In industrial applications, metal parts are often coated to prevent wear and thus extend their service
life. In some cases, metal parts are replaced with polymers for weight reduction and lower energy
consumption during manufacturing. One drawback is that polymers are softer than metals and hence
more susceptible to wear. A more recent approach is to coat the soft polymer with a hard, wearresistant
coating. The best-known coatings for this are diamond-like carbon coatings and their subset,
amorphous carbon coatings. The coating process is challenging considering the temperature limits and
the correlation between coating thickness and bonding.
In this study, a-C and ta-C coatings were deposited on polymers and tested under 3 different contact
conditions, i.e. ball-on-disc, pin-on-disc, and 2-disc-test. This represents a transition from model to
component testing. Indentation tests were performed to understand the interaction between polymer
and coating. Depending on the coating, the behaviour was either elastic or plastic, which helped to
understand the stress distribution in the contact.
Hertzian contact pressure with a steel ball causes wear on the mating part and the coating. By replacing
the mating part with a polymer, only the polymer mating part will wear. Changing the tribosystem to a
flat contact showed a significant reduction in wear. One reason for this is the increased contact area,
which leads to a changed stress distribution. With the change from flat to line contact and a change in
movement (from pure sliding to sliding-rolling), the shear forces between the coating and substrate are
significantly reduced. The effect of speed, load, and slip ratio on the performance of the different
material pairings was analysed. Coated polymers also allow the pairing of incompatible materials, which
would result in unstable frictional contact. Moreover, coated polymers exhibit high wear resistance as
long as the load is applied over an area rather than a small point.