## 3 Results and Discussion
### Analysis of Wetting Properties  
#### 3.2.1 Wetting Analysis of Cu-SiC Surfaces Processed by Abrasive Materials  
In the studies conducted during the manufacture of the bulk Cu-SiC composite materials, two main factors changed (Table 1) with other conditions being equal: (1) sintering temperature (from 700 \({}^{\circ}\)C to 850 \({}^{\circ}\)C) with the composition of the materials unchanged; (2) the content of SiC (from 5 to 20 wt.%) at a constant sintering temperature of 850 \({}^{\circ}\)C. Figure 3 presents water static contact angles on the surfaces of Cu-SiC grouped according to the above variation factors. It can be seen from Figure 3a that samples sintered at higher temperatures demonstrate higher static contact angles. The wetting properties are known to depend on the texture (roughness) and elemental composition of the surface [55]. According to the results of the texture (roughness) analysis conducted in Section 3.1, the values of the roughness parameters of samples No. 2-8 processed by abrasive materials were almost equal to each other. Therefore, the roughness does not significantly contribute to the difference in wetting properties of samples No. 2-8 (Figure 3a,b). In order to estimate wetting properties, in addition to the static contact angle, it is necessary to analyze the contact angle hysteresis or the roll-off angle [56]. In this study, the value of obtained contact angle hysteresis is presented in Figure 3 as the confidence interval for static contact angle. It can be seen from Figure 3a that the difference in the values of the static contact angles of samples No. 2-5 are close to the values of the contact angle hysteresis, which is more than \(10^{\circ}\). This indicates that the deterioration of wetting properties (an increase in the contact angle) recorded on surfaces fabricated at high sintering temperatures is insignificant. For example, the minimum difference between the largest value of the static contact angle on sample No. 5 and the smallest value on sample No. 4 (Figure 3a), taking into account the hysteresis, is:  
\[\Delta\theta_{min}=(\theta_{\text{No. 5}}-H_{\text{No. 5}}/2)-(\theta_{\text{No. 4}}+H_{\text{No. 4}}/2)=\]  
\[=(88.9-14.4/2)-(75.2+11.2/2)=0.9^{\circ}\]  
where \(\theta_{\text{No. 4}}\), \(\theta_{\text{No. 5}}\) are static contact angles on the surfaces of samples No. 4 and \(5^{\circ}\); and \(H_{\text{No. 4}}\), \(H_{\text{No. 5}}\) are contact angle hysteresis on the surfaces of samples No. 4 and \(5^{\circ}\). As the surface roughness of samples No. 2-8 are almost identical, the contact angle hysteresis of more than \(10^{\circ}\) on the Cu-SiC surfaces processed by the abrasive materials is connected with the chemical heterogeneity (chaotically arranged local sites of Si and C or Cu). Under the experimental conditions, the recorded effect of the sintering temperature of composite materials on the degradation of their wetting properties (Figure 3a), as well as in the case of hysteresis, could be mainly due to the difference in the elemental composition of surfaces No. 2-5. The higher the sintering temperature of composite materials, the more intense the surface oxidation. With oxidation, the surface energy increases, so the wetting properties should improve (the contact angle decreases at higher sintering temperatures). However, in the conducted experiments, the surface wetting properties deteriorate with an increase in the sintering temperature. After sintering and mechanical processing with abrasive materials, the samples were stored under ambient conditions. Therefore, the recorded degradation of wetting properties can be explained by the adsorption of airborne hydrocarbon contaminants, in comparison with the spontaneous hydrophobization of  
Figure 3: Static contact angles measured on Cu-SiC samples processed by abrasive materials. The samples are grouped according to the sintering conditions: (**a**) change of \(T_{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{\text{\text  
surfaces modified by laser radiation [4].