## 3 Results and Discussion  
### Microscopic Morphology and Organizational Structure  
#### 3.1.1 SEM Morphology Analysis of Ceramic Coatings  
Scanning electron microscope (SEM) was used to analyze the microscopic morphology of the prepared TiO\({}_{2}\)/CuO composite modified Al\({}_{2}\)O\({}_{3}\) microspheres and the sintered ceramic coating samples. Figure 4a,b show the alumina raw material and titanium oxide nanoparticles and copper oxide nanoparticles modified alumina, respectively. Figure 4c,d show the surface morphology of the ceramic coatings prepared by heating to 400 \({}^{\circ}\)C at different heating rates and holding for 1 h. The cross-section morphology of the coatings is shown in Figure 5, which further reveals their organizational structure and interfacial bonding. Figure 4: The surface morphology of different samples: (**a**) raw-Al\({}_{2}\)O\({}_{3}\); (**b**) Al\({}_{2}\)O\({}_{3}\)@TiO\({}_{2}\)/CuO; (**c**) nano-TiO\({}_{2}\) ceramic coating; 5\({}^{\circ}\)C/min; (**d**) nano-TiO\({}_{2}\) ceramic coating; 2\({}^{\circ}\)C/min. Figure 4a depicts the 13 \(\upmu\)m aluminum trioxide raw material, while Figure 4b illustrates the alumina modified with nano-TiO\({}_{2}\) and nano-CuO. The surface of the modified aluminum trioxide is evenly coated, and the nano-TiO\({}_{2}\) and nano-CuO particles are uniformly distributed on its surface, forming a well-defined core-shell structure. In Figure 4c, the ceramic composite coating prepared by warming up to 400 \({}^{\circ}\)C at 5 \({}^{\circ}\)C/min and holding temperature for 1 h has large pores on the surface, uneven size distribution of ceramic particles, rough surface and poor densification. Figure 4d shows that after the ceramic coating is warmed up to 400 \({}^{\circ}\)C at 2 \({}^{\circ}\)C/min and held at 400 \({}^{\circ}\)C for 1 h, the pores on the surface basically disappeared, the particles are uniformly distributed, the surface is relatively flat, and the densification is obviously improved. The defects such as porosity in ceramic coating are mainly attributed to the following two factors:  
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2. Insufficient room temperature drying time. After the coating is prepared, it needs to be dried at room temperature to remove the free moisture inside the coating. However, if the drying time is insufficient, the residual liquid moisture evaporates too quickly during the high-temperature curing process, making it easy to form air bubbles, which can create porosity inside and on the surface of the coating. 3. Influence of temperature rise rate. If the initial temperature rise rate is too fast during the curing process, it will easily lead to the formation of pores and cracks. The main reason for this is that the free water that is not completely removed from the coating is violently evaporated during the rapid temperature rise, resulting in the formation of tiny pores within the coating. To avoid this problem, a lower temperature is usually used to slowly increase the temperature, so that the coating is fully cured in the low-temperature stage, thus reducing the generation of pores and improving the densification of the coating. Figure 5a,b show the cross-sectional morphology of ceramic coatings prepared at different heating rates (5 \({}^{\circ}\)C/min and 2 \({}^{\circ}\)C/min). As can be seen in Figure 5a, the cross-section of the coating sintered at 5 \({}^{\circ}\)C/min heating rate is more disordered, and there are obvious pores; in contrast, the cross-section of the coating obtained at the 2 \({}^{\circ}\)C/min heating rate corresponding to Figure 5b is more regular, and no obvious voids or bubbles can be observed. In addition, from the cross-sectional morphology analysis, the ceramic coatings prepared at different heating rates are tightly bonded with the metal substrate, but there is a clear interfacial demarcation line between the two, which indicates that no fusion welding  
Figure 5: Cross-sectional morphology of nano-TiO\({}_{2}\) ceramic coating: (a) 5 \({}^{\circ}\)C/min; (b) 2 \({}^{\circ}\)C/min. phenomenon has occurred.