ASTM C1624-22

Standard Test Method for Adhesion Strength and Mechanical Failure Modes of Ceramic Coatings by Quantitative Single Point Scratch Testing

SIGNIFICANCE AND USE
5.1 This test is intended to assess the mechanical integrity, failure modes, and practical adhesion strength of a specific hard ceramic coating on a given metal or ceramic substrate. The test method does not measure the fundamental “adhesion strength” of the bond between the coating and the substrate. Rather, the test method gives a quantitative engineering measurement of the practical (extrinsic) adhesion strength and damage resistance of the coating-substrate system as a function of applied normal force. The adhesion strength and damage modes depend on the complex interaction of the coating-substrate properties (hardness, fracture strength, modulus of elasticity, damage mechanisms, microstructure, flaw population, surface roughness, and so forth) and the test parameters (stylus properties and geometry, loading rate, displacement rate, and so forth).  
5.2 The test method as described herein is not appropriate for polymer coatings, ductile metal coatings, very thin (30 μm) ceramic coatings.
Note 2: Under narrow circumstances, the test may be used for ceramic coatings on polymer substrates with due consideration of the differences in elastic modulus, ductility, and strength between the two types of materials. Commonly, the low comparative modulus of the polymer substrate means that the ceramic coating will generally tend to fail in bending (through-thickness adhesive failure) before cohesive failure in the coating itself.  
5.3 The quantitative coating adhesion scratch test is a simple, practical, and rapid test. However, reliable and reproducible test results require careful control of the test system configuration and testing parameters, detailed analysis of the coating damage features, and appropriate characterization of the properties and morphology of the coating and the substrate of the test specimens.  
5.4 The coating adhesion test has direct application across the full range of coating development, engineering, and production efforts. Measurements of t...
SCOPE
1.1 This test method covers the determination of the practical adhesion strength and mechanical failure modes of hard (Vickers Hardness HV = 5 GPa or higher), thin (≤30 μm) ceramic coatings on metal and ceramic substrates at ambient temperatures. These ceramic coatings are commonly used for wear/abrasion resistance, oxidation protection, and functional (optical, magnetic, electronic, biological) performance improvement.  
1.2 In the test method, a diamond stylus of defined geometry (Rockwell C, a conical diamond indenter with an included angle of 120° and a spherical tip radius of 200 μm) is drawn across the flat surface of a coated test specimen at a constant speed and a defined normal force (constant or progressively increasing) for a defined distance. The damage along the scratch track is microscopically assessed as a function of the applied force. Specific levels of progressive damage are associated with increasing normal stylus forces. The force level(s) which produce a specific type/level of damage in the coating are defined as a critical scratch load(s). The test method also describes the use of tangential force and acoustic emission signals as secondary test data to identify different coating damage levels.  
1.3 Applicability to Coatings—This test method is applicable to a wide range of hard ceramic coating compositions: carbides, nitrides, oxides, diamond, and diamond-like carbon on ceramic and metal substrates. The test method, as defined with the 200 μm radius diamond stylus, is commonly used for coating thicknesses in the range of 0.1 to 30 μm. Test specimens generally have a planar surface for testing, but cylinder geometries can also be tested with an appropriate fixture.  
1.4 Principal Limitations:  
1.4.1 The test method does not measure the fundamental adhesion strength of the bond between the coating and the substrate. Rather, the test method gives an engineering measurement of the practical (ext...

General Information

• Status: Published
• Publication Date: 14-Mar-2022
• ICS: 25.220.99 - Other treatments and coatings
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.04 - Applications

Relations

• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM E750-15(2020) - Standard Practice for Characterizing Acoustic Emission Instrumentation
• Effective Date: 01-Jun-2020
• Refers: ASTM E1316-19b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2019
• Refers: ASTM E1316-19 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Mar-2019
• Refers: ASTM E18-18 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2018
• Refers: ASTM E1316-18 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jan-2018
• Refers: ASTM E18-17 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM E1316-17a - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2017
• Refers: ASTM E1316-17 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2017
• Refers: ASTM E1316-16a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Aug-2016
• Refers: ASTM E1316-16 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2016
• Refers: ASTM E750-15 - Standard Practice for Characterizing Acoustic Emission Instrumentation
• Effective Date: 01-Dec-2015
• Refers: ASTM E1316-15a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2015
• Refers: ASTM E1316-15 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Sep-2015
• Refers: ASTM E1316-14 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014

Overview

ASTM C1624-22 specifies the standard test method for determining the adhesion strength and mechanical failure modes of hard ceramic coatings on metal or ceramic substrates using the quantitative single point scratch test. This robust and repeatable method quantitatively assesses the practical (extrinsic) adhesion strength and damage resistance of the coating-substrate system under prescribed testing conditions. While it offers tangible engineering insights, it does not measure the fundamental adhesion strength at the coating interface. Instead, it delivers valuable comparative data for materials development, quality control, and production monitoring of ceramic coatings.

This standard is widely used for evaluating thin (up to 30 μm), hard (Vickers Hardness HV ≥ 5 GPa) ceramic coatings, such as carbides, nitrides, oxides, diamond, and diamond-like carbon films. The method leverages a Rockwell C conical diamond indenter, ensuring high reproducibility and comparability across laboratories.

Key Topics

• Purpose and Scope: Measures practical adhesion strength and characterizes failure mechanisms of thin, hard ceramic coatings applied to flat or cylindrical metal and ceramic substrates at ambient temperatures.
• Test Method: A diamond stylus with precise geometry (120° apex angle, 200 μm radius) is drawn across the coating’s surface under controlled normal force, which may be constant or progressively increased.
• Damage Assessment: Microscopic evaluation (optical, confocal, or electron microscopy) identifies coating damage at specific critical scratch loads. Supplementary measurements such as tangential force and acoustic emission signals can provide additional insights.
• Types of Damage: Allows differentiation between adhesive failure (coating detachment at interface) and cohesive failure (crack or damage within coating).
• Testing Limitations: Not applicable for polymer or ductile metal coatings or for very thin (<0.1 μm) or thick (>30 μm) ceramic coatings. Some adaptation is possible for ceramic coatings on polymer substrates with careful consideration.
• Data Interpretation: Critical for users to control and document test parameters (stylus condition, force calibration, surface roughness, sample preparation) for reliable and reproducible results.

Applications

ASTM C1624-22 is essential for:

• Coating Research & Development: Quantifying the performance of new or modified ceramic coatings for desired applications.
• Process Engineering: Comparing effects of process variations (deposition methods, substrate preparation) on coating adhesion and durability.
• Quality Assurance in Manufacturing: Routine evaluation of ceramic coatings to ensure consistency in adhesion and resistance to mechanical damage.
• Failure Analysis: Diagnosing the root causes of coating failures in service, aiding in troubleshooting and improvement.
• Material Comparisons: Enabling objective selection between coating-substrate systems for demanding environments such as tools, machinery, or electronics that require wear resistance, oxidation protection, or specialized functional surfaces.

Related Standards

• ASTM B659 - Guide for Measuring Thickness of Metallic and Inorganic Coatings
• ASTM E18 - Test Methods for Rockwell Hardness of Metallic Materials
• ASTM E4 - Practices for Force Calibration and Verification of Testing Machines
• ASTM E1316 - Terminology for Nondestructive Examinations
• ASTM E750, E1932 - Acoustic emission standards for characterizing instrumentation and small parts
• IEEE/ASTM SI 10 - Standard for Use of the International System of Units (SI)
• ASME B46.1 - Surface Texture (Surface Roughness, Waviness, and Lay)
• CEN prEN 1071-3 - Advanced Technical Ceramics-Methods of Test for Ceramic Coatings-Adhesive and Mechanical Failure Modes by Scratch Test

