Microscale friction and deformation behavior of polydopamine/polytetrafluoroethylene-coated 60NiTi from nanoscratch tests

Abstract

The scratch behavior of polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings has traditionally been studied using macro-scale tribometers. However, in this study, a nanoindenter is used to scratch PDA/PTFE coatings on 60NiTi substrate to investigate the nanoscale deformation behavior and failure mechanisms of this coating under various scratch loads. Nanoscratch tests were also performed on the substrate coated only with the adhesive underlayer to study the behavior of PDA under various scratch loads. Scanning electron microscope imaging of the scratches provided further insights to the coating scratch deformation behavior. The study revealed the PDA/PTFE coating failure is strongly correlated with the removal of the PDA particles in the underlayer. The findings also suggest that the compaction of the thin PDA/PTFE coatings could be the main reason for the previously reported large initial wear depth in macro-scale tribology studies.