ASTM B487-85(2007)
(Test Method)Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section
Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section
SIGNIFICANCE AND USE
Coating thickness is an important factor in the performance of a coating in service and is usually specified in a coating specification.
This method is suitable for acceptance testing.
SCOPE
1.1 This test method covers measurement of the local thickness of metal and oxide coatings by the microscopical examination of cross sections using an optical microscope.
1.2 Under good conditions, when using an optical microscope, the method is capable of giving an absolute measuring accuracy of 0.8 m. This will determine the suitability of the method for measuring the thickness of thin coatings.
1.3 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. (This is especially applicable to the chemicals cited in X2.1.)
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B487 − 85(Reapproved 2007)
Standard Test Method for
Measurement of Metal and Oxide Coating Thickness by
Microscopical Examination of Cross Section
This standard is issued under the fixed designation B487; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 4. Significance and Use
1.1 This test method covers measurement of the local
4.1 Coating thickness is an important factor in the perfor-
thickness of metal and oxide coatings by the microscopical mance of a coating in service and is usually specified in a
examination of cross sections using an optical microscope. coating specification.
1.2 Under good conditions, when using an optical
4.2 This method is suitable for acceptance testing.
microscope, the method is capable of giving an absolute
measuring accuracy of 0.8 µm. This will determine the suit-
5. Factors Influencing the Measurement Result
ability of the method for measuring the thickness of thin
5.1 Surface Roughness—If the coating or its substrate has a
coatings.
rough surface, one or both of the interfaces bounding the
1.3 This standard does not purport to address all of the
coating cross section may be too irregular to permit accurate
safety concerns, if any, associated with its use. It is the
measurement. (See X1.4)
responsibility of the user of this standard to establish appro-
5.2 Taper of Cross Section—Iftheplaneofthecrosssection
priate safety and health practices and determine the applica-
is not perpendicular to the plane of the coating, the measured
bility of regulatory limitations prior to use. (This is especially
thickness will be greater than the true thickness. For example,
applicable to the chemicals cited in Table X2.1.)
an inclination of 10° to the perpendicular will contribute a
1.5% error.
2. Referenced Documents
5.3 Deformation of the Coating—Detrimental deformation
2.1 ASTM Standards:
of the coating can be caused by excessive temperature or
E3Guide for Preparation of Metallographic Specimens
pressure during mounting and preparation of cross sections of
soft coatings or coatings melting at low temperatures, and also
3. Summary of Test Method
by excessive abrasion of brittle materials during preparation of
3.1 This test method consists of cutting out a portion of the
cross sections.
test specimen, mounting it, and preparing the mounted cross
5.4 Rounding of Edge of Coating—Iftheedgeofthecoating
section by suitable techniques of grinding, polishing, and
cross section is rounded, that is, if the coating cross section is
etching.The thicknessofthecrosssectionismeasuredwithan
notcompletelyflatuptoitsedges,thetruethicknesscannotbe
optical microscope.
observed microscopically. Edge rounding can be caused by
NOTE 1—These techniques will be familiar to experienced metallogra-
improper mounting, grinding, polishing, or etching. It is
phersbutsomeguidanceisgiveninSection5andinAppendixX1forless
usually minimized by overplating the test specimen before
experienced operators.
mounting. (See X1.2.)
5.5 Overplating—Overplatingofthetestspecimenservesto
protect the coating edges during preparation of cross sections
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
and thus to prevent an erroneous measurement. Removal of
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.10 on
Test Methods.
coating material during surface preparation for overplating can
Current edition approved March 1, 2007. Published March 2007. Originally
cause a low-thickness measurement.
approved in 1968. Last previous edition approved in 2002 as B487–85 (2002).
DOI: 10.1520/B0487-85R07.
5.6 Etching—Optimum etching will produce a clearly de-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
fined and narrow dark line at the interface of two metals.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Excessive etching produces a poorly defined or wide line
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. which may result in an erroneous measurement.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B487 − 85 (2007)
5.7 Smearing—Improper polishing may leave one metal occurs between the time of calibration and the time of
smearedovertheothermetalsoastoobscurethetrueboundary measurement, the measurement will be in error. A change in
betweenthetwometals.Theapparentboundarymaybepoorly tubelengthmayoccurwhentheeyepieceisrepositionedwithin
defined or very irregular instead of straight and well defined. the tube, when the focus of the eyepiece tube is changed, and,
Toverifytheabsenceofsmearing,thecoatingthicknessshould for some microscopes, when the fine focus is adjusted or the
be measured and the polishing, etching, and thickness mea- interpupillary distance for binoculars is changed.
