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Research Papers: Coatings & Solid Lubricants

# Scuffing Performance of a Hard Coating Under EHL Conditions at Sliding Speeds up to $16m∕s$ and Contact Pressures up to $2.0GPa$

[+] Author and Article Information
R. W. Snidle, A. K. Dhulipalla, H. P. Evans

School of Engineering, Cardiff University, Cardiff CF24 3AA, UK

C. V. Cooper

United Technologies Research Center, 411 Silver Lane, East Hartford, CT 06108

J. Tribol 130(2), 021301 (Mar 03, 2008) (10 pages) doi:10.1115/1.2842253 History: Received February 28, 2007; Revised November 09, 2007; Published March 03, 2008

## Abstract

Scuffing experiments were conducted using $76mm$ diameter disks both with and without a metal-containing, carbon-based hard coating. The operating conditions in the experiments were severe with sliding speeds up to $16m∕s$ and maximum Hertzian contact pressures up to $2.0GPa$. The disks were of alloy steel, which was case carburized and hardened followed by axial grinding. Four different surface conditions were investigated as follows: ground/uncoated, ground/coated, superfinished/uncoated, and superfinished/coated. Experiments were also carried out in which ground/coated disks were run against ground/uncoated disks. The results of the experiments show that the addition of the hard coating to the ground disks significantly improved both their scuffing resistance and frictional behavior, but the coating was less effective in producing an improvement in the durability and friction of the superfinished disks.

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## Figures

Figure 1

Graph showing Knoop microhardness as a function of distance from the outside diameter (O.D.) of a disk specimen; Knoop microhardness experiments performed at indentation load of 200g

Figure 2

Main parts of disk machine. A, fast disk; B, slow disk; C, loading pushrod

Figure 12

SEM image of surface of the fast (uncoated) disk used in Experiment 22 after running. Image shows run surface to the left and unrun surface to the right.

Figure 11

Circumferential profiles of the disks used in Experiment 26. Profiles (a) and (b) are from the fast disk before and after running, respectively, and profiles (c) and (d) are from the slow disk. Profiles taken after scuffing are from the run-in but unscuffed part of the disks.

Figure 10

Circumferential profiles of the disks used in Experiment 22. Profiles (a) and (b) are from the fast disk before and after running, respectively, and profiles (c) and (d) are from the slow disk. Profiles taken after scuffing are from the run-in but unscuffed part of the disks.

Figure 9

Record of friction force and disk bulk temperatures during Experiment 24 with ground/hard-coated disk on the fast shaft and ground/uncoated disk on the slow shaft

Figure 8

Record of friction force and disk bulk temperatures during Experiment 22 with ground/uncoated disk on the fast shaft and ground/hard-coated disk on the slow shaft

Figure 7

SEM image of surface of the fast disk used in Experiment 13 after running. Image shows run surface to the right and unrun surface to the left.

Figure 6

SEM images of surface of the fast disk used in Experiment 12 after running. Upper image shows run surface to the left and unrun surface to the right. Lower image (at a higher magnification) shows the surface near the middle of the running track after running.

Figure 5

Circumferential profiles of the disks used in Experiment 7. Profiles (a) and (b) are from the fast disk before and after running, respectively, and profiles (c) and (d) are from the slow disk. Profiles taken after scuffing are from the run-in but unscuffed part of the disks.

Figure 4

SEM image of surface of the fast disk used in Experiment 7 after scuffing. Left side shows scuffing scar and right side is the unscuffed but run-in surface.

Figure 3

Record of friction force and disk bulk temperatures during a typical experiment with ground/uncoated disks at a sliding speed of 12m∕s (Experiment 28)

Figure 13

Variation of friction coefficient with load during stages preceding scuffing. A, ground versus ground; B, ground/coated versus ground/coated; C, superfinished versus superfinished; D, superfinished/coated versus superfinished/coated.

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