Effect of temperature and mating pair on tribological properties of DLC and GLC coatings under high pressure lubricated by MoDTC and ZDDP

Diamond-like carbon (DLC) and graphite-like carbon (GLC) coatings have good prospects for improving the surface properties of engine parts. However, further understanding is needed on the effect of working conditions on tribological behaviors. In this study, GLC and two types of DLC coatings were deposited on GCr15 substrate for investigation. The friction and wear properties of self-mated and steel-mated pairs were evaluated. Two temperatures (25 and 90 degrees C), three lubrication conditions (base oil, molybdenum dithiocarbamate (MoDTC)-containing oil, MoDTC+zinc dialkyldithiophosphate (ZDDP)-containing oil), and high Hertz contact stress (2.41 GPa) were applied in the experiments. The results showed that high temperature promoted the effect of ZDDP on steel-mated pairs, but increased wear under base oil lubrication. The increased wear for steel-mated pairs lubricated by MoDTC-containing oil was due to abrasive wear probably caused by MoO3 and beta-FeMoO4. It was also found that in most cases, the tribological properties of self-mated pairs were better than those of steel-mated pairs.

Automated summary

The study investigates the effects of working conditions on tribological behaviors of DLC and GLC coatings on engine parts. Results showed that high temperature promotes the effect of ZDDP on steel-mated pairs, while increasing wear under base oil lubrication. The tribological properties of self-mated pairs were generally better than those of steel-mated pairs.