ASTM E2109-01(2021)

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: E2109 − 01 (Reapproved 2021)
Standard Test Methods for
Determining Area Percentage Porosity in Thermal Sprayed
Coatings
This standard is issued under the fixed designation E2109; 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.
1. Scope 3. Terminology
1.1 These test methods cover procedures to perform poros- 3.1 Definitions—For definitions of terms used in these test
ity ratings on metallographic specimens of thermal sprayed methods refer to Terminology E7.
coatings (TSCs) prepared in accordance with Guide E1920 by
3.2 Definitions of Terms Specific to This Standard:
direct comparison to standard images and via the use of
3.2.1 halo effect—unwanted detection of the perimeter of
automatic image analysis equipment.
one phase (due to a shared gray value at the phase boundary)
1.2 These test methods deal only with recommended mea- when setting the detection limits of another.
suring methods and nothing in them should be construed as
3.2.2 linear detachment, n—a region within a TSC in which
defining or establishing limits of acceptability for any mea-
two successively deposited splats of coating material have not
sured value of porosity.
metallurgically bonded.
1.3 This standard does not purport to address all of the
3.2.3 porosity, n—cavity type discontinuities (voids) or
safety concerns, if any, associated with its use. It is the
linear detachments within a sprayed coating.
responsibility of the user of this standard to establish appro-
3.2.4 splat, n—an individual globule of thermal sprayed
priate safety, health, and environmental practices and deter-
material that has been deposited on a substrate.
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
4. Significance and Use
dance with internationally recognized principles on standard-
4.1 TSCs are susceptible to the formation of porosity due to
ization established in the Decision on Principles for the
a lack of fusion between sprayed particles or the expansion of
Development of International Standards, Guides and Recom-
gases generated during the spraying process. The determina-
mendations issued by the World Trade Organization Technical
tion of area percent porosity is important in order to monitor
Barriers to Trade (TBT) Committee.
the effect of variable spray parameters and the suitability of a
2. Referenced Documents
coating for its intended purpose. Depending on application,
2.1 ASTM Standards: some or none of this porosity may be tolerable.
E3 Guide for Preparation of Metallographic Specimens
4.2 These test methods cover the determination of the area
E7 Terminology Relating to Metallography
percentage porosity of TSCs. Method A is a manual, direct
E562 Test Method for Determining Volume Fraction by
comparison method utilizing the seven standard images in
Systematic Manual Point Count
Figs. 1-7 which depict typical distributions of porosity in
E1245 Practice for Determining the Inclusion or Second-
TSCs.MethodBisanautomatedtechniquerequiringtheuseof
Phase Constituent Content of Metals byAutomatic Image
a computerized image analyzer.
Analysis
4.3 These methods quantify area percent porosity only on
E1920 Guide for Metallographic Preparation of Thermal
the basis of light reflectivity from a metallographically pol-
Sprayed Coatings
ished cross section. See Guide E1920 for recommended
metallographic preparation procedures.
These test methods are under the jurisdiction of ASTM Committee E04 on
Metallography and are the direct responsibility of Subcommittee E04.14 on
4.4 The person using these test methods must be familiar
Quantitative Metallography.
with the visual features of TSCs and be able to determine
Current edition approved Sept. 1, 2021. Published November 2021. Originally
differences between inherent porosity and oxides. The indi-
approved in 2000. Last previous edition approved in 2014 as E2109 – 01(2014).
DOI: 10.1520/E2109-01R21.
vidual must be aware of the possible types of artifacts that may
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
be created during sectioning and specimen preparation, for
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
example, pullouts and smearing, so that results are reported
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. only on properly prepared specimens. Examples of properly
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2109 − 01 (2021)
FIG. 1 — 0.5 % Porosity
FIG. 2 — 1.0 % Porosity
preparedspecimensareshowninFigs.8-10.Iftherearedoubts 5. Apparatus
as to the integrity of the specimen preparation it is suggested
5.1 Test Method A—Test MethodArequires a reflected light
that other means be used to confirm microstructural features.
metallurgical microscope, upright or inverted, equipped with
This may include energy dispersive spectroscopy (EDS),
suitable objectives and capable of projecting an image onto a
wavelength dispersive spectroscopy (WDS) or cryogenic frac-
groundglassviewingscreen,videomonitororimagerecording
ture of the coating followed by analysis of the fractured
media, such as film or video prints.
surfaces with a scanning electron microscope (SEM).
