## 4 Conclusions  
Surface microstructuring of the gas-dynamic seal based on silicon carbide ceramics was carried out using an ultraviolet laser. The pulse-periodic treatment was conducted using an LCS-DTL-374 QT laser with a pulse duration smaller than 10 ns and a wavelength of 355 nm. This laser with a maximum energy of a pulse of 50 \(\upmu\)J and a maximum average power of 90 mW was installed in a circular laser writing station CLWS200.  
An optical profilometer was used to control the exposure results of the focused ultraviolet laser beam on the ceramic material. It was found that sequential treatment of tracks of 40 \(\upmu\)m width on the material with overlapping of neighboring tracks smaller than 2 \(\upmu\)m allows to carry out laser polishing modes. By this processing method, a decrease in the height difference of microreliefs from 1.5 \(\upmu\)m to 0.8 \(\upmu\)m, a decrease in the Ra parameter from 0.056 \(\upmu\)m to 0.035 \(\upmu\)m and a decrease in the RMS parameter from 0.074 \(\upmu\)m to 0.043 \(\upmu\)m were achieved.  
The coefficient of sliding friction was measured by a TRB-S-DE tribometer, CSM Instruments using a \"ball-on-disk\" scheme while no lubrication was applied. The indenter in this setup was a silicon carbide ball, of 6 mm diameter. It was established that the average value of the friction coefficient of the silicon carbide-based ceramic material surface after hot isostatic pressing and machining, as a result of pulse-periodic laser treatment decreased by 15%. Electron-microscopic studies of the wear surface revealed the absence of overlaps, micro-cutting strips, breaks, and cleavage, as well as only a small degree of local heterogeneity in the texture of the friction surface.  
Thus, the possibility of modifying the surface of a gas-dynamic seal made of silicon carbide-based ceramics by microstructuring to decrease the friction coefficient in stationary gas turbine equipment is determined. The reduction of the sliding friction coefficient when using the \"SiC-SiC\" friction pair can significantly reduce abrasion of the contact surfaces when the shaft rotates at low speeds, during start-up and shutdown modes, or during transient modes in which there is no stable gas layer between the stator and rotor rings. The application of optical systems based on diffractive computer optics elements, which offer the possibility to improve the quality of laser processing, is the considered perspective.  
Conceptualization, S.P.M., V.B.B. and N.L.K.; methodology, S.P.M., V.B.B. and C.G.; software, S.A.F. and M.V.B.; validation, V.B.B. and S.A.F.; formal analysis, S.P.M. and C.G.; investigation, V.B.B., S.A.F. and M.V.B.; resources, S.P.M., C.G. and N.L.K.; data curation, V.B.B. and S.A.F.; writing--original draft preparation, S.P.M. and S.A.F.; writing--review and editing, S.P.M. and C.G.; visualization, V.B.B. and S.A.F.; supervision, S.P.M.; project administration, S.P.M.; fundingacquisition, S.P.M., V.B.B., C.G. and N.L.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is contained within the article.  
**Conflicts of Interest:** The authors declare no conflict of interest.