Super-lubricious Diamond-like Carbon Coatings

This project advances understanding of the surface chemical properties of diamond-like carbon (DLC) in ambient air as well as in vacuum. DLC is a scientifically very rich and technologically important coating. Various types of DLC are used to control friction and wear in a wide range of engineering applications nowadays due to their superior mechanical and tribological properties and excellent adhesion to substrates. One of the latest and most exciting developments is hydrogenated DLC coatings which show near-frictionless and near-wearless properties in inert or vacuum environments; thus DLC coatings have great potentials to reduce frictional energy loss and increase service life of mechanical systems.

However, such ultra-low friction is observed only in vacuum or extremely dry conditions. In ambient air, the ultra-low friction and wear-free properties are lost. The overall goal of this study is to gain molecular-level understanding of the chemical properties of the DLC surface exposed at various environmental conditions so that this knowledge can be used to design better DLC coatings and operation conditions. We recently discovered that the near-wearless operation of DLC coatings in ambient conditions∗ and are currently studying the surface chemistry of DLC in atmospheric environmental conditions. We are collaborating with Dr. Ali Erdemir at Argonne National Laboratory for this study.

 

Friction coefficients measured with a reciprocating pin-on-disc tribometer for hydrogen-rich DLC films in contact with a 3mm diameter stainless steel (SS440C, applied load = 0.5N, Hertzian contact pressure = 0.85 GPa) ball in dry Ar and 75% P/Psat n-pentanol vapor environments. The insets are optical images of the ball surface after 400 reciprocating cycles (scale bar = 20 μm).
Friction coefficients measured with a reciprocating pin-on-disc tribometer for hydrogen-rich DLC films in contact with a 3mm diameter stainless steel (SS440C, applied load = 0.5N, Hertzian contact pressure = 0.85 GPa) ball in dry Ar and 75% P/Psat n-pentanol vapor environments. The insets are optical images of the ball surface after 400 reciprocating cycles (scale bar = 20 μm).