Carbon Fiber- vs. Glass Fiber-Reinforced PA12 Under Protic Ionic Liquid Lubrication: Friction, Wear and the Limits of Reinforcement in FFF-Printed Composites

Fused filament fabrication (FFF) is increasingly employed for functional components subjected to sliding contact, for which friction and wear determine service life as decisively as static strength. Tribological characterization of fiber-reinforced polyamide 12 has been conducted predominantly under dry sliding, and the influence of the lubrication regime on the contrast between reinforcement types remains insufficiently established. The present study investigated carbon fiber (PA12-CF) and glass fiber (PA12-GF) reinforced polyamide 12, both processed by FFF, under dry sliding and under two protic ionic liquid lubricants, bis (2-hydroxyethyl) ammonium succinate (MSu) and bis (2-hydroxyethyl) ammonium citrate (MCi). Discs were tested against a 100Cr6 bearing steel counterface on an Anton Paar TRB3 tribometer at a fixed normal load of 20 N, with sliding speeds of 0.5, 0.75 and 1.0 m/s for 60 min each. The coefficient of friction (COF) and the contact-point temperature were recorded throughout, the specific wear rate was obtained by contact profilometry, and worn surfaces were examined by scanning electron microscopy with energy dispersive X-ray analysis. MCi held the mean COF at 0.023 for both composites, against a dry mean of 0.071 across the study, whereas MSu increased the mean to 0.25 and produced the highest wear rates, concurrent with an increase in viscosity during testing. Reinforcement type governed the morphology of the worn surface consistently, yet lubricant selection proved more consequential than material selection.