1、Designation: E 2109 01 (Reapproved 2007)Standard Test Methods forDetermining Area Percentage Porosity in Thermal SprayedCoatings1This standard is issued under the fixed designation E 2109; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover procedures to perform poros-ity ratings on metallographic specimens of the
3、rmal sprayedcoatings (TSCs) prepared in accordance with Guide E 1920 bydirect comparison to standard images and via the use ofautomatic image analysis equipment.1.2 These test methods deal only with recommended mea-suring methods and nothing in them should be construed asdefining or establishing lim
4、its of acceptability for any mea-sured value of porosity.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bili
5、ty of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to MetallographyE 562 Test Method for Determining Volume Fraction bySystematic Manual Point CountE 1245 Practice for Determining the Inclus
6、ion or Second-Phase Constituent Content of Metals by Automatic ImageAnalysisE 1920 Guide for Metallographic Preparation of ThermalSprayed Coatings3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods refer to Terminology E7.3.2 Definitions of Terms Specific to This Standard
7、:3.2.1 halo effectunwanted detection of the perimeter ofone phase (due to a shared gray value at the phase boundary)when setting the detection limits of another.3.2.2 linear detachment, na region within a TSC in whichtwo successively deposited splats of coating material have notmetallurgically bonde
8、d.3.2.3 porosity, ncavity type discontinuities (voids) orlinear detachments within a sprayed coating.3.2.4 splat, nan individual globule of thermal sprayedmaterial that has been deposited on a substrate.4. Significance and Use4.1 TSCs are susceptible to the formation of porosity due toa lack of fusi
9、on between sprayed particles or the expansion ofgases generated during the spraying process. The determina-tion of area percent porosity is important in order to monitorthe effect of variable spray parameters and the suitability of acoating for its intended purpose. Depending on application,some or
10、none of this porosity may be tolerable.4.2 These test methods cover the determination of the areapercentage porosity of TSCs. Method A is a manual, directcomparison method utilizing the seven standard images inFigs. 1-7 which depict typical distributions of porosity inTSCs. Method B is an automated
11、technique requiring the use ofa computerized image analyzer.4.3 These methods quantify area percent porosity only onthe basis of light reflectivity from a metallographically pol-ished cross section. See Guide E 1920 for recommendedmetallographic preparation procedures.4.4 The person using these test
12、 methods must be familiarwith the visual features of TSCs and be able to determinedifferences between inherent porosity and oxides. The indi-vidual must be aware of the possible types of artifacts that maybe created during sectioning and specimen preparation, forexample, pullouts and smearing, so th
13、at results are reportedonly on properly prepared specimens. Examples of properlyprepared specimens are shown in Figs. 8-10. If there are doubtsas to the integrity of the specimen preparation it is suggestedthat other means be used to confirm microstructural features.1This test method is under the ju
14、risdiction of ASTM Committee E04 onMetallography and is the direct responsibility of Subcommittee E04.14 on Quanti-tative Metallography.Current edition approved May 1, 2007. Published May 2007. Originallyapproved in 2000. Last previous edition approved in 2001 as E 2109 01.2For referenced ASTM stand
15、ards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P
16、A 19428-2959, United States.This may include energy dispersive spectroscopy (EDS),wavelength dispersive spectroscopy (WDS) or cryogenic frac-ture of the coating followed by analysis of the fracturedsurfaces with a scanning electron microscope (SEM).FIG. 1 0.5 % PorosityFIG. 2 1.0 % PorosityE 2109 01
17、 (2007)25. Apparatus5.1 Test Method ATest MethodArequires a reflected lightmetallurgical microscope, upright or inverted, equipped withsuitable objectives and capable of projecting an image onto aground glass viewing screen, video monitor or image recordingmedia, such as film or video prints.5.2 Tes
