1、Designation: B 487 85 (Reapproved 2007)Standard Test Method forMeasurement of Metal and Oxide Coating Thickness byMicroscopical Examination of Cross Section1This standard is issued under the fixed designation B 487; the number immediately following the designation indicates the year oforiginal adopt
2、ion or, in the case of revision, 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.This standard has been approved for use by agencies of the Department of Defense.1.
3、Scope1.1 This test method covers measurement of the localthickness of metal and oxide coatings by the microscopicalexamination of cross sections using an optical microscope.1.2 Under good conditions, when using an optical micro-scope, the method is capable of giving an absolute measuringaccuracy of
4、0.8 m. This will determine the suitability of themethod for measuring the thickness of thin coatings.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 hea
5、lth practices and determine the applica-bility of regulatory limitations prior to use. (This is especiallyapplicable to the chemicals cited in Table X2.1.)2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic Specimens3. Summary of Test Method3.1 This test method cons
6、ists of cutting out a portion of thetest specimen, mounting it, and preparing the mounted crosssection by suitable techniques of grinding, polishing, andetching. The thickness of the cross section is measured with anoptical microscope.NOTE 1These techniques will be familiar to experienced metallogra
7、-phers but some guidance is given in Section 5 and inAppendix X1 for lessexperienced operators.4. Significance and Use4.1 Coating thickness is an important factor in the perfor-mance of a coating in service and is usually specified in acoating specification.4.2 This method is suitable for acceptance
8、 testing.5. Factors Influencing the Measurement Result5.1 Surface RoughnessIf the coating or its substrate has arough surface, one or both of the interfaces bounding thecoating cross section may be too irregular to permit accuratemeasurement. (See X1.4)5.2 Taper of Cross SectionIf the plane of the c
9、ross sectionis not perpendicular to the plane of the coating, the measuredthickness will be greater than the true thickness. For example,an inclination of 10 to the perpendicular will contribute a1.5 % error.5.3 Deformation of the CoatingDetrimental deformationof the coating can be caused by excessi
10、ve temperature orpressure during mounting and preparation of cross sections ofsoft coatings or coatings melting at low temperatures, and alsoby excessive abrasion of brittle materials during preparation ofcross sections.5.4 Rounding of Edge of CoatingIf the edge of the coatingcross section is rounde
11、d, that is, if the coating cross section isnot completely flat up to its edges, the true thickness cannot beobserved microscopically. Edge rounding can be caused byimproper mounting, grinding, polishing, or etching. It isusually minimized by overplating the test specimen beforemounting. (See X1.2.)5
12、.5 OverplatingOverplating of the test specimen serves toprotect the coating edges during preparation of cross sectionsand thus to prevent an erroneous measurement. Removal ofcoating material during surface preparation for overplating cancause a low-thickness measurement.5.6 EtchingOptimum etching wi
13、ll produce a clearly de-fined and narrow dark line at the interface of two metals.Excessive etching produces a poorly defined or wide linewhich may result in an erroneous measurement.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct
14、responsibility of Subcommittee B08.10 onTest Methods.Current edition approved March 1, 2007. Published March 2007. Originallyapproved in 1968. Last previous edition approved in 2002 as B 487 85 (2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servi
15、ce 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, PA 19428-2959, United States.5.7 SmearingImproper polishing may leave one
16、metalsmeared over the other metal so as to obscure the true boundarybetween the two metals. The apparent boundary may be poorlydefined or very irregular instead of straight and well defined.To verify the absence of smearing, the coating thickness shouldbe measured and the polishing, etching, and thi
17、ckness mea-surement repeated. A significant change in apparent thicknessindicates that smearing was probably present during one of themeasurements.5.8 MagnificationFor any given coating thickness, mea-surement errors generally increase with decreasing magnifica-tion. If possible, the magnification s
18、hould be chosen so that thefield of view is between 1.5 and 3 3 the coating thickness.5.9 Calibration of Stage MicrometerAny error in calibra-tion of the stage micrometer will be reflected in the measure-ment of the specimen. Errors of several percent are notunrealistic unless the scale has been cal
