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Surface treatment of medical CoCr alloys L605 by nitrogen plasma immersion ion implantation (PIII) leads to the formation of a hard and wear resistant surface layer, consisting of nitrogen in solid solution. However, a detailed investigation of the corrosion properties by potentiodynamic polarization and electrochemical impedance spectroscopy shows that even at processing temperatures of 350 °C, where no CrN precipitates are observed, no complete passivation of the surface by formation of a protective Cr 2 O 3 layer is possible leading to enhanced corrosion rates further increasing with increasing PIII processing temperature. It is postulated that the enhanced affinity of chromium for nitrogen leads to a reduced mobility inside the alloy, thus prohibiting a timely surface passivation. Nevertheless, a surface modification where a moderate decrease in corrosion resistance coupled with a significant reduction in generated wear particles should be feasible for biomedical applications.

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