Structure and tribological properties of multiphase carbon coatings fabricated by multi-arc ion plating

Carbon coating with excellent wear resistance will play a significant role in protecting metal materials, especially in piston rings. In this work, a series of multiphase carbon coatings were fabricated by multi-arc ion plating under different bias voltages ranging from 0 to 160 V. The microstructures were investigated by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Raman Spectroscopy and X-ray Photoelectron Spectrometry (XPS). The mechanical properties and tribological performances were measured by nanoindentation, scratching tester and reciprocating tribometer. The results demonstrated that the multiphase carbon coatings mainly compose different phases, including amorphous carbon, fullerene-like carbon, nanographite, nanodiamond and C60. The sp2 hybrid bond existed in the form of multi-bent carbon rings and increased from 46.82 % to 52.01 % with the increase of bias voltage. The content of seven-membered carbon rings (7A1) increased first and then decreased, with the highest value of 18.05 %. The hardness values of the coatings ranged from 18.33 +/- 3.55 GPa to 33.88 +/- 2.26 GPa. When Vickers indenter was pressed into the coating under high load, the coating exhibited good load strength and toughness. Under the load of 10 N, the friction coefficient between the coating and phi 3 mm 316 stainless steel (SS) balls in fresh 5 W-30 oil was about 0.13. In the degraded oil, the highest friction coefficient was 0.20, and the lowest was 0.11. The grinding ball's surface looked to have sustained severe damage, but there was no visible damage to the coating structure at the worn tracks. There was no significant difference in the coating surface profile curves before and after rubbing exhibiting super wear resistance of coatings.