ASTM E2109-00
(Test Method)Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings
Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings
SCOPE
1.1 These test methods cover procedures to perform porosity ratings on metallographic specimens of thermal sprayed coatings (TSCs) prepared in accordance with Guide E1920 by direct comparison to standard images and via the use of automatic image analysis equipment.
1.2 These test methods deal only with recommended measuring methods and nothing in them should be construed as defining or establishing limits of acceptability for any measured value of porosity.
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.
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Designation: E 2109 – 00
Test Methods for
Determining Area Percentage Porosity in Thermal Sprayed
Coatings
This standard is issued under the fixed designation E 2109; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope linear detachments within a sprayed coating.
3.2.4 splat, n—an individual globule of thermal sprayed
1.1 These test methods cover procedures to perform poros-
material that has been deposited on a substrate.
ity ratings on metallographic specimens of thermal sprayed
coatings (TSCs) prepared in accordance with Guide E 1920 by
4. Significance and Use
direct comparison to standard images and via the use of
4.1 TSCs are susceptible to the formation of porosity due to
automatic image analysis equipment.
a lack of fusion between sprayed particles or the expansion of
1.2 These test methods deal only with recommended mea-
gases generated during the spraying process. The determina-
suring methods and nothing in them should be construed as
tion of area percent porosity is important in order to monitor
defining or establishing limits of acceptability for any mea-
the effect of variable spray parameters and the suitability of a
sured value of porosity.
coating for its intended purpose. Depending on application,
1.3 This standard does not purport to address all of the
some or none of this porosity may be tolerable.
safety concerns, if any, associated with its use. It is the
4.2 These test methods cover the determination of the area
responsibility of the user of this standard to establish appro-
percentage porosity of TSCs. Method A is a manual, direct
priate safety and health practices and determine the applica-
comparison method utilizing the seven standard images in
bility of regulatory limitations prior to use.
Figs. 1-7 which depict typical distributions of porosity in
2. Referenced Documents TSCs. Method B is an automated technique requiring the use of
a computerized image analyzer.
2.1 ASTM Standards:
2 4.3 These methods quantify area percent porosity only on
E 3 Practice for Preparation of Metallographic Specimens
the basis of light reflectivity from a metallographically pol-
E 7 Terminology Relating to Metallography
ished cross section. See Guide E 1920 for recommended
E 562 Practice for Determining Volume Fraction by Sys-
metallographic preparation procedures.
tematic Point Count
4.4 The person using these test methods must be familiar
E 1245 Practice for Determining the Inclusion Content or
with the visual features of TSCs and be able to determine
Second-Phase Constituent Content of Metals by Automatic
differences between inherent porosity and oxides. The indi-
Image Analysis
vidual must be aware of the possible types of artifacts that may
E 1920 Guide for Metallographic Preparation of Thermal
be created during sectioning and specimen preparation, for
Sprayed Coatings
example, pullouts and smearing, so that results are reported
3. Terminology
only on properly prepared specimens. Examples of properly
prepared specimens are shown in Figs. 8-10. If there are doubts
3.1 Definitions—For definitions of terms used in these test
as to the integrity of the specimen preparation it is suggested
methods refer to Terminology E 7.
that other means be used to confirm microstructural features.
3.2 Definitions of Terms Specific to This Standard:
This may include energy dispersive spectroscopy (EDS),
3.2.1 halo effect—unwanted detection of the perimeter of
wavelength dispersive spectroscopy (WDS) or cryogenic frac-
one phase (due to a shared gray value at the phase boundary)
ture of the coating followed by analysis of the fractured
when setting the detection limits of another.
surfaces with a scanning electron microscope (SEM).
3.2.2 linear detachment, n—a region within a TSC in which
two successively deposited splats of coating material have not
5. Apparatus
metallurgically bonded.
5.1 Test Method A—Test Method A requires a reflected light
3.2.3 porosity, n—cavity type discontinuities (voids) or
metallurgical microscope, upright or inverted, equipped with
suitable objectives and capable of projecting an image onto a
This test method is under the jurisdiction of ASTM Committee E04 on
ground glass viewing screen, video monitor or image recording
Metallography and is the direct responsibility of Subcommittee E04.14 on Quanti-
media, such as film or video prints.
tative Metallography.
