Comparative Evaluation of Tribological Characteristics of CF/PEEK and CF/PTFE/Graphite Filled PEEK Sliding against AISI630 Steel for Seawater Hydraulic Piston Pumps/Motors

Tribological behaviors of 30 vol% carbon fiber-reinforced polyetheretherketone (PEEK-1) and 30 vol% carbon fiber/PTFE/graphite-reinforced polyetheretherketone (PEEK-2) sliding against AISI630 steel under seawater lubrication were investigated comparatively with a ring-on-ring contact test apparatus. The results revealed that PEEK-2 had a lower friction coefficient and much better wear resistance than PEEK-1, especially under a relatively heavy load. Furthermore, PEEK-2 exhibited much better friction and wear properties under seawater lubrication than under dry friction, and it was slightly inferior to that under pure water lubrication due to the corrosive effect of seawater on the surface of AISI630 steel. Additionally, the worn surface morphology of PEEK composites and AISI630 steel were obtained through scanning electron microscopy (SEM) and optical microscopy, respectively. The main tribological mechanisms of the friction pair under seawater lubrication were abrasive wear and indirect corrosive wear. The corrosion of the AISI630 surface caused by Cl- and SO4- of seawater performed more dramatically than the lubricating effect of Ca2+ and Mg2+ on the contacted surface and deteriorated the tribological behaviors of the matched material to some extent. This research will provide guidance for materials screening of key friction pairs in seawater hydraulic piston pumps/motors.