ASTM E7-22

Standard Terminology Relating to Metallography

SIGNIFICANCE AND USE
3.1 Standards of Committee E04 consist of test methods, practices, and guides developed to ensure proper and uniform testing in the field of metallography. In order for one to properly use and interpret these standards, the terminology used in these standards must be understood.  
3.2 The terms used in the field of metallography have precise definitions. The terminology and its proper usage must be completely understood in order to adequately communicate in this field. In this respect, this standard is also a general source of terminology relating to the field of metallography facilitating the transfer of information within the field.

General Information

• Status: Published
• Publication Date: 30-Sep-2022
• ICS: 01.040.77 - Metallurgy (Vocabularies)
• ICS: 77.040.99 - Other methods of testing of metals
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.02 - Terminology

Relations

• Refers: ASTM E45-18a(2023) - Standard Test Methods for Determining the Inclusion Content of Steel
• Effective Date: 01-Nov-2023
• Refers: ASTM E112-12 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 15-Nov-2012
• 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 E112-10 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Nov-2010
• Refers: ASTM E175-82(2010) - Standard Terminology of Microscopy (Withdrawn 2019)
• Effective Date: 01-Jul-2010
• Refers: ASTM E112-96(2004)e2 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 23-Oct-2006
• Refers: ASTM E45-05e3 - 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 E45-05 - 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 E175-82(2005)e1 - Standard Terminology of Microscopy
• Effective Date: 01-May-2005
• Refers: ASTM E112-96(2004) - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Nov-2004
• Refers: ASTM E112-96(2004)e1 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Nov-2004

Overview

ASTM E7-22 - Standard Terminology Relating to Metallography is a key terminology standard developed by ASTM Committee E04. It establishes uniform definitions for terms, acronyms, and symbols used in the field of metallography and metallographic testing. By providing standard language, ASTM E7-22 facilitates accurate communication, data interpretation, and knowledge sharing among professionals in metallurgy, materials science, and testing laboratories. The standard is essential for those who develop, execute, or interpret metallographic test methods, ensuring consistency and clarity across industry practices.

Key Topics

• Comprehensive Metallography Vocabulary
  ASTM E7-22 covers a wide range of terms used in metallography, including specimen preparation, microscopy techniques, microindentation, quantitative metallography, microstructure analysis, and photomicrography.

• Standardized Definitions
  The document focuses on terms that are unique to metallography or require precise technical definitions beyond general dictionary terms. This includes terminology related to grain size, phases, crystal structures, and defects within metals and alloys.

• Significance for Testing Standards
  Consistent terminology supports correct application and interpretation of test methods, practices, and guides published by ASTM’s Committee E04. Using standardized language helps ensure data accuracy and enables easy comparison of results across different organizations and studies.

• Detailed Explanations and Cross-References
  Many definitions in ASTM E7-22 are supported by explanatory notes, context, or references to related terms in other ASTM standards, contributing to a holistic understanding.

Applications

• Metallographic Testing and Analysis
  Essential for anyone preparing, examining, or interpreting microstructures in metals and alloys, such as laboratory technicians, quality assurance specialists, or research scientists.

• Materials Research and Development
  Researchers in materials science use ASTM E7-22 to ensure the correct use of metallographic terminology when describing new materials, microstructures, and testing results.

• Quality Control and Failure Analysis
  Metallurgical engineers rely on the standard for accurate communication in quality control, failure analysis, and when documenting results for traceability and compliance.

• Training and Education
  ASTM E7-22 is widely used as a reference in academic programs and training courses to introduce students and professionals to standard metallographic terms.

• International Collaboration
  As an internationally recognized standard, ASTM E7-22 aids multinational teams, suppliers, and customers in effective technical communication, promoting alignment in specifications and reports.

Related Standards

• ASTM E45: Test Methods for Determining the Inclusion Content of Steel - Provides guidance on examining nonmetallic inclusions in steel using metallographic techniques.
• ASTM E112: Test Methods for Determining Average Grain Size - Establishes procedures for measuring and evaluating grain size in metallic materials.
• ASTM E175: Terminology of Microscopy (Withdrawn) - Was previously used for standardizing microscopy terms related to metallography.
• ASTM E1122: Practice for Obtaining JK Inclusion Ratings Using Automatic Image Analysis (Withdrawn) - Addressed methodologies for automated image analysis of inclusions.