By following the practices outlined in ASTM C1624-22, organizations can ensure reliable, comparable, and meaningful measurements of practical adhesion strength and mechanical integrity for hard ceramic coatings-critical for advancing innovation and maintaining high performance in both product development and production environments.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1624 − 22
Standard Test Method for
Adhesion Strength and Mechanical Failure Modes of
Ceramic Coatings by Quantitative Single Point Scratch
Testing
This standard is issued under the fixed designation C1624; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.4.1 The test method does not measure the fundamental
adhesion strength of the bond between the coating and the
1.1 This test method covers the determination of the prac-
substrate. Rather, the test method gives an engineering mea-
tical adhesion strength and mechanical failure modes of hard
surement of the practical (extrinsic) adhesion strength of a
(Vickers Hardness HV = 5 GPa or higher), thin (≤30 µm)
coating-substrate system, which depends on the complex
ceramic coatings on metal and ceramic substrates at ambient
interaction of the test parameters (stylus properties and
temperatures. These ceramic coatings are commonly used for
geometry,loadingrate,displacementrate,andsoforth)andthe
wear/abrasion resistance, oxidation protection, and functional
coating-substrateproperties(hardness,fracturestrength,modu-
(optical, magnetic, electronic, biological) performance im-
lus of elasticity, damage mechanisms, microstructure, flaw
provement.
population, surface roughness, and so forth).
1.2 Inthetestmethod,adiamondstylusofdefinedgeometry
1.4.2 The defined test method is not directly applicable to
(Rockwell C, a conical diamond indenter with an included
metal or polymeric coatings which fail in a ductile, plastic
angle of 120° and a spherical tip radius of 200 µm) is drawn
manner, because plastic deformation mechanisms are very
across the flat surface of a coated test specimen at a constant
different than the brittle damage modes and features observed
speed and a defined normal force (constant or progressively
inhardceramiccoatings.Thetestmethodmaybeapplicableto
increasing) for a defined distance. The damage along the
hard metal coatings which fail in a brittle mode with appro-
scratch track is microscopically assessed as a function of the
priate changes in test parameters and damage analysis proce-
applied force. Specific levels of progressive damage are
dures and criteria.
associated with increasing normal stylus forces. The force
1.4.3 The test method, as defined with the Rockwell C
level(s) which produce a specific type/level of damage in the
diamond stylus and specific normal force and rate parameters,
coatingaredefinedasacriticalscratchload(s).Thetestmethod
isnotrecommendedforverythin(<0.1µm)orthickercoatings
alsodescribestheuseoftangentialforceandacousticemission
(>30 µm). Such coatings may require different stylus
signals as secondary test data to identify different coating
geometries, loading rates, and ranges of applied normal force
damage levels.
for usable, accurate, repeatable results.
1.3 Applicability to Coatings—This test method is appli-
1.4.4 The values stated in SI units are to be regarded as
cable to a wide range of hard ceramic coating compositions:
standard. No other units of measurement are included in this
carbides, nitrides, oxides, diamond, and diamond-like carbon
standard. Test data values in SI units (newtons (N) for force
on ceramic and metal substrates. The test method, as defined
andmillimetres(mm)fordisplacement)aretobeconsideredas
with the 200 µm radius diamond stylus, is commonly used for
standard and are in accordance with IEEE/ASTM SI10.
coating thicknesses in the range of 0.1 to 30 µm. Test
1.5 Organization—The test method is organized into the
specimens generally have a planar surface for testing, but
following sections:
cylinder geometries can also be tested with an appropriate
fixture. Section
Scope 1
1.4 Principal Limitations:
Purpose and Description 1.1
Applicability 1.3
Principal Limitations 1.4
Organization 1.5
Referenced Documents 2
This test method is under the jurisdiction of ASTM Committee C28 on
ASTM Standards 2.1
Advanced Ceramics and is the direct responsibility of Subcommittee C28.04 on
Other Standards and References 2.2
Applications.
Terminology 3
Current edition approved March 15, 2022. Published March 2022. Originally
Summary of Test Method 4
approved in 2005. Last previous edition approved in 2015 as C1624–05 (2015).
Significance and Use 5
DOI: 10.1520/C1624-22.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
C1624 − 22
2. Referenced Documents
Section
Test Methodology and Experimental Control 6
2.1 ASTM Standards:
Test Overview 6.1
Test Modes 6.2 B659Guide for Measuring Thickness of Metallic and Inor-
Primary and Supplementary Measurements 6.3
ganic Coatings
Critical Scratch Load Damage Criteria and Scratch Atlas 6.4
E4Practices for Force Calibration and Verification of Test-
Experimental Factors and Variables 6.5
Interferences 7
ing Machines
Material and Specimen Related 7.2
E18Test Methods for Rockwell Hardness of Metallic Ma-
Test Method Related 7.3
terials
Apparatus 8
General Description 8.1 E750Practice for Characterizing Acoustic Emission Instru-
Stylus and Stylus Mounting 8.2
mentation
Mechanical Stage and Displacement Control 8.3
E1316Terminology for Nondestructive Examinations
Test Frame and Force Application System 8.4
Force and Displacement Sensors 8.5
E1932Guide for Acoustic Emission Examination of Small
OpticalAnalysis and Measurement 8.6
Parts
Data Acquisition and Recording 8.7
IEEE/ASTM SI10American National Standard for Metric
Acoustic Emission (Optional) 8.8
Coating Adhesion Reference Specimens (Optional) 8.9
Practice
Coating Surface Profilometry (Optional) 8.10 3
2.2 ASME Standard:
Data Analysis and Output Software (Optional) 8.11
ASME B46.1 Surface Texture (Surface Roughness,
Test Specimens 9
Specimen Requirements 9.1
Waviness, and Lay)
Specimen Characterization 9.2
2.3 CEN Standard:
Specimen Size 9.3
Specimen Flatness and Level 9.4 CEN prEN 1071-3 Advanced Technical Ceramics—
Polishing (Optional) 9.5
Methods of Test for Ceramic Coatings—Part 3: Determi-
Specimen Exposure Conditioning (Optional) 9.6
nation of Adhesive and Other Mechanical Failure Modes
Specimen Cleaning 9.7
Specimen Handling and Storage 9.8 by a Scratch Test
Calibration 10
System Calibration 10.1
3. Terminology
Reference Specimens 10.2
Test Procedure 11
3.1 Definitions:
Calibration 11.1
3.1.1 acoustic emission, n—class of phenomenon in which
Test Mode Selection 11.2
elasticwavesaregeneratedbytherapidreleaseofenergyfrom
Test Planning 11.3
Stylus Inspection and Cleaning 11.4
localized sources within a material, or the transient waves so
Environmental Conditions 11.5
generated. E1316
System Setup and Check 11.6
Test Specimen Mounting 11.7
3.1.2 adhesive failure, n—detachment and separation of a
Conducting the Test 11.8
coating from the substrate with cracking and debonding at the
Specimen Count 11.9
coating-substrate interface.
Invalid and Censored Data 11.10
Scratch Damage Assessment 11.11
3.1.3 cohesive failure, n—material damage and cracking in
Calculations 12
the coating or in the substrate, separate and distinct from
Report 13
Test Identification 13.2
detachment and adhesive debonding at the coating-substrate
Specimen Information 13.3
interface.
Test Equipment and Procedure Information 13.4
Test Data and Statistics 13.5
3.1.4 critical scratch load (L ), n—appliednormalforceat
CN
Precision and Bias 14
which a specific, well-defined, recognizable damage/failure
Keywords 15
Rockwell Diamond Indenter Specifications Annex A1 event occurs or is observed in the scratch test of a specific
Alignment and Calibration Annex A2
coating on a specific substrate.
Repeatability and Reproducibility Studies Annex A3
3.1.4.1 Discussion—The subscript N is used to identify
Coating Damage Criteria and Scratch Atlas Appendix X1
Experimental Variables in Scratch Adhesion Testing Appendix X2 progressivefailureevents.Forexample, L isusedtoidentify
C1
Bibliography
thefirstfailureinthecoating-substratesample,and L isused
C2
1.6 This standard does not purport to address all of the
to identify the second failure in the coating-substrate sample.
safety concerns, if any, associated with its use. It is the
Multiple subscripts can be used for progressive levels of
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mine the applicability of regulatory limitations prior to use.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
1.7 This international standard was developed in accor-
Standards volume information, refer to the standard’s Document Summary page on
dance with internationally recognized principles on standard-
the ASTM website.
Available from American Society of Mechanical Engineers (ASME), ASME
ization established in the Decision on Principles for the
International Headquarters, Three ParkAve., NewYork, NY10016-5990, www.as-
Development of International Standards, Guides and Recom-
me.org.
mendations issued by the World Trade Organization Technical 4
Available from European Committee for Standardization (CEN), 36 rue de
Barriers to Trade (TBT) Committee. Stassart, B–1050 Brussels, www.cenorm.be.
C1624 − 22
distinct damage, such as cohesive failure, adhesive failure,
spalling, etc., in a specific coating-substrate system.
3.1.5 fundamental adhesion, n—summationofallinterfacial
intermolecular interactions between a film or coating and its
substrate.
3.1.6 normal force (L ), n—in a scratch test, the force
N
exerted by the stylus, perpendicular to the test surface of the
test specimen.
3.1.7 practical adhesion, n—force or work required to
remove or detach a film or coating from its substrate irrespec-
tive of the locus of failure.
3.1.7.1 Discussion—“Practical adhesion” is a test concept
which uses various engineering coating adhesion test methods
to obtain a quantitative, reproducible adhesion measurement
which can be related to the functional performance of the
FIG. 1 Test Method Schematic
coating. The practical adhesion is an extrinsic property which
depends on the complex interaction of coating-substrate prop-
erties and characteristics with the specific test parameters.
3.1.8 stylus drag coeffıcient, n—in scratch testing, the di-
mensionless ratio of the tangential force to the normal force
applied to the stylus at a specific point in the scratch test.
3.1.8.1 Discussion—The term stylus drag coefficient is pre-
ferred to the more common term scratch coefficient of friction
(SCF). The tangential force is primarily a measure of the
perpendicular force required to plow the indenter through the
coating, rather than to slide it on the surface (sliding friction is
arelativelyminorcontributiontothemeasuredtangentialforce
unless penetration is very small and surface properties domi-
nate). Thus the term friction coefficient is not appropriate for
these stylus scratch tests. The SCF term is too easily misun-
derstood or misused as a measurement of sliding friction.
FIG. 2 Schematic Example of Progressive Damage in Scratch
3.1.9 tangential force (L ), n—force that opposes the rela-
T Track in a Progressive Load Scratch Test
tive motion between a moving stylus and the surface that is
beingscratchedbythestylusandwhichisperpendiculartothe
normal force exerted by the stylus (also called the friction
4.3 Coating damage is assessed by optical microscopy
force, drag force, or the scratching force).
(standard microscope or with white light interferometry or
confocal microscopy) or scanning electron microscopy, or
4. Summary of Test Method
combined techniques, during or after the scratch test is done.
4.1 This test consists of producing and assessing controlled
The tangential force and acoustic emission signals can also be
damageinahardceramiccoatingbysinglepointscratchaction
measuredandrecordedduringthescratchtestprocessandused
(seeFig.1).Thescratchisdevelopedonacoatedtestspecimen
as supplementary test data to identify different coating damage
by drawing a diamond stylus of defined geometry and tip size
levels. In commercial instruments, computerized electronic
(Rockwell C, 200 µm radius) across the flat surface of the
systems are commonly used to apply, control, measure, and
specimen at a constant speed and a controlled and measured
