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TEER COATINGS LTD

The practical application of diamond-like carbon (DLC) coatings have been restricted by their high residual stress, poor adhesion and low load bearing c apacity.

Dymon-iC™ is an insulating DLC coating with significant sp3 content and excellent adhesion that is capable of sustaining contact pressures in excess of 3.5GPa(>500,000 pounds/inch2) more than double the maximum contact pressure of any other DLC to the authors’ knowledge [1].

Dymon-iC™ is suitable for dry and oil lubricated applications in atmospheric conditions [1] and under vacuum. Dymon-iC™ is especially suited for applications where protection of the uncoated counterpart from wear is also desired .

An industrial scale hybrid unbalanced magnetron sputtering/ PECVD deposition system has been used to deposit an advanced DLC coating. Unlubricated pin- on- disc experiments on these coatings have shown low friction behaviour and coating wear rates under high loading conditions corresponding to contact pressures in the range 1 to 3.5GPa. When higher loads are used the coefficient of friction reduces at a faster rate, reaches a lower steady state value and a lower specific wear rat e is also observed. A crystalline graphite transfer layer is observed on the WC -Co ball countersurface after all tests and is probably the cause of the low friction behaviour of the coatings and may also be responsible for the protection of the countersurface.

The new DLC coating Dymon-iC™ offers many advantages over previous solid lubricant coatings due to its good adhesion, wear resistance, load bearing capability and low friction. As a result the coating is currently used in a vast array of industrial applications. A selection are listed here.

An Advanced DLC Coating with Exceptional Wear Properties

M. Jarratt, X. Zhang, D. Teer

Magnetron sputtering is used to deposit an adherent interlayer and hard chromium carbide coating. This is followed by a DLC coating deposited using PECVD.

0.7 ?m1.0 ?m

1. Introduction

2. Deposition procedure

chromium

RF

butane

Pulsed DC

argon

chromiumN

S

N

S

N

S

S N S

N S N

RF

The deposition system is a hybrid of unbalanced magnetron sputtering and plasma enhanced chemical vapour deposition, PECVD [2]. Independent control of the bias voltage and current during all stages of deposition is achieved using pulsed d.c. bias and RF electrodes to enhance the plasma.

4.2 Friction and wear

00.5

11.5

22.5

3

20 40 60 80 100

Load ( N )

Spe

cific

wea

r ra

te (

x10

-17 m

3 N-1

m-1

)

00.5

11.5

22.5

3

20 40 60 80 100

Load ( N )

Spe

cific

wea

r ra

te (

x10

-17 m

3 N-1

m-1

) 100N

Friction versus sliding distance for different loads

Specific wear rate for different loads

ball crater on a wear track after testing at 100N

5. Discussion and conclusions

Fig. 1. Cross-section of the deposition chamber

Fig. 2. Artist ’s impression of the coating layers on an M42 steel substrate

3. TEM cross-section and SAD patterns

SubstrateCr interlayer

DLC layer

C (002)?-Al2O 3 (004)C (101)C (004)C (110)

C (002)?-Al2O 3 (004)C (101)C (004)C (110)

Transfer layer

Fig. 3. Transmission electron microscopy, (TEM) cross- section and SAD patterns from the different coating layers and the transfer layer after a pin-on-disk test

under a load of 80 N with a ? -Al2 O3 ball for 60 minutes.

amorphous

crystalline graphite

Selected area diffraction, (SAD) analysis shows the DLC layer is amorphous whereas the transfer layer formed during wear testing on the opposing surfac e is crystalline graphite.

Figure 5 shows the evolution of the friction coefficient as a function of the sliding distance for applied normal loads of 20, 40, 60, 80 and 100 N using a 5mm diameter WC-Co ball with a sliding speed of 200 mm/min. An optical image of the ball after testing is also inserted, the transfer layer is clearly visible.

0

0.05

0.1

0.15

0.2

0 80 160 240 320 400 480 560 640 720

Sliding distance (m)

Co

effic

ien

t o

f fr

ictio

n

20N 40N 60N 80N 100N

0

0.05

0.1

0.15

0.2

0 80 160 240 320 400 480 560 640 720

Sliding distance (m)

Co

effic

ien

t o

f fr

ictio

n

20N 40N 60N 80N 100N

running in period very low friction coefficients (<0.05)

WC-Co ball after 100N test

transfer layer

Fig. 5. Evolution of the friction coefficient as a function of the sliding distance for different applied normal loads

The specific wear rate was measured for the high load pin- on- disk tests using taper cross-sections from ball craters. Figure 6 shows the specific wear rates for different loads and an example of a ball crater on a wear track after testing at 100N.

Fig. 6. The effect of load on the specific wear rate

6. Current application examples

? CD stamper blocks

? Pick/place nozzles for electronic components

? Dies and Moulds

? Components for the automotive (particularly motorsport) and aerospace industries

? Forming tools for the semi -conductor industry

4. Testing results4.1 Adhesion

Fig. 4. Rockwell C indentation, load150kgF, classed as HF2 (a)

(a) (b)

Figure 4a shows a Rockwell-C indentation carried out using a standard Rockwell-C indentation tester (Wilson/Rockwell B503-R) with a load of 150kgf. Figure 4b shows a scratch channel performed using a Teer ST3001 scratch/wear tester with a Rockwell diamond tip and a final load of 60N (load rate 100Nmin-1, sliding speed 10.0mm min-1) on the Dymon-iC™ coating. They both indicate that the Dymon-iC™ coating was well adhered to the M42 substrate (in this case) with little cracking and no evidence of adhesive failure.

and scratch channel (final load 60N) (b) performed on a Dymon-iC™ coating

7. References

M. Jarratt, J. Stallard, N. M. Renevier and D. G. Teer “ An improved diamond-like carbon coating with exceptional wear properties”, Diamond and Related Materials, Volume 12, Issues 3- 7, 2003, Pages 1003-1007.

J. Stallard, D. Mercs, M. Jarratt, D. G. Teer and P. H. Shipway “A study of the tribological behaviour of three carbon-based coatings, tested in air, water and oil environments at high loads”, Surface and Coatings Technology, Volumes 177-178, 2004, Pages 545-551.

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