Evaluation of DLC Coatings for High-Temperature Foil Bearing Applications

Jahanmir, S., Heshmat, H. and Heshmat, C.A.  “Evaluation of DLC Coatings for High-Temperature Foil Bearing Applications,”  (2009) Journal of Tribology, Volume 131, No. 1, pp. 011301-1 – 011301-11.

Diamond like carbon (DLC) coatings, particularly in the hydrogenated form, provide extremely low coefficients of friction in concentrated contacts. The objective of this investigation was to evaluate the performance DLC coatings for potential application in foil bearings. Since in some applications the bearings experience a wide range of temperatures, tribological tests were performed using a single foil thrust bearing pad in contact with a rotating flat disk up to 500 oC.  The coatings deposited on the disks consisted of a hydrogenated diamond like carbon film (H-DLC), a non-hydrogenated DLC, and a thin dense chrome deposited by the ElectrolyzingÔ process.  The foil pads were coated with a tungsten disulfide coating (KorolonÔ 900). All three disk coatings provided excellent performance at room temperature. However, the H-DCL coating proved to be unacceptable at 300 oC due to lack of hydrodynamic lift, albeit the extremely low coefficient of friction when the foil pad and the disk were in contact during stop-start cycles. This phenomenon is explained by considering the effect of atmospheric moisture on the tribological behavior of H-DLC and using the Quasi-Hydrodynamic theory of powder lubrication.

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