19、ibrated or has beencertified by a responsible supplier. The distance between twolines of a stage micrometer used for the calibration shall beknown to within 0.2 m or 0.1 %, whichever is the greater. Ifa stage micrometer is not certified for accuracy, it should becalibrated. A generally satisfactory
20、means of calibration is toassume that the stated length of the full scale is correct, tomeasure each subdivision with a filar micrometer, and tocalculate the length of each subdivision by simple proportion.5.10 Calibration of Micrometer Eyepiece:5.10.1 A filar micrometer eyepiece generally provides
21、themost satisfactory means of making the measurement of thespecimen. The measurement will be no more accurate than thecalibration of the eyepiece. As calibration is operator depen-dent, the eyepiece shall be calibrated by the person making themeasurement.5.10.2 Repeated calibrations of the micromete
22、r eyepiececan be reasonably expected to have a spread of less than 1 %.5.10.3 Some image-splitting micrometer eyepieces have anonlinearity that introduces an error of up to 1 % for shortmeasurement distances.5.11 AlignmentErrors can be introduced by backlash inthe movement of the micrometer eyepiece
23、. If the final motionduring alignment of the hairline is always made in the samedirection, this error will be eliminated.5.12 Uniformity of MagnificationBecause the magnifica-tion may not be uniform over the entire field, errors can occurif both the calibration and the measurement are not made overt
24、he same portion of the field with the measured boundariescentered about the optical axis.5.13 Lens QualityLack of sharpness of the image contrib-utes to the uncertainty of the measurement. Poor quality lensescould preclude accurate measurements. Sometimes imagesharpness can be improved by using mono
25、chromatic light.5.14 Orientation of EyepieceThe movement of the hair-line of the eyepiece for alignment has to be perpendicular to theboundaries of the coating cross section. For example, 10misalignment will contribute a 1.5 % error.5.15 Tube LengthA change in the tube length of themicroscope causes
26、 a change in magnification and if this changeoccurs between the time of calibration and the time ofmeasurement, the measurement will be in error. A change intube length may occur when the eyepiece is repositioned withinthe tube, when the focus of the eyepiece tube is changed, and,for some microscope
27、s, when the fine focus is adjusted or theinterpupillary distance for binoculars is changed.6. Preparation of Cross Sections6.1 Prepare, mount, polish, and etch the specimen so that:6.1.1 The cross section is perpendicular to the coating;6.1.2 The surface is flat and the entire width of the coatingim
28、age is simultaneously in focus at the magnification used forthe measurement;6.1.3 All material deformed by cutting or cross sectioning isremoved.6.1.4 The boundaries of the coating cross section are sharplydefined by no more than contrasting appearance or by a narrow,well-defined line.NOTE 2Further
29、guidance is given in Appendix X1. Some typicaletchants are described in Appendix X2.7. Procedure7.1 Give appropriate attention to the factors listed in Section5 and Appendix X1.7.2 Calibrate the microscope and its measuring device witha certified or calibrated stage micrometer.7.3 Measure the width
30、of the image of the coating crosssection at no less than five points distributed along a length ofthe microsection, and calculate the arithmetic mean of themeasurements (see 8.1.5 and 8.1.6).8. Test Report8.1 The test report shall include the following information:8.1.1 The date of test;8.1.2 The nu
31、mber and title of this test method;8.1.3 The identification of the test specimens;8.1.4 The location on the coated item at which the crosssection was made;8.1.5 The measured thickness, in micrometres (millimetresif greater than 1 mm) at each point (7.3), and the length ofsection over which the measu
32、rements were distributed;8.1.6 The local thickness, that is, the arithmetic mean of themeasured thicknesses;8.1.7 Any deviations from this test method;8.1.8 Any factors that might influence interpretation of thereported results; and8.1.9 The name of the operator and testing laboratory.9. Precision a
33、nd Bias9.1 The microscope and associated equipment, its use, itscalibration, and the method of preparation of the cross sectionshall be chosen so as to allow the coating thickness to bedetermined to within 1 m or 10 %, whichever is the greater, ofthe actual coating thickness. Under good conditions,
34、whenusing an optical microscope, the method is capable of giving anabsolute measuring accuracy of 0.8 m and for thicknessesgreater than 25 m a reasonable error is of the order of 5 % orbetter.B 487 85 (2007)2APPENDIXES(Nonmandatory Information)X1. GUIDANCE ON THE PREPARATION AND MEASUREMENT OF CROSS
