NEW UNIDIRECTIONAL SINGLE PASS WEAR
TESTING PROCEDURE

N. M. Renevier, S. Poulat and D. G. Teer

Teer Coatings Ltd. (TCL)

290 Hartlebury Trading Estate,

Hartlebury, Worcestershire

DY104JB, U.K.

Abstract

The ST-3001 is a multi-mode testing system which can be used for scratch
adhesion tests, linear wear tests either reciprocating or uni-directional and
hardness testing. The system was based on an earlier tester ST-2000 [1] and
was further developed in a join project supported by the European Commis-
sion [2]. In conventional pin on disc or reciprocating wear tests, the same
track is rubbed repetitively and such tests can be used to simulate the wear
conditions for components but they do not simulate cutting or forming op-
erations where new material is continuously bought into the contact zone.
Recently, the ST-3001 has been used to provide an initial assessment for suit-
able coatings and substrate materials used in cold forming operations. Tests
have performed at several loads under several environmental conditions (dry
and lubricated) and a conditions for a new accelerated test have been es-
tablished. The new testing procedure will be fully described in the paper
and results will be correlated with industrial results. This is a powerful tech-
nique for simulation sticking of gummy materials such as aluminium, copper,
stainless steel, lead and zinc for forming operation.

This paper is an extension from the paper presented at ICMCTF 2002 in

San Diego 2002.

INTRODUCTION

Coatings are commonly used in a wide range of industries, such as au-

tomotive, aerospace, optics, construction, engineering and micro-electronic
sectors. In most of these sectors, the use of coatings is expanding and there

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is an increasing need to control coating specific parameters such as their
mechanical properties or adhesion between coating and substrate. Coating
technology is fundamentally dependent upon good adhesion between the
coating and the substrate, and in many cases adhesion is the limiting factor
for the wider application of the technology.

The scratch test is routinely used as a quick and simple tool to monitor the

adhesion of a coating onto the substrate and is designed for the assessment
of the mechanical integrity of coated surfaces. This technique is well docu-
mented for hard coating failure mechanism reconnaissance [3]. A European
pre-standard [4] has been accepted whose definite adoption is pending. Ball
on disc tests and reciprocating tests are used to assess fatigue and wear re-
sistance properties, whereas the ball cratering tests is used for testing the
abrasion resistance. Those tests are based on the principle that the two
parts in contact are rubbed repetitively at the same place [5], therefore these
tests are suitable for components but are less suitable for cutting or forming
process where a new material is in contact.

Approximately 20% of the down time in the press shop are due to galling.

Because most industries are relaying on ”just in time” and continuous pro-
duction, any disruption has a dramatic economical effect. On the technical
level there are, in addition, two major direct detrimental consequences.

a) Material loss owing to severe surface damage of the formed parts in the

functional regions making them unacceptable for further assembling.

b) Critical build up of well-adhered, highly work hardened material from

the workpiece material imperatively, requiring a reconditioning of the
tool surface and leading to an accelerated wear of the tools.

Tools are expensive and almost always-unique tools generally intended to
last over the entire production period for a specific part. Therefore, galling
is an extremely serious incident. Thus galling prevention must be integrated
from the very start of die and mould

conception. Therefore, there is a strong need for a ranking suitable coating

to prevent galling. Our approach starts with a laboratory simulation using a
newly developed procedure on the ST3001 for surface damage assessment.

Owing to the formation of adhesive junctions, material transfer from the

softer friction partner (the sheet surface) to the die may occur. The severity
of this junction formation is intimately related to the "chemical affinity"
(mutual solubility) of the friction partners at the contact interface. As a

New Unidirectional Single Pass Wear Testing Procedure

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general rule, for metals, the interaction is strongest for friction partners of
identical chemical composition. This adhesive interaction may be partially
screened by a "third body" [6] interlayer (surface oxide, contaminant film,
lubricant, etc.) and will result in a more or less continuous transfer layer.
Clearly, in the case of discontinuous asperity build-up, especially if the latter
corresponds to severely work hardened material, local stress concentrations
will be produced, leading to the evacuation of screening interlayers and will
result in macroscopic junctions and, possibly, deep scars: This is galling.
Therefore, engineers will aim for constant friction conditions with a low
adhesive contribution by the reduction of excessive local contact pressures
and "chemical affinity" optimisation of the friction partners.

THE DESIGN

THE OBJECTIVE

While indispensable as a final validation before press shop introduction,

real scale simulation experiments are expensive and time consuming. In
most cases, they are

inadequate for determining failure origin analysis. Therefore, a new pro-

cedure has been developed on the ST3001 and tested (Fig. 1) as a laboratory
simulation experiment for the optimisation and the realisation of data base
of various tool/ workpiece combinations. In this test, a ball (coated or un-
coated) will represent the working tool to be tested, whereas a flat sample
will represent the workpiece material to be formed by the end-use. Figure 2
shows a bending application where this new procedure can be used.

