## 2 Materials and Methods  
In this work, multilayer gradient coatings consisting of YSZ/NiCrAlY layers and 12 Kh18N10T stainless steel substrate with chemical composition: Fe--base, Ni--10%, C--0.12%, Ti--0.5%, Cr--18%, Mn--2% were used as samples. Metco 233B (YSZ) and PNH20K20 Yu13 (NiCrAlY) were used as starting powders. Figure 1 shows the SEM images, X-ray diffraction patterns, and particle size distribution of YSZ and NiCrAlY powders. According to the results of SEM image analysis, YSZ powder is characterized by spherical morphology with an average particle size of 30 \(\pm\) 5 \(\upmu\)m, whereas NiCrAlY powder has a spherical particle shape with an average particle size of 16 \(\pm\) 6 \(\upmu\)m. X-ray phase analysis showed that YSZ powder consists of monoclinic (m-ZrO) and tetragonal (t-ZrO) zirconium dioxide phases, whereas, in NiCrAlY powder, \(\beta\)-NiAl, \(\gamma\)-Ni\({}_{3}\)Al, and NiCoCr phases were identified. The multilayer gradient coatings of YSZ/NiCrAlY were obtained by detonation spraying (CCDS2000, LIH SB RAS, Novosibirsk, Russia) [38]. Figure 2 shows the external appearance of the CCDS2000 installation and a diagram of the principle of the operation of detonation spraying. Before coating application, the surface of the 12 Kh18N10T stainless steel substrate was sandblasted to form the required roughness. Corundum with a particle size of 60-80 \(\upmu\)m was used as an abrasive material at an air pressure of 0.6 MPa. After preparing the substrate, a NiCrAlY binder layer was applied first, then a gradient transition was formed by gradually changing the ratio of the supplied materials, ending with the top YSZ layer. To regulate the layer composition, two independent dispensers were used, providing a sequential change in the ratio of the supplied powders. The detonation spraying regimes of NiCrAlY and YSZ coatings are given in Table 1.  
Two different regimes of the deposition of multilayer gradient coatings were used in the experiment, in which the key adjustable parameter was the number of shots during the detonation spraying process. By changing the number of shots, it was possible to control the ratio of metal and ceramic phases in the coating, forming the required gradient in thickness. In the first regime (sample No. 1), the number of shots for the NiCrAlY metal layer was gradually decreased from 5 to 1, while the number of shots for the YSZ ceramic material was consistently increased from 1 to 20. In the second regime (sample No. 2), similarly, the number of shots for NiCrAlY varied from 10 to 2, while the number of shots for YSZ varied from 2 to 40. This method of spraying provided the formation of a more pronounced gradient structure with increased ceramic content in the upper part of the coating. Table 2  
Figure 1: SEM images (**a**,**b**,**d**,**e**), XRD patterns (**g**,**h**), and particle size distribution (**c**,**f**) of YSZ and NiCrAlY powders. shows the sequential layer application patterns and the corresponding number of shots for regime 1 (sample No. 1) and regime 2 (sample No. 2). The crystallographic structure of the initial powder and the obtained coatings was investigated by X-ray diffraction on an X'Pert Pro diffractometer (Philips Corporation, Amsterdam, The Netherlands) using a copper anode (Cu-K\(\alpha\) radiation, \(\lambda\) = 1.54 A). Imaging was performed in the 20 range from 20\({}^{\circ}\) to 90\({}^{\circ}\), with phase identification based on the JCPDS database (01-081-1545). The diffractograms were processed, and the phase composition was determined in the HighScore Plus (version 3.0e) software environment. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Coatings**} & **Ratio,** & **Barrel Filling** & **Spraying** & **Coating Dose,** \\  & **O2/C2H2** & **Volume, \%** & **Distance, mm** & **\(\mu\)m/Shot** \\ \hline NiCrA1Y & 0.97 & 35 & 200 & 2.3 \\ \hline YSZ & 2.529 & 61 & 200 & 1.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Technological parameters of detonation spraying of NiCrA1Y and YSZ coatings.