ASTM_E_1920_-_03_2014.pdf

Designation:E192003(Reapproved 2014)Standard Guide forMetallographic Preparation of Thermal Sprayed Coatings1This standard is issued under the fixed designation E1920;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.1.Scope1.1 This guide covers recommendations for sectioning,cleaning,mounting,grinding,and polishing to reveal themicrostructural features of thermal sprayed coatings(TSCs)and the substrates to which they are applied when examinedmicroscopically.Because of the diversity of availableequipment,the wide variety of coating and substratecombinations,and the sensitivity of these specimens to prepa-ration technique,the existence of a series of recommendedmethods for metallographic preparation of thermal sprayedcoating specimens is helpful.Adherence to this guide willprovide practitioners with consistent and reproducible results.Additional information concerning standard practices for met-allographic preparation can be found in Practice E3.1.2 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.2.Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to Metallography3.Terminology3.1 DefinitionsFor definitions of terms used in this guide,see Terminology E7.3.2 Definitions of Terms Specific to This Standard:3.2.1 linear detachment,na region within a TSC in whichtwo successively deposited splats of coating material have notmetallurgically bonded.3.2.2 splat,nan individual globule of thermal sprayedmaterial that has been deposited on a substrate.3.2.3 taper mount,na metallographic specimen created bymounting a feature,typically an interface or thin coating,at asmall angle to the polishing plane,such that the visible widthexhibited by the feature is expanded.3.2.4 TSC,nthermal sprayed coating,including,but notlimited to,those formed by plasma,flame,and high velocityoxyfuel.4.Significance and Use4.1 TSCs are used in a number of critical industrial compo-nents.TSCs can be expected to contain measurable levels ofporosity and linear detachment.Accurate and consistent evalu-ation of specimens is essential to ensure the integrity of thecoating and proper adherence to the substrate.4.1.1 Example 1:By use of inappropriate metallographicmethods,the apparent amount of porosity and linear detach-ment displayed by a given specimen can be increased,byexcessive edge rounding,or decreased by smearing of materialinto voids.Therefore inaccurate levels of porosity and lineardetachment will be reported even when the accuracy of themeasurement technique is acceptable.4.1.2 Example 2:Inconsistent metallographic preparationmethods can cause the apparent amount of voids to varyexcessively indicating a poorly controlled thermal sprayprocess,while the use of consistent practice will regularlydisplay the true microstructure and verify the consistency ofthe thermal spray process.4.2 During the development of TSC procedures,metallo-graphic information is necessary to validate the efficacy of aspecific application.4.3 Cross sections are usually taken perpendicular to thelong axis of the specimen and prepared to reveal informationconcerning the following:4.3.1 Variations in structure from surface to substrate,4.3.2 The distribution of unmelted particles throughout thecoating,4.3.3 The distribution of linear detachment throughout thecoating,4.3.4 The distribution of porosity throughout the coating,4.3.5 The presence of contamination within the coating,4.3.6 The thickness of the coating(top coat and bond coat,where applicable),4.3.7 The presence of interfacial contamination,1This guide is under the jurisdiction ofASTM Committee E04 on Metallographyand is the direct responsibility of Subcommittee E04.01 on Specimen Preparation.Current edition approved May 1,2014.Published September 2014.Originallyapproved in 1997.Last previous edition approved in 2008 as E192003(2008).DOI:10.1520/E1920-03R14.2For 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 4.3.8 The integrity of the interface between the coating andsubstrate,and,4.3.9 The integrity of the coating microstructure with re-spect to chemistry.5.Selection of Metallographic Specimens5.1 Selection of specimens for metallographic examinationis critical if their interpretation is to be of v