The Effects of PTFE Thickness on the Tribological Behavior of Thick PDA/PTFE Coatings
Sujan Ghosh, Charles W. Miller, Dipankar Choudhury, Josue A. Goss, Min Zou
Abstract
In this study, the effects of polytetrafluoroethylene (PTFE) thickness on the wear and friction properties of spin-coated PTFE and polydopamine (PDA)/PTFE coatings on stainless steel (SS) substrates were investigated. The PTFE coating thickness was varied by controlling the number of PTFE spin-coating deposition cycles. The PDA/PTFE coatings showed 1.4 to 4.9 times the wear life of that of the PTFE coating deposited at the same number of PTFE spin-coating cycles. The coefficients of friction and water contact angles of the PDA/PTFE coatings were found to be slightly higher than those of the PTFE coatings due to higher surface roughness. The addition of a PDA underlayer helped the PTFE to adhere more strongly to the SS substrate, which contributed to the coatings’ improved durability. The durability of the PDA/PTFE coating increased sharply when the PTFE thickness exceeded 30 μm. Notably, a 42-μm-thick PDA/PTFE coating had 105 times the wear life of that of a 3-μm-thick PTFE coating. The enhanced transfer film on the counterface and the larger contact area for supporting the load were responsible for the extended durability of the thicker coatings.