ASTM E2109-01(2007)
(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 E 1920 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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Standards Content (Sample)
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Designation: E2109 − 01(Reapproved 2007)
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 3.2.1 halo effect—unwanted detection of the perimeter of
one phase (due to a shared gray value at the phase boundary)
1.1 These test methods cover procedures to perform poros-
when setting the detection limits of another.
ity ratings on metallographic specimens of thermal sprayed
coatings (TSCs) prepared in accordance with Guide E1920 by
3.2.2 linear detachment, n—a region within a TSC in which
direct comparison to standard images and via the use of two successively deposited splats of coating material have not
automatic image analysis equipment. metallurgically bonded.
1.2 These test methods deal only with recommended mea- 3.2.3 porosity, n—cavity type discontinuities (voids) or
suring methods and nothing in them should be construed as
linear detachments within a sprayed coating.
defining or establishing limits of acceptability for any mea-
3.2.4 splat, n—an individual globule of thermal sprayed
sured value of porosity.
material that has been deposited on a substrate.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Significance and Use
responsibility of the user of this standard to establish appro-
4.1 TSCs are susceptible to the formation of porosity due to
priate safety and health practices and determine the applica-
a lack of fusion between sprayed particles or the expansion of
bility of regulatory limitations prior to use.
gases generated during the spraying process. The determina-
tion of area percent porosity is important in order to monitor
2. Referenced Documents
the effect of variable spray parameters and the suitability of a
2.1 ASTM Standards:
coating for its intended purpose. Depending on application,
E3 Guide for Preparation of Metallographic Specimens
some or none of this porosity may be tolerable.
E7 Terminology Relating to Metallography
E562 Test Method for Determining Volume Fraction by 4.2 These test methods cover the determination of the area
Systematic Manual Point Count percentage porosity of TSCs. Method A is a manual, direct
E1245 Practice for Determining the Inclusion or Second- comparison method utilizing the seven standard images in
Phase Constituent Content of Metals byAutomatic Image Figs. 1-7 which depict typical distributions of porosity in
Analysis TSCs.MethodBisanautomatedtechniquerequiringtheuseof
E1920 Guide for Metallographic Preparation of Thermal a computerized image analyzer.
Sprayed Coatings
4.3 These methods quantify area percent porosity only on
the basis of light reflectivity from a metallographically pol-
3. Terminology
ished cross section. See Guide E1920 for recommended
3.1 Definitions—For definitions of terms used in these test
metallographic preparation procedures.
methods refer to Terminology E7.
4.4 The person using these test methods must be familiar
3.2 Definitions of Terms Specific to This Standard:
with the visual features of TSCs and be able to determine
differences between inherent porosity and oxides. The indi-
This test method is under the jurisdiction of ASTM Committee E04 on
vidual must be aware of the possible types of artifacts that may
Metallography and is the direct responsibility of Subcommittee E04.14 on Quanti-
be created during sectioning and specimen preparation, for
tative Metallography.
example, pullouts and smearing, so that results are reported
Current edition approved May 1, 2007. Published May 2007. Originally
only on properly prepared specimens. Examples of properly
approved in 2000. Last previous edition approved in 2001 as E2109 – 01. DOI:
10.1520/E2109-01R07.
preparedspecimensareshowninFigs.8-10.Iftherearedoubts
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
as to the integrity of the specimen preparation it is suggested
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
that other means be used to confirm microstructural features.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. This may include energy dispersive spectroscopy (EDS),
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2109 − 01 (2007)
FIG. 1 — 0.5 % Porosity
FIG. 2 — 1.0 % Porosity
wavelength dispersive spectroscopy (WDS) or cryogenic frac- suitable objectives and capable of projecting an image onto a
ture of the coating followed by analysis of the fractured
groundglassviewingscreen,videomonitororimagerecording
surfaces with a scanning electron microscope (SEM).
media, such as film or video prints.