Current edition approved Sept. 10, 2000. Published January 2001.
5.2 Test Method B—Test Method B requires a reflected light
Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 2109
FIG. 1 — 0.5 % Porosity
FIG. 2 — 1.0 % Porosity
metallurgical microscope, upright or inverted, equipped with test equipment must be kept relatively clean. This will mini-
suitable objectives and interfaced to a video/digital image mize contamination of the specimen surface by dust that may
capture and analysis system. The microscope may be equipped settle on the polished surface of the specimen and influence the
with an automatic or manual stage. The use of an automated test results. In addition, adequate temperature and humidity
stage should reduce operator fatigue. controls must be in place to meet the computer or microscope
5.3 General Considerations—The work area housing the manufacturer’s specifications.
E 2109
FIG. 3 — 2.0 % Porosity
FIG. 4 — 5.0 % Porosity
6. Sampling a polished plane through the test panel or part that is deemed
critical. Specimens should include approximately 25 mm (1.0
6.1 Producer and purchaser shall agree upon the location
in.) of coating length.
and number of test specimens. Specimens may be metallo-
graphically sectioned from actual production pieces or from 6.3 Multiple specimens may be selected to determine the
test panels comprised of representative substrates with identi- homogeneity of the coating sprayed on the test panel or part.
cal production spraying parameters. For example, one may choose to sample from top-middle-
6.2 The specimens are metallographically prepared to reveal bottom or edge-center-edge locations.
E 2109
FIG. 5 — 8.0 % Porosity
FIG. 6 — 10.0 % Porosity
7. Specimen Preparation inherent porosity by excessive relief, pitting pullout, or smear-
ing.
7.1 Incorrect metallographic preparation of thermal sprayed
7.2 General metallographic specimen preparation guidelines
specimens may cause damage to the coating or produce
and recommendations are given in Practice E 3; however,
artifacts on the polished surface that may lead to biased
manual metallographic preparation methods are not recom-
analytical results. The polished surface must reveal a clear
mended for TSCs.
distinction between inherent porosity, foreign matter, scratches
and oxides. Polishing must not alter the true appearance of the 7.3 Use of automatic grinding and polishing equipment is
E 2109
FIG. 7 — 15.0 % Porosity
NOTE 1—V = void, O = oxide, L = linear detachment
FIG. 8 Ni/Al TSC—500X
recommended. Specific information regarding the preparation color when viewed with the appropriate light microscopy
of TSCs using automated techniques is addressed in Guide technique. This can eliminate any ambiguities concerning
E 1920. oxide content or pull-outs. Excitation and emission filters,
7.4 Damage to a brittle, porous TSC during specimen darkfield illumination or polarized light may be required to
preparation is minimized when the specimen is vacuum im- reveal the color created by the dye or pigment. Consult the
pregnated with a low viscosity epoxy. The epoxy mounting manufacturer’s directions for the proper use of these materials.
compound fills the surface connected porosity and adds support
8. Test Procedure
to the coating during preparation.
8.1 Test Method A (Direct Comparison):
7.5 Use of a dyed epoxy or fluorescent additive may be
,
3 4
8.1.1 This test method utilizes the images in Figs. 1-7 for
helpful in microstructural interpretation . Depending on the
comparison to microscopic fields of view on a polished
additive, a treated epoxy will fluoresce or appear as a distinct
Geary, A.R., “Metallographic Evaluation of Thermal Spray Coatings,” Micro-
Street, K.W. and Leonhardt, T.A., “Fluorescence Microscopy for the Charac- structural Science, Vol 19, D. A. Wheeler, et. al., eds., IMS and ASM Intl., Materials
terization of Structural Integrity,” NASA Technical Memorandum 105253, 1991. Park, OH, 1992, pp. 637–650.
E 2109
NOTE 1—V = void, G = embedded grit, L = linear detachment
FIG. 9 Monel TSC—200X
NOTE 1—V = void, O = ox
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