ASTM E3-11(2017)

Standard Guide for Preparation of Metallographic Specimens

SIGNIFICANCE AND USE
4.1 Microstructures have a strong influence on the properties and successful application of metals and alloys. Determination and control of microstructure requires the use of metallographic examination.  
4.2 Many specifications contain a requirement regarding microstructure; hence, a major use for metallographic examination is inspection to ensure that the requirement is met. Other major uses for metallographic examination are in failure analysis, and in research and development.  
4.3 Proper choice of specimen location and orientation will minimize the number of specimens required and simplify their interpretation. It is easy to take too few specimens for study, but it is seldom that too many are studied.
SCOPE
1.1 The primary objective of metallographic examinations is to reveal the constituents and structure of metals and their alloys by means of a light optical or scanning electron microscope. In special cases, the objective of the examination may require the development of less detail than in other cases but, under nearly all conditions, the proper selection and preparation of the specimen is of major importance. Because of the diversity in available equipment and the wide variety of problems encountered, the following text presents for the guidance of the metallographer only those practices which experience has shown are generally satisfactory; it cannot and does not describe the variations in technique required to solve individual specimen preparation problems.  
Note 1: For a more extensive description of various metallographic techniques, refer to Samuels, L. E.,  Metallographic Polishing by Mechanical Methods, American Society for Metals (ASM) Metals Park, OH, 3rd Ed., 1982; Petzow, G.,  Metallographic Etching, ASM, 1978; and VanderVoort, G.,  Metallography: Principles and Practice, McGraw Hill, NY, 2nd Ed., 1999.  
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2017
• ICS: 77.040.99 - Other methods of testing of metals
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.01 - Specimen Preparation

Relations

• Refers: ASTM E45-18a(2023) - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2023
• Refers: ASTM E7-15 - Standard Terminology Relating to Metallography
• Effective Date: 01-Jun-2015
• Refers: ASTM E7-14 - Standard Terminology Relating to Metallography
• Effective Date: 01-Nov-2014
• Refers: ASTM E45-11a - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Oct-2011
• Refers: ASTM E45-11 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Jun-2011
• Refers: ASTM E45-10 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2010
• Refers: ASTM E768-99(2010) - Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 01-Nov-2010
• Refers: ASTM E7-03(2009) - Standard Terminology Relating to Metallography
• Effective Date: 01-Oct-2009
• Refers: ASTM E1558-09 - Standard Guide for Electrolytic Polishing of Metallographic Specimens
• Effective Date: 01-May-2009
• Refers: ASTM E1920-03(2008) - Standard Guide for Metallographic Preparation of Thermal Sprayed Coatings
• Effective Date: 01-Oct-2008
• Refers: ASTM E1245-03(2008) - Standard Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis
• Effective Date: 01-Oct-2008
• Refers: ASTM E45-05 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2005
• Refers: ASTM E45-05e2 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2005
• Refers: ASTM E45-05e1 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2005
• Refers: ASTM E45-05e3 - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2005

Overview

ASTM E3-11(2017), Standard Guide for Preparation of Metallographic Specimens, provides essential guidance on preparing metals and alloys for metallographic examination. Developed by ASTM International, this standard is adopted widely for ensuring reliable and consistent preparation methods, which enable accurate analysis of microstructures using light optical or scanning electron microscopy. Proper specimen preparation is critical for microstructural evaluation, supporting applications in quality control, research, failure analysis, and compliance with industry specifications.

Key Topics

• Significance of Microstructure: The microstructure of metals and alloys has a profound effect on mechanical properties and performance. Accurate microstructural analysis depends on correct preparation techniques.
• Specimen Selection: Guidance on choosing locations and orientations for sampling to ensure materials are well-represented and results are meaningful.
• Sectioning Methods: Recommendations for cutting specimens with minimal alteration of the original structure, using appropriate tools such as saws or abrasive cutoff wheels matched to the material hardness.
• Mounting Techniques: Instructions for mechanical and plastic mounting. Discusses compression mounts, castable resins, vacuum impregnation for porous materials, and strategies to avoid distortion during the process.
• Grinding and Polishing: Stepwise approaches for removing surface damage and achieving a flat, scratch-free specimen suitable for microscopy. Covers both manual and automated methods, with advice on abrasive selection depending on material hardness.
• Plating and Cleaning: Solutions for edge retention in fragile samples, including plating with metals like nickel or copper, and best practices for cleaning specimens to avoid contamination or surface alteration.
• Special Procedures: Tips for preparing difficult materials such as composites, hard coatings, fragile or porous specimens, and recommendations to minimize preparation-induced artifacts.