Practical Value

By referencing ASTM E7-22, organizations and individuals in the metallurgical field benefit from:

• Improved precision in test reporting and documentation
• Reduced miscommunication in technical discussions and publications
• Consistency in interpretation of results across different laboratories and industries
• Compliance with industry expectations and regulatory requirements

ASTM E7-22 is indispensable for maintaining excellence, accuracy, and standardization in metallographic testing, analysis, and reporting.

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: E7 − 22
Standard Terminology Relating to
Metallography
This standard is issued under the fixed designation E7; the number immediately following the designation indicates the year of original
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.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. Scope testing in the field of metallography. In order for one to
properly use and interpret these standards, the terminology
1.1 This standard covers the definition of terms, acronyms,
used in these standards must be understood.
and symbols used in ASTM documents related to the field of
metallography and metallographic testing. Terms that are only
3.2 The terms used in the field of metallography have
relevant to a particular standard or that are adequately defined
precise definitions. The terminology and its proper usage must
in a general dictionary are not defined in this terminology
be completely understood in order to adequately communicate
standard.
in this field. In this respect, this standard is also a general
1.2 This standard includes terminology used in metallo-
source of terminology relating to the field of metallography
graphic areas, such as, but not limited to: light microscopy,
facilitating the transfer of information within the field.
microindentationhardnesstesting,specimenpreparation,x-ray
and electron metallography, quantitative metallography,
4. Terminology
photomicrography, and determination of grain size and inclu-
Abbe condenser—see condenser, Abbe. (E175)
sion content.
1.3 This standard may be of use to individuals utilizing
aberration—any error that results in image degradation. Such
standards of Committee E04 as well as by those in need of a
errors may be chromatic, spherical, astigmatic, comatic,
general reference source for terminology in the field of
distortion,orcurvatureoffield;andcanresultfromdesignor
metallography.
execution, or both. (E175)
2. Referenced Documents
absorption—the decrease in intensity which radiation under-
2.1 ASTM Standards:
goes during its passage through matter when the ratio of
E45Test Methods for Determining the Inclusion Content of
transmitted or reflected luminous flux to incident is less than
Steel
1.
E80Recommended Practice for Dilatometric Analysis of
absorption coefficient—specific factor characteristic of a
MetallicMaterials;ReplacedbyE228(Withdrawn1986)
substance on which its absorption radiation depends. The
E112Test Methods for Determining Average Grain Size
rate of decrease of the natural logarithm of the intensity of a
E175Terminology of Microscopy (Withdrawn 2019)
parallel beam per unit distance traversed in a substance. For
E1122Practice for Obtaining JK Inclusion Ratings Using
X-rays, the linear absorption coefficient is the natural loga-
Automatic Image Analysis (Withdrawn 2006)
rithm of the ratio of the incident intensity of an X-ray beam
3. Significance and Use
incident on unit thickness of an absorbing material to the
3.1 Standards of Committee E04 consist of test methods,
intensity of the beam transmitted. If I is the incident inten-
e
practices, and guides developed to ensure proper and uniform
sity of a beam of X-rays, Ithe transmitted intensity, and X
t
the thickness of the absorbing material, then:
This terminology is under the jurisdiction of ASTM Committee E04 on
I 5 I exp~2µX! (1)
t e
Metallography and are the direct responsibility of Subcommittee E04.02 on
Here µ is the linear absorption coefficient. The mass absorp-
Terminology.
tion coefficient is given by µ/ρ where ρ is the density.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
approved in 1926. Last previous edition approved 2017 as E7–17. DOI: 10.1520/
E0007-22. absorption edge—an abrupt change in absorption coefficient
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
at a particular wavelength. The absorption coefficient is
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
always larger on the short wavelength side of the absorption
Standards volume information, refer to the standard’s Document Summary page on
edge.
the ASTM website.
The last approved version of this historical standard is referenced on
