Wear-Corrosion Resistance of DLC/CoCrMo System for Medical Implants with Different Surface Finishing

The field of medical implants in the human body is a growing area with diverse tribological aspects. This application field has its own specific characteristics, dominated by stringent quality requirements due to the human suffering and sometimes life-threatening consequences of a surface failing to fulfil its required function. Combined wear-corrosion tests could provide more complete information about the implant behaviour in the aggressive body environment than separate wear and corrosion testing. Combined wear-corrosion experiments were performed using a reciprocating ball-on-plate apparatus equipped with an electrochemical cell. Untreated CoCrMo alloy samples as well as diamond-like carbon (DLC) coated samples were used as plate. The DLC coatings were tested with three different surface finishes: as-deposited, polished with diamond and brushed. All DLC coated samples with and without mechanical finishing had lower corrosion activity under wear-corrosion conditions and also smaller wear tracks when compared with the CoCrMo alloy. The current density for the coated alloy was about two orders of magnitude lower on average (10(-5) vs. 10(-3) A cm(-2)) and had a final coefficient of friction of only 50% of the uncoated metal (0.15 vs. 0.3). The brushed DLC showed the lowest current density and its behaviour was better than polished DLC and DLC as-deposited up to a potential of +0.93 V.