ASTM G171-03(2017)
(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
5.1 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.
5.2 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.
5.3 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.
5.4 This...
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 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.
General Information
Relations
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: G171 − 03 (Reapproved 2017)
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.
1. Scope 3. Terminology
1.1 This test method covers laboratory procedures for de- 3.1 Definitions—For definitions of terms applicable to this
termining the scratch hardness of the surfaces of solid materi- standard see Terminology G40.
als. Within certain limitations, as described in this guide, this
3.2 Definitions of Terms Specific to This Standard:
test method is applicable to metals, ceramics, polymers, and
3.2.1 scratch hardness number, n—a quantity, expressed in
coated surfaces.The scratch hardness test, as described herein,
units of force per unit area, that characterizes the resistance of
is not intended to be used as a means to determine coating
a solid surface to penetration by a moving stylus of given tip
adhesion, nor is it intended for use with other than specific
radius under a constant normal force and speed; namely,
hemispherically-tipped, conical styli.
kP
1.2 The values stated in SI units are to be regarded as HS 5
P 2
w
standard. No other units of measurement are included in this
where:
standard.
HS = scratch hardness number,
P
1.3 This standard may involve hazardous materials,
k = a geometrical constant,
operations, and equipment. This standard does not purport to
P = applied normal force, and
address all of the safety concerns, if any, associated with its
w = scratch width.
use. It is the responsibility of the user of this standard to
NOTE 1—The constant k may be chosen to include conversion factors
establish appropriate safety, health, and environmental prac-
forexpressing HS inunitsofGPa.For HS inGPa, Pingrams-force,and
P P
tices and determine the applicability of regulatory limitations
w in µm, k = 24.98.
prior to use.
3.2.2 scratching force, n—the force that opposes relative
1.4 This international standard was developed in accor-
motion between a moving stylus and the surface that is being
dance with internationally recognized principles on standard-
scratched by that stylus, and which is perpendicular to the
ization established in the Decision on Principles for the
normal force exerted by the stylus.
Development of International Standards, Guides and Recom-
3.2.3 stylus drag coeffıcient, n—in scratch testing, the di-
mendations issued by the World Trade Organization Technical
mensionless ratio of the scratching force to the normal force
Barriers to Trade (TBT) Committee.
applied to the stylus; namely,
2. Referenced Documents
F
scr
D 5
2 sc
P
2.1 ASTM Standards:
G40Terminology Relating to Wear and Erosion
where:
G117Guide for Calculating and Reporting Measures of
D = stylus drag coefficient,
sc
Precision Using Data from Interlaboratory Wear or Ero-
F = scratching force, and
scr
sion Tests (Withdrawn 2016)
P = normal force.
4. Summary of Test Method
This test method is under the jurisdiction of ASTM Committee G02 on Wear
and Erosion and is the direct responsibility of Subcommittee G02.30 on Abrasive
4.1 This test involves producing a scratch in a solid surface
Wear.
by moving a diamond stylus of specified geometry along a
Current edition approved Nov. 1, 2017. Published December 2017. Originally
ε2
approved in 2003. Last previous edition approved in 2009 as G171–03 (2009) .
specified path under a constant normal force and with a
DOI: 10.1520/G0171-03R17.
constant speed. The average width of the scratch is measured,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and that value is used to compute the scratch hardness number
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on in units of pressure.
the ASTM website.
4.2 As an option, the scratching force may be measured
The last approved version of this historical standard is referenced on
www.astm.org. during this test and used to compute a stylus drag coefficient,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G171 − 03 (2017)
which is a dimensionless measure of the resistance of the test 6. Apparatus
surface to deformation by a tangentially-moving stylus.
6.1 General Description—The apparatus consists of (1) the
4.3 This test is usually conducted under unlubricated con- rigidstylusmountandspecimenholdingfixture,(2)ameansto
ditions and at room temperature; however, it is possible to apply a normal force while traversing the stylus along the
conduct scratch hardness tests under lubricated and elevated surfaceatconstantspeed,and(3)ameanstomeasurethewidth
temperature conditions. The provisions of this standard allow of the scratch. Optionally, the apparatus can be equipped with
testing under both conditions provided that requirements for a sensor to detect the magnitude of the scratching force.
valid scratch hardness testing are met and that the testing
6.1.1 Stylus—The stylus shall be conical of apex angle 120
conditions are fully reported.
65°,andtheconeshallterminateinahemisphericaltipof200
µm(610µm)radius.Thematerialofthetipshallbediamond.