www.astm.org. absorption limit—See absorption edge.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E7−22
accelerating potential—a relatively high voltage applied be- alpha brass—a solid solution phase of one or more alloying
tweenthecathodeandanodeofanelectronguntoaccelerate elements in copper and having the same crystal lattice as
electrons. copper.
achromatic—literally, color-free.Alens or prism is said to be
alpha iron (Fe)—solid phase of pure iron which is stable at
achromatic when corrected for two colors. The remaining
temperatures below 910°C and possesses the body-centered
color seen in an image formed by such a lens is said to be
cubic lattice. It is ferro-magnetic below 768°C.
secondary chromatic aberration. See apochromatic objec-
amplifier—a negative lens, used in lieu of an eyepiece, to
tive
project under magnification the image formed by an objec-
achromatic objective—an objective that is corrected chro-
tive.The amplifier is especially designed for flatness of field
matically for two colors, and spherically for one, usually in
and should be used with an apochromatic objective.
the yellow-green part of the spectrum.
ampliphan eyepiece— See amplifier.
achromatic objective lens—an objective lens with longitudi-
analyzer—an optical device, capable of producing plane
nal chromatic correction for green and blue, and spherical
polarized light, used for detecting the state of polarization.
chromatic correction for green. Note—Lens should be used
with a green filter.
angle of reflection: ( 1) reflection —the angle between the
reflected beam and the normal to the reflecting surface.
acid extraction—See extraction.
(2) diffraction—the angle between the diffracted beam and
air-lock—an intermediate enclosed chamber of a vacuum or
the diffracting planes.
pressure system through which an object may be passed
without materially changing the vacuum or pressure of the
Angstrom unit (abbreviation)=A,Å , or A. U—a unit of
−8
system.
length equal to 10 cm. This is the standard unit of
measurement in X-ray crystallography.
airy disk—the image of a bright point object, as focused by a
lens system.
angular aperture—See aperture, optical.
DISCUSSION—With monochromatic light, it consists of a central point
anisotropic (replaces anisotropy)—having different values for
of maximum intensity surrounded by alternate circles of light and
a property, in different directions.
darkness caused by the reinforcement and interference of diffracted
rays.Thelightareasarecalledmaximaandthedarkareasminima.The
annealing-twin bands— See twin bands.
distribution of light from the center to the outer areas of the figure was
anode aperture—See aperture.
investigated mathematically by Sir George Airy. The diffraction disk
forms a basis for determining the resolving power of an ideal lens
anvil—the base on which objects for hardness test are placed.
system.The diameter of the disk depends largely on the aperture of the
lens. The diffraction of light causing the Airy disk is a factor limiting anvil effect—the effect caused by use of too high a load or
the resolution of a well corrected optical system. (E175)
whentestingthehardnessoftoothinaspecimen,resultingin
a bulge or shiny spot on the under side of the specimen.
alignment—a mechanical or electrical adjustment of the
components of an optical device in such a way that the path
aperture, angular—theanglebetweenthemostdivergentrays
oftheradiatingbeamcoincideswiththeopticalaxisorother
that can pass through a lens to form the image of an object
predeterminedpathinthesystem.Inelectronopticsthereare
(E175)
three general types:
aperture, effective—the diameter of the entrance pupil; it is
(1) magnetic alignment—an alignment of the electron
theapparentdiameterofthelimitingaperturemeasuredfrom
optical axis of the electron microscope such that the image
the front. (E175)
rotatesaboutapointinthecenteroftheviewingscreenwhen
the current flowing through a lens is varied.
aperture, electron:—
(2) mechanical alignment—a method of aligning the
anode aperture— the opening in the accelerating voltage
geometrical axis of the electron microscope by relative
anode shield of the electron gun through which the electrons
physical movement of the components, usually as a step
must pass to illuminate or irradiate the specimen.
preceding either magnetic or voltage alignment.
(3) voltage alignment—a condition of alignment of an condenser aperture—an opening in the condenser lens con-
electron microscope such that the image expands or con- trolling the number of electrons entering the lens and the
tracts symmetrically about the center of the viewing screen angular aperture of the illuminating beam. The angular aper-
