# Friction and Wear Performances of Materials for Wind Turbine Sliding Bearing Bushes
## 4 Wind Turbine Sliding Bearing Bush Friction and Wear Properties Analysis
### Load Calculation of Friction and Wear Test of Sliding Bearing Bush Material
In the stabilization stage, the micro-convex bodies between the grinding pairs interleave and rub until fatigue yield is reached, resulting in their detachment from the material surface in the form of debris. Some debris accumulates on the edge of the wear mark with reciprocating motion, while another portion intensifies friction as the wear pair moves within the contour of the wear mark. The remaining debris is compacted to form a protective layer during the movement of the wear pair. When the effects of the latter two reach equilibrium, the friction coefficient enters a stable stage marked by zigzag fluctuations. As illustrated in Figure 9a, the CoCrFeNiMo high-entropy alloy coating attains a minimum average friction coefficient of 0.45 under a 50 N load. As the applied load increases, the friction coefficient of the CoCrFeNiMo high-entropy alloy coating experiences an initial decrease followed by an increase. This phenomenon is attributed to the escalation of frictional shear stress under dry friction conditions with an increase in the applied load. Throughout the wear process, the generation of debris intensifies, some of which falls and embeds itself between the wear pairs. These debris are compacted under high loads, forming a relatively smooth protective layer. Simultaneously, the friction on the contact surface transitions from different materials to the same materials, further reducing the friction coefficient. However, as the load continues to increase, elastic deformation occurs on the specimen surface, leading to an increase in the contact area between the friction pairs. Consequently, the number of micro-convex peaks in actual contact increases, causing an increase in the friction coefficient. Additionally, under a 40 N load, the wear time for the sample to reach the stable stage is prolonged. This can be attributed to the enhanced  
Figure 9: Friction and wear analysis of coatings under different loads: (**a,b**) CoCrFeNiMo high-entropy alloy coatings, (**c,d**) Ni-Cr-Mo-Si alloy coatings. anti-friction wear resistance of the coating surface, necessitating an extended run-in time. Figure 9c indicates that the Ni-Cr-Mo-Si alloy coating achieves a minimum average friction coefficient of 0.49 under a 30 N load. The friction coefficient increases with the rise in the applied load, with the overall minimum occurring under a 30 N load, signifying optimal anti-friction properties. With the increasing applied load, the shear motion between the grinding pairs intensifies, and the extrusion deformation of the coating surface becomes more pronounced, leading to an increase in the friction coefficient. Additionally, higher loads result in elevated micro-temperature rise between grinding pairs, fostering the formation of an oxide film on the surface of the wear marks, thereby intensifying friction and subsequently increasing the coefficient of friction. The wear mass, wear rate, and relative wear resistance of the two groups were measured to characterize the coating surface's wear performance and determine the impact of different loads on the wear resistance of the coating surface. Wear rate (\(\omega\)) and relative wear resistance (\(\epsilon\)) can be calculated using Formula (2) and (3), respectively [33; 34]:  
\[\omega=\frac{\text{m}}{F*s} \tag{2}\]  
\[\epsilon=\frac{\overline{\text{m}}}{\overline{\text{m}_{i}}} \tag{3}\]  
where m represents the wear mass, \(F\) represents the applied load, \(s\) represents the wear travel, \(\overline{m}\) represents the average wear mass, and \(m_{i}\) represents the wear mass of a single sample (\(i\) = 1, 2, 3). As depicted in Figure 9b,d, the wear quality and wear rate of the CoCrFeNiMo high-entropy alloy coating exhibit an initial decrease followed by an increase with an increase in applied load.