Wear-resistant and hydrophobic characteristics of PTFE/CF composite coatings

Bit balling phenomenon usually occurs in the process of oil exploitation by polycrystalline diamond compact (PDC) bit. Carbon fiber (CF) reinforced polytetrafluoroethylene (PTFE) composite coatings are expected to apply to PDC bits for improving the friction and wear properties and hydrophobicity. In this study, a particular process was used to prepare PTFE/CF composite coatings with different content of CFs. The mass fractions of CF in PTFE are 10%, 15% and 20%, respectively. The surface morphology of the coatings was observed by scanning electron microscope (SEM) and 3D measuring laser microscope, and water contact angles (WCA) were measured. The results showed that when the mass fraction of CF is 20%, the friction coefficient is 0.17 +/- 0.01, which doesn't increase much; the wear rate is 2.74 x 10(-4) mm(3)/Nm, which is the lowest of all and decreases by about 29.7%, compared with that of pure PTFE. The WCA of PTFE/20%CF composite coating increases to 122.0 degrees +/- 2.0 degrees, which shows good hydrophobicity, while the WCA of pure PTFE coating is only 106.3 degrees +/- 1.5 degrees. Abrasive wear and adhesive wear are main wear mechanism of composite coatings under air condition.