## 3 Results and Discussions  
### Laser Treatment of Gas-Dynamic Seals by Laser Writing Station  
Laser treatment was applied as an additional step to the silicon carbide ceramic seals, which were machined with a mechanical polishing operation as the final step in the manufacturing process. The surface of the gas-dynamic seals of the compressor rotor and reference samples was cleaned from contamination using surface-active substances. Degreasing with acetone and rinsing with distilled water were carried out. Then, residual moisture was removed by air flow through the high efficiency particulate filter. The surface microrelief was formed in a continuous circular scanning mode. For this purpose, the sample was mounted on a rotating circular holder of the CLWS-200 laser writing station. After the sample was centered, the optical system focused the laser beam on the surface of the seal in shape of a ring. Using an interference method, the substrate holder was calibrated to eliminate beating during rotation (Figure 4). In the course of experimental studies, by selection of variable settings of the UV nanosecond laser with a pulse duration of less than 10 ns in the permissible range, the following treatment parameters were applied to the surface of the ring to be treated: pulse energy 30 uJ, pulse frequency 10 kHz, power 30 mW. During treatment, a protective gas, argon, was injected through a purge nozzle directed at the laser focusing area on the surface under treatment to prevent possible oxidation of the material in the heating area. Figure 4: Process of alignment and focusing of the laser beam on the ring-shaped surface. Figure 3: (**a**) Tribometer (CSM Instruments) used to measure the friction coefficient of the test sample and (**b**) the test scheme “ball-on-disk”. Processing was performed with a circular trajectory of tracks, where the width of each track had a value of 40 \(\upmu\)m and the overlapping of adjacent tracks was less than 2 \(\upmu\)m. The specimen was processed according to a program involving the sequential formation of each track on a ring-shaped sealing surface. The control program also maintained the stability of energy input to different treatment zones. The tracks were recorded with a summarized tracks width of about 3 mm. The angular rotation speed of the substrate holder with the sample was 600 rpm. It was determined that the use of diffractive optics for laser beam shaping [12; 13] in the treatment process makes it possible to obtain the required geometry of areas exposed to single pulses. Therefore, the use of optical systems based on diffractive computer optics elements is promising since their utilization will enable us to improve the quality of laser processing. Evaluation of the Morphology Transformation after Laser Treatment and Determination of the Sliding Friction Coefficient  
Condition for the laser polishing was implemented in the area of the laser beam exposure on the surface of silicon carbide samples and gas dynamic seals of the compressor rotor of the gas-turbine engine. When the samples were investigated with a \"Zygo NewView 7300\" optical profilometer, a reduction in the height of surface microroughnesses caused by laser treatment using a nanosecond UV laser was established. Typical height maps of the untreated and treated surfaces are shown in Figure 5. The dimensions of the observed regions in this Figure are 70.6 \(\upmu\)m \(\times\) 53.0 \(\upmu\)m.  
The assessment of changes in the morphology of the treated surface after pulsed-periodic laser irradiation was carried out. The microstructure studies of the treated material revealed that pulse-periodic laser irradiation with the specified mode parameters led to the smoothing of the microrelief on the already mechanical polished surface of the silicon carbide ceramics. It was established that during sequential formation of tracks by laser irradiation on the material leads to the creation of non-periodic surface microrelief that is in the form of altering cavities and protrusions.