Nanotechnologies - Nano- and micro- scale scratch testing

This document specifies a method for measuring the scratch resistance and failure behaviour for advanced materials and coatings by means of nano- and micro- scale scratch experiments. The method provides data on both the physical damage to test-pieces and the friction generated between the probe and the test-piece under single pass and multiple pass conditions. The force range in these tests is from 1 µN up to 2 N.
The test method is not applicable to coatings as defined in EN ISO 4618 [18].

Nanotechnologien - Nano- und Mikro-Ritzprüfung

Dieses Dokument legt ein Verfahren zur Messung der Ritzbeständigkeit und des Versagensverhaltens von modernen Werkstoffen und Beschichtungen mithilfe von nano- und mikroskaligen Ritzversuchen fest. Das Verfahren stellt sowohl Daten zur physischen Beschädigung an Proben als auch zur Reibung, die zwischen Eindringkörper und Probe bei einfachem oder mehrfachem Durchlauf erzeugt wird bereit. Der Kraftbereich dieser Prüfungen reicht von 1 µN bis zu 2 N.
Das Testverfahren ist nicht auf Beschichtungen nach EN ISO 4618 [18] anwendbar.

Nanotechnologies - Tests de résistance à l'échelle nanométrique et microscopique

Le présent document spécifie une méthode permettant de mesurer la résistance à la rayure et le comportement à la rupture des matériaux avancés et des revêtements, au moyen d’expériences de rayure aux échelles nano- et micro-métriques. La méthode fournit des données portant à la fois sur les dommages physiques occasionnés aux éprouvettes et sur le frottement généré entre la sonde et l’éprouvette en une seule ou plusieurs passes. Les forces à appliquer pour ces essais sont comprises entre 1 μN et 2 N.
La méthode d’essai n’est pas applicable aux revêtements tels que définis dans l’EN ISO 4618 [18].

Nanotehnologije - Nano- in mikropreskus praskanja

General Information

Status
Published
Public Enquiry End Date
31-Mar-2021
Publication Date
28-Jun-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
24-Jun-2021
Due Date
29-Aug-2021
Completion Date
29-Jun-2021

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SLOVENSKI STANDARD
SIST-TS CEN/TS 17629:2021
01-september-2021
Nanotehnologije - Nano- in mikropreskus praskanja
Nanotechnologies - Nano- and micro- scale scratch testing
Nanotechnologien - Nano- und Mikro-Ritzprüfung
Nanotechnologies - Tests de résistance à l'échelle nanométrique et microscopique
Ta slovenski standard je istoveten z: CEN/TS 17629:2021
ICS:
07.120 Nanotehnologije Nanotechnologies
SIST-TS CEN/TS 17629:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CEN/TS 17629:2021
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SIST-TS CEN/TS 17629:2021
CEN/TS 17629
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
June 2021
TECHNISCHE SPEZIFIKATION
ICS 07.120
English Version
Nanotechnologies - Nano- and micro- scale scratch testing

Nanotechnologies - Essais de rayure aux échelles nano- Nanotechnologien - Nano- und Mikro-Ritzprüfung

et micro métriques

This Technical Specification (CEN/TS) was approved by CEN on 9 May 2021 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to

submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS

available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in

parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 17629:2021 E

worldwide for CEN national Members.
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SIST-TS CEN/TS 17629:2021
CEN/TS 17629:2021 (E)
Contents Page

European foreword ................................................................................................................................................................ 3

Introduction ............................................................................................................................................................................. 3

1 Scope ............................................................................................................................................................................. 5

2 Normative references ............................................................................................................................................. 5

3 Terms and definitions ............................................................................................................................................ 5

4 Symbols and abbreviations .................................................................................................................................. 7

5 Principle ...................................................................................................................................................................... 9

5.1 General ......................................................................................................................................................................... 9

5.2 Friction ......................................................................................................................................................................... 9

5.3 Factors influencing the critical forces .............................................................................................................. 9

5.4 Multiple pass testing ............................................................................................................................................ 11

6 Apparatus and materials .................................................................................................................................... 12

6.1 Apparatus ................................................................................................................................................................. 12

6.2 Probes........................................................................................................................................................................ 14

6.3 Test environment .................................................................................................................................................. 16

7 Preparation of test-pieces .................................................................................................................................. 16

7.1 Roughness ................................................................................................................................................................ 16

7.2 Test-piece cleaning ............................................................................................................................................... 16

8 Test procedures ..................................................................................................................................................... 17

8.1 General ...................................................................................................................................................................... 17

8.2 Zero-point determination .................................................................................................................................. 17

8.3 Test force .................................................................................................................................................................. 18

8.4 Test profiles ............................................................................................................................................................ 18

8.5 Test procedures ..................................................................................................................................................... 18

9 Analysis of results ................................................................................................................................................. 23

9.1 General ...................................................................................................................................................................... 23

9.2 Single pass ramping force .................................................................................................................................. 23

9.3 Single pass constant force .................................................................................................................................. 26

9.4 Multi-pass ramping force ................................................................................................................................... 26

9.5 Multi-pass constant force ................................................................................................................................... 26

10 Test reproducibility, repeatability and limits ............................................................................................ 27

11 Test report ............................................................................................................................................................... 28

Annex A (normative) Procedures for determination of probe area function or radius function ........... 29

Bibliography .......................................................................................................................................................................... 34

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CEN/TS 17629:2021 (E)
European foreword

This document (CEN/TS 17629:2021) has been prepared by Technical Committee CEN/TC 352

“Nanotechnologies”, the secretariat of which is held by AFNOR.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN shall not be held responsible for identifying any or all such patent rights.

