Low-friction, wear-protecting coatings on polymers by atmospheric pressure plasma spraying

Deposition strategies to obtain low-friction and wear resistant coatings on 3D-printed rough polyamide 12 (PA12, nylon) surfaces were developed via atmospheric pressure plasma deposition. The feedstock materials for the DC plasma torch InoCoat 3 produced by INOCON Technologie GmbH were dry lubricants such as MoS2 and graphite. In addition, parameter sets that would not thermally damage the heat sensitive polymers were applied. Generally, microtribological characterisation indicates that coating composition and thickness particularly influence the coating performance significantly. Pure MoS2 coatings wear rapidly, particularly on the roughness tips (mean substrate roughness Ra up to 20 μm); this exposes the substrate and leads to friction coefficients similar to those of PA12 and rather limited potential for protection against wear. Composite coatings with graphite in a MoS2 matrix provide huge potential for wear protection (i.e. >20 times less penetration depth) even for exposed PA12 roughness tips, owing to the transfer of lubricating carbon into these exposed areas. If the thickness is sufficiently high, preventing the wear of tips results in low-friction properties (friction coefficients < 0.1, i.e. four times lower than those for uncoated PA12).