Standard Test Method for Scratch Hardness of Materials Using a Diamond Stylus

SIGNIFICANCE AND USE
This test method is intended to measure the resistance of solid surfaces to permanent deformation under the action of a single point (stylus tip). It is a companion method to quasi-static hardness tests in which a stylus is pressed into a surface under a certain normal load and the resultant depth or impression size is used to compute a hardness number. Scratch hardness numbers, unlike quasi-static hardness numbers, involve a different combination of properties of the surface because the indenter, in this case a diamond stylus, moves tangentially along the surface. Therefore, the stress state under the scratching stylus differs from that produced under a quasi-static indenter. Scratch hardness numbers are in principle a more appropriate measure of the damage resistance of a material to surface damage processes like two-body abrasion than are quasi-static hardness numbers.
This test method is applicable to a wide range of materials. These include metals, alloys, and some polymers. The main criteria are that the scratching process produces a measurable scratch in the surface being tested without causing catastrophic fracture, spallation, or extensive delamination of surface material. Severe damage to the test surface, such that the scratch width is not clearly identifiable or that the edges of the scratch are chipped or distorted, invalidates the use of this test method to determine a scratch hardness number. Since the degree and type of surface damage in a material may vary with applied load, the applicability of this test to certain classes of materials may be limited by the maximum load at which valid scratch width measurements can be made.
The resistance of a material to abrasion by a single point may be affected by its sensitivity to the strain rate of the deformation process. Therefore, this test is conducted under low stylus traversing speeds. Use of a slow scratching speed also minimizes the possible effects of frictional heating.
This test uses measurem...
SCOPE
1.1 This test method covers laboratory procedures for determining the scratch hardness of the surfaces of solid materials. Within certain limitations, as described in this guide, this test method is applicable to metals, ceramics, polymers, and coated surfaces. The scratch hardness test, as described herein, is not intended to be used as a means to determine coating adhesion, nor is it intended for use with other than specific hemispherically-tipped, conical styli.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard may involve hazardous materials, operations, and equipment. 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.

General Information

Status
Historical
Publication Date
30-Apr-2009
Technical Committee
Drafting Committee
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´2
Designation: G171 − 03 (Reapproved 2009)
Standard Test Method for
Scratch Hardness of Materials Using a Diamond Stylus
This standard is issued under the fixed designation G171; 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.
ε NOTE—Deleted erroneous reference in 8.4 editorially in May 2009.
ε NOTE—Reference to specific brand of scratch tester was removed from Appendix X1 editorially in September 2009.
1. Scope 3.2.1 scratch hardness number, n—a quantity, expressed in
units of force per unit area, that characterizes the resistance of
1.1 This test method covers laboratory procedures for de-
a solid surface to penetration by a moving stylus of given tip
termining the scratch hardness of the surfaces of solid materi-
radius under a constant normal force and speed; namely,
als. Within certain limitations, as described in this guide, this
test method is applicable to metals, ceramics, polymers, and kP
HS 5
P 2
coated surfaces.The scratch hardness test, as described herein, w
is not intended to be used as a means to determine coating
where:
adhesion, nor is it intended for use with other than specific
HS = scratch hardness number,
P
hemispherically-tipped, conical styli.
k = a geometrical constant,
1.2 The values stated in SI units are to be regarded as
P = applied normal force, and
standard. No other units of measurement are included in this
w = scratch width.
standard.
NOTE 1—The constant k may be chosen to include conversion factors
forexpressing HS inunitsofGPa.For HS inGPa, Pingrams-force,and
P P
1.3 This standard may involve hazardous materials,
w in µm, k = 24.98.
operations, and equipment. This standard does not purport to
3.2.2 scratching force, n—the force that opposes relative
address all of the safety concerns, if any, associated with its
motion between a moving stylus and the surface that is being
use. It is the responsibility of the user of this standard to
scratched by that stylus, and which is perpendicular to the
establish appropriate safety and health practices and deter-
normal force exerted by the stylus.
mine the applicability of regulatory limitations prior to use.
3.2.3 stylus drag coeffıcient, n—in scratch testing, the di-
2. Referenced Documents
mensionless ratio of the scratching force to the normal force
applied to the stylus; namely,
2.1 ASTM Standards:
G40Terminology Relating to Wear and Erosion
F
scr
D 5
sc
G117Guide for Calculating and Reporting Measures of
P
Precision Using Data from Interlaboratory Wear or Ero-
where:
sion Tests
D = stylus drag coefficient,
sc
F = scratching force, and
3. Terminology scr
P = normal force.
3.1 Definitions—For definitions of terms applicable to this
standard see Terminology G40.