According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following

countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus,

Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania,

Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

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CEN/TS 17629:2021 (E)
Introduction

The test procedure is intended to complement other standards which are concerned with the scratch

resistance of materials. This procedure extends the use of the nano- and micro- single pass scratch test to bulk

and coated materials, additionally covering the use of multiple pass nano- and micro- scratch tests.

The method described is not intended to be used to define how particles are released from a surface under

this type of damage.

Several measurement techniques are described, according to the following procedures:

— Constant force scratch test

Single movement of a normally loaded probe (constant force) onto a test piece; friction force and

displacement of the probe (relative to the test piece) are measured along the scratch path.

— Ramped force scratch test

Single movement of a progressively normally loaded probe (ramped force) onto a test piece; friction force

and displacement of the probe (relative to the test piece) are measured along the scratch path.

— Multi-pass unidirectional constant force scratch test

Repeated movement of a normally loaded probe (constant force) onto a test piece, following the same

track; the variation in friction force and displacement of the probe (relative to the piece test) are measured

along the scratch path. First introduced by Bull and Rickerby [1], this test is also called “nanowear” when

used in the nano scratch range and provides information regarding the fatigue behaviour of the test piece

as an effective low cycle fatigue test.
— Progressive force “3-scan” scratch test

Three repetitive unidirectional movement of a normally loaded probe onto a test piece, along the same

track. The first movement of the probe is carried out at constant force (low force) and performed as a

topography scan of a non-scratched test piece surface. The second movement of the probe is achieved

with a progressively increased normal force onto the test piece (from low to high forces). The third

movement of the probe is similar to the first movement, at low force, to acquire a topography of the

scratch carried out in the test piece. This test is also called “scratch topography multi-pass test” and was

first reported by Wu and co-workers [2], [3], which enables identification of failure mechanisms and

provides more details regarding the impact of stress such as the critical force for onset of non-elastic

deformation and the yield pressure (estimated from mean pressure at critical force).

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CEN/TS 17629:2021 (E)
1 Scope

This document specifies a method for measuring the scratch resistance and failure behaviour for advanced

materials and coatings by means of nano- and micro- scale scratch experiments. The method provides data on

both the physical damage to test-pieces and the friction generated between the probe and the test-piece under

single pass and multiple pass conditions. The force range in these tests is from 1 µN up to 2 N.

The test method is not applicable to coatings as defined in EN ISO 4618 [18].
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
nanoscale
size range between approximately 1 nm and 100 nm

Note 1 to entry: Properties that are not extrapolations from a larger size are predominately exhibited in this size range.

Note 2 to entry: The lower limit in this definition (approximately 1 nm) is introduced to avoid single and small groups

of atoms from being designated as nano-objects or elements of nanostructures, which might be implied by the absence

of a lower limit.

Note 3 to entry: EN ISO 14577-1 defines nano range for indentation depth as less than 200 nm and has a force criterion

for tests in the micro range.
[SOURCE: CEN ISO/TS 80004-1:2015, 2.1 [17], modified]
3.2
microscale
size range between 100 nm and 100 µm
3.3
topographical profiling

scans carried out for topographical profiling sequence (e.g. 3-pass scratch test: pre-scanning and post-

scanning under minimal force), the purpose of which is to measure the topographical profile of the surface

before and after the scratch test

Note 1 to entry: The load of the scan should be kept to a minimum to avoid plastic deformation.

Note 2 to entry: Scans have to move in the same direction to avoid uncertainties in displacement recording and scanning

movements have to be longer than scratching ones to cover the starting- and ending part of the scratch and providing

undeformed areas for checking instrument drift. The force during the scanning movements shall be low enough to ensure

that any deformation is elastic.

Note 3 to entry: The probe radius needs to be small enough to give sufficient resolution for the analysis of the profile of

the surface.
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CEN/TS 17629:2021 (E)
3.4
critical points on the scratch track

points on the scratch track, where any new damage process starts as a function of the track length, normal-

force or other measured signal (e.g. tangential force, acoustic emission, etc.)

Note 1 to entry: These processes can be identified as characteristics of the scratching track itself or as characteristic

of the recorded tracks (scanning – scratching – post-scanning).
3.4.1
onset of plastic deformation

point on the scratch track where the post- scanning track becomes significantly deeper (4 × instrument

displacement noise floor) than the pre-scanning track, if necessary, after thermal drift correction

Note 1 to entry: The normal force at this point is the threshold force for onset of plastic deformation (L ).

