Abstract
The sliding friction and wear characteristics of pyrimidine-containing polyimide (PI) coatings and PI-C
60 composite coatings on steel substrates have been investigated using a flat-on-ring friction geometry. The wear behavior of the coatings was found to proceed through three stages: a rapid increase in wear at the beginning of the friction experiment, a steady state condition with a moderate increase in wear, and a catastrophic wear behavior in the latest stage of the friction process. The friction coefficient of PI and PI-C
60 composite coatings was found to be only slightly determined by the conditions of material preparation and the presence of C
60. The wear resistance of these materials is, however, strongly influenced by the latest stages of the imidization reaction. In the initial two stages of the friction process, a strong reduction in specific wear rate (from values of
w
s∼15×10
−7 down to ∼2×10
−7
mm
3/N
m at pressures of
1
MPa÷3
MPa) was observed for both neat PI- and PI-C
60-coatings when they were treated in the region between 320 and 420
°C. The introduction of C
60 was found to improve further the wear characteristics of the coatings down to specific wear rates below 2×10
−7
mm
3/N
m when the coatings treatment took place at higher temperatures (420
°C). The structural analysis data of the polyamic acid-C
60 solutions and PI-C
60 coatings enabled us to suggest that the role of the C
60 molecules in reducing the wear of composite coatings is due to the interactions between C
60 and the PI.