Comparison of the tribological properties of carbon/glass fiber reinforced PA66-based composites in contact with steel, with and without grease lubrication

Polyamide 66 (PA66) is used for polymer sliding parts, and to increase its strength, reinforcement fibers such as glass fiber (GF) and carbon fiber (CF) are often added. Using fiber-reinforced composites for sliding parts leads to wear of the composites, which is related to peeled-off fibers and polymer scratching during sliding. Moreover, this has a destructive effect on the steel counterpart. In this work, the tribological properties of grease-lubricated CF-reinforced PA66 were studied and compared to those of GF-reinforced PA66; the effect of CF reinforcement was also studied under dry conditions. The CF composite exhibited poorer tribological properties than those of the GF composite under grease lubrication due to the insufficient interfacial adhesion between the PA66 and fibers, regardless of the PA66 molecular mass, whereas the CF composite exhibited lower friction under dry conditions. Higher wear of the steel counterpart was observed when tested with the CF composite; however, CF is softer than GF, indicating that the destructive effects are not determined by fiber hardness alone. Tribochemistry related to the grease additives on the sliding surface was studied based on the fiber type, ambient temperature, and contact pressure, and tribofilm formation can explain the improvement of the tribological properties.