4.4 Effects of moisture in the air and other ambient atmo-
spheric conditions may affect results depending on the sensi-
NOTE 2—The smaller the tip radius, the higher the contact stress under
tivityofthetestmaterialtotheenvironment.Ifsucheffectsare a given normal force. If a tip radius other than that indicated here is used,
resultsshallindicatethatamodifiedversionofthestandardwasused,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
document the relative humidity level should be taken and 6.1.2 Apparatus—A means to traverse the specimen under
reported.
the stylus, or the stylus across the specimen, under constant
speed and normal force, shall be provided. Fixtures shall be
5. Significance and Use sufficientlyrigidtowithstandthenormal,lateral,andtangential
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
5.2 This test method is applicable to a wide range of
long as the magnifications are properly calibrated.
materials. These include metals, alloys, and some polymers.
6.1.4 Scratching Force (Optional)—A load cell or similar
The main criteria are that the scratching process produces a
force-sensing device can be used to measure the scratching
measurable scratch in the surface being tested without causing
forces generated during sliding.This standard does not specify
catastrophic fracture, spallation, or extensive delamination of
a method for measuring the scratching force, only that the
surface material. Severe damage to the test surface, such that
sensor shall be capable of being calibrated in the direction of
the scratch width is not clearly identifiable or that the edges of
the scratching force and in line with the contact point between
the scratch are chipped or distorted, invalidates the use of this
the stylus and surface.
test method to determine a scratch hardness number. Since the
degreeandtypeofsurfacedamageinamaterialmayvarywith
7. Calibration
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
widthafterthestylushasbeenremovedtocomputethescratch
methodofnormalforcecalibrationshallbestatedinthereport.
hardnessnumber.Therefore,itreflectsthepermanentdeforma-
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
combined elastic and plastic deformation of the surface. stylus tip in the position where the test specimen is located.
G171 − 03 (2017)
7.3 Stylus Traverse Speed—The speed of the stylus across 8.5 Stroke Length and Shape—The stroke length shall be at
the surface s may be calibrated in any suitable manner such as least5mm.Strokesneednotbelinear,butmaybeintheshape
timing the period t required to produce a scratch of length L. of an arc, as in the case of turntable-type scratching apparatus.
Thus:
8.6 Scratching Speed—The scratching speed shall be con-
L
stant along the measured portion of the scratch, and in the
s 5 (1)
-1
t
range of 0.2 to 5.0 mm s .
7.4 Scratching Force Sensor (Optional)—The scratching
8.7 Conducting the Test—Ensure that the instrument is
force sensor shall be calibrated periodically in the direction of
leveled and that the stylus is normal to the test surface while
the scratching force, and as closely as possible in line with the
scratching. Lower the stylus to apply the load on the specimen
point of contact between the stylus and specimen.The interval surface gently to avoid impact damage.Activate the traversing
between calibrations shall be determined by the user to ensure
drive to produce the scratch of desired length. Raise the stylus
accurate readings of scratching force and compensate for any off of the surface. Select another location at least 5 scratch
electronic signal drift.
widths away from the previous scratch and produce another
scratch parallel to the first. Repeat as necessary, but with a
8. Procedure minimum of three (3) scratches per value of the normal force.
Measure the scratch width as described in 8.8.
8.1 Specimen Preparation—The test specimen shall be pre-
8.8 Scratch Width Measurement—Usingameasuringmicro-
pared in such a way as to represent the application of interest
scope or other calibrated magnifying or surface profiling
or polished to facilitate observation and measurement of
system, measure the width of each scratch at three locations
scratch width. A surface may be unsuitable for scratch testing
spaced approximately equally along the length of the scratch.
ifitsroughnessorporosityissuchthattheedgesofthescratch
The width of the scratch shall be determined optically, as
are indistinct or jagged, or if the stylus cannot traverse the
shown by the examples in Fig. 1. Owing to acceleration and
surface without skipping along it or catching in a pocket. In a
deceleration effects, scratch widths should not be measured
polished condition, the surface should be as free as possible
near the ends of the scratch.
from preparation artifacts such as grinding-induced cracks,
gross grinding marks, and grain pull-out. Surface roughnesses
NOTE5—Othermethods,suchassurfaceprofiling,mayproducevalues
of 0.02 to 0.05 µm R (arithmetic average roughness) are
a different from optical measurements. Therefore, to improve consistency,
typical of polished surfaces. Surfaces may be scratch tested in
widths should be measured on enlarged images.
the as-fabricated condition as long as the characteristics of the
8.8.1 Special Considerations in Optical Scratch
scratch do not display the types of artifacts described in this
Measurement—Thecharacteristicsofthesurfacesbeingtested,
paragraph.
such as their roughness, color, degree of light diffusion, extent
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 differen
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.