Effect of solid state ball milling on wear and structural properties of polytetrafluoroethylene/alumina nanocomposite coatings

The aim of this study was to investigate the effect of ball milling at different time periods on wear resistance and structural changes of polytetrafluoroethylene (PTFE)/nano-alumina coatings. For this purpose, PTFE/nano-alumina composite powders containing 10 wt% of the nanofillers were milled at 0, 8, 16, and 20 h and coated on a steel substrate using powder electrostatic technique, followed by sintering. Wear mass loss and coefficient of friction (COF) of the coatings were evaluated by a pin-on-disk tribometer. The morphology and structural properties of the unmilled and milled powders and the coatings were explored using scanning electron microscopy (SEM) and X-ray diffraction analysis. In addition, the chemical structure of the samples was tested using Fourier-transform infrared spectroscopy. The results showed that the wear rate of the 16 h milled sample showed tenfold decrease compared to the neat PTFE. However, the COF of the milled samples did not change significantly after milling. Also, less damage was observed for the worn surface of the 16 h milled sample which confirmed the obtained values for the wear rates. Therefore, the ball milling process was effective in enhancing the wear resistance of the coatings.