Tribological evaluation of PEEK/ceria composite coatings prepared from powders using ball milling and sonication methods

Two different dispersion techniques, namely ball milling and sonication, were implemented to prepare PEEK/1.5 wt% ceria nanopowders, which were deposited using an electrostatic spraying technique on mild steel substrates (post-heat treatment of the coated sample @370 ºC for 30 min). It was observed that the ball-milled powders failed to form a coating whereas the sonicated powders resulted in a coating of ~ 95 µm thickness. To investigate the reasons for this varying behavior, the ball-milled and sonicated powders were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) to evaluate their physical and chemical properties. XRD results revealed that the sonicated powders retained a higher crystallinity (~76.46%) as compared to the ball-milled powders (~66.84%). FTIR analysis indicated uniform dispersion of ceria nanoparticles in sonicated powders. TGA showed that the sonicated powders had better thermal stability than the ball-milled powders at higher temperatures. However, an increase in the post-heat treatment time for the ball-milled powders to 90 min did result in a coating of ~ 98 µm. Hence, tribological characterization of the coatings was conducted using a ball-on-disk configuration at a load of 70 N for 10,000 cycles at 0.4 m/s, which resulted in the failure of the coatings deposited from the ball-milled powders after 2500 cycles as compared to the nonfailure of the coatings deposited from the sonicated powders even until 10,000 cycles.