# Preparation and Tribological Behaviors
## 3 Results
### Tribological Behaviors
With increase of GO content, the fatigue wear becomes more and more dominant, and adhesive wear and abrasive wear gradually reduce. This indicates PEEK/GOs show signs of severe fatigue wear, adhesive wear, and mild abrasive wear. The PM5 (Figure 3e) represents more even grooves parallel to the sliding direction, plastic deformation, randomly adhered material, and wear debris. Nevertheless, the worn surface of PM15 (Figure 3f) exhibits a small quantity of shallow grooves, adhered material, and wear debris. Simultaneously, a water wave-like morphology is obviously observed. Similar to PEEK, the worn surfaces of PM5 and PM15 result from the same wear mechanism, i.e., mainly abrasive wear and adhesive wear, except the wear degree of individual components is different. Whereas in the case of PM25 (Figure 3g), the worn surface shows a completely different morphological feature from those of PM5 and PM15. It is very smooth and covered by an almost uniform and essentially continuous light gray layer. In addition, the gray layer can avoid direct contact between composites and counterpart, which further improves the tribological properties. It can be observed that there is very little adhesive material and plastic deformation on the worn surface, but no obvious grooves and wear debris. This indicates that PEEK/MoS2s possess better friction reduction and wear resistance compared to PEEK and PEEK/GOs. As shown in Figure 3e',','g', there are still obvious wear area boundaries. The accumulation of boundary materials is attributed to the plastic deformation of PEEK matrix. With increasing of MoS2 content, the wear depth reduces and the coverage rate of MoS2 film increases, which are due to the unique lubrication characteristics of MoS2. Furthermore, it is worth noting that MoS2 content has a positive contribution to wear resistance, i.e., the higher the MoS2 content, the better the wear resistance (Figure 2c). The PG07 PM15 (Figure 3h,h') represents very even, shallow, narrow grooves parallel to the sliding direction, a small quantity of microcracks, a water wave-like scratch, spalling pit, and plastic deformation. Its worn surface is smoother than those of PG07 and PM15. It can be observed that the worn surface shows neither the severe sheet spalling in the case of PG07, nor the deep grooves and wear debris in the case of PM15. Compared with other composites, a typical wear area boundary is observed in Figure 3h'. Such morphology features indicate that the wear mechanism of PG07 PM15 is the combination of slight fatigue wear, mild abrasive wear, and adhesive wear. It can be concluded that the synergism between GO and MoS\({}_{2}\) helps to form a good and tenacious lubricant film on the interface between composites and counterpart. Figure 3: _Cont._  
In order to better explain tribological behaviors of composites, Figure 4 presents a schematic diagram under a dry sliding condition. In the case of PEEK (Figure 4a), the grooves of worn surface are mostly due to the stiffness of counterpart of steel pin being much higher than that of PEEK. During the friction and wear process, the hard protuberances on the steel pin penetrate into the PEEK, and remove softer PEEK under applied contact load and friction shear. On account of the combination of the plastic deformation, delamination, and friction shear, PEEK is transferred to the counterpart surface to form a lubricant film. For the PEEK/GOs (Figure 4b), the wear characteristics may be due to the fact that the hardness and tensile strength of the composites is improved by addition of GO with large specific surface area and wrinkle, leading to less flow stress and considerably less plastic deformation for the sliding contact surface, as well as the decrease in the toughness of composites. Moreover, GO may agglomerate in the PEEK matrix, which is more likely to lead to the initiation of microcracks.