E2109 − 01 (2021)
FIG. 3 — 2.0 % Porosity
FIG. 4 — 5.0 % Porosity
5.2 Test Method B—Test Method B requires a reflected light settle on the polished surface of the specimen and influence the
metallurgical microscope, upright or inverted, equipped with test results. In addition, adequate temperature and humidity
suitable objectives and interfaced to a video/digital image controls must be in place to meet the computer or microscope
capture and analysis system. The microscope may be equipped manufacturer’s specifications.
with an automatic or manual stage. The use of an automated
stage should reduce operator fatigue. 6. Sampling
5.3 General Considerations—The work area housing the 6.1 Producer and purchaser shall agree upon the location
test equipment must be kept relatively clean. This will mini- and number of test specimens. Specimens may be metallo-
mize contamination of the specimen surface by dust that may graphically sectioned from actual production pieces or from
E2109 − 01 (2021)
FIG. 5 — 8.0 % Porosity
FIG. 6 — 10.0 % Porosity
test panels comprised of representative substrates with identi- For example, one may choose to sample from top-middle-
cal production spraying parameters.
bottom or edge-center-edge locations.
6.2 Thespecimensaremetallographicallypreparedtoreveal
7. Specimen Preparation
a polished plane through the test panel or part that is deemed
critical. Specimens should include approximately 25 mm (1.0
7.1 Incorrect metallographic preparation of thermal sprayed
in.) of coating length.
specimens may cause damage to the coating or produce
artifacts on the polished surface that may lead to biased
6.3 Multiple specimens may be selected to determine the
homogeneity of the coating sprayed on the test panel or part. analytical results. The polished surface must reveal a clear
E2109 − 01 (2021)
FIG. 7 — 15.0 % Porosity
NOTE 1—V = void, O = oxide, L = linear detachment
FIG. 8 Ni/Al TSC—500X
distinction between inherent porosity, foreign matter, scratches compoundfillsthesurfaceconnectedporosityandaddssupport
and oxides. Polishing must not alter the true appearance of the to the coating during preparation.
inherent porosity by excessive relief, pitting pullout, or smear-
7.5 Use of a dyed epoxy or fluorescent additive may be
ing.
3,4
helpful in microstructural interpretation . Depending on the
7.2 Generalmetallographicspecimenpreparationguidelines
additive, a treated epoxy will fluoresce or appear as a distinct
and recommendations are given in Practice E3; however,
color when viewed with the appropriate light microscopy
manual metallographic preparation methods are not recom-
technique. This can eliminate any ambiguities concerning
mended for TSCs.
oxide content or pull-outs. Excitation and emission filters,
darkfield illumination or polarized light may be required to
7.3 Use of automatic grinding and polishing equipment is
recommended. Specific information regarding the preparation
of TSCs using automated techniques is addressed in Guide
E1920.
Street, K.W. and Leonhardt, T.A., “Fluorescence Microscopy for the Charac-
terization of Structural Integrity,” NASA Technical Memorandum 105253, 1991.
7.4 Damage to a brittle, porous TSC during specimen
Geary, A.R., “Metallographic Evaluation of Thermal Spray Coatings,” Micro-
preparation is minimized when the specimen is vacuum im-
structural Science,Vol19,D.A.Wheeler,et.al.,eds.,IMSandASMIntl.,Materials
pregnated with a low viscosity epoxy. The epoxy mounting Park, OH, 1992, pp. 637–650.
E2109 − 01 (2021)
NOTE 1—V = void, G = embedded grit, L = linear detachment
FIG. 9 Monel TSC—200X
NOTE 1—V = void, O = oxide, G = embedded grit
FIG. 10 Alloy 625 TSC—200X
reveal the color created by the dye or pigment. Consult the to resolve all voids that contribute significantly to the total
manufacturer’s directions for the proper use of these materials. porosity area percentage. During this analysis the operator
must be able to distinguish the difference between oxides and
8. Test Procedure
epoxy infiltrated into voids.
8.1.4 Compare the image on the screen with Figs. 1-7. The
8.1 Test Method A (Direct Comparison):
8.1.1 This test method utilizes the images in Figs. 1-7 for image of interest and the figures should be approximately the
same size.Aminimum image area of 9 cm by 11 cm (3.5 in. by
comparison to microscopic fields of view on a polished
specimen. Each figure has been assigned a value representing 4.5 in.) is required. This is the image size of a typical 4 in. by
5 in. instant print. One may either mask the viewing screen or
varying degrees of porosity.
8.1.2 Place the properly prepared specimen o
...