Applications

Metallographic specimen preparation as outlined in ASTM E3-11(2017) is vital across various fields including:

• Quality Assurance: Ensures compliance with industry microstructure requirements by revealing inclusions, grain size, phase distribution, surface coatings, and defects.
• Failure Analysis: Supports root cause investigations by enabling detailed examination of regions adjacent to a fracture or flaw, crucial for understanding failure mechanisms.
• Material Research and Development: Facilitates fundamental studies on new alloys or heat treatments by providing reproducible specimen preparation methods.
• Process Control: Helps monitor manufacturing or casting processes by highlighting variations in structure, impurities, or surface conditions.
• Coatings and Surface Treatments: Evaluates thickness, composition, and integrity of protective or functional coatings, an important factor in corrosion resistance and wear performance.

Related Standards

ASTM E3-11(2017) is frequently used in conjunction with other ASTM standards relevant to metallography and materials characterization, including:

• ASTM E7: Terminology Relating to Metallography
• ASTM E45: Test Methods for Determining the Inclusion Content of Steel
• ASTM E1077: Estimating the Depth of Decarburization of Steel Specimens
• ASTM E768/E1245: Guide and Practice for Inclusion Content by Automatic Image Analysis
• ASTM E1920: Guide for Metallographic Preparation of Thermal Sprayed Coatings
• ASTM E1558: Guide for Electrolytic Polishing of Metallographic Specimens

By following the practices detailed in ASTM E3-11(2017), laboratories and manufacturing facilities can achieve consistent, high-quality metallographic specimens leading to reliable and reproducible microscopy results, underpinning critical decisions across materials engineering and quality management.