18、t Method BTest Method B requires a reflected lightmetallurgical microscope, upright or inverted, equipped withsuitable objectives and interfaced to a video/digital imagecapture and analysis system. The microscope may be equippedwith an automatic or manual stage. The use of an automatedstage should r
19、educe operator fatigue.5.3 General ConsiderationsThe work area housing thetest equipment must be kept relatively clean. This will mini-mize contamination of the specimen surface by dust that maysettle on the polished surface of the specimen and influence theFIG. 3 2.0 % PorosityFIG. 4 5.0 % Porosity
20、E 2109 01 (2007)3test results. In addition, adequate temperature and humiditycontrols must be in place to meet the computer or microscopemanufacturers specifications.6. Sampling6.1 Producer and purchaser shall agree upon the locationand number of test specimens. Specimens may be metallo-graphically
21、sectioned from actual production pieces or fromtest panels comprised of representative substrates with identi-cal production spraying parameters.6.2 The specimens are metallographically prepared to reveala polished plane through the test panel or part that is deemedcritical. Specimens should include
22、 approximately 25 mm (1.0in.) of coating length.FIG. 5 8.0 % PorosityFIG. 6 10.0 % PorosityE 2109 01 (2007)46.3 Multiple specimens may be selected to determine thehomogeneity of the coating sprayed on the test panel or part.For example, one may choose to sample from top-middle-bottom or edge-center-
23、edge locations.7. Specimen Preparation7.1 Incorrect metallographic preparation of thermal sprayedspecimens may cause damage to the coating or produceartifacts on the polished surface that may lead to biasedanalytical results. The polished surface must reveal a cleardistinction between inherent poros
24、ity, foreign matter, scratchesand oxides. Polishing must not alter the true appearance of theinherent porosity by excessive relief, pitting pullout, or smear-ing.7.2 General metallographic specimen preparation guidelinesand recommendations are given in Practice E3; however,manual metallographic prep
25、aration methods are not recom-mended for TSCs.7.3 Use of automatic grinding and polishing equipment isrecommended. Specific information regarding the preparationof TSCs using automated techniques is addressed in GuideE 1920.7.4 Damage to a brittle, porous TSC during specimenpreparation is minimized
26、when the specimen is vacuum im-pregnated with a low viscosity epoxy. The epoxy mountingcompound fills the surface connected porosity and adds supportto the coating during preparation.FIG. 7 15.0 % PorosityNOTE 1V = void, O = oxide, L = linear detachmentFIG. 8 Ni/Al TSC500XE 2109 01 (2007)57.5 Use of
27、 a dyed epoxy or fluorescent additive may behelpful in microstructural interpretation3,4. Depending on theadditive, a treated epoxy will fluoresce or appear as a distinctcolor when viewed with the appropriate light microscopytechnique. This can eliminate any ambiguities concerningoxide content or pu
28、ll-outs. Excitation and emission filters,darkfield illumination or polarized light may be required toreveal the color created by the dye or pigment. Consult themanufacturers directions for the proper use of these materials.8. Test Procedure8.1 Test Method A (Direct Comparison):8.1.1 This test method
29、 utilizes the images in Figs. 1-7 forcomparison to microscopic fields of view on a polishedspecimen. Each figure has been assigned a value representingvarying degrees of porosity.8.1.2 Place the properly prepared specimen on the micro-scope stage and divert the image to a ground glass viewingscreen
30、or video monitor. Alternately, it may be recorded as ahard copy print.8.1.3 Select a magnification that allows resolution of thevoids and best fills the screen with the entire coating thickness.Often, a compromise must be reached whereby the entirecoating thickness is not visible but a reduction in
31、magnificationwould jeopardize the resolution of voids. It is more importantto resolve all voids that contribute significantly to the totalporosity area percentage. During this analysis the operatormust be able to distinguish the difference between oxides andepoxy infiltrated into voids.3Street, K.W.
