Effect of the type of elastomeric substrate on the microstructural, surface and tribological characteristics of diamond-like carbon (DLC) coatings

Diamond-like carbon (DLC) coatings are deposited by a hybrid process involving plasma-assisted chemical vapor deposition (PACVD) and pulsed direct-current (DC) magnetron sputtering on three different elastomer substrates, namely, nitrile butadiene rubber (NBR), fluoroelastomer (FKM) and thermoplastic polyurethane (TPU), under self-biased conditions. These DLC coatings and the corresponding elastomer substrates are characterized using confocal optical microscopy, scanning electron microscopy, atomic force microscopy and a contact angle goniometer. Tribological tests are performed using ball-on-disc configuration at a fixed load of 1 N under ambient conditions. Friction reduction after deposition of DLC coatings is highly effective in NBR (56.4%), followed by that in FKM (49.8%) and TPU (28.8%) substrates. Best wear resistance was shown by DLC-coated FKM, which was followed by DLC-coated NBR and TPU. Transfer film formation is believed to be the main tribological mechanism favoring better frictional properties of DLC-coated elastomers. This study elucidates the possible reasons for the differing frictional and wear performance of the three different DLC-coated elastomers under consideration.