# Preparation and Tribological Behaviors
## 3 Results
### Mechanical Properties  
The tribological properties of a material are closely related to its hardness, which is always considered to represent the scratch resistance, abrasive resistance, and cutting resistance of the material surface [38; 39]. To investigate the reason for the super wear performance of composites, the Vickers hardness and tensile strength of PEEK, PEEK/GOs, PEEK/MoS\({}_{2}\)s, and PEEK/GO/MoS\({}_{2}\) are shown in Figure 6. As shown in Figure 6a, the Vickers hardness of PEEK/GOs increases with the increasing of GO content. The Vickers hardness of PG03 is 25.65 HV, and the value of PG1 reaches 28.39 HV, which is about 15% higher than that of PEEK. Interestingly, the Vickers hardness of PG07 is around 13% higher than that of PEEK, which is only 2% lower than that of PG1. This variation trend of the Vickers hardness of PEEK/GO is consistent with the reported results of [PERSON] et al. [3] and [PERSON] et al. [38]. It can be seen that the Vickers hardness of PEEK/MoS\({}_{2}\)s is gradually increased firstly, and then the Vickers hardness decreases after the MoS\({}_{2}\) content beyond 15 wt.%. The PM15 is the largest, which is 25.26 HV, and it is about 2% higher than that of PEEK. PM20 and PM25 are almost the same as that of PEEK. This coincides with the results of [PERSON] et al. [25; 40]. The Vickers hardness of PG07 PM15 is around 1.1 times that of PEEK, and it is 26.42 HV. Interestingly, its Vickers hardness is 5% higher than that of PM15, but 6% lower than that of PG07, so this confirms that GO has a better effect on  
Figure 4: Schematic illustration of friction and wear of PEEK (**a**), PEEK/GOs (**b**), PEEK/MoS\({}_{2}\)s (**c**), and PEEK/GO/MoS\({}_{2}\) (**d**). Figure 5: EDS mapping images of PG07 PM15. (**a**) C, (**b**) S, (**c**) Mo and (**d**) element scale diagram  
improving the Vickers hardness of composites than MoS\({}_{2}\). The addition of GO or MoS\({}_{2}\) could reinforce the formation of cross-networked structures and produce reorganization of amorphous polymer chains in composites, which provide a higher resistance against the normal load applied. The higher hardness of PEEK/GOs is related to the high hardness of GO [41]. The excellent hardness is beneficial to the tribological properties of composites, which coincides with the results of Figure 2.  
In general, the tensile strength of a material has a close relationship with its tribological behaviors [2; 3]. As shown in Figure 6b, the tensile strength of PEEK is 108.3 MPa, which is in agreement with [PERSON] et al. [42]. The tensile strength of PEEK/GOs increases with increasing of GO content. When the content is lower than 0.7 wt.%, the tensile strength and GO content has a linear relationship. After that, the increment of tensile strength begins to decrease. The tensile strength of PG07 is 6% higher than that of PEEK, while PG1 is only 0.5% higher than that of PG07. Moreover, the introduction of GO could drastically affect the toughness of composites. The contribution of GO to the improvement of tensile strength is due to GO having good compatibility with PEEK and strong binding force, which improves the crystallinity and uniformity of PEEK matrix. However, when the GO content exceeds 0.7 wt.%, the tensile strength of the PEEK/GOs increases very little, due to the stress concentration caused by GO agglomeration. The tensile strength of PEEK/MoS\({}_{2}\)s increases firstly, and then decreases with the increasing of MoS\({}_{2}\) content. The tensile strength of PM10 is 111.1 MPa, and it is 3% higher than that of PEEK. Interestingly, when the MoS\({}_{2}\) content exceeds 15 wt.%, the tensile strength of PEEK/MoS\({}_{2}\) is lower than that of PEEK. The tensile strength of PM25 decreases 12% compared with that of PEEK. It is worth noting that the MoS\({}_{2}\) has a positive effect on the tensile strength of composites, but excessive content will have a negative effect. The lamellar structure of MoS\({}_{2}\) causes shear slip of the composites under stress.