Effect of aramid fiber and Zno nanoparticles on friction and wear of PTFE composites in dry and LN₂ conditions

The tribological performance of PTFE and PTFE-based composites filled with aramid fiber and ZnO nanoparticles in dry sliding and liquid nitrogen (LN₂) conditions was studied comparitively. The wear scars on the test specimen were observed by scanning electron microscopy (SEM). The transfer films of the composite material formed on the sliding interfaces were studied by X-ray photoelectron spectroscopy (XPS). The tribological test results of the tribo-pairs with two ANSI 440C steel pins sliding on a composite disk showed that, compared with the pure PTFE, the friction coefficient of the PTFE-based composites filled with both aramid fiber and ZnO nanoparticles is reduced in dry sliding in room temperature (RT) air, whereas its friction coefficient is increased in LN₂. The friction coefficient of the composite filled with 5 wt% ZnO nanoparticles alone increases compared to unfilled PTFE in both RT air or in LN₂ conditions. While in LN₂, the friction coefficient of the same 5% ZnO material is lower, and the wear resistance is higher than those under dry sliding, the C-F bond cleavage in PTFE was found in transfer films formed in dry sliding or LN₂ conditions, and the F atoms were combined with Fe atoms from the sliding steel pins.