The building-up of particle of particle on tools is particularly significant

with copper and aluminium alloys. These may results in premature tearing
and/or scratching of workpiece in severely strained areas [7, 8]. To prevent
and delay the occurrence of the metal transfer and galling, three state of the
art low friction coatings have reported (Table 1).

BASIC MOTIONS OF ST3001 MULTI-MODE TESTING

SYSTEM

Loading and unloading system

The basic motions has been described in

[9]. (Fig. 3). The load is applied by the spring to the ball shaft through the
cantilever beam and the load cell. The spring is compressed by the bush

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6TH INTERNATIONAL TOOLING CONFERENCE

Table 1.

Material parameters

Tool

Surface finish

Dimension

WC-4% Co

Highly polished

5 mm diameter

Coatings

Thickness

Method

Type

Graphit-iC

TC

2.3-2.7

PVD CFUMSIP

Me-C

MoST

TM

1.0-1.2

PVD CFUMSIP

MoS2 / Ti

Dymon-iC

TC

2.5-3

Combined PVD

CFUMSIP and PECVD

DLC (-CH)

Workpiece

Surface finish

Pre-cleaning

AISI 316L

1200 SiC

solvent

Al 2014

1200 SiC

solvent

which is moved by operating the servo motor. The movement of the motor
is controlled via a load feedback loop assuring that the load applied on the
sample is correct.

Translation system

(Figure 3). The motorised translation table in the

direction perpendicular to the wear track direction is used solely to position
the sample under the ball shaft. The motorised translation table in the wear
track direction is used to position the sample under the ball and to provide
controlled motion during a test. The motorised translation table is fitted
with a frictionless table, which acts as a sample holder. The table is locked
in place by four screws; these screws need to be in place to ensure that
the sample holder rigidity is adequate for the test. The frictionless table is
locked on the sample bed by two locking nuts and can be moved by using the
adjusting screw. In order to avoid wear of the rails of the translation table,
this adjusting screw enables the operator to move the frictionless table along
the rails so that the wear of the rail is more homogenous.

New Unidirectional Single Pass Wear Testing Procedure

897

Data logging system

The ST-3001 software package then analyses, dis-

plays and saves the collected data.

New procedure principle

The newly developed procedure could be de-

scribed as a multi-single uni-directional scratch test with constant displace-
ment and under constant load. A procedure detailed below has been devel-
oped to operate semi-automatically. The

procedure consists on a succession of loading-unloading and small dis-

placements. The different sequences reported in Fig. 4 are the following:

Step 1 When the ball is at the chosen position, the ball is progressively

loaded to 30 N.

Step 2 A 2 mm displacement has been chosen to simulate bending of small

parts, this distance can be adjusted for other applications.

Step 3 When the rubbing test has been completed, the ball is progressively

unloaded.

Step 4 The ball is moving back at the beginning of the track where it is

possible capture a picture of the track and analyse the ball building up
or wear.

Step 5 The ball is moved 1mm after the end of the previous track, a new

test can be performed.

Step 6 This step is identical to step 1.

SAMPLE PREPARATION AND POSITIONING

5 mm diameter highly polished uncoated and coated balls have been used

to simulated the tool (See Table 1 for more details), whereas the metallic
workpiece materials (Table 1) have been polished to 1200 grain size with SiC
paper. Following extensive studies carried out as part of a European project
(S, M & T Contract No MAT1-CT 940045), the ball (coated or uncoated) is
cleaned before beginning of the test. The ball and the workpiece are wiped
with a soft tissue soaked with solvent to remove finger prints and a hair drier
is used to evaporate the solvent. Before the test, uncoated and coated ball
tip must be kept free of fingertips. The workpiece material is mounted in the
middle of the frictionless table, whereas the ball is positioned on the edge of

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6TH INTERNATIONAL TOOLING CONFERENCE

the sample using the step positioning of the table and using the microscope
for final examination. It is possible to move the sample either using the
step positioning option as described above or directly to the microscope.
Pictures of the workpiece material can be captured by the camera. It is now
possible to add comments, scale and arrows on the picture. The damaged
on the workpiece can be assessed and failure criteria can be imposed by the
operator.

RESULTS

The building-up of particle on tools is particularly significant with soft

alloys such as copper and aluminium alloys. These may results in premature
tearing and/or scratching of workpiece in severely strained areas [5, 6].

ALUMINIUM ALLOYS

Uncoated and coated (Graphit-iC

TC

[8, 9], MoST

TM

[10, 11] and DLC)

carbide balls have been rubbed against Al 5% Cu, where friction coefficient,
and damaged on the ball have been reported. From Fig. 5, it can be seen
that building up is occurring on the carbide and the Graphit-iC

TC

coating at

the beginning of the test. This results to a poor quality workpiece material
(scratching of workpiece) and increasing friction coefficient from 0.15 to
0.44 for the carbide and 0.49 to 0.60 for the Graphit-iC

TC

coating. On the

other hand, the hydrogenated DLC coating has a very different behaviour, it
was not possible to detect any building up, small particles are incrusted in
the ball due to the surface finishing, this could be eliminated by using even
higher quality polished balls. The surface finishing is an important factor in
the building up formation. The DLC coating retains a low friction coefficient
through the test from 0.36 to 0.17. Regarding the MoST

TM

coating, the

surface finishing of the ball is higher than the one of the workpiece material.
The copper is able to create scratches with would led to creation of a building
up with time. The surface finishing of the workpiece material is higher
quality at the beginning of the test, but deteriorate rapidly as the building up
increased. The friction coefficient is increasing through the test from 0.12
to 0.49. From these test the use of DLC coating is recommended.

