Interpreting the effects of interfacial chemistry on the tribology of diamond-like carbon coatings against steel in distilled water

Abstract

Three commercially available Diamond-Like Carbon (DLC) coatings were investigated to help understand the dynamics of transfer layer formation and decay, when sliding against AISI 52100 steel balls in distilled water.Optimum tribological behaviour was observed during interfacial sliding between the transfer layer and DLC coating. Alternatively, shear of the carbonaceous transfer layer from the contact region resulted in growth of an iron oxide layer comprised of magnetite, maghemite and hematite, as identified by Raman spectra. Threebody abrasive wear involving iron oxide wear particles explained the high wear rate of the DLC coatings in the case of shear.Friction was controlled by the formation of a transfer layer, reducing adhesive interactions between surfaces.Subsequently, a gradual increase in friction was observed, and suggested to relate to an increase in the shear strength of the transfer layer due to adsorption of oxidative species. This was modelled using the Elovich equation for gas adsorption kinetics.

The friction of diamond-like carbon coatings in a water environment

“…The effect of the third body on the friction of DLC coatings under water lubrication was examined recently by Sutton et al [18], who have linked the tribological response of a selection of commercial DLC coatings with the formation of transfer layers. Optimum tribological behaviour was observed when the VAM was interfacial sliding, where a low and steady coefficient of friction was observed.…”

“…In H 2 18 O, the spectra showed two peaks at 18.00 and 19.01 atomic mass unit (amu) which were absent in the spectra taken outside the wear track. These peaks were assigned to 18 O 2− and 18 OH − respectively, suggesting tribochemical reactions occurred directly between the DLC wear scar and the water. TOF-SIMS analysis of the transfer layer formed on the steel ball showed evidence of 18 O and 18 OH in greater concentration than O and OH, suggesting that the initial oxide layer on the ball was lost, and that tribochemical reactions with water occurred.…”

“…These peaks were assigned to 18 O 2− and 18 OH − respectively, suggesting tribochemical reactions occurred directly between the DLC wear scar and the water. TOF-SIMS analysis of the transfer layer formed on the steel ball showed evidence of 18 O and 18 OH in greater concentration than O and OH, suggesting that the initial oxide layer on the ball was lost, and that tribochemical reactions with water occurred. Wu et al [56] suggest that low friction in water is related to the formation of hydrophilic groups on the contact surfaces, such as hydroxyl and carboxyl functional groups on the DLC coating wear scar, and hydroxyl groups on the counterface surface, that they observed in their TOF-SIMS analysis.…”

“…However, a review of the effects of a water environment on different types of DLC coatings under different test conditions is missing in the literature, and it is the aim of this paper to draw together an up-to-date representation of this. In addition, some recent work on the effects of the transfer layer on the tribology of DLC coatings in a water environment is included [18].…”

RSM base study of the effect of deposition temperature and hydrogen flow on the wear behavior of DLC films

“…The G-peak is related to the bond stretching of all pairs of sp 2 atoms in both rings and chains. The D-peak is due to breathing modes of sp 2 bonded atoms in six fold rings [24,25].…”