record the force signals and acoustic emission signals and to
normal force (constant or progressively increasing). With
control the stylus-specimen movement.
increasing applied normal force, the stylus produces progres-
4.4 The two primary modes of scratch adhesion testing are
sive mechanical damage in the coating and the substrate
constant load and progressive load.
through the complex combination of elastic/plastic indentation
4.4.1 Inconstantload(CL)scratchtesting,thenormalforce
stresses, frictional forces, and residual internal stresses in the
on the stylus is maintained at a constant level as the stylus
coating-substrate system (Fig. 2).
moves in relation to the test specimen surface. Sequential
4.2 The specific levels and types of progressive damage in
scratch tests are done at increasing force increments to deter-
the scratch track are assessed and associated with the applied
mine the critical scratch load for a given damage level.
normal stylus forces. The normal force which produces a
NOTE 1—Test systems may have either a movable stage or a movable
specific, defined, reproducible type/level of damage is defined
stylus with the alternate component in a fixed position.
as a critical scratch load (L ). For a given coating-substrate
C
system, one or more different critical scratch loads (L ) can 4.4.2 In progressive load (PL) scratch tests, the applied
CN
be defined for progressive levels of defined coating damage. stylus force is linearly increased from zero (or a minimum
C1624 − 22
defined load) to a defined maximum force as the stylus moves 5.6 Ceramic coatings can be crystalline or amorphous, but
in relation to the test specimen surface. commonly have high relative density with limited porosity
(<5%). Porous coatings can be tested, but the effects of
4.5 The critical scratch loads at which a defined coating
porosity on the damage mechanisms in the coating must be
failure event occurs depend on a complex interaction of
carefully considered.
coating-substrate properties and test parameters/conditions. It
is the purpose of this test standard to: (1) describe and define
5.7 The test method, as defined with the 200 µm radius
the test equipment and procedures and the major and minor Rockwell diamond stylus, is commonly used for ceramic
coating-substrate properties which have to be controlled,
coating thicknesses in the range of 0.10 to 30 µm. Thinner
measured, and understood to produce reliable, comparable coatings may require a smaller diameter stylus and lower
coating adhesion test data, and (2) define a report format that
normalforcesforreliableresults.Thickercoatingsmayrequire
will provide complete and accurate test data. largerdiameterstylusandhighernormalforces.Anyvariations
instylussizeandgeometryanddesignatednormalforceranges
5. Significance and Use
shall be reported.
5.1 This test is intended to assess the mechanical integrity,
5.8 Specimens commonly have a flat planar surface for
failure modes, and practical adhesion strength of a specific
testing, but cylinder geometries can also be tested if they are
hard ceramic coating on a given metal or ceramic substrate.
properly fixtured and aligned and the scratch direction is along
The test method does not measure the fundamental “adhesion
the long axis of the specimen. The physical size of the test
strength” of the bond between the coating and the substrate.
specimenisdeterminedprimarilybythecapabilitiesandlimits
Rather, the test method gives a quantitative engineering mea-
of the test equipment stage and fixturing.
surement of the practical (extrinsic) adhesion strength and
5.9 The test is commonly conducted under unlubricated
damageresistanceofthecoating-substratesystemasafunction
conditionsandatroomtemperature.However,itisfeasibleand
of applied normal force. The adhesion strength and damage
possible to modify the test equipment and test conditions to
modes depend on the complex interaction of the coating-
conduct the test with lubrication or at elevated temperatures.
substrate properties (hardness, fracture strength, modulus of
elasticity, damage mechanisms, microstructure, flaw
5.10 Coatedspecimenscanbetested afterhightemperature,
population, surface roughness, and so forth) and the test
oxidative, or corrosive exposure to assess the retained proper-
parameters (stylus properties and geometry, loading rate,
ties and durability (short-term and long-term) of the coating.
displacement rate, and so forth).
Anyspecimenconditioningorenvironmentalexposureshallbe
fully documented in the test report, describing in detail the
5.2 The test method as described herein is not appropriate
exposure conditions (temperature, atmosphere, pressures,
for polymer coatings, ductile metal coatings, very thin
chemistry, humidity, and so forth), the length of time, and
(<0.1µm) ceramic coatings, or very thick (>30 µm) ceramic
resulting changes in coating morphology, composition, and
coatings.
microstructure.
NOTE2—Undernarrowcircumstances,thetestmaybeusedforceramic
coatingsonpolymersubstrateswithdueconsiderationofthedifferencesin
6. Test Methodology and Experimental Control
elasticmodulus,ductility,andstrengthbetweenthetwotypesofmaterials.
Commonly,thelowcomparativemodulusofthepolymersubstratemeans
6.1 Test Overview:
that the ceramic coating will generally tend to fail in bending (through-
6.1.1 Coatingadhesionisachallengingpropertytoquantify,
thickness adhesive failure) before cohesive failure in the coating itself.
because the material response to a scratch force is “not a basic
5.3 The quantitative coating adhesion scratch test is a
property but a response of a system to an applied test
simple, practical, and rapid test. However, reliable and repro-
condition” (from Blau’s Lab Handbook of Scratch Testing).
ducible test results require careful control of the test system
Butquantifieddataarestillneeded,andtheinstrumentedsingle
configuration and testing parameters, detailed analysis of the
point scratch test is the most widely used test for determining
coating damage features, and appropriate characterization of
quantitative practical adhesion of coatings.
the properties and morphology of the coating and the substrate
6.1.2 The instrumented single point scratch adhesion test is
of the test specimens.
simple and rapid when performed properly, but it requires a
detailedunderstandingandcarefulmeasurementandcontrolof
5.4 The coating adhesion test has direct application across
the full range of coating development, engineering, and pro- a wide range of specimen characteristics and test parameters
for the test to produce valid, repeatable, and reproducible data
duction efforts. Measurements of the damage mechanisms in a
coating as a function of applied normal forces are useful to (Blau, Bull, Meneve, Mittal, Ichimura, etc.).
understand material-process-property relations; quantify and
6.2 Test Modes:
qualify the mechanical response of coating-substrate systems;
6.2.1 The scratch adhesion test can be done in either of two
assess coating durability; measure production quality; and
test modes: constant load (CL) and progressive load (PL). In
support failure analysis.
the CLmode, the normal force on the stylus is maintained at a
5.5 This test method is applicable to a wide range of hard constant level as the stylus moves at a constant displacement
ceramic coating compositions (carbides, nitrides, oxides, rate in relation to the test specimen surface. Multiple scratch
diamond, and diamond-like carbon) applied by physical vapor tests are done at increasing force increments (and the same
deposition, chemical vapor deposition, and direct oxidation displacement rate) to determine the critical scratch load for a
methods to metal and ceramic substrates. given damage level (Fig. 3). In progressive load (PL) scratch
C1624 − 22
Insomecases,bothtestmodesmaybeusedformorecomplete
assessment of the coating properties.
6.3 Primary and Supplemental Measurements:
6.3.1 Normal Force and Optical Analysis:
6.3.1.1 The primary experimental measurements in the
scratch adhesion test are the applied normal stylus force and
the optical identification/analysis of the damage features in the
scratchtrack.Theappliednormalforce(underconstantloador
progressive load test modes) is independently controlled and
measured during stylus movement. The specific levels and
types of progressive damage in the scratch track are optically
assessedanddirectlycorrelatedwiththeappliednormalforces.
The force level which produces a specific, defined, reproduc-
ible type/level of damage is defined as a critical scratch load
(L ). For a given coating-substrate system, several different
C
critical scratch loads (L ) can be defined for progressive
CN
levels of coating damage (see Fig. 2).
6.3.1.2 Two other experimental measurements are also used
as dependent variables in scratch adhesion tests: tangential
force and acoustic emission analysis. They can serve as
supplemental indicators of coating damage events.
6.3.2 Tangential Force:
FIG. 3 Constant Load Graph
6.3.2.1 The tangential force on the stylus is the force that
opposes the relative motion between a moving stylus and the
tests, the normal stylus force is linearly increased as the stylus
surface that is being scratched by the stylus and which is
moves at constant displacement rate with respect to the test perpendicular to the normal force exerted by the stylus (see
specimen surface (Fig. 4). (Figs. 3 and 4 plot normal force
Fig.1).Thatforce(L )isanindicatorofhowthestylusandthe
T
(constant loads and progressive load) and scratch distance specimen are interacting through in-plane forces developed by
(stylus horizontal movement) against time.)
theappliednormalforce,indenterpenetration,andscratchpath
6.2.2 Table1showsrelativeadvantages,disadvantages,and features. Tangential force generally increases with increasing
appropriate applications for the two test modes.
normal force. (The ratio of tangential force to normal force is
6.2.3 The user should choose the test mode which best the stylus drag coefficient and serves to normalize the tangen-
meets the requirements for data completeness and confidence,
tial force against the applied normal force.)
specimen characteristics, material supply, and available time.
6.3.2.2 Inscratchtesting,thetangentialforcemaychangein
amplitude and shift into a stick-slip character (with more
frequent and higher amplitude signal spikes) as different types
of damage events occur in the scratch track. The tangential
forcedataareplottedagainsttheappliednormalforce(Fig.5).
Thetangentialforcemayalsochangethroughtipdamage,from
contamination (grease, debris, and so forth) between the stylus
and the coating, or from changes in surface roughness along
the scratch track.
6.3.2.3 Calculating the stylus drag coefficient for different
normal stylus force levels permits the direct comparison of
tangential force data done at different normal force levels.
Stylus drag coefficient data can be graphed versus time,
distance, and normal force and analyzed for the same type of
signal variations—stepwise changes in average signal value
and significant increases in the frequency and amplitude of
signal spikes.
6.3.2.4 Distinct changes in tangential forces and stylus drag
coefficient are indications of changes in stylus drag and stress
or damage events in the scratch test. However, these changes
cannot be associated a priori with specific coating damage-
failure events without optical analysis to correlate the damage
features with the changes in tangential force signals and
calculated stylus drag coefficients.
FIG. 4 Progressive Load Graph 6.3.3 Acoustic Emission:
C1624 − 22
TABLE 1 Comparison of Constant Load and Progressive Load Test Modes
Constant Load (CL) for Each Scratch Progressive Load (PL) for One Scratch
Advantages Better discrimination of different damage levels for each More rapid testing and better specimen utilization, with a single
incremental loading level. scratch covering a full load range.
Greater statistical confidence in damage events for a given Progressive force application covers the full range of force
loading level. without gaps.
Constant load discriminates for coating non-uniformity along the
scratch path.
Disadvantages Multiple increment testing requires more specimen area and Two experimental variables (load and location) changing at the
test time. same time.