Stainless steel AISI 316L

Uncoated carbide balls have been rubbed

against AISI 316L, where damaged on the ball and on the workpiece ma-

New Unidirectional Single Pass Wear Testing Procedure

899

terial have been reported. From Fig. 6, it can been seen that building up is
occurring on the carbide during the test. First there is accommodation of the
two surfaces followed by debris accumulation. This results in scratching of
workpiece and poor quality product.

CONCLUSIONS

While indispensable as a final validation before press shop introduction,

real scale simulation experiments are expensive and time consuming. In
most cases, they are

inadequate for precise failure origin analysis. A new procedure has been

developed and tested on the ST-3001 multi-mode testing

system as a laboratory simulation test for an initial assessment and optimi-

sation of suitable system substrate / coating / workpiece materials / lubricants
used in cold forming operations. In our present work, the new procedure
was tested for the simulation of sticking of gummy materials such as Al, Cu,
Sn, Ti and stainless steel or other materials. The procedure can be used dry
or even lubricated for testing the suitability of new systems.

ACKNOWLEDGMENTS

The Authors would like to thanks Dr Juergen Von Stebut for the useful

discussions and the European Commission for the financial support through
a Brite Euram project number SMT4-CT97-2150.

REFERENCES

[1] V. BELLIDO-GONZALEZ, N. STEFANOPOULOS and F. DEGUILHEN, Surface

and Coatings Technology 74-75 (1995) 884-889.

[2] Multimode scratch testing project SMT4-CR1997-2150

[3] R. REZAKHANLOU and J. VON STEBUT, "Damage mechanisms of hard coatings

on hard substrates : A critical analysis of failure in scratch and wear testing" .in
"Mechanics of Coatings", Tribology Series 17, Eds. : D. Dowson, C.M. Taylor, M.
Godet, Elsevier, Amsterdam 1990.

[4] Advanced technical ceramics - Methods of test for ceramic coatings - Part 3: Deter-

mination of adhesion by scratch test, ENV 1071 - 3: 1994

[5] K. J. WALH, M. BELIN and I. L. SINGER, Wear 214 (1998) 212.

[6] M. GODET, Wear, 100 (1984), 437

[7] J. M. STORY, G. W. JARVIS, H. R. ZONKER and S. J. MURTHA, Issues and trends

in automotive aluminium sheet forming, SAE Publication no. SP-944 (1993) 1.

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6TH INTERNATIONAL TOOLING CONFERENCE

[8] W. R. D. WILSON, tribology in cold metal forming, J. Manufac. Sci. Eng. 119 (1997)

695.

[9] N. M. RENEVIER, S. POULAT and D. G. TEER, Presented at ICMCTF 2002 in San

Diego, Ca, USA, 22-26 April 2002.

[10] D. G. TEER, D. CAMINO and A. H. S. JONES, UK Patent appl. GB 9 725 413, 1997

[11] D. CAMINO, A. H. S. JONES, D. MERCS and D.G. TEER, Vacuum, 52 (1999) 125.

[12] D. G. TEER, V. BELLIDO-GONZALES and J. HAMPHIRE, "MoS2/Titanium Coat-

ings" UK Patent GB9514773.2 (19/07/1995), EU Patent 0842306

[13] N. M RENEVIER, J. HAMPSHIRE, V. C FOX, J. WITTS, T. ALLEN and D. G TEER,

Surf. Coat. Technol., 142-144 (2001) 67.

New Unidirectional Single Pass Wear Testing Procedure

901

(a) general view

(b) main software window

Figure 1.

Teer Scratch and Wear tester ST 3001.

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6TH INTERNATIONAL TOOLING CONFERENCE

Figure 2.

Schematic diagram of a bending process.

New Unidirectional Single Pass Wear Testing Procedure

903

Figure 3.

Loading system and translation system.

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(a)

(b)

Figure 4.

(a) Description of the procedure and (b) parameters for step 2.

New Unidirectional Single Pass Wear Testing Procedure

905

№

Uncoated Carbide

Graphit-iC

TC

MoST

TM

DLC

0

1

5

10

50

100

Figure 5.

Aluminium-5% Copper Alloy- tool building up and Friction coefficient.

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6TH INTERNATIONAL TOOLING CONFERENCE

0

1

5

10

50

100

150

200

Figure 6.

Stainless steel - WC tool building up.