# Preparation and Tribological Behaviors
## 3 Results
### Tribological Behaviors
Figure 2e shows the variation of wear rate (\(K\)) of PEEK, PEEK/GOs, PEEK/MoS\({}_{2}\)s, and PEEK/GO/MoS\({}_{2}\). The wear rate of PEEK is \(6.213\times 10^{-6}\) mm\({}^{3}\)/Nm, which is in the same order of magnitude as the value obtained by [PERSON] et al. under a dry sliding condition [2]. The wear rate of PEEK/GOs significantly decreases, and then slightly fluctuates in a very small scale, with increasing of GO content. When the GO content increases from 0.5 wt.% to 0.7 wt.%, the wear rate obviously decreases. However, when the GO content exceeds 0.7 wt.%, the wear rate is basically constant. Regardless of the GO content, the wear rates of all PEEK/GOs are less than PEEK, indicating the positive effect of GO on the wear resistance. The wear rate of PG03 and PG05 reduces by 10% and 15% compared with PEEK,  
Figure 2: Friction coefficient of poly-ether-ether ketone (PEEK) and PEEK/graphene oxides (GOs) (**a**,**c**), PEEK/MoS\({}_{2}\)s and PEEK/GO/MoS\({}_{2}\) (**b**,**d**), and wear rate of PEEK, PEEK/GOs, PEEK/MoS\({}_{2}\)s, and PEEK/GO/MoS\({}_{2}\) (**e**). respectively. Nevertheless, PG07 has the lowest wear rate of \(4.169\times 10^{-6}\) mm\({}^{3}\)/Nm, which decreases by 32.9 % compared with PEEK. In other words, PG07 has the best wear resistance. The variation in wear rate of PEEK/MoS2s obviously decreases with the increasing of MoS2 content. When the MoS2 content is less than 20 wt.%, the wear rate of PEEK/MoS2s approximately reduces linearly, whereas the difference in wear rate between PM20 and PM25 is minimal; however, the wear resistance of PEEK/MoS2s is significantly increased in comparison with PEEK. For instance, the PM5 has a maximum wear rate of \(K=5.011\times 10^{-6}\) mm\({}^{3}\)/Nm, which decreases by 19% compared with PEEK; whereas PM25 has a minimum wear rate of \(3.333\times 10^{-6}\) mm\({}^{3}\)/Nm, reduced by 46% compared with PEEK. The wear rate of PG07 PM15 decreased by 35% compared with PEEK, which was almost equal to that of PM15 and less than that of PG07. It can be concluded that MoS2 plays a major role in the wear resistance of PG07 PM15. It is worth noting that the abilities of friction reduction and wear resistance of the composites with both GO and MoS2 are not necessarily better than those of the composites with single GO or MoS2. The wear resistance and friction reduction of composite are attributed to the enhancement of its hardness, tensile strength, and thermal stability. On the other hand, the self-lubrication properties of GO and MoS2 also have positive effects on tribological behaviors. To facilitate the understanding of the friction and wear mechanism, representative SEM images and 3D optical morphologies of the worn surface of PEEK, PEEK/GOs, PEEK/MoS2s, and PG07 PM15 are showed in Figure 3. The PEEK (Figure 3a,a') exhibits uneven grooves parallel to the sliding direction and irregular removed material adhered back to the surface, which shows signs of abrasive wear and adhesive wear mechanism. Meanwhile, there are large amount of debris on the worn surface. The typical combination mechanism of abrasive wear and adhesive wear has been previously observed under a dry sliding condition [35]. A clear boundary is produced between the worn area and non-worn area, owing to PEEK stacking under the compressive load and friction force. The PEEK surface shows deep wear scratching. The worn surface is very rough, too. The worn surface of PG03 (Figure 3b,b') is smoother than PEEK. It exhibits several very shallow grooves, lamellar dissection, fatigue fracture, short stripped pits, and wear debris, indicating wear characteristics of brittle materials to a certain extent. There are obvious partition boundaries similar with PEEK for PG03, PG07, and PG1. However, compared with PEEK, their wear depths are slighter (Figure 3c,d,c',d'). Such characteristics may be attributed to the decrease of melting temperature of PEEK/GO, but the wear degree of the PEEK/GOs is obviously different.