Keywords: metallographic specimen preparation, ASTM E3, metallography, microstructure, specimen mounting, grinding and polishing, materials analysis, metals and alloys, quality control, failure analysis, coatings evaluation.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E3 − 11(Reapproved 2017)
Standard Guide for
Preparation of Metallographic Specimens
This standard is issued under the fixed designation E3; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
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. Scope A90/A90M Test Method for Weight [Mass] of Coating on
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
1.1 The primary objective of metallographic examinations
E7 Terminology Relating to Metallography
is to reveal the constituents and structure of metals and their
E45 Test Methods for Determining the Inclusion Content of
alloys by means of a light optical or scanning electron
Steel
microscope. In special cases, the objective of the examination
E768 Guide for Preparing and Evaluating Specimens for
may require the development of less detail than in other cases
Automatic Inclusion Assessment of Steel
but, under nearly all conditions, the proper selection and
E1077 Test Methods for Estimating the Depth of Decarbur-
preparation of the specimen is of major importance. Because of
ization of Steel Specimens
the diversity in available equipment and the wide variety of
E1122 Practice for Obtaining JK Inclusion Ratings Using
problems encountered, the following text presents for the
Automatic Image Analysis (Withdrawn 2006)
guidance of the metallographer only those practices which
E1245 Practice for Determining the Inclusion or Second-
experience has shown are generally satisfactory; it cannot and
Phase Constituent Content of Metals by Automatic Image
does not describe the variations in technique required to solve Analysis
individual specimen preparation problems. E1268 Practice for Assessing the Degree of Banding or
Orientation of Microstructures
NOTE 1—For a more extensive description of various metallographic
E1558 Guide for Electrolytic Polishing of Metallographic
techniques, refer to Samuels, L. E., Metallographic Polishing by Mechani-
Specimens
cal Methods, American Society for Metals (ASM) Metals Park, OH, 3rd
E1920 Guide for Metallographic Preparation of Thermal
Ed., 1982; Petzow, G., Metallographic Etching, ASM, 1978; and
Sprayed Coatings
VanderVoort, G., Metallography: Principles and Practice, McGraw Hill,
NY, 2nd Ed., 1999.
3. Terminology
1.2 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 For definitions used in this practice, refer to Termi-
responsibility of the user of this standard to establish appro-
nology E7.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 castable mount—a metallographic mount generally
1.3 This international standard was developed in accor-
made from a two component castable plastic. One component
dance with internationally recognized principles on standard-
is the resin and the other hardener. Both components can he
ization established in the Decision on Principles for the
liquid or one liquid and a powder. Castable mounts generally
Development of International Standards, Guides and Recom-
do not require heat and pressure to cure.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.2.2 compression mount—a metallographic mount made
using plastic that requires both heat and pressure for curing.
2. Referenced Documents
3.2.3 planar grinding—is the first grinding step in a prepa-
ration procedure used to bring all specimens into the same
2.1 ASTM Standards:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction of ASTM Committee E04 on Metallography contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and is the direct responsibility of Subcommittee E04.01 on Specimen Preparation. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 1, 2017. Published June 2017. Originally the ASTM website.
approved in 1921. Last previous edition approved in 2011 as E3–11. DOI: The last approved version of this historical standard is referenced on
10.1520/E0003-11R17. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3 − 11(2017)
plane of polish. It is unique to semi or fully automatic 5.2.2 In hot-worked or cold-worked metals, both transverse
preparation equipment that utilize specimen holders. and longitudinal sections should be studied. Special investiga-
tions may require specimens with surfaces prepared parallel to
3.2.4 rigid grinding disc—a non-fabric support surface,
the original surface of the product.
such as a composite of metal/ceramic or metal/polymer
5.2.3 In the case of wire and small rounds, a longitudinal
charged with an abrasive (usually 6 to 15μm diamond
section through the center of the specimen proves advanta-
particles), and used as the fine grinding operation in a metal-
geous when studied in conjunction with the transverse section.
lographic preparation procedure.
5.3 Transverse sections or cross sections taken perpendicu-
