Lubricated sliding wear mechanism of chromium-doped graphite-like carbon coating

• Wear mechanism of C/Cr coating is described in dry and lubricated sliding conditions.
• Wear mechanism is found mainly oxidative during dry sliding.
• During boundary lubricated sliding, the wear mechanism becomes chemically reactive.
• Solid lubricant CrCl3 is formed during lubricated sliding.
• CrCl3 is considered as the key-factor for better tribological performance.

The current research aims to discuss the tribological behaviour of Chromium-doped graphite-like carbon coatings and suggest a wear mechanism under both dry (in air) and boundary lubricated sliding condition based on phase composition of the wear product generated in wear track during pin-on-disc experiments. As expected, the friction coefficient reduces from 0.22 to 0.12 due to addition of lubricant. Raman analysis indicates that wear mechanism is oxidative in dry sliding condition whereas it is chemically reactive in the presence of lubricant. It is speculated that the key-factor of reduced friction and wear coefficient in lubricated condition is the formation of CrCl3 due to tribochemical reaction between coating and oil. CrCl3 has graphite-like layered structure; therefore it acts like solid lubricant.