The influence of defects in ta-c coating deposited by fcva method on their tribological behavior

Diamond like-carbon (DLC) coatings is a form of amorphous consisting of sp²-bonded and sp³-bonded phase. Among the DLC series, DLC coatings containing a large percentage of sp³ ratio, referred as tetrahedral amorphous carbon (ta-C) coatings, have attracted significant attention as protective coatings in various fields such as tribological applications and automobile components that demand superior durability, chemical inertness and low friction at high temperature. Particularly, the filtered cathodic vacuum arc (FCVA) technique with an energetic plasma can deposit the ta-C coating, but it has a drawback such as decreasing deposition rate and occurring macroparticles. Research on morphological and structural change of defects in ta-C coatings fabricated by FCVA is important for understanding their wear and friction behavior. In this study, the types of defects presented on a ta-C coating were classified as spike, droplet and pore with their morphology, structural and mechanical properties. The tribological behavior of the coating was characterized by ball-on-disk test using a Si3N4 ball at a testing temperature of 170 °C. In order to confirm the effect of defects in the ta-C coating on the tribological behavior, the defects in a designated area were investigated as a function of different sliding cycles. Initially, a running-in cycle is maintained until 2,000 cycles, following which a steady-state value of 0.1 is observed from sliding cycles of 2,000 to 10,000. At the end of 10,000 cycles, the wear rate of the ta-C coating is 4.3×10^-6 mm³/Nm. Structural changes among the defects are apparent on droplet and pore after the friction test at 170 °C. The nodular defects including spikes and droplet is grinded off on top surface of that and is retained until 1,000 cycles. In steady state up to 6,000 cycles, droplet was survived, on the other hand, the spikes are almost polished from sliding.