ASTM_B_487_-_85_2013.pdf

Designation:B48785(Reapproved 2013)Standard Test Method forMeasurement of Metal and Oxide Coating Thickness byMicroscopical Examination of Cross Section1This standard is issued under the fixed designation B487;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.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 opticalmicroscope,the method is capable of giving an absolutemeasuring accuracy of 0.8 m.This will determine the suit-ability of the method for measuring the thickness of thincoatings.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 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 consists 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.NOTE1These techniques will be familiar to experienced metallogra-phers but some guidance is given in Section 5 and in Appendix 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 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 cross 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 excessive 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 rounded,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.)5.5 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 will 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 Coatingsand is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved Dec.1,2013.Published December 2013.Originallyapproved in 1968.Last previous edition approved in 2007 as B487 85(2007).DOI:10.1520/B0487-85R13.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.7 SmearingImproper polishing may leave one 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 thickness 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 d