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Research Papers: Coatings & Solid Lubricants

Evaluation of DLC Coatings for High-Temperature Foil Bearing Applications

[+] Author and Article Information
Said Jahanmir, Hooshang Heshmat, Crystal Heshmat

 Mohawk Innovative Technology Inc., 1037 Watervliet Shaker Road, Albany, NY 12205

J. Tribol 131(1), 011301 (Dec 02, 2008) (11 pages) doi:10.1115/1.2991181 History: Received December 03, 2007; Revised August 01, 2008; Published December 02, 2008

Diamondlike 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 of 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 in contact with a rotating flat disk up to 500°C. The coatings deposited on the disks consisted of a hydrogenated diamondlike carbon film (H-DLC), a nonhydrogenated DLC, and a thin dense chrome deposited by the Electrolyzing™ process. The top foil pads were coated with a tungsten disulfide based solid lubricant (Korolon™ 900). All three disk coatings provided excellent performance at room temperature. However, the H-DLC coating proved to be unacceptable at 300°C due to lack of hydrodynamic lift, albeit the very 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 quasihydrodynamic theory of powder lubrication.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

High-temperature tribometer: (1) test disk, (2) pad holder, (3) test pad, (4) dead weight, (5) gimbal joint, and (6) proximity probe. High-temperature section (HT); room temperature section (RT).

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Figure 2

Typical friction and speed for one test cycle (50th cycle at room temperature) for the tungsten disulfide based coating on the foil pad running against a chrome plated disk

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Figure 3

Friction and speed data for the chrome plated disk running against the tungsten disulfide based coating on the foil pad at room temperature

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Figure 4

Friction and speed data for a chrome plated disk running against the tungsten disulfide based coating on the foil pad at 300°C

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Figure 5

Friction and speed data for a chrome plated disk running against the tungsten disulfide based coating on the foil pad at 500°C

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Figure 6

Photographs of chrome plated disks and tungsten disulfide based coating on the foil pads after testing: (a) room temperature, (b) 300°C, and (c) 500°C. The disk surfaces were cleaned by a blast of compressed air.

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Figure 7

Photographs of the chrome plated disk after testing at low and high magnifications showing accumulated wear debris powder and small particles distributed on the wear track

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Figure 8

Friction and speed data for a chrome plated disk running against the tungsten disulfide based coating on the foil pad at different temperatures

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Figure 9

Friction and speed data for a DLC coated disk running against the tungsten disulfide based coating on the foil pad at room temperature

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Figure 10

Friction and speed data for a DLC coated disk running against the tungsten disulfide based coating on the foil pad at 300°C

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Figure 11

Photographs of DLC coated disks and tungsten disulfide based coating on the foil pads after testing and without cleaning: (a) room temperature and (b) 300°C

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Figure 12

Friction and speed data for a DLC coated disk running against the tungsten disulfide based coating on the foil pad at different temperatures

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Figure 13

Friction and speed data for a H-DLC coated disk running against the tungsten disulfide based coating on the foil pad at room temperature

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Figure 14

Friction and speed data for a H-DLC coated disk running against the tungsten disulfide based coating on the foil pad 300°C

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Figure 15

Friction and speed data for a H-DLC coated disk running against the tungsten disulfide based coating on the foil pad at 300°C during the 122nd cycle

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Figure 16

Photographs of H-DLC coated disks and tungsten disulfide based coating on the foil pads after testing and without cleaning: (a) room temperature and (b) 300°C

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Figure 17

Friction and speed data for a H-DLC coated disk running against the tungsten disulfide based coating on the foil pad at different temperatures

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Figure 18

Velocity profile based on the quasihydrodynamic lubrication theory for the H-DLC coated disk running against the tungsten disulfide coated foil pad at 10,000 rpm at 300°C

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