surement repeated. A significant change in apparent thickness
6. Preparation of Cross Sections
indicates that smearing was probably present during one of the
measurements. 6.1 Prepare, mount, polish, and etch the specimen so that:
6.1.1 The cross section is perpendicular to the coating;
5.8 Magnification—For any given coating thickness, mea-
6.1.2 The surface is flat and the entire width of the coating
surement errors generally increase with decreasing magnifica-
image is simultaneously in focus at the magnification used for
tion.Ifpossible,themagnificationshouldbechosensothatthe
the measurement;
field of view is between 1.5 and 3×the coating thickness.
6.1.3 Allmaterialdeformedbycuttingorcrosssectioningis
5.9 Calibration of Stage Micrometer—Any error in calibra-
removed.
tion of the stage micrometer will be reflected in the measure-
6.1.4 Theboundariesofthecoatingcrosssectionaresharply
ment of the specimen. Errors of several percent are not
definedbynomorethancontrastingappearanceorbyanarrow,
unrealistic unless the scale has been calibrated or has been
well-defined line.
certified by a responsible supplier. The distance between two
NOTE 2—Further guidance is given in Appendix X1. Some typical
lines of a stage micrometer used for the calibration shall be
etchants are described in Appendix X2.
known to within 0.2 µm or 0.1%, whichever is the greater. If
a stage micrometer is not certified for accuracy, it should be
7. Procedure
calibrated. A generally satisfactory means of calibration is to
7.1 GiveappropriateattentiontothefactorslistedinSection
assume that the stated length of the full scale is correct, to
5 and Appendix X1.
measure each subdivision with a filar micrometer, and to
7.2 Calibrate the microscope and its measuring device with
calculate the length of each subdivision by simple proportion.
a certified or calibrated stage micrometer.
5.10 Calibration of Micrometer Eyepiece :
7.3 Measure the width of the image of the coating cross
5.10.1 A filar micrometer eyepiece generally provides the
section at no less than five points distributed along a length of
most satisfactory means of making the measurement of the
the microsection, and calculate the arithmetic mean of the
specimen.The measurement will be no more accurate than the
measurements (see 8.1.5 and 8.1.6).
calibration of the eyepiece. As calibration is operator depen-
dent, the eyepiece shall be calibrated by the person making the
8. Test Report
measurement.
8.1 The test report shall include the following information:
5.10.2 Repeated calibrations of the micrometer eyepiece
8.1.1 The date of test;
can be reasonably expected to have a spread of less than 1%.
8.1.2 The number and title of this test method;
5.10.3 Some image-splitting micrometer eyepieces have a
8.1.3 The identification of the test specimens;
nonlinearity that introduces an error of up to 1% for short
8.1.4 The location on the coated item at which the cross
measurement distances.
section was made;
5.11 Alignment—Errors can be introduced by backlash in
8.1.5 The measured thickness, in micrometres (millimetres
the movement of the micrometer eyepiece. If the final motion
if greater than 1 mm) at each point (7.3), and the length of
during alignment of the hairline is always made in the same
section over which the measurements were distributed;
direction, this error will be eliminated.
8.1.6 The local thickness, that is, the arithmetic mean of the
5.12 Uniformity of Magnification—Because the magnifica-
measured thicknesses;
tion may not be uniform over the entire field, errors can occur
8.1.7 Any deviations from this test method;
if both the calibration and the measurement are not made over
8.1.8 Any factors that might influence interpretation of the
the same portion of the field with the measured boundaries
reported results; and
centered about the optical axis.
8.1.9 The name of the operator and testing laboratory.
5.13 Lens Quality—Lack of sharpness of the image contrib-
9. Precision and Bias
utes to the uncertainty of the measurement. Poor quality lenses
9.1 The microscope and associated equipment, its use, its
could preclude accurate measurements. Sometimes image
calibration, and the method of preparation of the cross section
sharpness can be improved by using monochromatic light.
shall be chosen so as to allow the coating thickness to be
5.14 Orientation of Eyepiece—The movement of the hair-
determinedtowithin1µmor10%,whicheveristhegreater,of
lineoftheeyepieceforalignmenthastobeperpendiculartothe
the actual coating thickne
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