THE ROLE OF HYDROGEN IN THE TEST ATMOSPHERE ON THE TRIBOLOGICAL BEHAVIOR OF THE NON-HYDROGENATED DIAMOND-LIKE CARBON COATINGS AGAINST 319 ALUMINUM ALLOY

摘要

Diamond-like carbon (DLC) coatings are promising candidates as tool coatings for dry machining of aluminum alloys since aluminum has a lower tendency to adhere to the DLC surface in ambient conditions compared to other hard coatings. In this study, the tribological behavior of the nonhydrogenated DLC coatings against 319 Al alloy was investigated in various environments including ambient air (32-47% RH), vacuum (6.65×10-4 Pa), inert gas (Ar, He and N2) and a mixture of 60% He- 40% H2. Unlike the other test conditions, very low coefficient of friction (COF) values (0.01-0.02) were observed in the 60% He-40% H2 mixture after a brief high COF (0.70) period. The formation of a carbonaceous tribolayer on the counterface and the passivation of the sliding surfaces by the chemisorption of hydrogen were suggested as possible mechanisms responsible for the very low COF behavior of the non-hydrogenated DLC coatings in the 60% He-40% H2 mixture.