Note 2 to entry: When the objective is to identify coating properties one has to confirm that the yield event takes place

in the coating.
3.4.2
onset of cracking

critical point in the scratch experiment where initial cracking is experienced as evidenced by subsequent

imaging of the scratch path, or through analysis of the friction force, acoustic emission [4], or displacement

data (L )
3.4.3
onset of partial coating failure

critical point in the scratch experiment where the beginning of material removal inside or outside the scratch

track can be identified

Note 1 to entry: Typically, the removed material is smaller than the film thickness. This critical point is called L . The

failure mode correlated to L is not always occurring. In this case L should not be given.

C2 C2
3.4.4
onset of severe coating failure

critical point in the scratch experiment where a significant removal of material can be identified by subsequent

imaging of the scratch path or by the difference of post- and pre-scan depth

Note 1 to entry: If this is greater or equal to the coating thickness, then delamination may have been occurred. This

critical point is called L . If the difference of post- and pre-scan depth is less than the coating thickness the failure mode

may be cohesive.
3.5
probe area function

geometrical relationship between projected normal area of probe and distance from the end of the probe

Note 1 to entry: The probe area function should be verified periodically to determine the shape of the tip (refer to

Annex A).
3.6
spherical probe effective radius
radius of an ideal spherical probe that gives same depth as an imperfect probe

Note 1 to entry: For other probes with other nominal shapes such as pyramidal probes, there is always some

imperfection in the shape of the tip at the point such that the tip has an effective radius.

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CEN/TS 17629:2021 (E)
3.7
scratch depth

h is the scratch depth under force and h is the residual depth determined from a subsequent topographical

t r

profile as the depth determined by subtracting the pre-scan profile from the post-scan profile

3.8
friction force

resisting force tangential to the interface between two bodies when, under the action of an external force, one

body moves or tends to move relative to the other
Note 1 to entry: See also coefficient of friction.
[SOURCE: ASTM G40-17:2017]
4 Symbols and abbreviations

For the purposes of this document, the following symbols and abbreviations in Table 1 apply.

Table 1 — Symbols and abbreviations
Symbol Definition Unit
h On-force scratch depth mm
h Contact depth mm
h Initial depth (pre-scan) mm
h Residual depth (after scratch) mm
t Coating thickness mm
R Arithmetic average of the roughness mm
S Effective adhesion strength GPa
R Tip radius mm
A Tip contact area
x Scratch distance mm
t Scratch time s
F Normal force N
F Scan force N
F Tangential force N
P Contact pressure GPa
L Initial yield force N
L Force at which first cracking occurs N
L Force at which partial failure occurs N
L Force at which complete failure occurs N
L Critical force N
µ Friction coefficient
tot
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SIST-TS CEN/TS 17629:2021
CEN/TS 17629:2021 (E)
Symbol Definition Unit
µ Interfacial friction component
interfacial
µ Ploughing friction component
ploughing
C Contact compliance nm/mN
C Frame compliance nm/mN
E Young’s modulus GPa
E Young’s modulus of the probe GPa
E Young’s modulus of test specimen GPa
E Reduced Young’s modulus GPa
H Hardness GPa
ν Poisson’s ratio of the probe
ν Poisson’s ratio of the test specimen
a Probe contact radius mm
ε Epsilon factor
Some of the abbreviations listed above are schematically described in Figure 1.
Key
1 substrate 6 h contact depth
h residual depth (after scratch)
2 coating 7
3 probe 8 h on-force scratch depth
4 F normal force 9 R tip radius
5 x scratch distance 10 t coating thickness
Figure 1 — Schematic representation of a scratch test and its cross-section
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SIST-TS CEN/TS 17629:2021
CEN/TS 17629:2021 (E)
5 Principle
5.1 General

In the test, a probe of known geometry is loaded against a test-piece and moved across the test-piece. The

depth of penetration of the probe into the test-piece is measured to provide a real-time measure of damage to

the test-piece as the test is being carried out, and the force generated by the resistance of the motion is

measured to provide information on friction. To determine the response of the material to repeated contacts,

multiple pass experiments can be carried out. Both constant loading and ramping loading can also be carried

out.

A key parameter in these measurements is the measurement and control of the geometry of the probe that is

used to carry out the experiments.
5.2 Friction

The measured friction force in the nano- or micro-scratch test typically varies with the applied force. When a

hard surface is slid over a softer surface part of the frictional resistance is due to the force required to plough

asperities of the harder surface through the softer. The friction coefficient (frictional force/normal force) can

therefore be separated into its interfacial and ploughing components so that the interfacial friction coefficient

can be reported:
µ total = µ + µ [5] (1)
interfacial ploughing

Interfacial friction comes from the adhesion force that normally occurs between two surfaces in contact. No

change to the surface occurs from this effect. Interfacial friction can be determined by different approaches:

1) performing constant force friction test at very low force where contact is completely elastic and the

ploughing contribution is zero;
2) performing repetitive scratches to eliminate the ploughing contribution;

3) performing progressive force scratch and extrapolating the low force friction data to zero force.

Typically, the friction coefficient at yield is of the order of 0,05, rising to about 0,2 to 0,5 at failure. The impact

of ploughing on friction has a complex mechanism and depends strongly on mechanical properties of the test

specimen.

Although frictional measurements are often reported to differ at different length scales it appears that when

the extent of deformation is taken into account there is much better agreement [6], [8].

