ASTM B748-90(2021)

Standard Test Method for Measurement of Thickness of Metallic Coatings by Measurement of Cross Section with a Scanning Electron Microscope

SIGNIFICANCE AND USE
4.1 This test method is useful for the direct measurement of the thicknesses of metallic coatings and of individual layers of composite coatings, particularly for layers thinner than normally measured with the light microscope.  
4.2 This test method is suitable for acceptance testing.  
4.3 This test method is for the measurement of the thickness of the coating over a very small area and not of the average or minimum thickness per se.  
4.4 Accurate measurements by this test method generally require very careful sample preparation, especially at the greater magnifications.  
4.5 The coating thickness is an important factor in the performance of a coating in service.
SCOPE
1.1 This test method covers the measurement of metallic coating thicknesses by examination of a cross section with a scanning electron microsope (SEM).  
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 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

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 17.040.20 - Properties of surfaces
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.10 - Test Methods

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: B748 − 90 (Reapproved 2021)
Standard Test Method for
Measurement of Thickness of Metallic Coatings by
Measurement of Cross Section with a Scanning Electron
1
Microscope
This standard is issued under the fixed designation B748; 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 4. Significance and Use
1.1 This test method covers the measurement of metallic 4.1 This test method is useful for the direct measurement of
coating thicknesses by examination of a cross section with a the thicknesses of metallic coatings and of individual layers of
scanning electron microsope (SEM). composite coatings, particularly for layers thinner than nor-
mally measured with the light microscope.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 4.2 This test method is suitable for acceptance testing.
standard.
4.3 Thistestmethodisforthemeasurementofthethickness
1.3 This standard does not purport to address all of the
of the coating over a very small area and not of the average or
safety concerns, if any, associated with its use. It is the
minimum thickness per se.
responsibility of the user of this standard to establish appro-
4.4 Accurate measurements by this test method generally
priate safety, health, and environmental practices and deter-
require very careful sample preparation, especially at the
mine the applicability of regulatory limitations prior to use.
greater magnifications.
1.4 This international standard was developed in accor-
4.5 The coating thickness is an important factor in the
dance with internationally recognized principles on standard-
performance of a coating in service.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
5. Equipment
mendations issued by the World Trade Organization Technical
5.1 The scanning electron microscope shall have a resolu-
Barriers to Trade (TBT) Committee.
tion of at least 50 nm. Suitable instruments are available
commercially.
2. Referenced Documents
2
2.1 ASTM Standards:
6. Factors Affecting the Measurement Reliability
E3Guide for Preparation of Metallographic Specimens
6.1 Surface Roughness—If the coating or its substrate is
E766Practice for Calibrating the Magnification of a Scan-
rough relative to the coating thickness, one or both of the
ning Electron Microscope
interfaces bounding the coating cross section may be too
irregular to permit accurate measurement of the average
3. Summary of Test Method
thickness in the field of view.
3.1 A test specimen is cut, ground, and polished for metal-
6.2 Taper of Cross Section—If the plane of the cross section
lographic examination by an SEM of a cross section of the
is not perpendicular to the plane of the coating, the measured
coating. The measurement is made on a conventional micro-
thickness will be greater than the true thickness. For example,
graph or on a photograph of the video waveform signal for a
an inclination of 10° to the perpendicular will contribute a
single scan across the coating.
1.5% error. True thickness, (t), equals measured thickness,
(t ), multiplied by the cosine of the angle of inclination (θ):
m
1
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
t=t ×cos(θ). (See X1.3.2.)
m
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
Test Methods.
6.3 Specimen Tilt—Any tilt of the specimen (plane of the
Current edition approved Oct. 1, 2021. Published November 2021. Originally
cross section) with respect to the SEM beam, may result in an
approvedin1985.Lastpreviouseditionapprovedin2016asB748–90(2016).DOI:
erroneous measurement. The instrument should always be set
10.1520/B0748-90R21.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or for zero tilt.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
6.4 Oblique Measurement—If the thickness measurement is
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. not perpendicular to the plane of the coating, even when there
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