32、 and Leonhardt, T.A., “Fluorescence Microscopy for the Charac-terization of Structural Integrity,” NASA Technical Memorandum 105253, 1991.4Geary, A.R., “Metallographic Evaluation of Thermal Spray Coatings,” Micro-structural Science, Vol 19, D.A. Wheeler, et. al., eds., IMS andASM Intl., MaterialsPar
33、k, OH, 1992, pp. 637650.NOTE 1V = void, G = embedded grit, L = linear detachmentFIG. 9 Monel TSC200XNOTE 1V = void, O = oxide, G = embedded gritFIG. 10 Alloy 625 TSC200XE 2109 01 (2007)68.1.4 Compare the image on the screen with Figs. 1-7. Theimage of interest and the figures should be approximately
34、 thesame size. A minimum image area of 9 by 11 cm (3.5 by 4.5in.) is required. This is the image size of a typical 4 by 5 in.instant print. One may either mask the viewing screen or alterthe size of the figures (enlarge on a copier for instance) toachieve this requirement.8.1.5 Record the value of t
35、he figure that most resembles theimage of the present field of view. If the image does not closelymatch a figure, it may be rounded to the nearest whole numberbetween figures values. For example, if the porosity in thecurrent field of view falls between Figs. 4 and 5 representingporosity values of 5
36、.0 % and 8.0 % respectively, a 6.0 or 7.0may be recorded as appropriate.8.1.6 If a field of view exhibits less than 0.5 % porosity, asdepicted in Fig. 1, it shall be reported as 0.5. These fieldsshould be considered zero when computing the average areapercentage porosity for the specimen.8.1.7 If an
37、y single field has more porosity present thandepicted in Fig. 7 that field shall be recorded as Outside Range(OR) along with a numerical value denoting the operatorsestimate of the area percentage porosity. For example, a fieldthought to contain 25.0 % porosity should be recorded as:OR-25.8.1.8 Usin
38、g the same magnification, continue the procedureoutlined above and record a value for at least ten random orcontiguous fields. Do not overlap or re-measure fields of view.8.1.9 If photomicrographs are used for comparisons, at leastten prints representing distinct fields of view at the samemagnificat
39、ion are required. Do not overlap or re-photographfields of view.8.1.10 The point counting techniques in E 562 may beemployed if direct comparison proves too difficult or tocorroborate a Test Method A result.8.2 Test Method B (Image Analysis):8.2.1 Place the properly prepared specimen on the micro-sc
40、ope stage and direct the image to the viewing screen.Guidelines for setting up a microscope and image analysissystem including thresholding and interferences are given inPractice E 1245.8.2.2 Select a magnification that allows resolution of thevoids and best fills the screen with the entire coating
41、thickness.If some of the substrate or mount is visible on the screen itmust be masked in a manner that eliminates it from the totalarea used to calculate the area percentage porosity. Often, acompromise must be reached whereby the entire coatingthickness is not visible but a reduction in magnificati
42、on wouldjeopardize the detection of significantly sized voids. It is moreimportant to resolve all voids that contribute significantly to thetotal porosity area percentage.8.2.3 Once the best magnification has been determined,adjust the microscopes aperture and field diaphragms for thebest resolution
43、 and contrast, saturate the light according tomanufacturers instructions for the image analysis system and,if necessary, incorporate the appropriate shading corrector forthe objective in use.8.2.4 Next threshold the porosity in the field of view.Thresholding, or image segmentation, is the process of
44、 select-ing the appropriate range of gray values used to create a binaryimage. When thresholding the porosity, take care not to detectany oxides or other features close to the porositys thresholdlimits.8.2.5 Often, coating/oxide interfaces will begin to be de-tected when thresholding the porosity. T
45、his is referred to as thehalo effect. To minimize this interference a binary editingfunction, such as masking, sieving or chord sizing may beused. Again, refer to the manufacturers instructions for waysto eliminate small, unwanted features.8.2.6 Alternately, a common binary image processing func-tio
46、n known as opening may be used. Opening is a two stepprocess (erosion and dilation) in which a layer of pixels isremoved from the perimeter of each object represented in thebinary image and then a layer of pixels is added back to theperimeter of any remaining objects. The net effect is that verysmal
47、l and very thin objects can be entirely removed from theimage while large objects will remain and retain near originaldimensions.8.2.7 Care must be taken not to significantly alter the areapercentage porosity whenever employing any binary imageprocessing functions.8.2.8 The use of alternative micros
48、copy techniques, forexample, darkfield, polarized light or fluorescence, is permittedto facilitate thresholding of porosity that has been filled with adyed or treated epoxy.8.2.9 After a thresholding and image processing routine hasbeen developed, check several fields of view to ensure that theporos
49、ity detection is correct.8.2.10 Analyze at least 20 separate fields of view either in arandom pattern or contiguously being careful not to overlap aprevious field.8.2.11 Do not incorporate any routine or technique thateliminates coating features that are touching the border of animage or guard frame.8.2.12 If specimens are to be compared, one should use thesame objective lens and instrument settings.9. Statistical Analysis9.1 No determination of porosity can be an exact measure-ment. Many specimens vary measurably in porosity from onefield
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