## 3 Results and Discussion
### Analysis of Wetting Properties
#### 3.2.2 Wetting Analysis of Cu-SiC Surfaces Processed by Laser Radiation  
Figure 4 shows the wetting inversion over time of Cu-SiC surfaces modified by laser radiation. Immediately after laser modification, samples No. 2-8 demonstrated superhydrophilic properties; water droplets spread into a thin film. When Cu-SiC samples were stored under laboratory conditions, the wetting properties deteriorated (contact angle increased). After 19 days from the moment of surface modification, samples No. 4-6 had hydrophobic properties (\(\theta>90^{\circ}\)); samples No. 2 and No. 3--after 26 days; sample No. 8--42 days; and No. 7--60 days. Stabilization of the wetting properties of samples No. 2-6 was registered after 53 days, No. 7 and 8 after 73 days. After stabilization, the contact angle hysteresis did not exceed \(10^{\circ}\), after which it was constant over time. This is in good agreement with the recommendations [37] for determining the stabilization time of surface properties during \"spontaneous hydrophobization\" of metal surfaces. It should be noted that among the studied group of samples modified by laser radiation, the surfaces of samples No. 2-6 have the worst wetting properties (\(\theta\approx 135\)-\(150^{\circ}\)), and the surface of sample No. 7 (\(\theta\approx 98^{\circ}\)) is the best under conditions of contact angle stabilization (Figure 4). Based on the analysis of the typical time intervals of the wetting inversion (achievement of superhydrophilicity, hydrophobicity, stabilization of wetting properties), it was concluded that the inversion mechanism and, accordingly, the reason for the \"spontaneous hydrophobization\" of the surfaces of Cu-SiC composite materials modified by nanosecond laser radiation, are similar to the studied mechanism and cause of wetting inversion of metal surfaces [16, 22, 23, 24, 25, 26, 27, 28]. Consequently, the wetting inversion of the surfaces of Cu-SiC composite materials modified by nanosecond laser radiation is due to the adsorption of hydrocarbon compounds from the environment. It was also concluded that SiC precursors with a content of 5 to 20 wt.% in the composition of the initial powder, as well as the sintering temperature (from 700 to 850 \({}^{\circ}\)C) in the manufacture of bulk material, do not affect the values of the steady-state contact angles due to wetting inversion of the surfaces of this material modified by laser radiation. The change in the static contact angle under conditions of the wetting inversion of Cu-SiC composite materials during their storage in laboratory conditions can be described by an exponential dependence, similar to metals [16]:  
\[\theta=\theta_{\text{steady}}\cdot(1-\text{e}^{-t/a}),\]  
where \(\theta_{\text{steady}}\) is the steady-state contact angle on the surface modified by laser radiation, \({}^{\circ}\); \(a\) is a constant characterizing the time during which the contact angle exceeds 50% of the steady-state value, days; \(t\)--stabilization time of wetting properties, days. The values of the fitting coefficients and the times of wetting stabilization are summarized in Table 3. The fitting curves and experimental data show good agreement (Figure 4). Figure 4: Wetting properties inversion over time on Cu-SiC surfaces modified by laser radiation. The samples are grouped according to the sintering conditions: (**a**) change of \(T_{\text{sps}}\) at a constant content; (**b**) change in the content of SiC at a constant \(T_{\text{sps}}\) of 850 \({}^{\circ}\)C. Symbols are experimental data, solid lines are fitting curves. An analysis based on a comparison of wetting properties (static contact angles) of Cu-SiC samples after abrasive processing (Figure 3) and after modification by laser radiation at the stage of achieving wetting stabilization (Figure 4) allowed the following conclusions to be drawn.