## 5 Result and Discussion
### Analysis of Optimal Structural Properties Through Orthogonal Simulated Calculation  
The orthogonal simulation results indicate that fiber content significantly impacts the thermal shock resistance of the coating, transition layer, and substrate, while coating porosity has a weaker effect. Optimal configurations involve a thicker coating, appropriate porosity (20%), and moderate fiber content to prevent crack initiation. Under cyclic thermal shock loads, increased fiber content enhances thermal shock resistance across all layers. Although a 100 \(\upmu\)m coating thickness generally improves resistance, this benefit diminishes compared to 20 \(\upmu\)m and declines further at 60 \(\upmu\)m. A small amount of porosity (10%) improves the coating's resistance, but a dense coating optimally protects the transition layer and substrate. Given the substrate's susceptibility, particularly porous carbon, the A\({}_{1}\)B\({}_{3}\)C\({}_{3}\) configuration (porosity = 0%, 100 \(\upmu\)m, and 60% fiber) is recommended for overall thermal shock resistance improvement.  
Experiments by [PERSON] et al. [65] on SiC gradient coatings for C/C composites also show that a dense outer layer resists oxygen diffusion, while a microporous intermediate layer inhibits through-thickness crack formation, thus enhancing thermal shock resistance. This study's optimal configuration features a dense outer layer without pores, aligning with [PERSON]'s findings, as the transition layer porosity in all experimental groups was set to 20%.  
Figures 9 and 10 present the thermal shock damage map and stress nephograms for the A\({}_{1}\)B\({}_{3}\)C\({}_{3}\) configuration (100 \(\upmu\)m thickness, porosity = 0%, and 60% fiber content). For comparison, Figures 11 and 12 present the corresponding results for the original configuration. The black regions in the figures represent damage zones, indicating areas of crack formation under experimental conditions [66]. A larger extent of black areas signifies more severe damage. The optimized parameters result in significantly reduced thermal shock damage, enhancing the material's resistance. After optimization, damage is mainly observed at the interfaces between the coating and transition layer, and between the transition layer and substrate, whereas the original configuration shows more extensive damage. This indicates that these interfaces are weak points in the material system. Minimizing compositional differences across these boundaries is recommended to improve thermal shock resistance [67]. After the third thermal shock, the optimized coating layer still maintains its load-bearing capacity, while the original coating layer fails. Additionally, the stress distribution in the optimized transition layer is more uniform, facilitating better stress tolerance.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Factor A** & **Factor B** & **Factor C (Fiber Content)** & **Mean SDEG** \\  & **(Porosity)** & **(Coating Thickness)** & **Content)** & **Value** \\ \hline k\({}_{1}\) & 0.62 & 0.64 & 0.89 & \\ \hline k\({}_{2}\) & 0.66 & 0.65 & 0.55 & \\ \hline k\({}_{3}\) & 0.63 & 0.62 & 0.48 & \\ \hline R & 0.04 & 0.03 & 0.41 & \\ \hline Priority of & & & C \(>\) A \(>\) B & \\ Factors & & & \\ \hline Optimal & A\({}_{1}\)B\({}_{3}\)C\({}_{3}\) (no Porosity, 100 \(\upmu\)m Thickness, and 60\% Fiber Configuration & Content) & \\ \hline \hline \end{tabular}
\end{table}
Table 11: _Cont._Figure 10: Stress nephograms for the A\({}_{1}\)B\({}_{3}\)C\({}_{3}\) model (unit: 10\({}^{3}\) GPa): (**a**) after the first thermal shock, (**b**) after the second thermal shock, and (**c**) after the third thermal shock.  
Figure 9: Damage maps for the A\({}_{1}\)B\({}_{3}\)C\({}_{3}\) model: (**a**) after the first thermal shock, (**b**) after the second thermal shock, and (**c**) after the third thermal shock.