when the accelerating voltage is changed. ture can also be controlled by the condenser lens current.
physical objective aperture—a metal diaphragm, centrally
allotriomorphic crystal—a crystal whose lattice structure is
pierced with a small hole, used to limit the cone of electrons
normal, but whose outward shape is imperfect since it is
accepted by the objective lens. This improves image contrast
determinedtosomeextentbythesurroundings;thegrainsin
since highly scattered electrons are prevented from arriving at
a metallic aggregate are allotriomorphic crystals.
the Gaussian image plane and therefore can not contribute to
alloy system—a complete series of compositions produced by
background fog.
mixing in all proportions any group of two, or more,
components, at least one of which is a metal. aperture, optical—the working diameter of a lens or a mirror.
E7−22
angular aperture— the angle between the most divergent automatic image analysis—the separation and quantitative
rays which can pass through a lens to form the image of an evaluation of an image into its elements with or without
object. operator interaction. It includes the enhancement, detection,
and quantification of the features contained in an image
aplanatic—corrected for spherical aberration and coma.
through the use of optical, geometrical, and stereological
(E175)
parameters and a computer program. Image analysis data
output can provide individual measurements on each sepa-
aperture diaphragm—a device to define the aperture.
rate feature (feature specific) or totals for all features of a
apochromatic objective—anobjectivewithlongitudinalchro-
particular type in the field (field specific).
matic correction for red, green and blue, and spherical
automatic image analyzer—a device which can be pro-
chromatic correction for green and blue. This is the best
grammed to detect and measure features of interest in an
choice for high resolution or color photomicrography.
image. It may include accessories such as automatic focus
arcing—in electron diffraction, the production of segments of
and an automatic traversing stage to permit unattended
circular patterns, indicating a departure from completely
operation.
random orientation of the crystals of the specimen.
average coefficient of cubical expansion—averagechangein
arrest—thatportionofacoolingcurveinwhichtemperatureis
unit volume of a substance per unit change in temperature
invariant with time (for example, thermal or eutectic arrest).
over a specified range of temperature.
artifact—a false microstructural feature that is not an actual
average coefficient of linear expansion— average change in
characteristic of the specimen; it may be present as a result
unit length of a body per unit change in temperature over a
of improper or inadequate preparation, handling methods, or
specified range of temperature.
optical conditions for viewing.
average coefficient of thermal expansion— general term.
ascending fork point—in a ternary phase diagram, the con- (See also average coefficient of cubical expansion and
figuration at the convergence of the three bivariant curves
average coefficient of linear expansion.)
uponeachofthefourphasesassociatedinClassIIunivariant
average grain diameter— See grain size.
equilibrium; for example, the union of two ascending liqui-
axial ratio—the ratio of the length of one axis to that of
dus surface valleys to form one ascending liquidus surface
another (for example, c/a) or the continued ratio of three
valley.
axes (for example, a:b:c).
aspect ratio—the length-to-width ratio of a microstructural
axis (crystal)—the edge of the unit cell of a space lattice.Any
feature in a two-dimensional plane.
oneaxisofanyonelatticeisdefined,inlengthanddirection,
asterism—a lengthening of diffraction spots usually in the with respect to the other axes of that lattice.
radial direction.
axis, optical—thelineformedbythecoincidingprincipalaxes
astigmatism—a defect in a lens or optical system which of a series of optical elements comprising an optical system.
It is the line passing through the centers of curvature of the
causes rays in one plane parallel to the optical axis to focus
at a distance different from those in the plane at right angles optical surfaces. (E175)
to it.
axis, optic—the direction, or directions in an anisotropic
crystal along which light is not doubly refracted. (E175)
ASTM grain size number— See grain size.
athermal—not isothermal, with changing rather than constant
Babo’s law—the vapor pressure over a liquid solvent is
temperature conditions.
lowered approximately in proportion to the quantity of a
nonvolatile solute dissolved in the liquid.
