ASTM_E_1558_-_09_2014.pdf

Designation:E155809(Reapproved 2014)Standard Guide forElectrolytic Polishing of Metallographic Specimens1This standard is issued under the fixed designation E1558;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 deals with electrolytic polishing as a meansof preparation of specimens for metallographic purposes.Procedures are described for polishing a variety of metals.NOTE1References(1-133)2on electrolytic polishing will provide thereader with specific information beyond the scope of this guide.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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.Specific safetyprecautions are described in Section 5 and 6.3.1.2.Referenced Documents2.1 ASTM Standards:3E7 Terminology Relating to MetallographyE407 Practice for Microetching Metals and Alloys3.Terminology3.1 DefinitionsAll terms used in this guide are eitherdefined in Terminology E7 or are discussed in 3.2.3.2 Definitions of Terms Specific to This Standard:3.2.1 electrolytic polish(electropolish)A method of pol-ishing metals and alloys in which material is removed from thesurface by making the metal the anode in an electrolytic bath.4.Significance and Use4.1 Advantages of Electrolytic Polishing:4.1.1 For some metals,a high quality surface finish can beproduced that is equivalent to,or better than,that which can beobtained by mechanical methods.4.1.2 Once procedures have been established,satisfactoryresults can be obtained rapidly with reproducibility.4.1.3 There can be a marked saving of time if manyspecimens of the same material are polished sequentially.4.1.4 Electropolishing a selected area on the surface of arelativelylargemetalpartcanbeaccomplishednondestructively,that is,without the need for sectioning toremove a piece.4.1.5 Soft,single-phase metals,which may be difficult topolish by mechanical methods,may be successfully electrop-olished.4.1.6 The true microstructure of a specimen can be obtainedbecause artifacts(such as disturbed metal,scratches,andmechanical twins)produced on the surface,even by carefulgrinding and mechanical polishing operations,can be removed.These features are important in low-load hardness testing,X-ray diffraction studies,and in electron microscopy,wherehigher resolution puts a premium on undistorted metal sur-faces.4.1.7 After electropolishing is completed,etching can oftenbe accomplished by reducing the voltage(generally to aboutone-tenth that required for polishing)for a short time before itis turned off.NOTE2Not all electropolishing solutions produce good etchingresults.4.2 Disadvantages of Electrolytic Polishing:4.2.1 Many of the chemical mixtures used in electropolish-ing are poisonous or dangerous if not properly handled(seeSection 5).These hazards are similar to those involved in themixing and handling of etchants,see Test Methods E407.4.2.2 In multi-phase alloys,the polishing rate of each phasemay be different.The result may be a non-planar surface.4.2.3 Electropolished surfaces may be slightly undulatedrather than perfectly planar and,therefore,may not be suitablefor examination at all magnifications.4.2.4 The rate of polishing in areas adjacent to variousinhomogeneities,such as nonmetallic inclusions and voids,isusually greater than that in the surrounding matrix and tends toexaggerate the size of the inclusions and voids.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 Oct.1,2014.Published December 2014.Originallyapproved in 1993.Last previous edition approved in 2009 as E1558 09.DOI:10.1520/E1558-09R14.2The boldface numbers in parentheses refer to the references at the end of thisstandard.3For 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 4.2.5 Dimples,pits,and waviness limit applications involv-ing surface phenomena,coatings,interfaces,and cracks.Edgestend to be attacked preferentially,resulting in edge rounding.4.2.6 Artifacts may be produced by electropolishing.4.2.7 Specimen mounting materials may react with theelectrolyte.4.2.8 The electropolished surfaces of certain materials maybe passive a