Tribological behaviors of carbon series additions reinforced CF/PTFE composites at high speed

Effect of different molding pressures on the properties of glass fiber / molybdenum disulfide / Polytetrafluoroethylene composites

Both glass fiber (GF) and molybdenum disulfide (MoS2) can enhance the comprehensive properties of PTFE (polytetrafluoroethylene)-based composites, however the properties of the composites are significantly influenced by the molding pressure utilized. In this study, GF/MoS2/PTFE composites were produced under varied molding pressures (50–70 MPa), and the composites’ mechanical and tribological properties were evaluated. The results showed that the tribological parameters (such as friction coefficient and volumetric wear rate) and mechanical parameters (such as density, hardness, tensile strength, and elongation at break) varied depending on the molding pressure. When the molding pressure was 50 MPa, the GF/MoS2/PTFE composites displayed their finest mechanical properties. The composite had the best wear resistance with the lowest wear rate of only of 2.135 × 10−6 mm3/Nm at a molding pressure of 60 MPa and the lowest friction coefficient of 0.166 at a molding pressure of 70 MPa. The increased molding pressure that was employed to make the samples, as predicted by SEM analysis, would lead to greater residual stresses inside the specimens, which would ultimately result in cracking and peeling. In the friction test, specimens with a lower forming pressure are more likely to have surface furrows that are deeper and wider, as well as to shed their filler. Due to the increased molding pressure, the depth of furrows and filler shedding on the composite surface are also more apparent.

Tribological Behavior of Reinforced PTFE Composites and Un-Reinforced Polyketone-Based Materials against Coated Steel

In this study, two polymeric materials were tested in a dry rotating “pin-on-disc” configuration against differently coated surfaces, to evaluate their tribological response under conditions, such as those of rotary lip seals, and to identify the wear mechanism of each coupling. A PTFE based material, reinforced with glass fibers and a solid lubricant, and unreinforced polyketone were tested against a chromium oxide coating deposited by plasma thermal spraying, a CrN/NbN superlattice coating deposited by Physical Vapor Deposition (PVD), and a Diamond-Like Carbon (DLC) coating obtained through a hybrid PVD/PECVD (Plasma-Enhanced Chemical Vapor Deposition) process. The PTFE matrix composite offers better overall performance, in terms of specific wear rates and friction coefficients than polyketone. Although the tribological behavior of this material is generally worse than that of the PTFE matrix composite, it can be used without reinforcing fillers. Our analysis demonstrates the importance of transfer-film formation on the counter-surfaces, which can prevent further wear of the polymer if it adheres well to the counterpart. However, the tribofilm has opposing effects on the friction coefficient for the two materials: its formation leads to lower friction for PTFE and higher friction for polyketone.