5.3 Factors influencing the critical forces
5.3.1 General

In addition to the strength of adhesion between any coating that is present and substrate, the critical force can

be influenced by a range of extrinsic and intrinsic factors [9] as well as the mechanical properties of the test-

piece (E and H) and the lateral stiffness of the instrument [10], [11]. The intrinsic factors include scratching

speed, loading rate, tip radius and extrinsic factors can include the mechanical properties of both the coating

and the substrate, and roughness, thickness and friction force generated in the contact of the probe with the

surface of the test-piece. In addition, the environment conditions, namely, the temperature, pressure, relative

humidity and gas composition may have a signification impact on the test results.

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SIST-TS CEN/TS 17629:2021
CEN/TS 17629:2021 (E)
5.3.2 Probe radius

For coated samples, the ability of the test to investigate features of the structure like the interface between

coating and substrate is controlled by the magnitude of the applied force and the ratio of the probe radius to

coating thickness, R/t . This ratio is much less than the ratio used in macro-scale scratch tests. For coatings,

the probe radius can be chosen to generate a maximum stress above, at, or below an interface, depending on

what information is most critical in the application. The different R/t ratio can associated with different stress

field, enabling to focus on cohesive or adhesive failure of coatings.

Higher critical forces are observed when larger probe radii are used (low stresses). For the condition where

plastic deformation starts in the substrate a rough estimation of the critical force may follow a power law

dependence on the probe radius [7] of the type shown in Formula (2) where S is a parameter which can be

correlated with the effective adhesion strength in the scratch test. The exponent m is usually in the range 1 to

2 when spherical probes are used.
L = SR [10] (2)
If coatings are present, their thickness can influence the critical force since:

a) thicker films that are harder than the underlying substrate provide more load support and so delay the

onset of substrate deformation that can occur before film failure (higher critical force);

b) thicker films can be more highly stressed and more easily through-thickness crack and delaminate when

deformed (lower critical force) since the driving force for spallation to reduce stored elastic energy is

greater.

In practice when the film is not highly stressed the ratio L /t may be approximately constant.

c f

Materials, such as metals, that show an indentation size effect will also show a size effect in the nano-scratch

test. For materials such as these, the yield stress determined from the onset of plastic deformation in the nano-

scratch test will be higher than when determined at greater length scale in bulk testing. This means that the

yield stress can increase for smaller radii probes.
5.3.3 Scan speed and loading rate

The critical force may vary with choice of scan speed and loading rate, but practice has shown that within the

typical range of these most materials show relatively low sensitivity [12]. When tests are performed at a

constant dF /dx ratio (the increase in normal force per unit scratch distance), the critical force can be

approximately constant over a large range of scratching speeds. While nano-scratch tests carried out under

varying loading rate (<1 N/mm) can be compared to one another (low sensitivity), micro-scratch tests with

loading rates exceeding 1 N/mm have an effect on the critical force; the critical force decreases as the dF /dx

ratio decreases as a result of higher probability to encounter a defective adhesion region [10].

5.3.4 Roughness

The critical force can be influenced by test-piece roughness and by the direction of scratching relative to

polishing marks on the surface made prior to coating deposition [13]. The critical force may be lower when

scratching perpendicular to the grinding marks than parallel to them. In addition, high roughness tends to

decrease the critical force but load carrying capability of thick coating has a higher effect; the critical force

increases with coating thickness when coating is harder than substrate, which delays substrate deformation

[5], [14].
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CEN/TS 17629:2021 (E)
5.4 Multiple pass testing

Multiple pass constant force scratch tests can be carried out with the nano- and micro-scratch technique. The

test effectively becomes a low cycle [15] nano- or micro-wear test where the test parameters are less severe

than in a progressive force scratch test. Constant force wear tests are often used to determine rates of wear

and investigate the role of surface fatigue. The low-cycle wear experiments can often be much more

informative regarding the influence of, e.g. coating stress leading to poor adhesion than single pass scratch

tests. When compared to progressive force scratch testing, wear testing has the advantage that the force can

be varied to tune the maximum stress to be close to the coating-substrate interface.

The applied force used in the multiple pass scratch test is usually lower than the critical force (Lc ) in a

progressive force scratch test. The number of scratch passes to failure is a convenient parameter to compare

the durability of different trial coatings. Either the variation in friction or the on-force depth with number of

scratches can be used to determine the number of cycles to film failure.

Typically, a test is composed of 10 to 20 scratch cycles; an example of the multi-pass test is presented in

Figure 2. Optionally, it can be combined with alternate low-force passes. For example, a test involving 20

scratches under constant force could be set as a total of 41 passes over the same scratch track - an initial low

force scan would be followed by 20 times (scratch-topography) pairs.

In contrast to progressive force scratch tests, failure may initially occur at isolated regions of the film surface

requiring several subsequent passes until the film is completely removed from the scratch track. The mean

depth over the constant force region is a convenient parameter to follow the evolution of the damage process.

