DLC coatings for cam follower applications: The role of the surface on tribochemical reactions, friction and wear

In this study, the tribological properties of steel, Mn-phosphate, Si doped (S1s), and hydrogenated tetrahedral amorphous carbon (ta-C:H) diamond like carbon (DLC) coatings were investigated in a pin on reciprocating plate tribometer and single cam test rig. S1s and taC-H DLC coating architectures were obtained with plasma assisted chemical vapor deposition technique with hardness 20 ± 4 GPa and 35 ± 7 GPa respectively. All materials had a centre-line average surface roughness (Ra) of 0.02-0.03 µm except for the Mn(PO3)2 which had Ra of 0.30 µm. The S1s showed severe delamination after tests on the reciprocating tribometer while spots of wear flakes were observed in the bench test. Both single cam rig and reciprocating tests have shown similar wear and friction results which can be used to rank materials, surface coatings and lubricants for optimum performance of valve train components.