## 3 Results and Discussions
### Determination of the Coefficient of Sliding Friction  
The coefficient of sliding friction was determined according to the \"ball-on-disk\" scheme at an ambient temperature of 22 \({}^{\circ}\)C, under conditions without lubrication for 40 s with a relative humidity of 63%. In this scheme, a ball with a diameter of 6 mm, also made of silicon carbide (SiC), was used as an indenter. The friction coefficient was determined as the ratio of the measured friction force to the clamping force. This force was achieved by placing a weight holder with a known load of 1 N on the base. The coefficient of friction was measured while the specimen was rotating relative to the counterbody, with the wear groove on the specimen having a circular shape. The sliding length was 100 m, the linear speed of sliding was 2.5 m/s, and the test radius had the value of approximately 40 mm. The coefficient of friction was measured with a frequency of 1000 measurements per minute; these values were statistically processed by the software installed in the CSM tribometer. Using this software, the minimum, maximum and mean values as well as the standard deviation were determined. For each series of tests, the arithmetic mean values obtained after computing the statistical matrix of more than 1650 measurements were determined. This quantity of measurements for each test series provided a 99.7% measurement accuracy. The standard deviation of the mean value of the coefficient of friction was determined using the experimental equipment software. For each point, this deviation was in the range of 0.002-0.04. The coefficient of friction before and after the laser treatment was compared using the average value. The systematic error was addressed by calibrating the experimental setup before each measurement series. In the course of experimental studies, it was determined that the average value of the friction coefficient for the initial surface of the ceramic material based on silicon carbide, which was subjected to hot isostatic pressing and mechanical polishing, was 0.26. Figure 6 illustrates the dependence of the friction coefficient on the sliding length for the surface of such a sample that was not exposed to laser treatment. The value of the friction coefficient decreased to 0.22, i.e., by 15% (Figure 7), after pulsed-periodic laser irradiation with a short-pulse duration of less than 10 ns. Thus, the potential to improve the tribological properties of silicon carbide ceramics through pulse-periodic treatment using ultraviolet nanosecond laser was established. Figure 5: Typical (at the top) surface irregularities maps, (in the middle) height maps, and (at the bottom) profilograms of roughness of (**a**) the initial surface and (**b**) the irradiated surface. Electron-microscopic studies of the surface after friction tests revealed the absence of overlaps, micro-cutting strips, breaks, and cleavage, as well as a small degree of local heterogeneity in the texture of the friction surface. There is some minor wear, which is reflected in a slight smoothing of the surface topography, as illustrated in Figure 8. The average coefficient of friction does not change during this process. This is important for ensuring the serviceability of the hydrodynamic mechanical seals. It is known that the coatings used for the contact surfaces of mechanical seals are not long lasting. These will abrade during start/stop periods, even if these periods are 2-3 s short. In [36], it was shown that modern coatings can last only 10-15 start/stop cycles. The conducted tests indicate a better serviceability of silicon carbide contact surfaces after laser treatment than after application of antifriction coatings. Figures 9 and 10 show SEM images of the laser treated surface, and the wear area of the sample surface. Figure 6: Dependence of friction coefficient on sliding length for a sample surface that was not laser exposed. Figure 7: Dependence of friction coefficient on sliding length for the laser treated sample surface.