Incremental loads can miss damage events at intermediate load Limited statistical analysis of scratch damage features.
levels.
Application Detailed load specific assessment of coatings (for research, Screening assessment and QA tests of coatings (for research,
process development, and durability studies) process development, and durability studies)
Single value tests are suitable for 9pass-fail9 QA and for
assessing coating uniformity.
coating system and correlation with the optical analysis of the
damage events for that specific coating system.
6.4 Critical Scratch Load Damage Criteria and Scratch
Atlas:
6.4.1 A primary requirement in using the scratch adhesion
test is to clearly identify and categorize the specific coating
damage features which are used to define the critical scratch
load(s). Since different coating systems can fail with different
types of damage, there is no universal set of “critical scratch
damage features” that can be applied to all types of coatings.
6.4.2 Appendix X1 gives an overview of typical types of
ceramiccoatingdamagemechanismsandascratchatlaswhich
lists a set of descriptive terms for different types of scratch
damage supported by sketches and micrographs. The scratch
atlas is not totally comprehensive, but it provides a baseline
and framework for users to assess and describe crack damage
with a set of generally accepted and understood terms.
6.4.3 Each test user will select the particular levels and
classes of coating damage features for a specific coating-
substrate system that best meets the coating performance
FIG. 5 Tangential Force and Acoustic Emission versus Applied
Normal Force in Progressive Load Test
requirements and testing needs. For example, the simplest
critical scratch load criteria may be a single level (L )at
C1
which the first cohesive failure occurs in the coating. A
6.3.3.1 Brittle damage events (cracking, delamination,
two-level critical scratch load (L and L ) might be defined
C1 C2
chipping, spalling, buckling, and so forth) can produce high-
for cohesive cracking/failure (L ) in the coating and for
C1
frequency elastic waves in the coating and substrate which can
subsequent adhesive failure/spalling (L ) between the coating
C2
be detected by acoustic emission (AE) systems.As the applied
andthesubstrateatahigherappliednormalforce.Ifnecessary,
normal force increases in the scratch test, coating damage
for complete damage mechanism mapping (for research, fail-
events occur with increasing frequency and severity and the
ure analysis, or durability assessment), multiple (>2 levels)
resultingelasticwavesaredetected,measured,andrecordedby
criticalscratchloadsmaybedefinedtoidentifyeachdistinctive
the acoustic emission equipment. TheAE data record for each
type of damage feature.
scratch test is analyzed for significant changes in AE signal
6.4.4 It is critically important to the validity and reproduc-
characteristics (peak amplitude, frequency, event counts, rise
ibility of the scratch test for a given coating-substrate system
time, signal duration, and energy intensity) that correlate with
that the damage events for a given critical scratch load be well
a given normal stylus force. AE data can be plotted against
defined and described in the test report. This is best done with
time, horizontal displacement distance, or normal stylus force
micrographs and sketches to show the typical damage features
(Fig. 5).
of interest.Alternatively, the damage features may be verbally
6.3.3.2 It should be noted that changes in acoustic emission
described in the report. Valid comparisons between different
eventsatgivennormalforcelevelscannotdiscriminate a priori
test specimens require that they have the same failure/damage
between the different damage events and coating failure
mechanisms, which can only be confirmed by optical analysis.
modes.Acoustic emission event/signal identification with spe-
cificcoatingfailureeventsrequiresextensivetestingofagiven 6.5 Experimental Factors and Variables:
C1624 − 22
6.5.1 AppendixX2providesanoverviewofthefullrangeof 7.2.3 Contaminationanddebrisonthesurfaceofthecoating
experimental and material variables which have varying de- may interfere with the stylus and increase data variability.
grees of impact in a scratch adhesion test.The different factors
7.3 Test Method Related:
can be categorized into six sets of variables: coating variables,
7.3.1 Test data are not comparable between specimens and
substrate variables, interface variables, equipment and proce-
specimen sets unless the scratch adhesion tests are conducted
durevariables,specimenvariables,andenvironmentvariables.
under directly comparable conditions using:
6.5.2 The required depth and detail of specimen character-
7.3.1.1 Identical styluses (composition, geometry, size, and
ization and test parameter control will depend on the purpose,
orientation), and
scope, and level of confidence and detail required by the user.
7.3.1.2 Identical force application rates and horizontal dis-
The experimenter needs to understand and carefully consider
placement rates.
how each of these variables can impact a particular test and to
7.3.2 Stylus damage and contamination will modify the
what degree each needs to be controlled and measured.This is
stylus-surface interaction and increase data variability.
necessary for the scratch adhesion test is to be used with an
7.3.3 The definitions and documentation of the damage
acceptable degree of confidence, accuracy, and reliability.
criteria for each critical scratch load level for a given coating-
6.5.3 Table 2 lists the test parameters and specimen charac-
substrate shall be clearly defined in complete detail to mini-
teristics that have the top priority for control and measurement
mize subjective analysis and improve reproducibility between
to ensure acceptable scratch adhesion test results.
operators and laboratories.
6.5.4 Additional test parameters and specimen characteris-
tics may need to be measured and controlled for full analysis
8. Apparatus
and understanding; but, at a minimum, the characteristics and
parameters in Table 2 shall be well controlled and documented
8.1 General Description:
to ensure valid and reproducible scratch adhesion test results.
8.1.1 The quantitative scratch adhesion test system com-
monly consists of six equipment subsystems: (1) stylus and
7. Interferences
stylus mounting, (2) mechanical stage and displacement
7.1 The repeatability, reproducibility, and precision in the
control, (3) test frame and force application system, (4) force
scratch adhesion test requires that variations in test parameters
sensors, (5) optical measurement, and (6) data acquisition/
and specimen characteristics be minimized. As described in
recording. The test system may also include additional mea-
Appendix X2, there are many variables that may have an
surement systems, such as acoustic emission and displacement
impact on the test data and need to be considered to varying
sensors (Fig. 6).
degrees. However, the following material and test parameters
8.1.2 Commercial scratch adhesion test systems are widely
are the primary source of test interference and need to be
available and extensively used. They commonly include com-
understood and controlled.
puter feedback control of normal force and horizontal
displacement,computerdataacquisition,andvideomicroscope
7.2 Material and Specimen Related:
recording systems.
7.2.1 Variations (in individual specimens and between
specimens) in the coating thickness and in the surface rough-
8.2 Stylus and Stylus Mounting:
ness of the coating are a major source of variability in the
8.2.1 The stylus shall be a diamond indenter that meets the
critical scratch load values.
specifications for a Rockwell sphericonical diamond indenter,
as described in 13.1.2.1 of Test Methods E18 and commonly
NOTE 3—Deposition techniques and residual stresses have also shown
variability in the critical load values. calledaRockwellCdiamondindenter.TheRockwelldiamond
indenter has an apex angle of 120° and terminates in a
7.2.2 Major variations (in specimens and between speci-
hemispherical tip with a mean radius of 200 µm (400 µm
mens) in the microstructure, morphology, mechanical
diameter). Full specifications for the Rockwell C diamond
properties, and flaw population of the coating may change the
indenter from Test Methods E18 are included in Annex A1.
damage mechanisms and modes of failure and modify the
The use of the Rockwell C diamond indenter is specified for
critical scratch load values.
this test to ensure comparability and reproducibility of test
results within and between laboratories.
TABLE 2 Top Priority for Control and Measurement of Specimen
Characteristics and Test Parameters
NOTE 4—It is recommended that the Rockwell C diamond stylus
Factor Details
geometry be definitively checked, verified (SEM, interferometry,
profilometry, interference microscopy, and so forth), and documented
Diamond Stylus Verified geometry, size, condition (damage free
and clean) against specifications by the supplier or by the end user. Significant
variations can occur between nominally identical styluses and will have a
Force and Displacement Accurate calibration, precise and accurate control,
significant effect on test results.
Control measurement, and data recording
NOTE5—Ifadiamondstyluswithsmallerorlargertipradiusisrequired
andused(forthinnerorthickercoatings),thetestreportshallindicatethat
Damage Assessment Optical analysis with well-defined damage criteria
a modified version of the standard was used, and the size of the tip radius
and complete documentation with photos/sketches
shall be reported. Scratch test data produced with different stylus
geometries, tip radii, or compositions are not directly comparable.
Coating Characterization Detailed information (by analysis or from coating
supplier) on composition, thickness, pedigree, and
8.2.2 The stylus mounting system shall be designed and
surface roughness
constructed to rigidly and securely hold the diamond stylus
C1624 − 22
FIG. 6 Scratch Adhesion Test System Schematic
with a minimum of vertical and horizontal compliance or specimenstagemusthaveverticalaxis(Z)adjustment(manual
backlash, given the applied normal and tangential forces. or motorized) to raise and lower the specimen (or the stylus)
8.2.3 The diamond stylus shall be secured in a consistent
into the test position.
orientation in the mounting holder, either by index marks or
8.3.4 The scratch adhesion test is commonly conducted
alignment flats. This is necessary to eliminate variation be-
under unlubricated conditions and at room temperature.
tween tests caused by spatial variations in the condition,
However, it is feasible and possible to modify the test equip-
orientation, or shape of the diamond stylus, or a combination
ment and test conditions to conduct the test with lubrication or
thereof, found either in the as-received condition or after
at cryogenic or elevated temperatures. For elevated tempera-
accumulated wear from testing.
ture(>100°C)testing,testequipmentwillhavetobespecially
8.2.4 Thediamondstylusshallbemicroscopicallyinspected
modified to develop and maintain specimen temperature,
fortipwearanddamageandcontaminationatthebeginningof
minimize oxidation and thermal degradation of the test speci-
eachtestseriesoraftertenscratchtests.See11.4foradetailed
mens and test equipment, and maintain precise control and
discussion and description of the stylus inspection procedure.
accurate measurement of the experimental parameters. Any
8.3 Mechanical Stage and Displacement Control System:
modificationsofthetestsystemortestprocedureshallbefully
8.3.1 The mechanical stage serves to rigidly secure and
documented in the test report.
accurately align and position the test specimen. Relative
NOTE 6—Some commercial test systems now offer temperature-
movement between the diamond stylus and the specimen can
controlled stages for testing specimens across a range of cryogenic and
be produced by either of two methods: (1) movement of the
elevated temperatures.
mechanical stage with respect to a fixed stylus, or (2) move-
ment of the stylus with respect to a fixed stage. 8.3.5 The movement control system shall produce straight-
8.3.2 The mounting stage fixture shall be designed and linehorizontalmovementbetweenthestylusandthespecimen
constructed of hard metal (tool steel, stainless steel) to be
at a constant, controlled, and repeatable speed. This controlled
