## 3 Tests Results
### Wear Mechanism  
As shown in Figure 7, the wear area of the SCF-modified bearing bush was photographed using a confocal scanning laser microscope, thus revealing the microscopic wear morphology of the modified bush under different test pressures.  
Figure 7: Micromorphology of SCF-modified bearing bush under different test pressures: (**a**) the wear micromorphology of 320 \(\upmu\)m at 15 MPa; (**b**) the wear micromorphology of 80 \(\upmu\)m at 15 MPa;(**c**) the wear micromorphology of 320 \(\upmu\)m at 20 MPa; (**d**) the wear micromorphology of 80 \(\upmu\)m at 20 MPa; (**e**) the wear micromorphology of 320 \(\upmu\)m at 25 MPa; (**f**) the wear micromorphology of 80 \(\upmu\)m at 25 MPa; (**g**) the wear micromorphology of 320 \(\upmu\)m at 30 MPa; (**h**) the wear micromorphology of 80 \(\upmu\)m at 30 MPa.  
As depicted in Figure 7, the phenomenon of stacking on the surface of the SCF-modified bearing bush is relatively noticeable when the test pressure is at 15 and 20 MPa, while at test pressures of 25 MPa and above, specifically 30 MPa, there is no obvious sign of stacking. Upon observation, it was noted that only a few isolated regions under certain pressures exhibited furrows on the worn surface. These furrows were not highly concentrated, and the extent of scratching was not severe, attributed to the slight furrows caused by the peeling metal particles on the roller. The self-lubricating layer of the bearing bush generates a less severe furrow scratch due to the small size of the metal particles.  
With the continuous increase of experimental pressure, severe accumulation occurs at the friction boundary, accompanied by a large number of fiber shear fractures and fiber edge peeling. During the friction process, the carbon fiber has varying degrees of wear, with some of the carbon fiber being cut or scattered and the carbon fiber adhering to the matrix material and lubricant. It can be seen that the carbon fiber-modified bearing bush is more sensitive to speed changes and is seriously damaged in high-speed working conditions. The friction coefficient is related to the bonding strength of the interface between the filler fiber and the matrix and the antifriction effect of the lubricant. The amount of wear is related to the bearing capacity of high-strength carbon fiber and the formation of a well-established dual sliding surface transfer film.  
The wear mechanism of the modified bearing bush was analyzed through the use of scanning electron microscopy (SEM) under different test pressures, with the results presented in Figure 8. As the test pressure continues to increase, the pressure exerted on the three-layer composite bearing bush also rises. Due to the soft nature of its self-lubricating layer, it is prone to compression deformation under increased pressure, which in turn enhances the compactness of the self-lubricating layer. During this process, the fibers embedded within the self-lubricating layer are able to more tightly integrate with the PEEK matrix, reducing wear caused by fiber breakage and subsequently lowering the friction coefficient of the three-layer composite bearing bush. Moreover, with the escalation of test pressure, PTFE solid lubricant is able to more effectively fill the wear areas, thereby preventing the extensive material disintegration caused by localized wear.  
Figure 8: Wear diagram of the modified three-layer composite bearing bush under different test pressures: (**a**) SCF-modified bearing bush at 15 MPa; (**b**) SCF-modified bearing bush at 30 MPa.  
As shown in Figure 8, the SCF-modified three-layer composite bearing bush did not show obvious SCF peel modification of the PEEK matrix. However, under the test pressure of 15 MPa, the extrusion action on the micro-convex surface of the self-lubricating layer is not enough to make it smooth, and obvious material avulsion and micro-cracks are produced. When the test pressure increased to 30 MPa, the bulges on the wear surface were smoothed, and the material avulsion phenomenon was significantly reduced.