4. Significance and Use lar to the main axis of the material are often used for revealing
the following information:
4.1 Microstructures have a strong influence on the proper-
5.3.1 Variations in structure from center to surface,
ties and successful application of metals and alloys. Determi-
5.3.2 Distribution of nonmetallic impurities across the
nation and control of microstructure requires the use of
section,
metallographic examination.
5.3.3 Decarburization at the surface of a ferrous material
4.2 Many specifications contain a requirement regarding
(see Test Method E1077),
microstructure; hence, a major use for metallographic exami-
5.3.4 Depth of surface imperfections,
nation is inspection to ensure that the requirement is met. Other
5.3.5 Depth of corrosion,
major uses for metallographic examination are in failure
5.3.6 Thickness of protective coatings, and
analysis, and in research and development.
5.3.7 Structure of protective coating. See Guide E1920.
4.3 Proper choice of specimen location and orientation will 5.4 Longitudinal sections taken parallel to the main axis of
minimize the number of specimens required and simplify their
the material are often used for revealing the following infor-
interpretation. It is easy to take too few specimens for study, mation:
but it is seldom that too many are studied.
5.4.1 Inclusion content of steel (see Practices E45, E768,
E1122, and E1245),
5. Selection of Metallographic Specimens 5.4.2 Degree of plastic deformation, as shown by grain
distortion,
5.1 The selection of test specimens for metallographic
5.4.3 Presence or absence of banding in the structure (see
examination is extremely important because, if their interpre-
Practice E1268), and
tation is to be of value, the specimens must be representative of
5.4.4 The microstructure attained with any heat treatment.
the material that is being studied. The intent or purpose of the
5.5 The locations of surfaces examined should always be
metallographic examination will usually dictate the location of
the specimens to be studied. With respect to purpose of study, given in reporting results and in any illustrative micrographs. A
suitable method of indicating surface locations is shown in Fig.
metallographic examination may be divided into three classi-
fications: 1.
5.1.1 General Studies or Routine Work—Specimens should
6. Size of Metallographic Specimens
be chosen from locations most likely to reveal the maximum
variations within the material under study. For example,
6.1 For convenience, specimens to be polished for metallo-
specimens could be taken from a casting in the zones wherein
graphic examination are generally not more than about 12 to 25
maximum segregation might be expected to occur as well as
mm (0.5 to 1.0 in.) square, or approximately 12 to 25 mm in
specimens from sections where segregation could be at a
diameter if the material is cylindrical. The height of the
minimum. In the examination of strip or wire, test specimens
specimen should be no greater than necessary for convenient
could be taken from each end of the coils.
handling during polishing.
5.1.2 Study of Failures—Test specimens should be taken as
6.1.1 Larger specimens are generally more difficult to pre-
closely as possible to the fracture or to the initiation of the
pare.
failure. Before taking the metallographic specimens, study of
6.1.2 Specimens that are, fragile, oddly shaped or too small
the fracture surface should be complete, or, at the very least,
to be handled readily during polishing should be mounted to
the fracture surface should be documented. In many cases,
ensure a surface satisfactory for microscopical study. There
specimens should be taken from a sound area for a comparison
are, based on technique used, three fundamental methods of
of structures and properties.
mounting specimens (see Section 9).
5.1.3 Research Studies—The nature of the study will dictate
specimen location, orientation, etc. Sampling will usually be
7. Cutting of Metallographic Specimens
more extensive than in routine examinations.
7.1 In cutting the metallographic specimen from the main
5.2 Having established the location of the metallographic
body of the material, care must be exercised to minimize
samples to be studied, the type of section to be examined must
altering the structure of the metal. Three common types of
be decided.
sectioning are as follows:
5.2.1 For a casting, a section cut perpendicular to the 7.1.1 Sawing, whether by hand or machine with lubrication,
surface will show the variations in structure from the outside to is easy, fast, and relatively cool. It can be used on all materials
the interior of the casting. with hardnesses below approximately 350 HV. It does produce
E3 − 11(2017)
TABLE 1 Cutoff Blade Selection
Hardness Bond
Materials Abrasive Bond
HV Hardness
up to 300 non-ferrous (Al, Cu) SiC P or R hard
up to 400 non-ferrous (Ti) SiC P or R med.
hard
up to 400 soft ferrous Al O P or R hard
2 3
up to 500 medium soft ferrous Al O P or R med.
2 3
hard
up to 600 medium hard ferrous Al O P or R medium