sufficiently rigid to withstand the normal and lateral forces horizontal displacement is most easily produced with an
associated with the scratching action without undue elastic or
electromechanicalstage.Therangeoftranslation/displacement
plastic deflection.The fixture must secure the test specimen so
(scratchlength)shallbeatleast10mm.Translationalaccuracy
that there is no lateral movement, rocking, or backlash of the
and repeatability shall be 0.5% of the minimum displacement
specimen during the scratch test. The fixture shall have
range or 50 µm, whichever is smaller. The system shall be
alignmentmechanismstoensurethatthetestspecimensurface
capable of a specimen displacement speed of 10 mm/min with
plane(orlongaxis/testdirectionforcylinderspecimens)canbe
an accuracy of 60.1 mm/min (higher or lower translation
aligned orthogonal and level with respect to the loading
speeds, or both, may be necessary for modified tests).
direction of the stylus along the length of a given scratch track
NOTE 7—Current test systems (commercial and in-house built) com-
(see Section 10 and Annex A2 on stage alignment).
monly have a range of displacement motion of 20 to 150 mm and a range
8.3.3 The stage should have two-axis (X and Y) manual
of displacement speeds of 10 to 100 mm/min. It is also common in
horizontal adjustment (to position the specimen for scratch
commercial systems for the specimen positioning and stage movement to
testing). Horizontal accuracy (straight-line position) should be
be feedback controlled by displacement sensors and computer-controlled
10 µm or better in both the X and Y directions. The test translation motors.
C1624 − 22
8.3.6 The movement control system shall be calibrated for of1%orbetterofthemaximumexpectedtangentialforce.The
accuracy and precision in accordance with Annex A2. sensor shall be calibrated in accordance with Section 10 and
AnnexA2. If the tangential force is measured, the stylus drag
8.3.7 The test system may also be instrumented with an
coefficient (tangential force/normal force) can also be calcu-
independent horizontal displacement sensor to independently
lated.
measure the specimen horizontal translation as a function of
time. The horizontal displacement sensor shall have a resolu- 8.5.4 The unit of displacement measurement shall be the
tion and accuracy of 10 µm or 1% (or better) of the maximum millimeter. It is recommended that the test system be instru-
measured translation, whichever is smaller. Current commer- mented with an independent horizontal displacement sensor to
cial systems commonly have horizontal positioning precisions record the displacement of the specimen relative to the stylus
of 1 µm or better (see Section 10 and Annex A2 for calibra- with a resolution and accuracy of 50 µm or better. The
tion). horizontal displacement sensor shall be calibrated in accor-
dance with Section 10 and Annex A2.
8.4 Test Frame and Force Application System:
8.5.5 The test system may also be instrumented with a
8.4.1 The test frame system (specimen stage, stylus mount-
verticaldisplacementsensortomeasuretheverticalmovement
ing system, and load frame) shall be sufficiently rigid so that
of the stylus as a function of time or normal force. If the
the vertical compliance (µm/N) of the system does not signifi-
specimenisflatandlevel,theverticalstylusmovementwillbe
cantly affect the application of force to the specimen or the
directly related to stylus penetration into the coating. Stylus
determination of stylus indent depth. A recommended system
penetration may be related to different damage levels. The
compliance value is 5% or less of the compliance of the test
vertical displacement sensor shall have a resolution and accu-
specimen.
racy of 1% or better of the maximum measured displacement.
8.4.2 The force application system shall be designed to
Current commercial systems commonly have a vertical dis-
apply the desired normal force to the stylus in a controlled and
placement range of 1 mm and a precision of 10 nm or better.
repeatable manner across the full range of stylus vertical and
Theverticaldisplacementsensorshallbecalibratedinasimilar
horizontal displacement. The maximum force required will
manner as the horizontal displacement sensor.
depend on the properties of the specific coating-substrate
8.6 Optical Analysis and Measurement:
system being tested, but a force range of 0 to 150 N will be
sufficient for most hard coatings tested with the Rockwell C 8.6.1 The scratch test method requires a means of optically
indenter. Force control shall be precise and repeatable to an analyzing the condition of the coating and the damage events
accuracy of at least 0.5 N or better. Depending on the type of alongthescratchtrack.Thisiscommonlydonewithareflected
test (constant load or progressive load), the applied force is light optical microscope having an objective lens with magni-
either held constant or linearly increased during the specimen/ ficationof5to20×andtotalmagnificationof100to500×.The
stylus translation. For progressive loading, the minimum force actual magnification required will depend on the scale and
application rate shall be 5 N/min. morphology of the damage features of interest in the scratch
track. The optical system shall have sufficient resolution and
NOTE 8—Current commercial test systems commonly use a spring-
depth of focus to clearly observe and identify crack damage
loaded cantilever beam load train with a servo motor compressing the
features on the scale of 5 µm and greater.
spring to control the force. Such systems commonly have a maximum
force of 200 N and a range of force application speeds of 0 to 500 N/min.
NOTE 10—Microscopic examination of the scratch track is mandatory
It is also increasingly common for normal force application to be
for determining critical scratch load values because it is the only reliable
programmed, controlled, and recorded by a computer-controlled system
method of associating a specific damage/failure event with a measured
with active feedback and control based on force sensors, force actuators,
normal force.
and electric motors. Specimen and stage translation is also controlled
NOTE11—Specialopticalmicroscopetechniques(obliqueillumination,
through the same computer system with displacement sensors and
polarized light, differential interference contrast, dark field illumination,
electronic motors.
in-focus/out-of-focus, white light interferometry, confocal, and so forth)
8.5 Force and Displacement Sensors:
may be of value in identifying and evaluating smaller, more detailed
damage features.
8.5.1 The unit of force measurement shall be the newton.
The test system shall be instrumented with a force sensor to
8.6.2 The optical system must be capable of accurately
measureandrecordthenormalforceonthestylusasafunction
measuring the position of the defined damage along the length
oftimethroughthefullrangeofappliedforcewitharesolution
of the scratch tra
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1624 − 05 (Reapproved 2015) C1624 − 22
Standard Test Method for
Adhesion Strength and Mechanical Failure Modes of
Ceramic Coatings by Quantitative Single Point Scratch
Testing
This standard is issued under the fixed designation C1624; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of the practical adhesion strength and mechanical failure modes of hard (Vickers
Hardness HV = 5 GPa or higher), thin (≤30 μm) ceramic coatings on metal and ceramic substrates at ambient temperatures. These
ceramic coatings are commonly used for wear/abrasion resistance, oxidation protection, and functional (optical, magnetic,
electronic, biological) performance improvement.
1.2 In the test method, a diamond stylus of defined geometry (Rockwell C, a conical diamond indenter with an included angle of
120° and a spherical tip radius of 200 μm) is drawn across the flat surface of a coated test specimen at a constant speed and a
defined normal force (constant or progressively increasing) for a defined distance. The damage along the scratch track is
microscopically assessed as a function of the applied force. Specific levels of progressive damage are associated with increasing
normal stylus forces. The force level(s) which produce a specific type/level of damage in the coating are defined as a critical scratch
load(s). The test method also describes the use of tangential force and acoustic emission signals as secondary test data to identify
different coating damage levels.
1.3 Applicability to Coatings—This test method is applicable to a wide range of hard ceramic coating compositions: carbides,
nitrides, oxides, diamond, and diamond-like carbon on ceramic and metal substrates. The test method, as defined with the 200 μm
radius diamond stylus, is commonly used for coating thicknesses in the range of 0.1 to 30 μm. Test specimens generally have a
planar surface for testing, but cylinder geometries can also be tested with an appropriate fixture.
1.4 Principal Limitations:
1.4.1 The test method does not measure the fundamental adhesion strength of the bond between the coating and the substrate.
Rather, the test method gives an engineering measurement of the practical (extrinsic) adhesion strength of a coating-substrate
system, which depends on the complex interaction of the test parameters (stylus properties and geometry, loading rate,
displacement rate, and so forth) and the coating/substratecoating-substrate properties (hardness, fracture strength, modulus of
elasticity, damage mechanisms, microstructure, flaw population, surface roughness, and so forth).
1.4.2 The defined test method is not directly applicable to metal or polymeric coatings which fail in a ductile, plastic manner,
because plastic deformation mechanisms are very different than the brittle damage modes and features observed in hard ceramic
coatings. The test method may be applicable to hard metal coatings which fail in a brittle mode with appropriate changes in test
parameters and damage analysis procedures and criteria.
This test method is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.04 on Applications.
Current edition approved Jan. 1, 2015March 15, 2022. Published April 2015March 2022. Originally approved in 2005. Last previous edition approved in 20102015 as
C1624 – 05 (2015).(2010). DOI: 10.1520/C1624-05R15.10.1520/C1624-22.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1624 − 22
1.4.3 The test method, as defined with the Rockwell C diamond stylus and specific normal force and rate parameters, is not
recommended for very thin (<0.1 μm) or thicker coatings (>30 μm). Such coatings may require different stylus geometries, loading
rates, and ranges of applied normal force for usable, accurate, repeatable results.
1.4.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
Test data values in SI units (newtons (N) for force and millimetres (mm) for displacement) are to be considered as standard and
are in accordance with IEEE/ASTM SI 10.
1.4.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.5 Organization—The test method is organized into the following sections:
Section
Scope 1
Purpose and Description 1.1
Applicability 1.3
Principal Limitations 1.4
Organization 1.5
Referenced Documents 2
ASTM Standards 2.1
Other Standards and References 2.2
Terminology 3
Summary of Test Method 4
Significance and Use 5
Test Methodology and Experimental Control 6
Test Overview 6.1
Test Modes 6.2
Primary and Supplementary Measurements 6.3
Critical Scratch Load Damage Criteria and Scratch Atlas 6.4
Experimental Factors and Variables 6.5
Interferences 7
Material and Specimen Related 7.2
Test Method Related 7.3
Apparatus 8
General Description 8.1
Stylus and Stylus Mounting 8.2
Mechanical Stage and Displacement Control 8.3
Test Frame and Force Application System 8.4
Force and Displacement Sensors 8.5
Optical Analysis and Measurement 8.6
Data Acquisition and Recording 8.7
Acoustic Emission (Optional) 8.8
Coating Adhesion Reference Specimens (Optional) 8.9
Coating Surface Profilometry (Optional) 8.10
Data Analysis and Output Software (Optional) 8.11
Test Specimens 9
Specimen Requirements 9.1
Specimen Characterization 9.2
Specimen Size 9.3
Specimen Flatness and Level 9.4
Polishing (Optional) 9.5
Specimen Exposure Conditioning (Optional) 9.6
Specimen Cleaning 9.7
Specimen Handling and Storage 9.8
Calibration 10
System Calibration 10.1
Reference Specimens 10.2
Test Procedure 11