35、 SECTIONSX1.1 IntroductionThe preparation of test specimens andmeasurement of coating thickness are greatly dependent onindividual techniques and there is a variety of suitable tech-niques available. It is not reasonable to specify only one set oftechniques, and it is impractical to include all suit
36、able tech-niques. The techniques described in this appendix are intendedas guidance for metallographers not experienced in measure-ments of coating thickness. For additional guidance see Meth-ods E3.X1.2 Mounting:X1.2.1 To prevent rounding of the edge of the cross section,the free surface of the coa
37、ting should be supported so that thereis no space between the coating and its support. This is usuallyachieved by overplating the specimen with a coating at least10-m thick of a metal of similar hardness to the coating. Forhard, brittle coatings (for example oxide or chromium coat-ings) tightly wrap
38、ping the specimen in soft aluminum foilbefore mounting has proved successful.X1.2.2 If the coating is soft, overplating with a metal whichis softer will make polishing more difficult, because the softermetal tends to be polished away more rapidly.X1.2.3 Overplating of zinc or cadmium coatings with c
39、op-per may cause difficulty because of the tendency, duringsubsequent etching, of dissolved copper to deposit on thecoatings. It is better to overplate zinc with cadmium and viceversa.X1.3 Grinding and Polishing:X1.3.1 It is essential to keep the cross-section surface of themount perpendicular to th
40、e coating. This is facilitated byincorporating additional pieces of a similar metal in the plasticmounting, near the outer edges, by periodically changing thedirection of grinding (rotating through 90) and by keeping thegrinding time and pressure to a minimum. If, before grinding,reference marks are
41、 inscribed on the side of the mount, anyinclination from horizontal is easily measurable.X1.3.2 Grind the mounted test specimens on suitable abra-sive paper, using an acceptable lubricant, such as water ormineral spirits, and apply minimum pressure to avoid bevellingof the surface. Initial grinding
42、should employ 100 or 180 gradeabrasive to reveal the true specimen profile and to removedeformed metal. Subsequently, use Grades 240, 320, 500, and600 without exceeding grinding times of 30 to 40 s on eachpaper; alter the direction of scratches by 90 for each change ofpaper. A final polish of 2 to 3
43、 min on a rotating wheel chargedwith 4 to 8-m diamond paste particles and lubricated withmineral spirits should suffice to remove scratches for finalexamination. If an especially high degree of surface finish isrequired, a further treatment, using diamond paste of approxi-mately 1-m particles, may b
44、e employed.X1.3.3 If very soft materials are being prepared, abrasiveparticles may become embedded during grinding. This may beminimized by totally immersing abrasive papers in a lubricantduring grinding or by using a copious flow of lubricant. Ifabrasive particles do become embedded, they may be re
45、movedby applying a short, light hand polish with metal polish aftergrinding and before diamond finishing or by one or morecycles of alternate etching and polishing.X1.4 EtchingEtching is usually advisable to promotecontrast between the metal layers, to remove traces of smearedmetal, and to develop a
46、 fine line at the boundary of the coating.Some typical etchants are given in Appendix X2.X1.5 Measurement:X1.5.1 The measuring device may be a filar micrometer ora micrometer eyepiece. The latter has a lower precision. Animage-splitting eyepiece is advantageous for thin coatings onrough substrate su
47、rfaces. Measurement of the image projectedon to a ground-glass plate is usually less satisfactory because ofthe lack of sharpness of the image and poor legibility of theruler when the projected image is visible.X1.5.2 The measuring device should be calibrated at leastonce before and once after a mea
48、surement, unless repeatedexperience indicates otherwise.X1.5.3 When making calibration and coating measure-ments, both should be made by the same operator, the stagemicrometer and the coating should be centered in the field, andeach measurement at a point should be made at least twice andaveraged.X1
49、.5.4 For critical and referee measurements, all steps forthe preparation of cross sections and measurement of coatingthickness, from grinding with 600 grade or coarser abrasive, upto and including the determination, should be performed atleast twice. With good techniques and equipment, and smoothcoating and substrate surfaces, repeatability within 2 % or 0.5m, whichever is the greater, is reasonable.X1.5.5 Some microscopes are subject to a spontaneousmovement of the stage relative to the objective, possibly due tononuniform thermal effects from the ligh
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