The Effect of Temperature on the Friction and Wear Properties of PTFE/Kevlar Fabric Composites

Self-lubricating fabric composites are the key materials in self-lubricating joint bearings, however, during the friction process, high temperature and high speed working conditions, the large accumulation of frictional heat leads to a significant decrease in the overall stability of the composites. It is of great significance to explore the transformation of friction coefficient and wear rate of composites under different temperatures and the evolution of material friction and wear behavior and damage mechanism to improve the self-lubricating performance and wear life of spherical plain bearings. In this paper, the prepared PTFE (Polytetrafluoroethylene)/Kevlar fabric composites were subjected to reciprocating friction and wear tests at different temperatures (25~150 ℃), loads (20~40 MPa), and frequencies (6~10 Hz) by using a heavy-duty reciprocating friction and wear tester. The test results showed that the change of load and frequency had much less effect on the composites than the temperature. The change of frequency could be defined as the change of friction temperature. At 25 ℃, the friction coefficient and wear rate of the material decreased gradually with the increase of frequency from 6~10 Hz. As the load increased from 20 MPa to 40 MPa, the friction coefficient and wear rate of the material first decreased and then increased. However, when the temperature started to act, as the temperature increased from 25 ℃ to 150 ℃, the friction coefficient and wear rate of the composite material showed a tendency of decreasing and then increasing under the influence of temperature. When the temperature was 75 ℃, the composites showed excellent friction and wear performance, and their friction coefficient and wear rate reached the minimum value. When the ambient temperature, load and frequency were 75 ℃, 30 MPa and 6 Hz, the friction coefficient of the composite material was about 0.039 and the wear rate was about 5.98×10⁻¹⁵ m³/(N·m). As the temperature increased above 100 ℃, the material friction coefficient and wear rate increased dramatically and the friction coefficient fluctuated drastically, and the mean value of the friction coefficient was as high as 0.117 and the standard deviation was as high as 0.024 5 at 150 ℃. In-depth analyses of the composites' wear surfaces, transfer films, and abrasive debris using scanning electron microscopy (SEM) and X-ray spectroscopy (EDS) revealed that the wear behaviors of the composites were related to the fracture behavior of PTFE fibers. As the temperature increased from 25 ℃ to 150 ℃, the PTFE fiber fracture behavior gradually changed from sliding shear extrusion to fiber pulling out, cutting off, and fatigue spalling. 75 ℃, the PTFE fiber plastic flow phenomenon was extremely obvious, and the wear surface of the F element content accounted for as high as 34.2%. At this time, the friction process formed in the abrasive debris presented a fine block form, and the transfer film formed on the surface of the dyadic pin uniformity and stability was better, so at this time the material's friction coefficient fluctuation was more stable, the standard deviation of the standard deviation was low to 0.005 3. Correspondingly, with the temperature increased from 25 ℃ to 150 ℃, the composite material of the abrasive wear mechanism, from abrasive wear into a slight adhesive wear, and then transformed into a serious adhesive wear. wear and accompanied by thermal composite fatigue wear. In order to ensure the wear resistance of self-lubricating materials, the friction temperature of 50~75 ℃ could make the composites maintain in the stage of slight adhesive wear for a long time.