Calibration 11.1
Test Mode Selection 11.2
Test Planning 11.3
Stylus Inspection and Cleaning 11.4
Environmental Conditions 11.5
System Set-Up and Check 11.6
System Setup and Check 11.6
Test Specimen Mounting 11.7
Conducting the Test 11.8
Specimen Count 11.9
Invalid and Censored Data 11.10
C1624 − 22
Section
Scratch Damage Assessment 11.11
Calculations 12
Report 13
Test Identification 13.2
Specimen Information 13.3
Test Equipment and Procedure Information 13.4
Test Data and Statistics 13.5
Precision and Bias 14
Keywords 15
Rockwell Diamond Indenter Specifications Annex A1
Alignment and Calibration Annex A2
Repeatability and Reproducibility Studies Annex A3
Coating Damage Criteria and Scratch Atlas Appendix X1
Experimental Variables in Scratch Adhesion Testing Appendix X2
Bibliography
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B659 Guide for Measuring Thickness of Metallic and Inorganic Coatings
E4 Practices for Force Calibration and Verification of Testing Machines
E18 Test Methods for Rockwell Hardness of Metallic Materials
E750 Practice for Characterizing Acoustic Emission Instrumentation
E1316 Terminology for Nondestructive Examinations
E1932 Guide for Acoustic Emission Examination of Small Parts
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (The Modern Metric System)American National
Standard for Metric Practice
2.2 ASME Standard:
ASME B46.1 Surface Texture (Surface Roughness, Waviness, and Lay)
2.3 CEN Standard:
CEN prEN 1071-3 Advanced Technical Ceramics—Methods of Test for Ceramic Coatings—Part 3: Determination Ofof
Adhesive Andand Other Mechanical Failure Modes By Aby a Scratch Test
3. Terminology
3.1 Definitions:
3.1.1 acoustic emission, n—class of phenomenon in which elastic waves are generated by the rapid release of energy from
localized sources within a material, or the transient waves so generated. E1316
3.1.2 adhesive failure, n—detachment and separation of a coating from the substrate with cracking and debonding at the
coating-substrate interface.
3.1.3 cohesive failure, n—material damage and cracking in the coating or in the substrate, separate and distinct from detachment
and adhesive debonding at the coating-substrate interface.
3.1.4 critical scratch load (L ), n—applied normal force at which a specific, well-defined, recognizable damage/failure event
CN
occurs or is observed in the scratch test of a specific coating on a specific substrate.
3.1.4.1 Discussion—
The subscript N is used to identify progressive failure events. For example, L is often used to identify the first level of cohesive
CC1
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, Three Park Ave., New York, NY 10016-5990, www.asme.org.
Available from European Committee for Standardization (CEN), 36 rue de Stassart, B–1050 Brussels, www.cenorm.be.
C1624 − 22
failure in the coating itself; coating-substrate sample, and L is often used to identify first adhesivethe second failure between
CC2
the coating and the substrate. in the coating-substrate sample. Multiple subscripts can be used for progressive levels of distinct
damage damage, such as cohesive failure, adhesive failure, spalling, etc., in a specific coating-substrate systems.system.
3.1.5 fundamental adhesion, n—summation of all interfacial intermolecular interactions between a film or coating and its
substrate.
3.1.6 normal force (L ), n—in a scratch test, the force exerted by the stylus, perpendicular to the test surface of the test specimen.
N
3.1.7 practical adhesion, n—force or work required to remove or detach a film or coating from its substrate irrespective of the
locus of failure.
3.1.7.1 Discussion—
“Practical adhesion” is a test concept which uses various engineering coating adhesion test methods to obtain a quantitative,
reproducible adhesion measurement which can be related to the functional performance of the coating. The practical adhesion is
an extrinsic property which depends on the complex interaction of coating/substratecoating-substrate properties and characteristics
with the specific test parameters.
3.1.8 stylus drag coeffıcient, n—in scratch testing, the dimensionless ratio of the tangential force to the normal force applied to
the stylus at a specific point in the scratch test.
3.1.8.1 Discussion—
The term stylus drag coefficient is preferred to the more common term scratch coefficient of friction (SCF). The tangential force
is primarily a measure of the perpendicular force required to plow the indenter through the coating, rather than to slide it on the
surface (sliding friction is a relatively minor contribution to the measured tangential force unless penetration is very small and
surface properties dominate). Thus the term friction coefficient is not appropriate for these stylus scratch tests. The SCF term is
too easily misunderstood or misused as a measurement of sliding friction.
3.1.9 tangential force (L ), n—force that opposes the relative motion between a moving stylus and the surface that is being
T
scratched by the stylus and which is perpendicular to the normal force exerted by the stylus (also called the friction force, drag
force, or the scratching force).
4. Summary of Test Method
4.1 This test consists of producing and assessing controlled damage in a hard ceramic coating by single point scratch action (see
Fig. 1). The scratch is developed on a coated test specimen by drawing a diamond stylus of defined geometry and tip size (Rockwell
C, 200 μm radius) across the flat surface of the specimen at a constant speed and a controlled and measured normal force (constant
or progressively increasing). With increasing applied normal force, the stylus produces progressive mechanical damage in the
coating and the substrate through the complex combination of elastic/plastic indentation stresses, frictional forces, and residual
internal stresses in the coating/substratecoating-substrate system (Fig. 2).
FIG. 1 Test Method Schematic
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FIG. 2 Schematic Example of Progressive Damage in Scratch Track in a Progressive Load Scratch Test
4.2 The specific levels and types of progressive damage in the scratch track are assessed and associated with the applied normal
stylus forces. The normal force which produces a specific, defined, reproducible type/level of damage is defined as a critical scratch
load (L ). For a given coating-substrate system, one or more different critical scratch loads (L ) can be defined for progressive
C CN
levels of defined coating damage.
4.3 Coating damage is assessed by optical microscopy or (standard microscope or with white light interferometry or confocal
microscopy) or scanning electron microscopy, or both, combined techniques, during or after the scratch test is done. The tangential
force and acoustic emission signals can also be measured and recorded during the scratch test process and used as supplementary
test data to identify different coating damage levels. In commercial instruments, computerized electronic systems are commonly
used to apply, control, measure, and record the force signals and acoustic emission signals and to control the stylus-specimen
movement.
4.4 The two primary modes of scratch adhesion testing are constant load and progressive load. In constant load (CL) scratch
testing, the normal force on the stylus is maintained at a constant level as the stylus moves in relation to the test specimen surface.
Sequential scratch tests are done at increasing force increments to determine the critical scratch load for a given damage level.
4.4.1 In constant load (CL) scratch testing, the normal force on the stylus is maintained at a constant level as the stylus moves
in relation to the test specimen surface. Sequential scratch tests are done at increasing force increments to determine the critical
scratch load for a given damage level.
NOTE 1—Test systems may have either a movable stage or a movable stylus with the alternate component in a fixed position.
4.4.2 In progressive load (PL) scratch tests, the applied stylus force is linearly increased from zero (or a minimum defined load)
to a defined maximum force as the stylus moves in relation to the test specimen surface.
NOTE 1—Test systems may have either a movable stage or a movable stylus with the alternate component in a fixed position.
4.5 In progressive load (PL) scratch tests, the applied stylus force is linearly increased to a defined maximum force as the stylus
moves in relation to the test specimen surface.
4.5 The critical scratch loads at which a defined coating failure event occurs depend on a complex interaction of coating-substrate
properties and test parameters/conditions. It is the purpose of this test standard to: ((1)1) describe and define the test equipment
and procedures and the major and minor coating-substrate properties which have to be controlled, measured, and understood to
produce reliable, comparable coating adhesion test data, and ((2)2) define a report format that will provide complete and accurate
test data.
5. Significance and Use
5.1 This test is intended to assess the mechanical integrity, failure modes, and practical adhesion strength of a specific hard ceramic
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coating on a given metal or ceramic substrate. The test method does not measure the fundamental “adhesion strength” of the bond
between the coating and the substrate. Rather, the test method gives a quantitative engineering measurement of the practical
(extrinsic) adhesion strength and damage resistance of the coating-substrate system as a function of applied normal force. The
adhesion strength and damage modes depend on the complex interaction of the coating/substratecoating-substrate properties
(hardness, fracture strength, modulus of elasticity, damage mechanisms, microstructure, flaw population, surface roughness, and
so forth) and the test parameters (stylus properties and geometry, loading rate, displacement rate, and so forth).
5.2 The test method as described herein is not appropriate for polymer coatings, ductile metal coatings, very thin (<0.1 μm)
ceramic coatings, or very thick (>30 μm) ceramic coatings.
NOTE 2—Under narrow circumstances, the test may be used for ceramic coatings on polymer substrates with due consideration of the differences in elastic
modulus, ductility, and strength between the two types of materials. Commonly, the low comparative modulus of the polymer substrate means that the
ceramic coating will generally tend to fail in bending (through-thickness adhesive failure) before cohesive failure in the coating itself.
5.3 The quantitative coating adhesion scratch test is a simple, practical, and rapid test. However, reliable and reproducible test
results require careful control of the test system configuration and testing parameters, detailed analysis of the coating damage
features, and appropriate characterization of the properties and morphology of the coating and the substrate of the test specimens.
5.4 The coating adhesion test has direct application across the full range of coating development, engineering, and production
efforts. Measurements of the damage mechanisms in a coating as a function of applied normal forces are useful to understand
material-process-property relations; quantify and qualify the mechanical response of coating-substrate systems; assess coating
durability; measure production quality; and support failure analysis.
5.5 This test method is applicable to a wide range of hard ceramic coating compositions—carbides, compositions (carbides,
nitrides, oxides, diamond, and diamond like carbon—applieddiamond-like carbon) applied by physical vapor deposition, chemical
vapor deposition, and direct oxidation methods to metal and ceramic substrates.
NOTE 2—Under narrow circumstances, the test may be used for ceramic coatings on polymer substrates with due consideration of the differences in elastic
modulus, ductility, and strength between the two types of materials. Commonly, the low comparative modulus of the polymer substrate means that the
ceramic coating will generally tend to fail in bending (through-thickness adhesive failure) before cohesive failure in the coating itself.
5.6 Ceramic coatings can be crystalline or amorphous, but commonly have high relative density with limited porosity (<5 %).
Porous coatings can be tested, but the effects of porosity on the damage mechanisms in the coating must be carefully considered.
