# Friction and Wear Performances of Materials for Wind Turbine Sliding Bearing Bushes
## 3 Wind Turbine Sliding Bearing Bearing Bush Coating Preparation
### Experimental Verification of Laser Power Parameters  
The macro morphologies of two groups of single coatings prepared under varying laser powers are depicted in Figure 6. As illustrated in Figure 6a-c, when the laser power is low, inadequate laser irradiation prevents powder melting, resulting in the deposition of large powder particles. Simultaneously, uneven heat in the molten pool leads to varied solidification rates, influencing the coating contour. Local overheating contributes to a yellowish tint on the coating. When the laser power increases to 1300 W, the coating surface becomes notably flat, displaying a metallic luster. Higher energy irradiation accelerates powder particle dissolution, mitigates the deposition effect, and enhances the forming quality of the coating surface. However, excessive laser power induces elevated melting pool temperatures, causing over-liquefaction of the powder and darkening of the coating color. Slow solidification rates and continuous flow in the molten pool result in oblique folds on the surface. Thus, at 1300 W, the optimal forming quality for the CoCrFeNiMo high-entropy alloy coating can be achieved through laser cladding.  
As illustrated in Figure 6d-f, at 800 W laser power, insufficient irradiation energy causes incomplete melting of the cladding powder, leading to a phenomenon of sticky powder. The coating surface appears rough, high, narrow, and prone to peeling off, contributing to poor metallurgical fusion quality. At 1000 W laser power, the coating surface quality significantly improves, and the sticky powder phenomenon disappears.  
Figure 6: Macroscopic morphologies of the single-channel coating corresponding to different process parameters: (**a–c**) CoCrFeNiMo high-entropy alloy coating: (**a**) 1100 W, (**b**) 1300 W, (**c**) 1500 W; (**d–f**) Ni-Cr-Mo-Si alloy coating: (**d**) 800 W, (**e**) 1000 W, (**f**) 1200 W.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **CoCrFeNiMo High Entropy** & **Ni-Cr-Mo-Si Alloy Coating** \\ \hline \multirow{2}{*}{Laser power/W} & 1100 & 800 \\  & 1300 & 1000 \\  & 1500 & 1200 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Different laser power schemes.  
Higher energy density enhances molten pool wetting and fluidity, promoting uniform heat and mass transfer and increasing the dilution rate. The cladding trajectory exhibits regular and smooth contours. However, further increases in laser power result in excessive energy density, deepening and widening the molten pool. The cladding layer becomes flat, losing its effectiveness in surface modification. Simultaneously, the temperature gradient inside the molten pool rises, and the solidification rate increases, causing powder adhesion to the coating before complete melting. The sticky powder phenomenon reoccurs. In summary, for optimal forming quality in the preparation of Ni-Cr-Mo-Si alloy coating through laser cladding, the corresponding laser power is determined to be 1000 W.  
The optimal process parameters were established through an interactive verification method involving simulation and single-pass cladding experiments. Based on a scanning speed of 6 mm/s, powder feeding capacity of 1.6 r/min, and defocusing capacity of 16 mm, CoCrFeNiMo high-entropy alloy coating was prepared on the surface of 9 Cr18 bearing steel at 1300 W and 1000 W, respectively. Similarly, Ni-Cr-Mo-Si alloy coating was prepared on the surface of MTCrMoCu30 wear-resistant cast iron.