atomic replica—See replica.
atomic scattering factor—the ratio of the amplitude of the
backing film—a film used as auxiliary support for the thin
wave scattered by an atom to that scattered by a single
replica or specimen-supporting film.
electron. Symbol=f.
back reflection—the diffraction of X-rays at a Bragg angle
austenite—a face-centered cubic solid solution of carbon or
approaching 90°.
other elements in gamma iron.
bainite—upper, lower, intermediate— metastable micro-
austenite grain size—the grain size which exists or existed in
structure or microstructures resulting from the transforma-
austenite at a given temperature. See Test Methods E112.
tion of austenite at temperatures between those which
produce pearlite and martensite. These structures may be
autographic dilatometer—a dilatometer that automatically
formed on continuous (slow) cooling if the transformation
recordsinstantaneousandcontinuouschangesindimensions
rate of austenite to pearlite is much slower than that of
and some other controlled variable such as temperature or
austenite to bainite. Ordinarily, these structures may be
time.
formed isothermally at temperatures within the above range
autographic pyrometer— See pyrometer. by quenching austenite to a desired temperature and holding
E7−22
for a period of time necessary for transformation to occur. If binodal curve—in a two-dimensional phase diagram, a con-
the transformation temperature is just below that at which tinuous line consisting of both of the pair of conjugate
the finest pearlite is formed, the bainite (upper bainite) has a boundaries of a two-phase equilibrium and which join,
featheryappearance.Ifthetransformationtemperatureisjust without inflection, at a critical point. See miscibility gap.
above that at which martensite is produced, the bainite
birefringent—having more than one refractive index. Such
(lower bainite) is acicular, resembling slightly tempered
materials exhibit alternately bright and dark reflections at
martensite. At the higher resolution of the electron
45° intervals during a 360° rotation with plane-polarized
microscope, upper bainite is observed to consist of plates of
light. (See also anisotropic.)
cementite in a matrix of ferrite.These discontinuous carbide
plates tend to have parallel orientation in the direction of the bivariant equilibrium—a stable state among a number of
longerdimensionofthebainiteareas.Lowerbainiteconsists phases equal to the number of components in a system and
of ferrite needles containing carbide platelets in parallel in which any two of the external variables (temperature,
array cross-striating each needle axis at an angle of about pressure, or concentrations) may be varied, at will, without
60°. Intermediate bainite resembles upper bainite; however, necessarily causing a change in the number of phases;
the carbides are smaller and more randomly oriented. sometimes called divariant equilibrium.
bisectrix, acute—in biaxial crystals, that principal axis of the
balsam, Canada——a resin from the balsam fir Abies bal-
ellipsoid of indexes which bisects the smaller angle between
samea.
the optic axes. (E175)
DISCUSSION—Dissolved in xylene, toluene, or benzene it is used as a
mountant for permanent microscopical preparations. Its refractive
bisectrix, obtuse—inbiaxialcrystals,thatprincipalaxisofthe
index may vary from 1.530 to 1.545 and its softening point from room
ellipsoid of indexes which bisects the larger angle between
temperature to 100°C, these properties varying with age and solvent
the optic axes. (E175)
content. If impure it discolors with age. (E175)
blowholes—a hole produced in a casting by gas which was
band—inelectrondiffraction,abroadintensitymaximumwith
trapped during solidification.
sharp edges.
body-centered—havinganatom(orgroupofatoms)separated
banded structure (banding)—alternate bands parallel with
1 1 1
by a translation of ⁄2, ⁄2, ⁄2 from a similar atom (or group
the direction of working resulting from the elongation of
ofatoms).Thenumberofatomsinabody-centeredcellmust
segregated areas.
be a multiple of two.
barrel distortion— See distortion.
boiling pressure—at a specified temperature, the pressure at
basal plane—that plane of a hexagonal or tetragonal crystal
which a liquid and its vapor are in equilibrium.
which is perpendicular to the axis of highest symmetry. Its
Miller indices are (0001) or (001), respectively. boiling temperature—at a specified pressure, the temperature
at which a liquid and its vapor are in equilibrium.
bellows length—the distance from the eyepiece to the photo-
bonded abrasive disk—a rigid support surface with an
sensitive material or viewing screen in a photomicrographic