5. Apparatus
5.2 Test Method B—Test Method B requires a reflected light
metallurgical microscope, upright or inverted, equipped with
5.1 Test Method A—Test MethodArequires a reflected light
suitable objectives and interfaced to a video/digital image
metallurgical microscope, upright or inverted, equipped with
E2109 − 01 (2007)
FIG. 3 — 2.0 % Porosity
FIG. 4 — 5.0 % Porosity
capture and analysis system. The microscope may be equipped mize contamination of the specimen surface by dust that may
with an automatic or manual stage. The use of an automated
settle on the polished surface of the specimen and influence the
stage should reduce operator fatigue.
test results. In addition, adequate temperature and humidity
controls must be in place to meet the computer or microscope
5.3 General Considerations—The work area housing the
manufacturer’s specifications.
test equipment must be kept relatively clean. This will mini-
E2109 − 01 (2007)
FIG. 5 — 8.0 % Porosity
FIG. 6 — 10.0 % Porosity
6. Sampling 6.2 Thespecimensaremetallographicallypreparedtoreveal
a polished plane through the test panel or part that is deemed
6.1 Producer and purchaser shall agree upon the location
critical. Specimens should include approximately 25 mm (1.0
and number of test specimens. Specimens may be metallo-
in.) of coating length.
graphically sectioned from actual production pieces or from
test panels comprised of representative substrates with identi- 6.3 Multiple specimens may be selected to determine the
cal production spraying parameters. homogeneity of the coating sprayed on the test panel or part.
E2109 − 01 (2007)
FIG. 7 — 15.0 % Porosity
NOTE 1—V = void, O = oxide, L = linear detachment
FIG. 8 Ni/Al TSC—500X
For example, one may choose to sample from top-middle- 7.2 Generalmetallographicspecimenpreparationguidelines
bottom or edge-center-edge locations. and recommendations are given in Practice E3; however,
manual metallographic preparation methods are not recom-
7. Specimen Preparation
mended for TSCs.
7.1 Incorrect metallographic preparation of thermal sprayed
7.3 Use of automatic grinding and polishing equipment is
specimens may cause damage to the coating or produce
recommended. Specific information regarding the preparation
artifacts on the polished surface that may lead to biased
of TSCs using automated techniques is addressed in Guide
analytical results. The polished surface must reveal a clear
E1920.
distinction between inherent porosity, foreign matter, scratches
and oxides. Polishing must not alter the true appearance of the 7.4 Damage to a brittle, porous TSC during specimen
inherent porosity by excessive relief, pitting pullout, or smear- preparation is minimized when the specimen is vacuum im-
ing. pregnated with a low viscosity epoxy. The epoxy mounting
E2109 − 01 (2007)
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
compoundfillsthesurfaceconnectedporosityandaddssupport 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 8.1.1 This test method utilizes the images in Figs. 1-7 for
3,4
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 specimen. Each figure has been assigned a value representing
color when viewed with the appropriate light microscopy varying degrees of porosity.
technique. This can eliminate any ambiguities concerning
8.1.2 Place the properly prepared specimen on the micro-
oxide content or pull-outs. Excitation and emission filters,
scope stage and divert the image to a ground glass viewing
darkfield illumination or polarized light may be required to
screen or video monitor. Alternately, it may be recorded as a
reveal the color created by the dye or pigment. Consult the hard copy print.
manufacturer’s directions for the proper use of these materials.
8.1.3 Select a magnification that allows resolution of the
voids and best fills the screen with the entire coating thickness.
Often, a compromise must be reached whereby the entire
Street, K.W. and Leonhardt, T.A., “Fluorescence Microscopy for the Charac-
coatingthicknessisnotvisiblebutareductioninmagnification
terization of Structural Integrity,” NASA Technical Memorandum 105253, 1991.
would jeopardize the resolution of voids. It is more important
Geary, A.R., “Metallographic Evaluation of Thermal Spray Coatings,” Micro-
to resolve all voids that contribute significantly to the total
structural Science,Vol19,D.A.Wheeler,et.al.,eds.,IMSandASMIntl.,Materials
Park, OH, 1992, pp. 637–650. porosity area percentage. During this analysis the operator
E2109 − 01 (2007)
must be able to distinguish the difference between oxides and 8.2.4 Next threshold the po
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