Friction and Electrical Contact Resistance of Iridium-Containing DLC Coatings for Electrically Conductive Tribo-Elements

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Electrically conductive tribo-coatings (i.e. Ir-DLCs) were developed using a hybrid deposition process, combining RF-PECVD with DC magnetron sputtering of Ir. Pin-on-plate tribotests in reciprocating motion were performed in air on Ir, DLC and Ir-DLC coated plates against bearing steel pins under 0.5 N load. The electrical contact resistance was measured during the tribotests, and for Ir-DLC it was below 30 Ω. Neither the pure DLC layer nor the pure Ir layer reached friction coefficients lower than 0.2, while the Ir-DLC went down to 0.05. For Ir-DLCs, however, relatively high and unstable friction was occasionally observed. Possible causes of the instability are discussed by focusing on the characteristics of the tribofilm and the formation of wear debris.