2 3
up to 700 hard ferrous Al O P or R&R med. soft
2 3
up to 800 very hard ferrous Al O P or R&R soft
2 3
> 800 extremely hard ferrous CBN P or M hard
more brittle ceramics diamond P or M very hard
tougher ceramics diamond M ext. hard
P—phenolic
R—rubber
R&R—resin and rubber
M—metal
Symbol in
Suggested Designation cutoff blades on the specimen should be removed by some
Diagram
suitable organic solvent. Failure to clean thoroughly can
A Rolled surface
prevent cold mounting resins from adhering to the specimen
B Direction of rolling
surface. Ultrasonic cleaning may be effective in removing the
C Rolled edge
last traces of residues on a specimen surface.
D Planar section
E Longitudinal section perpendicular to rolled surface
8.2 Any coating metal that will interfere with the subse-
F Transverse section
G Radial longitudinal section quent etching of the base metal should be removed before
H Tangential longitudinal section
polishing, if possible. If etching is required, when studying the
underlying steel in a galvanized specimen, the zinc coating
FIG. 1 Method of Designating Location of Area Shown in Photo-
should be removed before mounting to prevent galvanic effects
micrograph.
during etching. The coating can be removed by dissolving in
cold nitric acid (HNO , sp gr 1.42), in dilute sulfuric acid
a rough surface containing extensive plastic flow that must be
(H SO ) or in dilute hydrochloric acid (HCl). The HNO
2 4 3
removed in subsequent preparation.
method requires care to prevent overheating, since large
7.1.2 An abrasive cut-off blade will produce a smooth
samples will generate considerable heat. By placing the clean-
surface often ready for fine grinding. This method of sectioning
ing container in cold water during the stripping of the zinc,
is normally faster than sawing. The choice of cut-off blade,
attack on the underlying steel will be minimized. More
lubricant, cooling conditions, and the grade and hardness of
information may be found in Test Method A90/A90M.
metal being cut will influence the quality of the cut. A poor
choice of cutting conditions can easily damage the specimen,
NOTE 2—Picral etchant produces little or no galvanic etching effects
when used on galvanized steel.
producing an alteration of the microstructure. Generally, soft
NOTE 3—The addition of an inhibitor during the stripping of Zn from
materials are cut with a hard bond blade and hard materials
galvanized coatings will minimize the attack of the steel substrate. NEP
with a soft bond blade. Aluminum oxide abrasive blades are
(polethylinepolyamine) or SbCl are two useful inhibitors.
preferred for ferrous metals and silicon carbide blades are
8.3 Oxidized or corroded surfaces may be cleaned as
preferred for nonferrous alloys. Abrasive cut-off blades are
described in Appendix X1.
essential for sectioning metals with hardness above about 350
HV. Extremely hard metallic materials and ceramics may be
9. Mounting of Specimens
more effectively cut using diamond-impregnated cutting
9.1 There are many instances where it will be advantageous
blades. Manufacturer’s instructions should be followed as to
to mount the specimen prior to grinding and polishing. Mount-
the choice of blade. Table 1 lists the suggested cutoff blades for
ing of the specimen is usually performed on small, fragile, or
materials with various Vickers (HV) hardness values.
oddly shaped specimens, fractures, or in instances where the
7.1.3 A shear is a type of cutting tool with which a material
specimen edges are to be examined.
in the form of wire, sheet, plate or rod is cut between two
opposing blades. 9.2 Specimens may be either mechanically mounted,
mounted in plastic, or a combination of the two.
7.2 Other methods of sectioning are permitted provided they
do not alter the microstructure at the plane of polishing. All 9.3 Mechanical Mounting:
cutting operations produce some depth of damage, which will
9.3.1 Strip and sheet specimens may be mounted by binding
have to be removed in subsequent preparation steps. or clamping several specimens into a pack held together by two
end pieces and two bolts.
8. Cleanliness
9.3.2 The specimens should be tightly bound together to
8.1 Cleanliness (see Appendix X1) during specimen prepa- prevent absorption and subsequent exudation of polishing
ration is essential. All greases, oils, coolants and residue from materials or etchants.
E3 − 11(2017)
TABLE 2 Characteristics of Hot-Compression Mounting Compounds
Type of Compound Characteristics
Acrylic thermoplastic, cure time 10-15 min, optically clear, moderate shrinkage, low abrasion resistance, degraded by hot
etchants
A
Diallyl phthalate thermosetting, cure time 5-10 min, opaque, minimal shrinkage, good resistance to etchants, moderate abrasion resistance
A
Epoxy thermosetting, cure time 5-10 min, opaque, very low shrinkage, good resistance to etchants, high abrasion resistance
A
Phenolic (Bakelite) thermosetting, cure time 5-10 min, opaque, moderate shrinkage, degraded by hot etchants, moderate abrasion resistance
