Friction Measurements of Ultra-Thin Carbon Overcoats in Air
P M. McGuiggan, C S. Bhatia, D Bogy, W Fong, Stephen M. Hsu
The friction force as a function of humidity was measured between 5 nm thick carbon films coated onto mica surfaces. The friction was found to be proportional to the area of contact. The shear stress at 0%, 33%, and 100% humidity was measured to be 25 +6 MPa, 12.5 +1 MPa, and 5 +0.5 MPa, respectively, and was independent of the pressure for pressures less than 20 MPa. Water acts as a lubricant decreasing the friction between the carbon surfaces. The shear stress at 0% humidity corresponds to the shear stress of a solid paraffin film, and indicates that the shear is dominated by a thin organic film adsorbed from air, at least at the pressures less than 20 MPa and a velocity of 1 um/s. At 100% humidity, the shear stress for carbon coated surfaces was about double that for mica surfaces, indicating a stronger influence of the water for the more hydrophilic mica surface than the more hydrophobic surface. The friction between one uncoated mica and one carbon coated mica surface resulted in immediate damage and generation of wear debris.
, Bhatia, C.
, Bogy, D.
, Fong, W.
and Hsu, S.
Friction Measurements of Ultra-Thin Carbon Overcoats in Air, Journal of Tribology-Transactions of the Asme
(Accessed December 3, 2023)