Key
1 number of pass – scratch and scan
2 depth, h (nm)
3 friction coefficient, µ
4 on-force scratch depth, h
5 residual depth, h

Figure 2 — Progression of scratch depth, residual depth and friction coefficient repetitive nano-

scratch of a 1 µm DLC at 70 mN with a R = 6,5 μm probe -the arrows associate each data set with their

respective y-axis
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SIST-TS CEN/TS 17629:2021
CEN/TS 17629:2021 (E)

By performing tests at various sub-critical forces (

to failure varied with the constant force and build up a picture of the film behaviour in low cycle fatigue

analogously to a stress-life diagram. An increase in residual depth and decrease in scratch recovery after each

cycle enables the use of the multi-pass test as a fatigue process [8]. The combination of multi-pass test at

various loading levels provides information regarding the suitability of the sample for contact application; the

cycle for failure is taken as the cycle when failure starts. Therefore, the lifetime of the test specimen (number

of cycles to failure) can be plotted as a function of the applied force, as described in Figure 3.

Key
1 number of scratch pass at failure
2 normal force, F (mN)
Figure 3 —
...

SLOVENSKI STANDARD
kSIST-TS FprCEN/TS 17629:2021
01-marec-2021
Nanotehnologije - Nano in mikro preskus praskanja
Nanotechnologies - Nano- and micro- scale scratch testing
Nanotechnologien - Nano- und Mikro-Ritzprüfung
Nanotechnologies - Tests de résistance à l'échelle nanométrique et microscopique
Ta slovenski standard je istoveten z: FprCEN/TS 17629
ICS:
07.120 Nanotehnologije Nanotechnologies
kSIST-TS FprCEN/TS 17629:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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kSIST-TS FprCEN/TS 17629:2021
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kSIST-TS FprCEN/TS 17629:2021
FINAL DRAFT
TECHNICAL SPECIFICATION
FprCEN/TS 17629
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
January 2021
ICS 07.120
English Version
Nanotechnologies - Nano- and micro- scale scratch testing

Nanotechnologies - Tests de résistance à l'échelle Nanotechnologien - Nano- und Mikro-Ritzprüfung

nanométrique et microscopique

This draft Technical Specification is submitted to CEN members for Vote. It has been drawn up by the Technical Committee

CEN/TC 352.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a Technical Specification. It is distributed for review and comments. It is subject to change

without notice and shall not be referred to as a Technical Specification.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TS 17629:2021 E

worldwide for CEN national Members.
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kSIST-TS FprCEN/TS 17629:2021
FprCEN/TS 17629:2021 (E)
Contents Page

European foreword ................................................................................................................................................................ 3

Introduction ............................................................................................................................................................................. 4

1 Scope ............................................................................................................................................................................. 5

2 Normative references ............................................................................................................................................. 5

3 Terms and definitions ............................................................................................................................................ 5

4 Symbols and abbreviations .................................................................................................................................. 7

5 Principle ...................................................................................................................................................................... 8

5.1 General ......................................................................................................................................................................... 8

5.2 Friction ......................................................................................................................................................................... 9

5.3 Factors influencing the critical forces .............................................................................................................. 9

5.4 Multiple pass testing ............................................................................................................................................ 10

6 Apparatus and materials .................................................................................................................................... 12

6.1 Apparatus ................................................................................................................................................................. 12

6.2 Probes........................................................................................................................................................................ 14

6.3 Test environment .................................................................................................................................................. 16

7 Preparation of test-pieces .................................................................................................................................. 16

7.1 Roughness ................................................................................................................................................................ 16

7.2 Test-piece cleaning ............................................................................................................................................... 16

8 Test procedures ..................................................................................................................................................... 17

8.1 General ...................................................................................................................................................................... 17

8.2 Zero-point determination .................................................................................................................................. 17

8.3 Test force .................................................................................................................................................................. 18

8.4 Test profiles ............................................................................................................................................................ 18

8.5 Test procedures ..................................................................................................................................................... 18

9 Analysis of results ................................................................................................................................................. 23

9.1 General ...................................................................................................................................................................... 23

9.2 Single pass ramping force .................................................................................................................................. 23

9.3 Single pass constant force .................................................................................................................................. 26

9.4 Multi-pass ramping force ................................................................................................................................... 26

9.5 Multi-pass constant force ................................................................................................................................... 26

10 Test reproducibility, repeatability and limits ............................................................................................ 27

11 Test report ............................................................................................................................................................... 28

Annex A (normative) Procedures for determination of probe area function or radius function ........... 29

Bibliography .......................................................................................................................................................................... 34

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European foreword

This document (FprCEN/TS 17629:2021) has been prepared by Technical Committee CEN/TC 352

“Nanotechnologies”, the secretariat of which is held by AFNOR.
This document is currently submitted to the Vote on TS.
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Introduction

The test procedure is intended to complement other standards which are concerned with the scratch

resistance of materials. This procedure extends the use of the nano- and micro- single pass scratch test to bulk

and coated materials, additionally covering the use of multiple pass nano- and micro- scratch tests.

The method described is not intended to be used to define how particles are released from a surface under

this type of damage.

Several measurement techniques are described, according to the following procedures:

— Constant force scratch test

Single movement of a normally loaded probe (constant force) onto a test piece; friction force and

displacement of the probe (relative to the test piece) are measured along the scratch path.

