ASTM G171-03(2009)e1
(Test Method)Standard Test Method for Scratch Hardness of Materials Using a Diamond Stylus
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.
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Designation: G 171 – 03 (Reapproved 2009)
Standard Test Method for
Scratch Hardness of Materials Using a Diamond Stylus
This standard is issued under the fixed designation G 171; 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.
´ NOTE—Deleted erroneous reference in 8.4 editorially in May 2009.
1. Scope a solid surface to penetration by a moving stylus of given tip
radius under a constant normal force and speed; namely,
1.1 This test method covers laboratory procedures for de-
termining the scratch hardness of the surfaces of solid materi- kP
HS 5
P
als. Within certain limitations, as described in this guide, this
w
test method is applicable to metals, ceramics, polymers, and
where:
coated surfaces. The scratch hardness test, as described herein,
HS = scratch hardness number,
P
is not intended to be used as a means to determine coating
k = a geometrical constant,
adhesion, nor is it intended for use with other than specific
P = applied normal force, and
hemispherically-tipped, conical styli.
w = scratch width.
1.2 The values stated in SI units are to be regarded as
NOTE 1—The constant k may be chosen to include conversion factors
standard. No other units of measurement are included in this
forexpressing HS inunitsofGPa.For HS inGPa, Pingrams-force,and
standard. P P
w in µm, k = 24.98.
1.3 This standard may involve hazardous materials, opera-
tions, 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
dimensionless ratio of the scratching force to the normal force
2. Referenced Documents
applied to the stylus; namely,
2.1 ASTM Standards:
F
scr
D 5
G40 Terminology Relating to Wear and Erosion
sc
P
G117 Guide for Calculating and Reporting Measures of
where:
Precision Using Data from Interlaboratory Wear or Ero-
D = stylus drag coefficient,
sion Tests sc
F = scratching force, and
scr
3. Terminology P = normal force.
3.1 Definitions—For definitions of terms applicable to this
4. Summary of Test Method
standard see TerminologyG40.
4.1 This test involves producing a scratch in a solid surface
3.2 Definitions of Terms Specific to This Standard:
by moving a diamond stylus of specified geometry along a
3.2.1 scratch hardness number, n—a quantity, expressed in
specified path under a constant normal force and with a
units of force per unit area, that characterizes the resistance of
constant speed. The average width of the scratch is measured,
and that value is used to compute the scratch hardness number
This test method is under the jurisdiction of ASTM Committee G02 on Wear
in units of pressure.
and Erosion and is the direct responsibility of Subcommittee G02.30 on Abrasive
4.2 As an option, the scratching force may be measured
Wear.
during this test and used to compute a stylus drag coefficient,
Current edition approved May 1, 2009. Published May 2009. Originally
approved in 2003. Last previous edition approved in 2003 as G 171–03.
which is a dimensionless measure of the resistance of the test
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
surface to deformation by a tangentially-moving stylus.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.3 This test is usually conducted under unlubricated con-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. ditions and at room temperature; however, it is possible to
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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G 171 – 03 (2009)
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 (6 10 µm) radius.The material of the tip shall be diamond.
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
spheric conditions may affect results depending on the sensi-
a given normal force. If a tip radius other than that indicated here is used,
tivity of the test material to the environment. If such effects are
results shall indicate that a modified version of the standard was used, and
either expected or observed during the course of testing, the size of the tip radius shall be reported (see also 10.1.1).
precautions to control the surrounding atmosphere and to
6.1.2 Apparatus—A means to traverse the specimen under
document the relative humidity level should be taken and
the stylus, or the stylus across the specimen, under constant
reported.
speed and normal force, shall be provided. Fixtures shall be
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
straight line or an arc, as produced using a rotating table-type
solid surfaces to permanent deformation under the action of a
single point (stylus tip). It is a companion method to quasi- device.
6.1.3 Scratch Width Measurement System—A means for
static hardness tests in which a stylus is pressed into a surface
under a certain normal load and the resultant depth or impres- measuring the width of the scratch shall be provided. This can
consistofanyimagingsystemthatiscapableofmagnifyingthe
sion size is used to compute a hardness number. Scratch
hardness numbers, unlike quasi-static hardness numbers, in- scratch such that its width can be accurately determined. The
measuring system shall be capable of measuring the width of
volve a different combination of properties of the surface
because the indenter, in this case a diamond stylus, moves the scratch to a precision of at least 2 %. For example, the
required resolution for a measuring optical microscope needed
tangentially along the surface. Therefore, the stress state under
the scratching stylus differs from that produced under a for an average 50 µm-wide scratch shall be (0.02 3 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
materials. These include metals, alloys, and some polymers. 6.1.4 Scratching Force (Optional)—A load cell or similar
force-sensing device can be used to measure the scratching
The main criteria are that the scratching process produces a
measurable scratch in the surface being tested without causing forces generated during sliding. This standard does not specify
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
degree and type of surface damage in a material may vary with
7.1 Thepartsoftheapparatusthatrequirecalibrationare(1)
applied load, the applicability of this test to certain classes of
the normal force application system, (2) stylus traverse speed,
materials may be limited by the maximum load at which valid
and optionally (3) the scratching force sensor.
scratch width measurements can be made.