4. Summary of Test Method
3.2 Definitions of Terms Specific to This Standard:
4.1 This test involves producing a scratch in a solid surface
by moving a diamond stylus of specified geometry along a
specified path under a constant normal force and with a
This test method is under the jurisdiction of ASTM Committee G02 on Wear
constant speed. The average width of the scratch is measured,
and Erosion and is the direct responsibility of Subcommittee G02.30 on Abrasive
Wear.
and that value is used to compute the scratch hardness number
Current edition approved May 1, 2009. Published May 2009. Originally
in units of pressure.
approved in 2003. Last previous edition approved in 2003 as G171–03. DOI:
10.1520/G0171-03R09E02.
4.2 As an option, the scratching force may be measured
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
during this test and used to compute a stylus drag coefficient,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
which is a dimensionless measure of the resistance of the test
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. surface to deformation by a tangentially-moving stylus.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´2
G171 − 03 (2009)
4.3 This test is usually conducted under unlubricated con- apply a normal force while traversing the stylus along the
ditions and at room temperature; however, it is possible to surfaceatconstantspeed,and(3)ameanstomeasurethewidth
conduct scratch hardness tests under lubricated and elevated of the scratch. Optionally, the apparatus can be equipped with
temperature conditions. The provisions of this standard allow a sensor to detect the magnitude of the scratching force.
testing under both conditions provided that requirements for 6.1.1 Stylus—The stylus shall be conical of apex angle 120
valid scratch hardness testing are met and that the testing 65°,andtheconeshallterminateinahemisphericaltipof200
conditions are fully reported. µm(610µm)radius.Thematerialofthetipshallbediamond.
4.4 Effects of moisture in the air and other ambient atmo-
NOTE 2—The smaller the tip radius, the higher the contact stress under
a given normal force. If a tip radius other than that indicated here is used,
spheric conditions may affect results depending on the sensi-
resultsshallindicatethatamodifiedversionofthestandardwasused,and
tivityofthetestmaterialtotheenvironment.Ifsucheffectsare
the size of the tip radius shall be reported (see also 10.1.1).
either expected or observed during the course of testing,
6.1.2 Apparatus—A means to traverse the specimen under
precautions to control the surrounding atmosphere and to
the stylus, or the stylus across the specimen, under constant
document the relative humidity level should be taken and
speed and normal force, shall be provided. Fixtures shall be
reported.
sufficientlyrigidtowithstandthenormal,lateral,andtangential
5. Significance and Use
forces associated with the scratching process without undue
5.1 Thistestmethodisintendedtomeasuretheresistanceof
elastic or plastic deflection. The path of the stylus may be in a
solid surfaces to permanent deformation under the action of a
straight line or an arc, as produced using a rotating table-type
single point (stylus tip). It is a companion method to quasi-
device.
static hardness tests in which a stylus is pressed into a surface
6.1.3 Scratch Width Measurement System—A means for
under a certain normal load and the resultant depth or impres-
measuring the width of the scratch shall be provided. This can
sion size is used to compute a hardness number. Scratch
consistofanyimagingsystemthatiscapableofmagnifyingthe
hardness numbers, unlike quasi-static hardness numbers, in-
scratch such that its width can be accurately determined. The
volve a different combination of properties of the surface
measuring system shall be capable of measuring the width of
because the indenter, in this case a diamond stylus, moves
the scratch to a precision of at least 2%. For example, the
tangentially along the surface.Therefore, the stress state under
required resolution for a measuring optical microscope needed
the scratching stylus differs from that produced under a
for an average 50 µm-wide scratch shall be (0.02 × 50 µm) =
quasi-staticindenter.Scratchhardnessnumbersareinprinciple
1.0 µm or better. Reflecting-type, optical microscopes using
a more appropriate measure of the damage resistance of a
monochromatic illumination or interference-contrast and hav-
material to surface damage processes like two-body abrasion ingameasuringeyepiecearesuitableforscratchmeasurement.
than are quasi-static hardness numbers.
Alternatively, photographic or video images may be used as
long as the magnifications are properly calibrated.
5.2 This test method is applicable to a wide range of
6.1.4 Scratching Force (Optional)—A load cell or similar
materials. These include metals, alloys, and some polymers.
force-sensing device can be used to measure the scratching
The main criteria are that the scratching process produces a
forces generated during sliding.This standard does not specify
measurable scratch in the surface being tested without causing
a method for measuring the scratching force, only that the
catastrophic fracture, spallation, or extensive delamination of
sensor shall be capable of being calibrated in the direction of
surface material. Severe damage to the test surface, such that
the scratching force and in line with the contact point between
the scratch width is not clearly identifiable or that the edges of
the stylus and surface.
the scratch are chipped or distorted, invalidates the use of this
test method to determine a scratch hardness number. Since the
7. Calibration
degreeandtypeofsurfacedamageinamaterialmayvarywith
applied load, the applicability of this test to certain classes of
7.1 Thepartsoftheapparatusthatrequirecalibrationare(1)
materials may be limited by the maximum load at which valid
the normal force application system, (2) stylus traverse speed,
scratch width measurements can be made.
and optionally (3) the scratching force sensor.
