Repetitive nanoindenter scratch testing of polydopamine/polytetrafluoroethylene-based thin coatings

Abstract

Repetitive nanoindenter scratch testing and scanning electron microscopy were used to evaluate the scratch resistance, deformation, and mechanisms of failure of polydopamine (PDA)/polytetrafluoroethylene (PTFE)-based coatings deposited on both polished and roughened 60NiTi substrates. PDA was used as an adhesive layer between the substrate and the PTFE top layer with and without 0.25 wt% graphite particles (GPs). The roughened substrate enabled mechanical interlocking with the coatings that prevented global delamination which occurred with the coatings on the polished substrate due to weak adhesion. The inclusion of GPs improved the coating cohesion and enabled the PDA/PTFE coating with GPs on the roughened substrate to compact into a more plowing-resistant layer with stronger interlocking with the substrate roughness. Therefore, the GP-containing coating deposited on a roughened substrate showed far superior performance, and it is a promising solid lubricant for tribological applications that involve repetitious sliding at high contact pressures, such as bearings and gears.