— Ramped force scratch test

Single movement of a progressively normally loaded probe (ramped force) onto a test piece; friction force

and displacement of the probe (relative to the test piece) are measured along the scratch path.

— Multi-pass unidirectional constant force scratch test

Repeated movement of a normally loaded probe (constant force) onto a test piece, following the same

track; the variation in friction force and displacement of the probe (relative to the piece test) are measured

along the scratch path. First introduced by Bull and Rickerby [1], this test is also called “nanowear” when

used in the nano scratch range and provides information regarding the fatigue behaviour of the test piece

as an effective low cycle fatigue test.
— Progressive force “3-scan” scratch test

Three repetitive unidirectional movement of a normally loaded probe onto a test piece, along the same

track. The first movement of the probe is carried out at constant force (low force) and performed as a

topography scan of a non-scratched test piece surface. The second movement of the probe is achieved

with a progressively increased normal force onto the test piece (from low to high forces). The third

movement of the probe is similar to the first movement, at low force, to acquire a topography of the

scratch carried out in the test piece. This test is also called “scratch topography multi-pass test” and was

first reported by Wu and co-workers [2,3], which enables identification of failure mechanisms and

provides more details regarding the impact of stress such as the critical force for onset of non-elastic

deformation and the yield pressure (estimated from mean pressure at critical force).

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1 Scope

This document specifies a method for measuring the scratch resistance and failure behaviour for advanced

materials and coatings by means of nano- and micro- scale scratch experiments. The method provides data on

both the physical damage to test-pieces and the friction generated between the probe and the test-piece under

single pass and multiple pass conditions. The force range in these tests is from 1 µN up to 2 N.

The test method is not applicable to coatings as defined in EN ISO 4618 [18].
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
nanoscale
size range between approximately 1 nm and 100 nm

Note 1 to entry: Properties that are not extrapolations from a larger size are predominately exhibited in this size range.

Note 2 to entry: The lower limit in this definition (approximately 1 nm) is introduced to avoid single and small groups

of atoms from being designated as nano-objects or elements of nanostructures, which might be implied by the absence

of a lower limit.

Note 3 to entry: EN ISO 14577-1 defines nano range for indentation depth as less than 200 nm and has a force criterion

for tests in the micro range.
[SOURCE: CEN ISO/TS 80004-1:2015, 2.1 [17], modified]
3.2
microscale
size range between 100 nm and 100 µm
3.3
topographical profiling

scans carried out for topographical profiling sequence (e.g. 3-pass scratch test: pre-scanning and post-

scanning under minimal force), the purpose of which is to measure the topographical profile of the surface

before and after the scratch test

Note 1 to entry: The load of the scan should be kept to a minimum to avoid plastic deformation.

Note 2 to entry: Scans have to move in the same direction to avoid uncertainties in displacement recording and scanning

movements have to be longer than scratching ones to cover the starting- and ending part of the scratch and providing

undeformed areas for checking instrument drift. The force during the scanning movements shall be low enough to ensure

that any deformation is elastic.

Note 3 to entry: The probe radius needs to be small enough to give sufficient resolution for the analysis of the profile of

the surface
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3.4
critical points on the scratch track

points on the scratch track, where any new damage process starts as a function of the track length, normal-

force or other measured signal (e.g. tangential force, acoustic emission, etc.)

Note 1 to entry: These processes can be identified as characteristics of the scratching track itself or as characteristic

of the recorded tracks (scanning – scratching – post-scanning).
3.4.1
onset of plastic deformation

point on the scratch track where the post- scanning track becomes significantly deeper (4 × instrument

displacement noise floor) than the pre-scanning track, if necessary, after thermal drift correction

Note 1 to entry: The normal force at this point is the threshold force for onset of plastic deformation (Ly).

Note 2 to entry: When the objective is to identify coating properties one has to confirm that the yield event takes place

in the coating.
3.4.2
onset of cracking

critical point in the scratch experiment where initial cracking is experienced as evidenced by subsequent

imaging of the scratch path, or through analysis of the friction force, acoustic emission [4], or displacement

data (Lc1)
3.4.3
onset of partial coating failure

critical point in the scratch experiment where the beginning of material removal inside or outside the scratch

track can be identified

Note 1 to entry: Typically, the removed material is smaller than the film thickness. This critical point is called Lc2. The

failure mode correlated to LC2 is not always occurring. In this case LC2 should not be given.

3.4.4
onset of severe coating failure

critical point in the scratch experiment where a significant removal of material can be identified by subsequent

imaging of the scratch path or by the difference of post- and pre-scan depth

Note 1 to entry: If this is greater or equal to the coating thickness, then delamination may have been occurred. This

critical point is called Lc3. If the difference of post- and pre-scan depth is less than the coating thickness the failure mode

may be cohesive.
3.5
probe area function

geometrical relationship between projected normal area of probe and distance from the end of the probe

Note 1 to entry: The probe area function should be verified periodically to determine the shape of the tip (refer to

Annex A).
3.6
spherical probe effective radius
radius of an ideal spherical probe that gives same depth as an imperfect probe

Note 1 to entry: For other probes with other nominal shapes such as pyramidal probes, there is always some

imperfection in the shape of the tip at the point such that the tip has an effective radius.