5.7 The test method, as defined with the 200 μm radius Rockwell diamond stylus, is commonly used for ceramic coating
thicknesses in the range of 0.10 to 30 μm. Thinner coatings may require a smaller diameter stylus and lower normal forces for
reliable results. Thicker coatings may require larger diameter stylus and higher normal forces. Any variations in stylus size and
geometry and designated normal force ranges shall be reported.
5.8 Specimens commonly have a flat planar surface for testing, but cylinder geometries can also be tested if they are properly
fixtured and aligned and the scratch direction is along the long axis of the specimen. The physical size of the test specimen is
determined primarily by the capabilities and limits of the test equipment stage and fixturing.
5.9 The test is commonly conducted under unlubricated conditions and at room temperature. However, it is feasible and possible
to modify the test equipment and test conditions to conduct the test with lubrication or at elevated temperatures.
5.10 Coated specimens can be tested after high temperature, oxidative, or corrosive exposure to assess the retained properties and
durability (short-term and long-term) of the coating. Any specimen conditioning or environmental exposure shall be fully
documented in the test report, describing in detail the exposure conditions (temperature, atmosphere, pressures, chemistry,
humidity, and so forth), the length of time, and resulting changes in coating morphology, composition, and microstructure.
5.10 The test method as described herein is not appropriate for polymer coatings, ductile metal coatings, very thin (<0.1 μm)
ceramic coatings, or very thick (>30 μm) ceramic coatings.
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6. Test Methodology and Experimental Control
6.1 Test Overview:
6.1.1 Coating adhesion is a challenging property to quantify, because the material response to a scratch force is “not a basic
property but a response of a system to an applied test condition” (from Blau’s Lab Handbook of Scratch Testing); but,). But
quantified data are still needed, and the instrumented single point scratch test is the most widely-used widely used test for
determining quantitative practical adhesion of coatings.
NOTE 3—Practical adhesion is the force or work required to remove or detach a film or coating from its substrate irrespective of the locus of failure.
“Practical adhesion” is a test concept which uses direct engineering test methods to obtain a quantitative, reproducible adhesion measurement which can
be related to the functional performance of the coating.
6.1.2 The instrumented single point scratch adhesion test is simple and rapid when performed properly, but it requires a detailed
understanding and careful measurement and control of a wide range of specimen characteristics and test parameters for the test
is to produce valid, repeatable, and reproducible data (Blau, Bull, Meneve, Mittal, Ichimura, etc.).
6.2 Test Modes:
6.2.1 The scratch adhesion test can be done in either of two test modes—constant modes: constant load (CL) and progressive load
(PL). In the CL mode, the normal force on the stylus is maintained at a constant level as the stylus moves at a constant displacement
rate in relation to the test specimen surface. Multiple scratch tests are done at increasing force increments (and the same
displacement rate) to determine the critical scratch load for a given damage level (Fig. 3). In progressive load (PL) scratch tests,
the normal stylus force is linearly increased as the stylus moves at constant displacement rate with respect to the test specimen
surface (Fig. 4). [(Figs. 3 and 4 plot normal force (constant loads and progressive load) and scratch distance (stylus horizontal
movement) against time.]time.)
6.2.2 Table 1 shows relative advantages, disadvantages, and appropriate applications for the two test modes.
6.2.3 The user should choose the test mode which best meets the requirements for data completeness and confidence, specimen
characteristics, material supply, and available time. In some cases, both test modes may be used for more complete assessment of
the coating properties.
FIG. 3 Constant Load Graph
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FIG. 4 Progressive Load Graph
6.3 Primary and Supplemental Measurements:
6.3.1 Normal Force and Optical Analysis:
6.3.1.1 The primary experimental measurements in the scratch adhesion test are the applied normal stylus force and the optical
identification/analysis of the damage features in the scratch track. The applied normal force (under constant load or progressive
load test modes) is independently controlled and measured during stylus movement. The specific levels and types of progressive
damage in the scratch track are optically assessed and directly correlated with the applied normal forces. The force level which
produces a specific, defined, reproducible type/level of damage is defined as a critical scratch load (L ). For a given
C
coating-substrate system, several different critical scratch loads (L ) can be defined for progressive levels of coating damage (see
CN
Fig. 2).
6.3.1.2 Two other experimental measurements are also used as dependent variables in scratch adhesion tests—tangential tests:
tangential force and acoustic emission analysis. They can serve as supplemental indicators of coating damage events.
6.3.2 Tangential Force:
6.3.2.1 The tangential force on the stylus is the force that opposes the relative motion between a moving stylus and the surface
that is being scratched by the stylus and which is perpendicular to the normal force exerted by the stylus (see Fig. 1). That force
(L ) is an indicator of how the stylus and the specimen are interacting through in-plane forces developed by the applied normal
T
force, indenter penetration, and scratch path features. Tangential force generally increases with increasing normal force. (The ratio
of tangential force to normal force is the stylus drag coefficient and serves to normalize the tangential force against the applied
normal force.)
6.3.2.2 In scratch testing, the tangential force may change in amplitude and shift into a stick-slip character (with more frequent
and higher amplitude signal spikes) as different types of damage events occur in the scratch track. The tangential force data are
plotted against the applied normal force (Fig. 5)). The tangential force may also change through tip damage, from contamination
(grease, debris, and so forth) between the stylus and the coating, or from changes in surface roughness along the scratch track.
6.3.2.3 Calculating the stylus drag coefficient for different normal stylus force levels permits the direct comparison of tangential
force data done at different normal force levels. Stylus drag coefficient data can be graphed versus time, distance, and normal force
and analyzed for the same type of signal variations; stepwise variations—stepwise changes in average signal value and significant
increases in the frequency and amplitude of signal spikes.
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TABLE 1 Comparison of Constant Load and Progressive Load Test Modes
Constant Load (CL) for Each Scratch Progressive Load (PL) for One Scratch
Advantages Better discrimination of different damage levels for each More rapid testing and better specimen utilization, with a single
incremental loading level. scratch covering a full load range.
Greater statistical confidence in damage events for a given Progressive force application covers the full range of force
loading level. without gaps.
Constant load discriminates for coating non-uniformity along the
scratch path.
Disadvantages Multiple increment testing requires more specimen area and Two experimental variables (load and location) changing at the
test time. same time.
Incremental loads can miss damage events at intermediate load Limited statistical analysis of scratch damage features.
levels.
Application Detailed load specific assessment of coatings (for research, Screening assessment and QA tests of coatings (for research,
process development, and durability studies) process development, and durability studies)
Single value tests are suitable for 9pass-fail9 QA and for
assessing coating uniformity.
FIG. 5 Tangential Force and Acoustic Emission Versusversus Applied Normal Force in Progressive Load Test
6.3.2.4 Distinct changes in tangential forces and stylus drag coefficient are indications of changes in stylus drag and stress or
damage events in the scratch test. However, these changes cannot be associated a priori with specific coating damage-failure events
without optical analysis to correlate the damage features with the changes in tangential force signals and calculated stylus drag
coefficients.
6.3.3 Acoustic Emission:
6.3.3.1 Brittle damage events (cracking, delamination, chipping, spalling, buckling, and so forth) can produce high frequency
high-frequency elastic waves in the coating and substrate which can be detected by acoustic emission (AE) systems. As the applied
normal force increases in the scratch test, coating damage events occur with increasing frequency and severity and the resulting
elastic waves are detected, measured, and recorded by the acoustic emission equipment. The AE data record for each scratch test
is analyzed for significant changes in AE signal characteristics (peak amplitude, frequency, event counts, rise-time, rise time, signal
duration, and energy intensity) that correlate with a given normal stylus force. AE data can be plotted against time, horizontal
displacement distance, or normal stylus force (Fig. 5).
6.3.3.2 It should be noted that changes in acoustic emission events at given normal force levels cannot discriminate a priori
between the different damage events and coating failure modes. Acoustic emission event/signal identification with specific coating
failure events requires extensive testing of a given coating system and correlation with the optical analysis of the damage events
for that specific coating system.
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6.4 Critical Scratch Load Damage Criteria and Scratch Atlas:
6.4.1 A primary requirement in using the scratch adhesion test is to clearly identify and categorize the specific coating damage
features which are used to define the critical scratch load(s). Since different coating systems can fail with different types of damage,
there is no universal set of “critical scratch damage features” that can be applied to all types of coatings.
6.4.2 Appendix X1 gives an overview of typical types of ceramic coating damage mechanisms and a scratch atlas which lists a
set of descriptive terms for different types of scratch damage supported by sketches and micrographs. The scratch atlas is not totally
comprehensive, but it provides a baseline and framework for users to assess and describe crack damage with a set of generally
accepted and understood terms.
6.4.3 Each test user will select the particular levels and classes of coating damage features for a specific coating/substratecoating-
substrate system that best meets the coating performance requirements and testing needs. For example, the simplest critical scratch
load criteria may be a single level (L ) at which the first cohesive failure occurs in the coating. A two-level critical scratch load
CC1
(L and L ) might be defined for cohesive cracking/failure (L ) in the coating and for subsequent adhesive failure/spalling
CC1 CC2 CC1
(L ) between the coating and the substrate at a higher applied normal force. If necessary, for complete damage mechanism
CC2
mapping (for research, failure analysis, or durability assessment), multiple (>2 levels) critical scratch loads may be defined to
identify each distinctive type of damage feature.
6.4.4 It is critically important to the validity and reproducibility of the scratch test for a given coating-substrate system that the
damage events for a given critical scratch load be well defined and described in the test report. This is best done with micrographs
and sketches to show the typical damage features of interest. Alternatively, the damage features may be verbally described in the
report. Valid comparisons between different test specimens require that they have the same failure/damage mechanisms, which can