5.3 Theresistanceofamaterialtoabrasionbyasinglepoint
7.2 Loading System—Thenormalforceappliedtothestylus
may be affected by its sensitivity to the strain rate of the
while it is traversing the surface shall be calibrated in such a
deformation process. Therefore, this test is conducted under
way that the normal force is known to within 1%. For
low stylus traversing speeds. Use of a slow scratching speed
example, a normal force of 1 N shall be applied to within an
also minimizes the possible effects of frictional heating.
accuracyof 60.01N.Themeanstocalibratethescratchtester
5.4 This test uses measurements of the residual scratch shall be determined by its individual design; however, the
methodofnormalforcecalibrationshallbestatedinthereport.
widthafterthestylushasbeenremovedtocomputethescratch
NOTE 3—One method to calibrate the normal force on the stylus is to
hardnessnumber.Therefore,itreflectsthepermanentdeforma-
use a quasi-static system such as a button-type load cell placed under the
tionresultingfromscratchingandnottheinstantaneousstateof
stylus tip in the position where the test specimen is located.
combined elastic and plastic deformation of the surface.
7.3 Stylus Traverse Speed—The speed of the stylus across
6. Apparatus
the surface s may be calibrated in any suitable manner such as
6.1 General Description—The apparatus consists of (1) the timing the period t required to produce a scratch of length L.
rigidstylusmountandspecimenholdingfixture,(2)ameansto Thus:
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G171 − 03 (2009)
L 8.7 Conducting the Test—Ensure that the instrument is
s 5 (1)
t leveled and that the stylus is normal to the test surface while
scratching. Lower the stylus to apply the load on the specimen
7.4 Scratching Force Sensor (Optional)—The scratching
surface gently to avoid impact damage.Activate the traversing
force sensor shall be calibrated periodically in the direction of
drive to produce the scratch of desired length. Raise the stylus
the scratching force, and as closely as possible in line with the
off of the surface. Select another location at least 5 scratch
point of contact between the stylus and specimen.The interval
widths away from the previous scratch and produce another
between calibrations shall be determined by the user to ensure
scratch parallel to the first. Repeat as necessary, but with a
accurate readings of scratching force and compensate for any
minimum of three (3) scratches per value of the normal force.
electronic signal drift.
Measure the scratch width as described in
8.8.
8. Procedure
8.8 Scratch Width Measurement—Usingameasuringmicro-
8.1 Specimen Preparation—The test specimen shall be pre-
scope or other calibrated magnifying or surface profiling
pared in such a way as to represent the application of interest
system, measure the width of each scratch at three locations
or polished to facilitate observation and measurement of
spaced approximately equally along the length of the scratch.
scratch width. A surface may be unsuitable for scratch testing
The width of the scratch shall be determined optically, as
ifitsroughnessorporosityissuchthattheedgesofthescratch
shown by the examples in Fig. 1. Owing to acceleration and
are indistinct or jagged, or if the stylus cannot traverse the
deceleration effects, scratch widths should not be measured
surface without skipping along it or catching in a pocket. In a
near the ends of the scratch.
polished condition, the surface should be as free as possible
from preparation artifacts such as grinding-induced cracks,
NOTE5—Othermethods,suchassurfaceprofiling,mayproducevalues
gross grinding marks, and grain pull-out. Surface roughnesses different from optical measurements. Therefore, to improve consistency,
widths should be measured on enlarged images.
of 0.02 to 0.05 µm R (arithmetic average roughness) are
a
typical of polished surfaces. Surfaces may be scratch tested in
8.8.1 Special Considerations in Optical Scratch
the as-fabricated condition as long as the characteristics of the
Measurement—Thecharacteristicsofthesurfacesbeingtested,
scratch do not display the types of artifacts described in this
such as their roughness, color, degree of light diffusion, extent
paragraph.
of plastic deformation, and reflectivity, will all affect the ease
8.2 Specimen Cleaning—Since many different kinds of
or difficulty in precisely locating scratch edges. In general,
materials can be scratch tested, one specific cleaning treatment
finer scratches present more difficulties in width measurement
cannotbegiven.Specimensshallbecleanedinsuchawaythat
thanwiderscratches(seealso11.2).Itmaybenecessarytouse
the surface is free from grit, grease, fingerprints, or other
special lighting methods, such as oblique illumination, polar-
contaminants. Metals and alloys may be cleaned in non-polar
ized light, or differential inference contrast microscopy to
solvents. Plastics may require alternative cleaning with eye-
provide sufficient contrast to measure the scratch widths
glass cleaner or similar. If contact with solvents or cleaners
optically. Report the use of special lighting methods, when
could result in changes to their properties, surfaces may be
applicable.
tested as-received. The method of cleaning, if any, shall be
described in the report.
9. Calculations
8.3 Inspection of the Stylus—Inspect the stylus tip with a
9.1 Scratch Hardness Number—The scratch hardness num-
microscope or other topographic inspection method to ensure
ber is calculated by dividing the applied normal force on the
that there are no defects (cracks, chips), wear or adhering
...

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