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3.7
scratch depth

h is the scratch depth under force and h is the residual depth determined from a subsequent topographical

t r

profile as the depth determined by subtracting the pre-scan profile from the post-scan profile

3.8
friction force

resisting force tangential to the interface between two bodies when, under the action of an external force, one

body moves or tends to move relative to the other
Note 1 to entry: See also coefficient of friction.
[SOURCE: ASTM G40-17:2017]
4 Symbols and abbreviations

For the purposes of this document, the following symbols and abbreviations apply.

Table 1 — Symbols and abbreviations
Symbol Definition Unit
h On-force scratch depth mm
h Contact depth mm
h Initial depth (pre-scan) mm
h Residual depth (after scratch) mm
t Coating thickness mm
R arithmetic average of the roughness mm
S Effective adhesion strength GPa
R Tip radius mm
A Tip contact area mm
x Scratch distance mm
t Scratch time s
F Normal force N
F Scan force N
F Tangential force N
P Contact pressure GPa
L Initial yield force N
L Force at which first cracking occurs N
L Force at which partial failure occurs N
L Force at which complete failure occurs N
L Critical force N
µtot Friction coefficient
µ Interfacial friction component
interfacial
µ Ploughing friction component
ploughing
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Symbol Definition Unit
C Contact compliance nm/mN
C Frame compliance nm/mN
E Young’s modulus GPa
E Young’s modulus of the probe GPa
E Young’s modulus of test specimen GPa
E Reduced Young’s modulus GPa
H Hardness GPa
ν Poisson’s ratio of the probe
ν Poisson’s ratio of the test specimen
a Probe contact radius mm
ε Epsilon factor
Some of the abbreviations listed above are schematically described in Figure 1.
Key
1 substrate 6 h contact depth
2 coating 7 h residual depth (after scratch)
3 probe 8 ht on-force scratch depth
4 FN normal force 9 R tip radius
5 x scratch distance 10 t coating thickness
Figure 1 — Schematic representation of a scratch test and its cross-section
5 Principle
5.1 General

In the test, a probe of known geometry is loaded against a test-piece and moved across the test-piece. The

depth of penetration of the probe into the test-piece is measured to provide a real-time measure of damage to

the test-piece as the test is being carried out, and the force generated by the resistance of the motion is

measured to provide information on friction. To determine the response of the material to repeated contacts,

multiple pass experiments can be carried out. Both constant loading and ramping loading can also be carried

out.

A key parameter in these measurements is the measurement and control of the geometry of the probe that is

used to carry out the experiments.
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5.2 Friction

The measured friction force in the nano- or micro-scratch test typically varies with the applied force. When a

hard surface is slid over a softer surface part of the frictional resistance is due to the force required to plough

asperities of the harder surface through the softer. The friction coefficient (frictional force/normal force) can

therefore be separated into its interfacial and ploughing components so that the interfacial friction coefficient

can be reported:
µ total = µ + µ [5] (1)
interfacial ploughing

Interfacial friction comes from the adhesion force that normally occurs between two surfaces in contact. No

change to the surface occurs from this effect. Interfacial friction can be determined by different approaches:

1) performing constant force friction test at very low force where contact is completely elastic and the

ploughing contribution is zero;
2) performing repetitive scratches to eliminate the ploughing contribution;

3) performing progressive force scratch and extrapolating the low force friction data to zero force.

Typically, the friction coefficient at yield is of the order of 0,05, rising to about 0,2 to 0,5 at failure. The impact

of ploughing on friction has a complex mechanism and depends strongly on mechanical properties of the test

specimen.

Although frictional measurements are often reported to differ at different length scales it appears that when

the extent of deformation is taken into account there is much better agreement [6-8].

5.3 Factors influencing the critical forces
5.3.1 General

In addition to the strength of adhesion between any coating that is present and substrate, the critical force can

be influenced by a range of extrinsic and intrinsic factors [9] as well as the mechanical properties of the test-

piece (E and H) and the lateral stiffness of the instrument [10,11]. The intrinsic factors include scratching

speed, loading rate, tip radius and extrinsic factors can include the mechanical properties of both the coating

and the substrate, and roughness, thickness and friction force generated in the contact of the probe with the

surface of the test-piece. In addition, the environment conditions, namely, the temperature, pressure, relative

humidity and gas composition may have a signification impact on the test results.

5.3.2 Probe radius

For coated samples, the ability of the test to investigate features of the structure like the interface between

coating and substrate is controlled by the magnitude of the applied force and the ratio of the probe radius to

. This ratio is much less than the ratio used in macro-scale scratch tests. For coatings,

coating thickness, R/tf

the probe radius can be chosen to generate a maximum stress above, at, or below an interface, depending on

what information is most critical in the application. The different R/t ratio can associated with different stress

field, enabling to focus on cohesive or adhesive failure of coatings.

