Tribological Performance of PDA/PTFE + Graphite Particle Coatings on 60NiTi

Abstract 60NiTi has unique combinations of high shock load and corrosion resistance, which is suitable for load-bearing applications exposed to chemically aggressive environments. However, it exhibits poor tribological properties in dry sliding contact conditions. Polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings are shown to reduce friction and wear of 60NiTi significantly. In this study, using Si3N4 balls as the counterface material, the effects of adding graphite particles (GrP) to the PTFE layers of the PDA/PTFE coatings on the sliding properties of 60NiTi were studied. The obtained results were compared to those of the PDA/PTFE coated and uncoated 60NiTi. The results showed that both types of coatings significantly decreased the coefficient of friction (COF) and wear of the 60NiTi substrates and the wear of the counterface balls. The PDA/PTFE + 0.25 wt% GrP coatings have less porosity and approximately 2.4 times durability when compared to the PDA/PTFE coatings. Scratch tests on the coated surfaces also revealed better adhesion strength, higher load-carrying capacity, and enhanced transfer films on the counterface balls for the PDA/PTFE + 0.25 wt% GrP coatings. The less porosity, the enhanced adhesion strength, and the transfer film contributed to the longer wear life of PDA/PTFE + 0.25 wt% GrP coatings on 60NiTi.