentation and detachment of coating particles from the HC structure as a result of crack formation during tribological loading. In contrast, the GC structure, with its gradient distribution of aluminum and higher structural integrity, demonstrates superior resistance to wear. The high-temperature tribological properties of GC and HC NiCr-Al were determined by the friction coefficient (\(\mu\)) and wear rate (Wv, mm\({}^{3}\)/N \(\times\) m) (Figure 13). The results of the average friction coefficient after high-temperature tribological testing using the \"ball-on-disk\" method for NiCr-Al coatings are as follows: GC \(\mu_{\text{ave}}\)= 0.50 \(\pm\) 0.03; HC \(\mu_{\text{ave}}\)= 0.46 \(\pm\) 0.02. The slightly higher friction coefficient of the GC NiCr-Al can be explained by the higher amount of aluminum on the coating surface, which leads to the formation of a thicker Al\({}_{2}\)O\({}_{3}\) oxide layer. This oxide layer then interacts with the Al\({}_{2}\)O\({}_{3}\) ball used as the counterbody, resulting in friction between the two hard bodies. Figure 11: Results of tribological testing and wear volume of gradient (**a**,**c**) and homogeneous (**b**,**d**) NiCr-Al coatings obtained by the detonation spraying method. Figure 14a,b show the two-dimensional and three-dimensional profiles of the GC NiCr-Al after the high-temperature tribological testing.