Higher critical forces are observed when larger probe radii are used (low stresses). For the condition where

plastic deformation starts in the substrate a rough estimation of the critical force may follow a power law

dependence on the probe radius [7] of the type shown in Formula (2) where S is a parameter which can be

correlated with the effective adhesion strength in the scratch test. The exponent m is usually in the range 1 to

2 when spherical probes are used.
Lc = SR [10] (2)
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If coatings are present, their thickness can influence the critical force since

a) thicker films that are harder than the underlying substrate provide more load support and so delay the

onset of substrate deformation that can occur before film failure (higher critical force);

b) thicker films can be more highly stressed and more easily through-thickness crack and delaminate when

deformed (lower critical force) since the driving force for spallation to reduce stored elastic energy is

greater.

In practice when the film is not highly stressed the ratio L /t may be approximately constant.

c f

Materials, such as metals, that show an indentation size effect will also show a size effect in the nano-scratch

test. For materials such as these, the yield stress determined from the onset of plastic deformation in the nano-

scratch test will be higher than when determined at greater length scale in bulk testing. This means that the

yield stress can increase for smaller radii probes.
5.3.3 Scan speed and loading rate

The critical force may vary with choice of scan speed and loading rate, but practice has shown that within the

typical range of these most materials show relatively low sensitivity [12]. When tests are performed at a

constant dF /dx ratio (the increase in normal force per unit scratch distance), the critical force can be

approximately constant over a large range of scratching speeds. While nano-scratch tests carried out under

varying loading rate (<1 N/mm) can be compared to one another (low sensitivity), micro-scratch tests with

loading rates exceeding 1 N/mm have an effect on the critical force; the critical force decreases as the dF /dx

ratio decreases as a result of higher probability to encounter a defective adhesion region [10].

5.3.4 Roughness

The critical force can be influenced by test-piece roughness and by the direction of scratching relative to

polishing marks on the surface made prior to coating deposition [13]. The critical force may be lower when

scratching perpendicular to the grinding marks than parallel to them. In addition, high roughness tends to

decrease the critical force but load carrying capability of thick coating has a higher effect; the critical force

increases with coating thickness when coating is harder than substrate, which delays substrate deformation

[5,14].
5.4 Multiple pass testing

Multiple pass constant force scratch tests can be carried out with the nano- and micro-scratch technique. The

test effectively becomes a low cycle [15] nano- or micro-wear test where the test parameters are less severe

than in a progressive force scratch test. Constant force wear tests are often used to determine rates of wear

and investigate the role of surface fatigue. The low-cycle wear experiments can often be much more

informative regarding the influence of, e.g. coating stress leading to poor adhesion than single pass scratch

tests. When compared to progressive force scratch testing, wear testing has the advantage that the force can

be varied to tune the maximum stress to be close to the coating-substrate interface.

The applied force used in the multiple pass scratch test is usually lower than the critical force (Lc ) in a

progressive force scratch test. The number of scratch passes to failure is a convenient parameter to compare

the durability of different trial coatings. Either the variation in friction or the on-force depth with number of

scratches can be used to determine the number of cycles to film failure.

Typically, a test is composed of 10 to 20 scratch cycles; an example of the multi-pass test is presented in

Figure 2. Optionally, it can be combined with alternate low-force passes. For example, a test involving 20

scratches under constant force could be set as a total of 41 passes over the same scratch track - an initial low

force scan would be followed by 20 times (scratch-topography) pairs.

In contrast to progressive force scratch tests, failure may initially occur at isolated regions of the film surface

requiring several subsequent passes until the film is completely removed from the scratch track. The mean

depth over the constant force region is a convenient parameter to follow the evolution of the damage process.

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Key
1 number of pass – scratch and scan
2 depth, h (nm)
3 friction coefficient, µ
4 on-force scratch depth, ht
5 residual depth, hr

Figure 2 — Progression of scratch depth, residual depth and friction coefficient repetitive nano-

scratch of a 1 µm DLC at 70 mN with a R = 6,5 μm probe -the arrows associate each data set with their

respective y-axis

By performing tests at various sub-critical forces (

to failure varied with the constant force and build up a picture of the film behaviour in low cycle fatigue

analogously to a stress-life diagram. An increase in residual depth and decrease in scratch recovery after each

cycle enables the use of the multi-pass test as a fatigue process [8]. The combination of multi-pass test at

various loading levels provides information regarding the suitability of the sample for contact application; the

cycle for failure is taken as the cycle when failure starts. Therefore, the lifetime of the test specimen (number

of cycles to failure) can be plotted as a function of the applied force, as described in Figure 3.

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Key
1 number of scratch pass at failure
2 normal force, F (mN)

Figure 3 — Mean number of cycles to failure of a 500 nm DLC film on Si in multiple pass nano-scratch

test
6 Apparatus and materials
6.1 Apparatus
6.1.1 General

The apparatus shall have appropriate mechanisms to apply controlled loading between a test probe and the

test-piece. The system will have the capability of measuring normal and lateral forces and measure the

displacement of the probe relative to the test-piece. The lateral stiffness of the instrument is important. The

test instrument should combine high frictional sensitivity with sufficiently high lateral stiffness in the

direction of the scratch to prevent slip stick effects so that the probe tracks remain very smooth until film

failure. The lateral stiffness of the instrument perpendicular to the scratch direction should al

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