A
These compounds may be filled with wood flour, glass fiber or mineral particulate.
9.3.3 The use of filler sheets of a softer material alternated is clean and dry, and (2) the cured mount is cooled under full
with the specimen may be used in order to minimize the pressure to below 40°C before ejection from the press. This
seepage of polishing materials and etchants. Use of filler will ensure minimal shrinkage gap formation.
material is especially advantageous if the specimens have a 9.4.4 Castable Plastics—Castable mounts are usually pre-
high degree of surface irregularities. pared at room temperature. Some may require an external heat
9.3.4 Filler material must be chosen so as not to react source or applied pressure in order to cure. These resins consist
electrolytically with the specimen during etching. Thin pieces of two or more components which must be mixed just prior to
of plastic, lead, or copper are typical materials that are used. use. There are four kinds of castable plastics in common use
Copper is especially good for steel specimens since the usual (see Table 3).
etchants for steels will not attack the copper. 9.4.5 The molds for castable plastics are often simple cups
9.3.5 Alternatively, the specimens may be coated with a that hold the resin until it cures. They may be reusable or not;
layer of epoxy resin before being placed in the clamp in order the choice is a matter of convenience and cost. Handling
to minimize the absorption of polishing materials or etchants. castable resins requires care. They all can cause dermatitis.
9.3.6 The clamp material should be similar in composition Manufacturers’ recommendations for mixing and curing must
to the specimen to avoid galvanic effects that would inhibit be followed to obtain best results.
etching. The specimen will not etch if the clamp material is
9.5 Mounting Porous Specimen:
more readily attacked by the etchant.
9.5.1 Porous or intricate specimens may be vacuum impreg-
9.3.7 The clamp should preferably be of similar hardness as
nated in order to fill voids, prevent contamination and seepage,
the specimens to minimize the rounding of the edges of the
and prevent loss of friable or loose components. Impregnation
specimens during grinding and polishing.
is accomplished by placing the specimen in a mold in a vacuum
9.3.8 Exercise care in clamping the specimen. Excessive
chamber and then introducing the resin into the mold after the
clamping pressure may damage soft specimen.
chamber has been evacuated. The introduction of the resin into
9.4 Plastic Mounting: the mold can be accomplished either by having a funnel or
9.4.1 Specimens may be embedded in plastic to protect stopcock fitted to the vacuum chamber or by having a basin of
them from damage and to provide a uniform format for both the resin present inside the chamber. A low-viscosity resin will
manual and automatic preparation. This is the most common produce the best results. The pressure in the chamber must
method for mounting metallographic specimens. Mounting remain above the critical vapor pressure of the hardener to
plastics may be divided into two classes—compression and avoid boiling away the hardener. After the pressure has
castable. equilibrated, the resin is introduced into the mold and the
9.4.2 The choice of a mounting compound will influence the vacuum is released and air admitted to the chamber. Atmo-
extent of edge rounding observed during the grinding and spheric pressure will force the resin into fine pores, cracks, and
polishing operations. There are several methods available that holes.
minimize rounding. The specimen may be surrounded by hard 9.5.2 If a low-viscosity resin is used, the funnel and stop-
shot, small rivets, rings, etc., of approximately the same cock may be eliminated. The specimen and resin are placed in
hardness or, when using a castable resin, a slurry of resin and the mold prior to evacuation. The air in the specimen will
alumina may be poured around the specimen. The specimen bubble out through the resin. Exercise care to ensure the
may also be plated before mounting (see Section 10). Many hardening agent is not evaporated during evacuation. Dipping
mounting procedures result in sharp edges on the mount the specimen in the resin prior to placing it in the mold may
corners. The corners should be beveled to remove any plastic help in filling voids.
mounting flash. 9.5.3 Vacuum impregnation is an effective method for
9.4.3 Compression Mounting—There are four types of com- ensuring optimal results for porous metallographic mounts. It
pression mounting plastics used predominantly in the metallo- is imperative that the specimens be completely dry prior to
graphic laboratory (see Table 2). These plastics require the use impregnation.
of a mounting press providing heat (140-180°C) and force 9.5.4 A more rapid technique but less effective method is to
(27-30 MPa). Thermosetting plastics can be ejected hot but the lacquer the specimens with one of the formulations used by the
