## 3 Results and Discussion
### Wear Performance  
To analyze the addition of TiC and NbC particles on the wear resistance and reveal the wear mechanism, the friction coefficient, wear volume, 2D and 3D worn surfaces of each coating, and wear ball were obtained and analyzed. The test was conducted on  
Figure 5: Microhardness distribution of 316L and composite coatings along building direction. a multi-functional surface performance tester (MFT-4000). The variation of the friction coefficient of the 316L coating and the composite coating with sliding time is shown in Figure 6. It is noted that the friction coefficients of the two coatings had similar trends over time. In the initial friction stage, the friction coefficient fluctuated greatly because of the small contact area between the GCr15 ball and the coating. In addition, the friction coefficient of the composite coating was more stable than that of the 316L coating. As the coating material was gradually removed, the friction coefficient of the coating stabilized after about 20 min. The friction coefficient of the 316L coating was 0.451 \(\pm\) 0.075 in the stable stage. The friction coefficient of the composite coating decreased to 0.381 \(\pm\) 0.030 due to the addition of TiC and NbC particles, which was 0.846 times that of the 316L coating. The 3D worn surfaces of the 316L coating and the composite coating are shown in Figure 7. Large plastic deformation can be found at the edges of the wear tracks of the two coatings, which indicates that both coatings provide good toughness. However, the depth and width of the wear tracks of the composite coating were smaller than those of the 316L coating. The cross-sectional area of the 316 coating and the composite coating after wear were also measured with 3D laser microscopy. The cross-sectional area of 316 coatings was 13,540.933 \(\upmu\)m\({}^{2}\). When TiC and NbC particles were added to the 316L alloy, the cross-sectional area of composite coating was 8164.732 \(\upmu\)m\({}^{2}\), which was 0.603 times that of the 316L coating. The results show that TiC and NbC ceramic particles can effectively reduce the wear rate of the 316L coating. Figure 6: Friction coefficient of 316L coating and composite coating. Figure 7: Three-dimensional wear morphology and sectional wear area: (**a1,a2**) 316L coating and (**b1,b2**) composite coating. To further reveal the wear mechanism of each coating, 2D and 3D magnified morphologies of the worn surfaces of the 316L and composite coatings were obtained, as shown in Figure 8. Obvious plastic deformation is observed on the worn surface of the 316L coating (see Figure 8a), and large grooves were generated along the sliding direction. When the GCr15 ball reciprocates on the surface of the 316L coating with low microhardness, it results in high local contact pressure. As a result, the material on the surface was removed by extrusion, deformation, and shearing. These tough abrasive chips are prone to adhere to the surface of the GCr15, leading to adhesive wear of the 316L coating. Therefore, the wear mechanism of the 316L coating is mainly severe plastic deformation and adhesive wear. Figure 8b indicates that no deep grooves were found on the worn surface of the composite coating. Some pits and smooth areas appeared alternately due to the peeling of the material. According to the Archard wear model, the wear resistance of materials is proportional to their microhardness [31]. These results indicate that TiC and NbC particles play an important role in preventing plastic deformation and the shear removal of composite coatings. At the initial stage of wear, the matrix material with lower microhardness was removed first. As the wear progressed, TiC and NbC hard ceramic particles in the composite coating were exposed to contact with the GCr15 ball gradually, which plays a role in the frame and reduces the removal of the matrix. At the same time, the fine grain strengthening effect leads the material to have good toughness and increases the bonding force between the ceramic particles and matrix.