7.2 Loading System—Thenormalforceappliedtothestylus
5.3 Theresistanceofamaterialtoabrasionbyasinglepoint
while it is traversing the surface shall be calibrated in such a
may be affected by its sensitivity to the strain rate of the
way that the normal force is known to within 1 %. For
deformation process. Therefore, this test is conducted under
example, a normal force of 1 N shall be applied to within an
low stylus traversing speeds. Use of a slow scratching speed
accuracy of 6 0.01 N.The means to calibrate the scratch tester
also minimizes the possible effects of frictional heating.
shall be determined by its individual design; however, the
5.4 This test uses measurements of the residual scratch
methodofnormalforcecalibrationshallbestatedinthereport.
width after the stylus has been removed to compute the scratch
hardness number.Therefore, it reflects the permanent deforma-
NOTE 3—One method to calibrate the normal force on the stylus is to
tionresultingfromscratchingandnottheinstantaneousstateof use a quasi-static system such as a button-type load cell placed under the
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
timing the period t required to produce a scratch of length L.
6.1 General Description—The apparatus consists of (1) the
Thus:
rigidstylusmountandspecimenholdingfixture,(2)ameansto
apply a normal force while traversing the stylus along the L
s 5 (1)
surfaceatconstantspeed,and(3)ameanstomeasurethewidth t
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G 171 – 03 (2009)
7.4 Scratching Force Sensor (Optional)—The scratching scratching. Lower the stylus to apply the load on the specimen
force sensor shall be calibrated periodically in the direction of surface gently to avoid impact damage.Activate the traversing
the scratching force, and as closely as possible in line with the drive to produce the scratch of desired length. Raise the stylus
point of contact between the stylus and specimen. The interval off of the surface. Select another location at least 5 scratch
between calibrations shall be determined by the user to ensure widths away from the previous scratch and produce another
accurate readings of scratching force and compensate for any scratch parallel to the first. Repeat as necessary, but with a
electronic signal drift. minimum of three (3) scratches per value of the normal force.
Measure the scratch width as described in 8.8.
8.8 Scratch Width Measurement—Using a measuring mi-
8. Procedure
croscope or other calibrated magnifying or surface profiling
8.1 Specimen Preparation—The test specimen shall be
system, measure the width of each scratch at three locations
prepared in such a way as to represent the application of
spaced approximately equally along the length of the scratch.
interest or polished to facilitate observation and measurement
The width of the scratch shall be determined optically, as
of scratch width. A surface may be unsuitable for scratch
shown by the examples in Fig. 1. Owing to acceleration and
testing if its roughness or porosity is such that the edges of the
deceleration effects, scratch widths should not be measured
scratch are indistinct or jagged, or if the stylus cannot traverse
near the ends of the scratch.
thesurfacewithoutskippingalongitorcatchinginapocket.In
a polished condition, the surface should be as free as possible
NOTE 5—Other methods, such as surface profiling, may produce values
from preparation artifacts such as grinding-induced cracks, different from optical measurements. Therefore, to improve consistency,
widths should be measured on enlarged images.
gross grinding marks, and grain pull-out. Surface roughnesses
of0.02to0.05µmR (arithmeticaverageroughness)aretypical
a 8.8.1 Special Considerations in Optical Scratch
of polished surfaces. Surfaces may be scratch tested in the
Measurement—Thecharacteristicsofthesurfacesbeingtested,
as-fabricated condition as long as the characteristics of the
such as their roughness, color, degree of light diffusion, extent
scratch do not display the types of artifacts described in this
of plastic deformation, and reflectivity, will all affect the ease
paragraph.
or difficulty in precisely locating scratch edges. In general,
8.2 Specimen Cleaning—Since many different kinds of
finer scratches present more difficulties in width measurement
materials can be scratch tested, one specific cleaning treatment
than wider scratches (see also 11.2). It may be necessary to use
cannot be given. Specimens shall be cleaned in such a way that
special lighting methods, such as oblique illumination, polar-
the surface is free from grit, grease, fingerprints, or other
ized light, or differential inference contrast microscopy to
contaminants. Metals and alloys may be cleaned in non-polar
provide sufficient contrast to measure the scratch widths
solvents. Plastics may require alternative cleaning with eye-
optically. Report the use of special lighting methods, when
glass cleaner or similar. If contact with solvents or cleaners
applicable.
could result in changes to their properties, surfaces may be
9. Calculations
tested as-received. The method of cleaning, if any, shall be
described in the report.
9.1 Scratch Hardness Number—The scratch hardness num-
8.3 Inspection of the Stylus—Inspect the stylus tip with a ber is calculated by dividing the applied normal force on the
microscope or other topographic inspection method to ensure
stylus by the projected area of scratching contact, assuming
that there are no defects (cracks, chips), wear or adhering thatthehemispherically-tippedstylusproducesagroovewhose
material left from manufacturing o
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