Tribological performance of fluorinated polyimide-based nanocomposite coatings reinforced with PMMA-grafted-MWCNT

The tribological behavior of PMMA-grafted-MWCNT nanocomposite coatings that were prepared by applying the direct casting method to aluminum surfaces was investigated. Amino-functionalized MWCNTs were first covalently functionalized with PMMA to introduce the interaction force. The PMMA-g-MWCNT exhibited a higher dispersive capacity in the 6FDA-based polyimide matrix than pure MWCNT composite due to strong interfacial interactions in the nanocomposite. The maximum possible amount of PMMA-g-MWCNT was 5 wt.% because excessive MWCNT in the nanocomposites makes them fragile and brittle. Sliding tests were performed in ball-on-disk configurations under dry conditions. The normal contact force was 9.7 N against a 12.7-mm-diameter steel ball resulting in a Hertzian circular contact stress of 0.65 GPa. The sliding speed was 0.02 m/s and sliding tests were continued until the coefficient of friction stabilized. The nanocomposite coating reinforced with 3 wt.% MWCNT was the most stable and had the lowest coefficient of friction in this study. This was due to the formation of a thin, uniform friction film on the wear track during sliding, and we concluded that the friction film plays an important role in facilitating the stable frictional behavior of the nanocomposite coatings.