best results are obtained when the cured mount is cooled under canning industry to line food containers. The formulations are
pressure. Thermoplastic compounds do not harden until cooled highly penetrating and the cure is a short time at low
and therefore should not be ejected while hot. Regardless of the temperatures. After lacquering, the specimens are mounted in
resin used, the best results are obtained when (1) the specimen the usual fashion.
E3 − 11(2017)
TABLE 3 Characteristics of Castable Mounting Compounds
Type of Compound Characteristics
Acrylic Cure time 8-15 min, moderate shrinkage, peak curing temperature can reach 90-120°C during polymerization, low
abrasion resistance, opaque to transparent
Polyester-acrylic (quartz-filled) Cure time 8-15 min, very low shrinkage, peak curing temperature can reach 90-120°C during polymerization, high
abrasion resistance, opaque
Polyester Cure time 30-60 min, high shrinkage, peak curing temperature can reach 90- 120 C during polymerization, moderate
abrasion resistance, transparent
Epoxy Cure time ⁄2-20 h, very low shrinkage, good adhesion, low heat generation during polymerization, moderate abrasion
resistance, low viscosity (good for vacuum impregnation), transparent
10. Plating of Specimens Supplies and instructions for grinding, lapping, and polishing
are readily obtainable from laboratory supply houses.
10.1 Specimens such as fractures or those where it is
necessary to examine the edges, are often plated to obtain good 11.2 Grinding—Grinding can be done in a number of ways,
edge retention. Plating can be done electrolytically or with
ranging from rubbing the specimen on a stationary piece of
electroless solutions. These specimens are invariably mounted abrasive paper to the use of automatic devices. The choice of
prior to the grinding and polishing procedures. Electroless
method depends on the number and type of specimens to be
plating solutions can be purchased commercially. done, financial considerations and requirements such as flat-
ness and uniformity.
10.2 Thoroughly clean the specimen surface prior to plating
11.2.1 Abrasive grit size designations in this practice are
to ensure good adhesion of the plating. Avoid industrial
expressed in the ANSI (American National Standards Institute)
cleaning treatments that are too harsh and may cause damage
or CAMI (Coated Abrasives Manufacturers Institute) system
to the specimen surface. Milder cleaning treatments that
units with the corresponding FEPA (European Federation of
involve detergents, solvents, mild alkaline, or acidic solutions
Abrasive Producers) numbers in parentheses. Table 4 provides
are recommended.
a correlation between these two systems and the approximate
10.3 Chromium, copper, iron, nickel, gold, silver, and zinc
median particle diameter for a given size in micrometres.
may be electrolytically deposited although copper and nickel
11.2.2 Grinding should start with the finest paper, platen or
are predominantly used in metallographic laboratories.
stone capable of flattening the specimen and removing the
10.3.1 Ferrous metals are commonly plated electrolytically
effects of prior operations, such as sectioning. The subsequent
with nickel or copper. A flash coat in a copper or electroless
steps should remove the effects of previous ones in a short
nickel bath can be first applied for specimens that are difficult
time. Grinding consists of two stages- planar (rough) and fine.
to electroplate.
11.2.3 Planar or rough grinding [240 grit (P220) and
10.3.2 Nonferrous metals may be plated with silver and the
coarser] may be performed on belts, rotating wheels or stones.
precious metals may be plated with nickel, gold, or silver.
In some methods, diamond abrasives are used on rigid platens.
10.4 The plating material should not react galvanically with
Planar grinding may be used to accomplish the following:
the base metal of the specimen during plating, polishing, or
11.2.3.1 Flatten an irregular or damaged cut surface,
etching.
11.2.3.2 Remove sectioning damage, scale and other surface
conditions prior to mounting,
10.5 Electroless plating is preferred to electrolytic plating
11.2.3.3 Remove substantial amounts of specimen material
for specimens with rough, porous, or irregular surfaces, be-
to reach a desired plane for polishing,
cause the electroless solution provides better surface coverage
and penetration. 11.2.3.4 Level the mount surface.
11.2.4 In fine grinding, damage to the specimen incurred
10.6 Active metals such as zinc and aluminum are difficult
from the planar or rough grinding step must be removed. The
to plate. Sometimes a flash cyanide copper plate can be
specimen is either ground on successively finer abrasive papers
deposited, which then can be followed by normal plating from
(using water to wash away grinding debris and to act as a
a sulfate bath. Evaporated coatings of copper, gold, or chro-
coolant) or on a rigid disc or cloth charged with a suitable
mium may also be used as starter coatings.
