ASTM B487-20

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: B487 − 85 (Reapproved 2013) B487 − 20
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. A number 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 U.S. Department of Defense.
1. 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 μm. This 0.8 μm. Accuracy will determine the suitability of the method for measuring the thickness of thin coatings.
Accuracy is dependent upon the setup of the microscope and preparation of the sample; 0.8 μm should not be taken as an absolute
and instead as guideline.
1.2.1 Optical microscopes may use digital image capture devices and software to evaluate those images.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. (This is especially applicable to the chemicals cited in Table X2.1.)
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.
2. Referenced Documents
2.1 ASTM Standards:
E3 Guide for Preparation of Metallographic Specimens
3. Summary of Test Method
3.1 This test method consists of cutting out a portion of the test specimen, mounting it, and preparing the mounted cross section
by suitable techniques of grinding, polishing, and etching. The thickness of the cross section is measured with an optical
microscope.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
Methods.
Current edition approved Dec. 1, 2013Nov. 1, 2020. Published December 2013November 2020. Originally approved in 1968. Last previous edition approved in 20072013
as B487 – 85 (2007).(2013). DOI: 10.1520/B0487-85R13.10.1520/B0487-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 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 the ASTM website.
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B487 − 20
NOTE 1—These techniques will be familiar to experienced metallographers, but some guidance is given in Section 5 and in Appendix X1 for less
experienced operators.
4. Significance and Use
4.1 Coating thickness is an important factor in the performance of a coating in service and is usually specified in a coating
specification.
4.2 This method is suitable for acceptance testing.
5. Factors Influencing the Measurement Result
5.1 Surface Roughness—If the coating or its substrate has a rough surface, one or both of the interfaces bounding the coating cross
section may be too irregular to permit accurate measurement. (See X1.4).)
5.2 Taper of Cross Section—If the plane of the cross section is not perpendicular to the plane of the coating, the measured thickness
will be greater than the true thickness. For example, an inclination of 10° to the perpendicular will contribute a 1.5 % error.
5.3 Deformation of the Coating—Detrimental deformation of the coating can be caused by excessive temperature or pressure
during mounting and preparation of cross sections of soft coatings or coatings melting at low temperatures, and also by excessive
abrasion of brittle materials during preparation of cross sections.
5.4 Rounding of Edge of Coating—If the edge of the coating cross section is rounded, that is, if the coating cross section is not
completely flat up to its edges, the true thickness cannot be observed microscopically. Edge rounding can be caused by improper
mounting, grinding, polishing, or etching. It is usually minimized by overplating the test specimen before mounting. (See X1.2.)
5.5 Overplating—Overplating of the test specimen serves to protect the coating edges during preparation of cross sections and thus
to prevent an erroneous measurement. Removal of coating material during surface preparation for overplating can cause a
low-thickness measurement.
5.6 Etching—Optimum etching will produce a clearly defined and narrow dark line at the interface of two metals. Excessive
etching produces a poorly defined or wide line which may result in an erroneous measurement.
5.7 Smearing—Improper polishing may leave one metal smeared over the other metal so as to obscure the true boundary between
the two metals. The apparent boundary may be poorly defined or very irregular instead of straight and well defined. To verify the
absence of smearing, the coating thickness should be measured and the polishing, etching, and thickness measurement repeated.
A significant change in apparent thickness indicates that smearing was probably present during one of the measurements.
5.8 Magnification—For any given coating thickness, measurement errors generally increase with decreasing magnification. If
possible, the magnification should be chosen so that the field of view is between 1.5 and 3 × the coating thickness.
5.9 Calibration of Stage Micrometer—Any error in calibration of the stage micrometer will be reflected in the measurement of the
specimen. Errors of several percent are not unrealistic unless the scale has been calibrated or has been certified by a responsible
supplier. The distance between two lines of a stage micrometer used for the calibration shall be 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 calibrated. A generally satisfactory means
of calibration is to assume that the stated length of the full scale is correct, to measure each subdivision with a filar micrometer,
and to calculate the length of each subdivision by simple proportion.
5.10 Calibration of Micrometer Eyepiece : Eyepiece:
5.10.1 A filar micrometer eyepiece generally provides the most satisfactory means of making the measurement of the specimen.
The measurement will be no more accurate than the calibration of the eyepiece. As calibration is operator dependent, the eyepiece
shall be calibrated by the person making the measurement.
5.10.2 Repeated calibrations of the micrometer eyepiece can be reasonably expected to have a spread of less than 1 %.
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5.10.3 Some image-splitting micrometer eyepieces have a nonlinearity that introduces an error of up to 1 % for short measurement
distances.
5.11 Alignment—Errors can be introduced by backlash in the movement of the micrometer eyepiece. If the final motion during
alignment of the hairline is always made in the same direction, this error will be eliminated.
5.12 Uniformity of Magnification—Because the magnification may not be uniform over the entire field, errors can occur if both
the calibration and the measurement are not made over the same portion of the field with the measured boundaries centered about
the optical axis.
5.13 Lens Quality—Lack of sharpness of the image contributes to the uncertainty of the measurement. Poor quality lenses could
preclude accurate measurements. Sometimes image sharpness can be improved by using monochromatic light.
5.14 Orientation of Eyepiece—The movement of the hairline of the eyepiece for alignment has to be perpendicular to the
boundaries of the coating cross section. For example, 10° misalignment will contribute a 1.5 % error.
5.15 Tube Length—A change in the tube length of the microscope causes a change in magnification, and if this change occurs
between the time of calibration and the time of measurement, the measurement will be in error. A change in tube length may occur
when the eyepiece is repositioned within the tube, when the focus of the eyepiece tube is changed, and, for some microscopes,
when the fine focus is adjusted or the interpupillary distance for binoculars is changed.
5.16 Calibration and Setup of Camera System and Measurement Software—If included as part of the measurement system, the
camera system may have the same errors as the calibration of the microscope eyepiece.
6. Preparation of Cross Sections
6.1 Prepare, mount, polish, and etch the specimen so that:
6.1.1 The cross section is perpendicular to the coating;
6.1.2 The surface is flat and the entire width of the coating image is simultaneously in focus at the magnification used for the
measurement;
6.1.3 All material deformed by cutting or cross sectioning is removed.removed;
6.1.4 The boundaries of the coating cross section are sharply defined by no more than contrasting appearance or by a narrow,
well-defined line.
NOTE 2—Further guidance is given in Appendix X1. Some typical etchants are described in Appendix X2.
7. Procedure
7.1 Give appropriate attention to the factors listed in Section 5 and Appendix X1.
7.2 Calibrate the microscope and its measuring device with a certified or calibrated stage micrometer.
7.3 Measure the width of the image of the coating cross section at no less than five points distributed along a length of the
microsection, and calculate the arithmetic meanaverage of the measurements as well as the standard deviation (see 8.1.5, 8.1.6and
, and 8.1.68.1.7).
8. Test Report
8.1 The test report shall include the following information:
8.1.1 The date of test;
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8.1.2 The number and title of this test method;
8.1.3 The identification of the test specimens;
8.1.4 The location on the coated item at which the cross section was made;
8.1.5 The measured thickness, in micrometres (millimetres if greater than 1 mm) at each point (7.3), and the length of section over
which the measurements were distributed;
8.1.6 The local thickness, that is, t
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