## 3 Tests Results
### EDS Spectral Analysis  
Different friction morphologies of the bearing bush under various pressure conditions were selected, and the test results are shown in Figure 9. When the applied pressure rises from 15 to 25 MPa, a notable improvement in the surface finish is observed, reflecting the increased densification of the natural lubrication layer. At this higher pressure range of 20 to 30 MPa, individual carbon fibers demonstrated compromised integrity, with isolated instances of failure resulting in fragmented fibers rather than complete fiber breakage or removal. The material that detaches from the pure PEEK base mostly appears in the form of debris, which is expelled from the friction interface. Consequently, no transfer film is formed on the metal counterface [33]. The content of fluorine elements on the friction surface of the metal counterface represents the degree to which material is effectively transferred from the matrix to the metal mating surface during the friction process [34].  
After completing the friction test, an Energy Dispersive Spectroscopy (EDS) analysis was conducted on the counterface of the bearing bush, as depicted in Figure 10. The EDS analysis provided elemental composition data, revealing the elemental distribution and  
Figure 9: SEM micrographs of wear of SCF modified bearing bush: (**a**) at 15 MPa; (**b**) at 20 MPa; (**c**) at 25 MPa; (**d**) at 30 MPa. Black circles: gullies, white dotted line: interface differentiation, red circles: resin fragments, yellow rectangular box: fiber fracture.  
potential material transfer or degradation that occurred during the friction interaction. Further observation of the distribution maps of carbon, oxygen, and sulfur elements on the bearing bush counterface revealed that these elements have relatively high contents on the surface. The carbon and oxygen elements are primarily derived from the PEEK resin matrix and the filled PTFE, respectively, while the sulfur element is mainly from the PTW resin matrix. At different wear locations, the distribution of carbon in the resin accumulation friction morphology is more extensive, which is linked to the particles impurities predominantly being resin-based.  
The distribution of oxygen is relatively uniform across various pressures. The distribution degree of sulfur increases first and then decreases with the gradual increase of pressure. Given that the chemical composition of the rollers consists of GCr15 SiMn with  
Figure 10: EDS analysis of worn surfaces of bearing bush surface after abrading: (**a**) friction morphology under different pressures; (**b**) EDS distribution of C element in counterface transfer film of bearing bush; (**c**) EDS distribution of O element in counterface transfer film of bearing bush; (**d**) EDS distribution of S element in counterface transfer film of bearing bush; (**e**) EDS distribution of Zn element in counterface transfer film of bearing bush.  
sulfur less than 0.020%, it can be essentially ascertained that they originate from the PTW resin matrix. Based on the changing pattern of friction coefficients under different operating conditions, it is inferred that the addition of a small amount of PTW facilitates its complete transfer to the friction interface, thereby promoting the growth of the transfer film. It can be observed from the distribution map of zinc that there is basically no zinc present at the location of carbon fibers, which proves that it originates from the bearing itself. During the frictional wear between the metal and the self-lubricating bearing bush, the film that grows plays a crucial role in not only decreasing the friction coefficient but also boosting the bearing capacity.