abrasive.
10.7 It is recommended that the plating thickness be at least
11.2.5 After all grinding is done, the specimen must be
5μm.
cleaned thoroughly. Ultrasonic cleaning in a water/soap solu-
tion containing a corrosion inhibitor may prove beneficial.
11. Grinding and Polishing
11.3 Polishing—Polishing is usually distinguished from
General Information
grinding by the use of loose abrasive (≤6μm) embedded in an
appropriately lubricated supporting surface. The choice of
11.1 Many metals and alloys can be prepared using a similar
sequence of grinding and polishing. Hard alloys may require abrasive, lubricant, and polishing surface support is often
specific to the metal and the object of the investigation.
greater pressure than soft alloys. The major differences will be
in the final polishing. Some metals and alloys will require Polishing can be divided into rough and fine (final) stages.
specific combinations of abrasive and support material, but a 11.3.1 Rough polishing is often sufficient for routine evalu-
surprising number can be handled by the same procedure. ations like microindentation hardness and grain size.
E3 − 11(2017)
TABLE 4 European/USA Grit Grade Comparison Guide
11.7 A traditional manual preparation sequence consists of a
FEPA ANSI/CAMI series of grinding and polishing steps and may be similar to
Grit Number Size (μm) Grit Number Size (μm)
those listed in Table 5.
P120 125.0 120 116.0
P150 100.0 180 78.0
Automated Methods
P220 68.0 220 66.0
P240 58.5 . . . . . .
11.8 Many styles of automated specimen preparation ma-
P280 52.2 240 51.8
chinery are available. Most units can perform grinding and
P320 46.2 . . . . . .
polishing steps. Many use holders capable of accommodating
P360 40.5 280 42.3
P400 35.0 320 34.3
multiple specimens. Major advantages of automated grinding
P500 30.2 . . . . . .
and polishing procedures are the consistent quality of specimen
P600 25.8 360 27.3
preparation and the substantial decrease in time. Therefore,
P800 21.8 400 22.1
P1000 18.3 500 18.2
automated techniques are recommended over manual tech-
P1200 15.3 600 14.5
niques.
P1500 12.6 800 11.5
P2000 10.3 1000 9.5
11.9 Most of the devices for automated grinding and pol-
P2500 8.4 1500 8.0
A
ishing move the specimen around a rotating wheel covered
P4000 5.0 . . . . . .
with abrasive so that the specimen follows an epicycloid path.
A
Not found in the FEPA grading system.
In some devices, the specimen rotates on its own axis as well.
ANSI—American National Standards Institute
The resulting scratch pattern now consists of randomly ori-
CAMI—Coated Abrasives Manufacturers Institute
ented arcs. Deciding when the previous scratches have been
FEPA—European Federation of Abrasive Producers
removed is more difficult than with directional (manual)
grinding. The specimen surface should show uniform scratches
before proceeding to the next step. Cleaning between stages is
required to prevent carryover of abrasives and contamination
11.3.2 When fine polishing is required, it may be performed
of subsequent preparation surfaces.
with diamond or an oxide slurry step or both. The choice of
11.10 Table 5 illustrates a traditional automated preparation
final polishing abrasive type and size is dictated by the
method. This method uses conventional SiC papers for grind-
hardness of the specimen. For instance, a lμm diamond final
ing and is suitable for all but the hardest of materials. Tables 6
polish is often sufficient for many grades of steel, however,
and 7 are preparation methods that utilize rigid grinding discs
softer steels and non-ferrous materials often require an addi-
or cloths for fine grinding. The method in Table 6 has been
tional polishing step with an oxide slurry or suspension of SiO
shown to be effective for the preparation of materials harder
or Al O . Final polishing cloths are generally softer and higher
2 3
than HRC45. The method in Table 7 may be used for the
in nap than rough polishing cloths. Therefore, polishing time
preparation of materials softer than HRC45. These procedures
and force must be kept to a minimum to avoid artifacts such as
may produce excellent results outside of the recommended
edge rounding and relief.
hardness ranges.
11.3.3 Careful cleaning of the specimen between stages is
mandatory to prevent contamination by coarser abrasive.
12. Special Procedures
Ultrasonic cleaning may be effective.
11.3.4 The polishing operations may be conducted by
12.1 Occasionally, the metallographer is faced with the
manual or by automated methods (preferred).
preparation of unfamiliar specimens or with special situations.
Anticipation of every possible situation is, of course, impos-
Manual (Hand-held) Methods
sible but some guidance can be offered.
11.4 When grinding manually, the specimen should be
12.1.1 When used properly, electrolytic polishing can pro-
moved back and forth across the paper to allow for even wear.
duce near deformation-free surfaces but works best on solid
Between grinding steps, the specim
...