Polytetrafluoroethylene matrix composites synergistically filled with mullite and carbon fiber and its tribological performances

In order to improve the tribological performances of polytetrafluoroethylene (PTFE), PTFE matrix composites filled with mullite and carbon fiber were prepared by processes such as mechanical blending, heat pre-compression and sintering etc., and the microscopic structures, mechanical properties and thermal properties of PTFE matrix composites were characterized by FTIR, XRD, universal material testing machine, Rockwell hard meter, DSC and thermomechanical analyzer respectively. Then, the friction coefficients and wear rates of the composites were measured by MRH-3 high speed ring-on-block wear tester, and a self-designed sand slurry wear apparatus with silicone oil was used to detect the sand slurry wear resistance of the composites at different temperatures. Finally, the morphologies of friction surfaces for the composites were investigated by 3D measurement laser microscope, and the friction and wear mechanisms were analyzed. The results show that mullite and carbon fiber play a role of filling and toughening in PTFE system, and the elastic modulus of 20wt% mullite-10wt% carbon fiber/PTFE composite is enhanced from 364 MPa to 874 MPa. The dry friction coefficient of 20wt% mullite-10wt% carbon fiber/PTFE composite is higher, while its wear rate decreases by more than three orders compared with pure PTFE, and the composite maintains relatively good friction coefficient and wear rate under water friction condition, the friction coefficient is 0.157 and the wear rate is 7.40 × 10^-6 mm³·N^-1·m^-1. Further, 20wt% mullite-10wt% carbon fiber/PTFE composite also shows favorable sand slurry wear resistant even at relatively high temperature. The conclusions obtained suggest that the tribological performances of PTFE matrix composites obtained by modification improve significantly, and the composites can be applied to the eccentric wear of the sucker-rod pumping well.