## 3 Results and Discussion
These coatings were formed by successively depositing layers with varying ratios of ceramic (YSZ) and metallic (NiCrAlY) phases. This approach allows obtaining a gradient structure in which the concentration of components smoothly changes from the substrate to the outer surface. The results of the microstructural analysis showed that the proportion of the ceramic component (YSZ) increases towards the coating surface, while the content of the metallic phase (NiCrAlY) consistently decreases. This confirms that the gradient transition between the layers was successfully implemented. Energy-dispersive X-ray analysis (EDS) confirmed the phase distribution: the light areas in the image correspond to yttrium oxide-stabilized zirconium dioxide (YSZ), and the dark areas to the NiCrAlY metallic alloy. The resulting coatings are characterized by a dense structure without visible defects, inclusions, or cracks, which indicates the high quality of layer formation and the efficiency of the selected technological parameters. Figure 5 shows enlarged SEM micrographs of the cross-sections of the ceramic coatings, on the basis of which the porosity was quantitatively assessed. The upper row of images shows the original structure of coatings in high resolution (5 \(\upmu\)m scale), and the lower  
Figure 4: Microstructure of the cross-section of multilayer gradient coatings: (**a,e**) linear scanning, (**b,f**) BSE image, and (**c,d,g,h**) elemental mapping. \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Sample No. 1** & **Sample No. 2** \\ \hline Space group: & P42/nmc & P42/nmc \\ \hline Phase composition: & 100 wt.\% tetragonal & 100 wt.\% tetragonal \\ \hline Lattice Parameters & & \\ \hline a = b, Å: & 3.6082 & 3.6117 \\ \hline c, Å: & 5.1436 & 5.1539 \\ \hline Tetragonality & 1.008 & 1.009 \\ \hline \end{tabular}
\end{table} 
Table 3: Quantitative results of X-ray diffraction analysis. row shows the processed images with pore extraction for porosity quantification. Both coatings demonstrate a uniform distribution of pores, with no signs of large cavities or structural defects. However, the coating of sample No. 1 is characterized by a more homogeneous structure with a smaller number and size of pores. Quantitative evaluation showed porosity at 3.21%, indicating a dense and well-compacted structure. In contrast, sample No. 2 shows a more developed porous network with a porosity of 4.47%, and the pores tend to aggregate, which may indicate instability of the spraying process at the selected regime. The increase in porosity may be due to a decrease in the kinetic energy of the particles, their insufficient heating, or a decrease in the frequency of detonation pulses, which leads to a decrease in the degree of compaction of the particles during their deposition on the substrate. Differences in porosity directly affect the resistance of coatings to CMAS and high-temperature corrosion. Lower porosity helps to limit the penetration of aggressive components such as CMAS, melting deep into the material, reducing the risk of chemical reactions and cracking. Additionally, the differences in coating thicknesses, also noted in the analysis, may be due to the same technological reasons. In particular, sample No. 1 has a coating thickness of 963.67 \(\pm\) 13.59 \(\upmu\)m, while sample No. 2 has only 273.72 \(\pm\) 1.26 \(\upmu\)m. This may indicate a more intense deposition of the material in the first case, possibly due to a greater number of detonation pulses or higher temperature and particle velocity. A detailed analysis of the effect of detonation spraying regimes on the physical and mechanical properties of multilayer gradient coatings based on YSZ/NiCrAlY is presented in our previous studies [37; 38]. In thermal corrosion experiments of multilayer gradient coatings conducted at 1150 \({}^{\circ}\)C with exposure to CMAS melt, changes in the surface morphology of the coatings were studied using scanning electron microscopy in the backscattered electron (BSE) mode (Figure 6).