1、Designation: E2109 01 (Reapproved 2014)Standard Test Methods forDetermining Area Percentage Porosity in Thermal SprayedCoatings1This standard is issued under the fixed designation E2109; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 therma
3、l sprayedcoatings (TSCs) prepared in accordance with Guide E1920 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 limits
4、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-bility o
5、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to MetallographyE562 Test Method for Determining Volume Fraction bySystematic Manual Point CountE1245 Practice for Determining the Inclusion or
6、 Second-Phase Constituent Content of Metals by Automatic ImageAnalysisE1920 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:3.2.1
7、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 bonded.3.2.3
8、 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 fusion betw
9、een 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 none of
10、 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 techniq
11、ue 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 E1920 for recommendedmetallographic preparation procedures.4.4 The person using these test methods
12、 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 that resul
13、ts 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.This may include energy dispersive spectr
14、oscopy (EDS),1These test methods are under the jurisdiction of ASTM Committee E04 onMetallography and are the direct responsibility of Subcommittee E04.14 onQuantitative Metallography.Current edition approved May 1, 2014. Published September 2014. Originallyapproved in 2000. Last previous edition ap
15、proved in 2007 as E2109 01(2007).DOI: 10.1520/E2109-01R14.2For referenced ASTM standards, 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.Cop
16、yright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1wavelength dispersive spectroscopy (WDS) or cryogenic frac-ture of the coating followed by analysis of the fracturedsurfaces with a scanning electron microscope (SEM).5. Apparatus5.1 Test M
17、ethod ATest Method A requires 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 Test Method BTest Method B requ
18、ires a reflected lightmetallurgical microscope, upright or inverted, equipped withsuitable objectives and interfaced to a video/digital imageFIG. 1 0.5 % PorosityFIG. 2 1.0 % PorosityE2109 01 (2014)2capture and analysis system. The microscope may be equippedwith an automatic or manual stage. The use
19、 of an automatedstage should reduce 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 thetest results
20、. In addition, adequate temperature and humiditycontrols must be in place to meet the computer or microscopemanufacturers specifications.FIG. 3 2.0 % PorosityFIG. 4 5.0 % PorosityE2109 01 (2014)36. Sampling6.1 Producer and purchaser shall agree upon the locationand number of test specimens. Specimen
21、s may be metallo-graphically 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 deemedcriti
22、cal. Specimens should include approximately 25 mm (1.0in.) of coating length.6.3 Multiple specimens may be selected to determine thehomogeneity of the coating sprayed on the test panel or part.FIG. 5 8.0 % PorosityFIG. 6 10.0 % PorosityE2109 01 (2014)4For example, one may choose to sample from top-m
23、iddle-bottom or edge-center-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 cleardistin
24、ction between inherent porosity, 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; howeve
25、r,manual metallographic preparation 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 GuideE1920.7.4 Damage to a brittle, porous TSC during specim
26、enpreparation is minimized when the specimen is vacuum im-pregnated with a low viscosity epoxy. The epoxy mountingFIG. 7 15.0 % PorosityNOTE 1V = void, O = oxide, L = linear detachmentFIG. 8 Ni/Al TSC500XE2109 01 (2014)5compound fills the surface connected porosity and adds supportto the coating dur
27、ing preparation.7.5 Use of 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 con
28、cerningoxide content or pull-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 Comparis
29、on):8.1.1 This test method 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 g
30、round glass viewingscreen 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 v
31、isible but a reduction in 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 operator3Street, K.W. and Leonhardt, T.A., “Fluorescence Microscopy for the Charac-te
32、rization 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., MaterialsPark, OH, 1992, pp. 637650.NOTE 1V = void, G = embedded grit, L = l
33、inear detachmentFIG. 9 Monel TSC200XNOTE 1V = void, O = oxide, G = embedded gritFIG. 10 Alloy 625 TSC200XE2109 01 (2014)6must be able to distinguish the difference between oxides andepoxy infiltrated into voids.8.1.4 Compare the image on the screen with Figs. 1-7. Theimage of interest and the figure
34、s should be approximately 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.
35、1.5 Record the value of the 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 represe
36、ntingporosity values of 5.0 % 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
37、 the specimen.8.1.7 If any 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 rec
38、orded as:OR-25.8.1.8 Using 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 v
39、iew at the samemagnification are required. Do not overlap or re-photographfields of view.8.1.10 The point counting techniques in E562 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
40、specimen on the micro-scope 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 E1245.8.2.2 Select a magnification that allows resolution of thevoids and best fills the screen w
41、ith the entire coating 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 r
42、eduction in magnification 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
43、 for thebest resolution 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 segmenta
44、tion, is the process of 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 thres
45、holding the porosity. This 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 im
46、age processing func-tion 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
47、effect is that verysmall 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 us
48、e of alternative microscopy 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
49、to ensure that theporosity 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