only be confirmed by optical analysis.
6.5 Experimental Factors and Variables:
6.5.1 Appendix X2 provides an overview of the full range of experimental and material variables which have varying degrees of
impact in a scratch adhesion test. The different factors can be categorized into six sets of variables: coating variables, substrate
variables, interface variables, equipment and procedure variables, specimen variables, and environment variables.
6.5.2 The required depth and detail of specimen characterization and test parameter control will depend on the purpose, scope,
and level of confidence and detail required by the user. The experimenter needs to understand and carefully consider how each of
these variables can impact a particular test and to what degree each needs to be controlled and measured. This is necessary for the
scratch adhesion test is to be used with an acceptable degree of confidence, accuracy, and reliability.
6.5.3 Table 2 lists the test parameters and specimen characteristics that have the top priority for control and measurement to ensure
acceptable scratch adhesion test results.
TABLE 2 Top Priority for Control and Measurement of Specimen
Characteristics and Test Parameters
Factor Details
Diamond Stylus Verified geometry, size, condition (damage free
and clean)
Force and Displacement Accurate calibration, precise and accurate control,
Control measurement, and data recording
Damage Assessment Optical analysis with well-defined damage criteria
and complete documentation with photos/
sketches.
Damage Assessment Optical analysis with well-defined damage criteria
and complete documentation with photos/sketches
Coating Characterization Detailed information (by analysis or from coating
supplier) on composition, thickness, pedigree, and
surface roughness.
Coating Characterization Detailed information (by analysis or from coating
supplier) on composition, thickness, pedigree, and
surface roughness
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6.5.4 Additional test parameters and specimen characteristics may need to be measured and controlled for full analysis and
understanding; but, at a minimum, the characteristics and parameters in Table 2 shall be well-controlled well controlled and
documented to ensure valid and reproducible scratch adhesion test results.
7. Interferences
7.1 The repeatability, reproducibility, and precision in the scratch adhesion test requires that variations in test parameters and
specimen characteristics arebe minimized. As described in Appendix X2, there are many variables that may have an impact on the
test data and need to be considered to varying degrees. However, the following material and test parameters are the primary source
of test interference and need to be understood and controlled.
7.2 Material and Specimen Related:
7.2.1 Variations (in individual specimens and between specimens) in the coating thickness and in the surface roughness of the
coating are a major source of variability in the critical scratch load values.
NOTE 3—Deposition techniques and residual stresses have also shown variability in the critical load values.
7.2.2 Major variations (in specimens and between specimens) in the microstructure, morphology, mechanical properties, and flaw
population of the coating may change the damage mechanisms and modes of failure and modify the critical scratch load values.
7.2.3 Contamination and debris on the surface of the coating may interfere with the stylus and increase data variability.
7.3 Test Method Related:
7.3.1 Test data are not comparable between specimens and specimen sets unless the scratch adhesion tests are conducted under
directly comparable conditions using:
7.3.1.1 Identical styluses (composition, geometry, size, and orientation), and
7.3.1.2 Identical force application rates and horizontal displacement rates.
7.3.2 Stylus damage and contamination will modify the stylus-surface interaction and increase data variability.
7.3.3 The definitions and documentation of the damage criteria for each critical scratch load level for a given coating-substrate
shall be clearly defined in complete detail to minimize subjective analysis and improve reproducibility between operators and
laboratories.
8. Apparatus
8.1 General Description:
8.1.1 The quantitative scratch adhesion test system commonly consists of six equipment subsystems: ((1)1) stylus and stylus
mounting, ((2)2) mechanical stage and displacement control, ((3)3) test frame and force application system, ((4)4) force sensors,
((5)5) optical measurement, and ((6)6) data acquisition/recording. The test system may also include additional measurement
systems, such as acoustic emission and displacement sensors (Fig. 6).
8.1.2 Commercial scratch adhesion test systems are widely available and extensively used. They commonly include computer
feedback control of normal force and horizontal displacement, computer data acquisition, and video microscope recording systems.
8.2 Stylus and Stylus Mounting:
8.2.1 The stylus shall be a diamond indenter that meets the specifications for a Rockwell sphericonical diamond indenter, as
described in 13.1.2.1 of Test Methods E18 and commonly called a Rockwell C diamond indenter. The Rockwell diamond indenter
has an apex angle of 120° and terminates in a hemispherical tip with a mean radius of 200 μm (400 μm diameter). Full
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FIG. 6 Scratch Adhesion Test System Schematic
specifications for the Rockwell C diamond indenter from Test Methods E18 are included in Annex A1. The use of the Rockwell
C diamond indenter is specified for this test to ensure comparability and reproducibility of test results within and between
laboratories.
NOTE 4—It is recommended that the Rockwell C diamond stylus geometry be definitively checked, verified (SEM, interferometry, profilometry,
interference microscopy, and so forth)forth), and documented against specifications by the supplier or by the end user. Significant variations can occur
between nominally identical styluses and will have a significant effect on test results.
NOTE 5—If a diamond stylus with smaller or larger tip radius is required and used (for thinner or thicker coatings), the test report shall indicate that a
modified version of the standard was used, and the size of the tip radius shall be reported. Scratch test data produced with different stylus geometries,
tip radii, or compositions are not directly comparable.
8.2.2 The stylus mounting system shall be designed and constructed to rigidly and securely hold the diamond stylus with a
minimum of vertical and horizontal compliance or backlash, given the applied normal and tangential forces.
8.2.3 The diamond stylus shall be secured in a consistent orientation in the mounting holder, either by index marks or alignment
flats. This is necessary to eliminate variation between tests caused by spatial variations in the condition, orientation, or shape of
the diamond stylus, or a combination thereof, found either in the as-received condition or after accumulated wear from testing.
8.2.4 The diamond stylus shall be microscopically inspected for tip wear and damage and contamination at the beginning of each
test series or after ten scratch tests. See 11.4 for a detailed discussion and description of the stylus inspection procedure.
8.3 Mechanical Stage and Displacement Control System:
8.3.1 The mechanical stage serves to rigidly secure and accurately align and position the test specimen. Relative movement
between the diamond stylus and the specimen can be produced by either of two methods: ((1)1) movement of the mechanical stage
with respect to a fixed stylus, or ((2)2) movement of the stylus with respect to a fixed stage.
8.3.2 The mounting stage fixture shall be designed and constructed of hard metal (tool steel, stainless steel) to be sufficiently rigid
to withstand the normal and lateral forces associated with the scratching action without undue elastic or plastic deflection. The
fixture must secure the test specimen so that there is no lateral movement, rocking, or backlash of the specimen during the scratch
test. The fixture shall have alignment mechanisms to ensure that the test specimen surface plane (or long axis/test direction for
cylinder specimens) can be aligned orthogonal and level with respect to the loading direction of the stylus along the length of a
given scratch track (see Section 10 and Annex A2 on stage alignment).
8.3.3 The stage should have 2-axistwo-axis (X and Y) manual horizontal adjustment (to position the specimen for scratch testing).
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Horizontal accuracy (straight-line position) should be 10 μm or better in both the X and Y directions. The test specimen stage must
have vertical axis (Z) adjustment (manual or motorized) to raise and lower the specimen (or the stylus) into the test position.
8.3.4 The scratch adhesion test is commonly conducted under unlubricated conditions and at room temperature. However, it is
feasible and possible to modify the test equipment and test conditions to conduct the test with lubrication or at cryogenic or
elevated temperatures. For elevated temperature (>100°C)(>100 °C) testing, test equipment will have to be specially modified to
develop and maintain specimen temperature, minimize oxidation and thermal degradation of the test specimens and test equipment,
and maintain precise control and accurate measurement of the experimental parameters. Any modifications of the test system or
test procedure shall be fully documented in the test report.
NOTE 6—Some commercial test systems now offer temperature-controlled stages for testing specimens across a range of cryogenic and elevated
temperatures.
8.3.5 The movement control system shall produce straight-line horizontal movement between the stylus and the specimen at a
constant, controlled, and repeatable speed. This controlled horizontal displacement is most easily produced with an electrome-
chanical stage. The range of translation/displacement (scratch length) shall be at least 10 mm. Translational accuracy and
repeatability shall be 0.5 % of the minimum displacement range or 50 μm, whichever is smaller. The system shall be capable of
a specimen displacement speed of 10 mm/min with an accuracy of 60.1 mm/min (higher or lower translation speeds, or both, may
be necessary for modified tests).
NOTE 7—Current test systems (commercial and in-house built) commonly have a range of displacement motion of 20 to 150 mm and a range of
displacement speeds of 10 to 100 mm/min. It is also common in commercial systems for the specimen positioning and stage movement to be feedback
controlled by displacement sensors and computer controlled computer-controlled translation motors.
8.3.6 The movement control system shall be calibrated for accuracy and precision in accordance with Annex A2.
8.3.7 The test system may also be instrumented with an independent horizontal displacement sensor to independently measure the
specimen horizontal translation as a function of time. The horizontal displacement sensor shall have a resolution and accuracy of
10 μm or 1 % (or better) of the maximum measured translation, whichever is smaller. Current commercial systems commonly have
horizontal positioning precisions of 1 μm or better (see Section 10 and Annex A2 for calibration).
8.4 Test Frame and Force Application System:
8.4.1 The test frame system (specimen stage, stylus mounting system, and load frame) shall be sufficiently rigid so that the vertical
compliance (μm/N) of the system does not significantly affect the application of force to the specimen or the determination of stylus
indent depth. A recommended system compliance value is 5 % or less of the compliance of the test specimen.
8.4.2 The force application system shall be designed to apply the desired normal force to the stylus in a controlled and repeatable
manner across the full range of stylus vertical and horizontal displacement. The maximum force required will depend on the
properties of the specific coating-substrate system being tested, but a force range of 0 to 150 N will be sufficient for most hard
coatings tested with the Rockwell C indenter. Force control shall be precise and repeatable to an accuracy of at least 0.5 N or better.
Depending on the type of test (constant load
...