abrasive, typically diamond, bonded to the surface by a
apparatus.
ceramic, resin, or metal based material.
Bertrand lens—an auxiliary removable lens in the body of a
boundary grain—in the Jeffries’ method for grain size
microscope, used to examine images in the back focal plane
measurement, a grain that is intersected by the boundary of
of the objective, for example, interference figures with
the standard area and is, therefore, counted only as one-half
polarized light.
grain. (See also Jeffries’ Method.)
beta structure—structurally analogous body-centered cubic
Bragg angle—the angle between the incident beam and the
phases (similar to beta brass), or electron compounds, that
lattice planes considered.
have ratios of 3 valence electrons to 2 atoms.
Bragg equation:—
biased gun—an electron gun in which there is a bias voltage
on the cathode cap. (See also self-biased gun.) nλ 5 2dsinθ (2)
where:
bifilar eyepiece—aFilareyepiecewithmotionintwomutually
perpendicular directions. n = order of reflection,
λ = wavelength of X-rays,
bi-modal grain size distribution—a condition where the
d = distance between lattice planes, and
distribution of individual grain areas or intercept lengths,
θ = Bragg angle.
converted to ASTM grain size numbers (based on the area
Bragg method—a method of X-ray diffraction in which a
percent or length percent per G class) exhibits two peaks.
single crystal is mounted on a spectrometer with a crystal
binary alloy—any specific composition in a binary system.
face parallel to the axis of the instrument.
binary system—thecompleteseriesofcompositionsproduced Braun’s law—the ratio of the solubility change with pressure,
by mixing a pair of components in all proportions. temperature being constant, (δ X/δP)T, to the solubility
E7−22
changewithtemperature,pressurebeingconstant,(δX/δT)P, commonly known as iron carbide and possesses an ortho-
is equal to the negative of the product of the absolute rhombic lattice. In “plain-carbon steels” some of the iron
temperature, T, and the (fictitious) volume change (∆v) atoms in the cementite lattice are replaced by manganese,
which accompanies the solution of 1 g·molecular weight of and in “alloy steels” by other elements such as chromium or
the solute in an infinitely large quantity of the saturated tungsten. Cementite will often appear as distinct lamellae or
solution at T degrees, divided by the amount of heat, Q, as spheroids or globules of varying size in hypo-eutectoid
developed in the process: steels. Cementite is in metastable equilibrium and has a
tendency to decompose into iron and graphite, although the
δX/δP T/ δXδT P52T·∆v/Q (3)
~ ! ~ !
reaction rate is very slow.
brightfield illumination— for reflected light, the illumination
central pencil—abundleofraysoriginatingintheaxiswithan
whichcausesspecularlyreflectedsurfacesnormaltotheaxis
angular aperture equal to the effective aperture of the lens.
of a microscope to appear bright. For transmission electron
These rays pass through the lens aperture and contribute to
microscopy, the illumination of an object so that it appears
the formation of the image.
on a bright background.
certified reference material—a reference material, the com-
burning (burnt, burned)—a term applied to metal which has
position or properties of which are certified by a recognized
been permanently damaged by having been heated to a
standardizing agency or group. Typically such a material is
temperatureclosetoorwithinthemeltingrange.Thisresults
accompanied by documentation (certificate).
in a structure exhibiting incipient melting or intergranular
oxidation.
characteristic curve—the curve showing the relationship
between exposure and resulting density in a photographic
calibration—1) the act or process of determining the relation-
image. It is usually plotted as the density against the log
ship between a set of standard units of measure and the
exposure. Called also the “H and D curve” and the “sensi-
output of an instrument or test procedure,
tometric curve.”
2) the graphical or mathematical relationship relating the
desired property (expressed in a standard unit of measure
characteristic radiation—X-radiation of a particular set of
such as micrometers or Kg/mm ) to the instrument output
wavelengths, produced by and characteristic of a particular
(instrument units such as filar divisions or pixels).
element used as a target whenever its excitation potential is
exceeded.
caliper diameter (Feret’s diameter)—the length of a line
normal to two parallel lines, tangent to opposite edges of a
charge neutralizer gun—anelectrongunusedtodissipatethe
phase or object.
charges which tend to build up on specimen surfaces, within
an electron-diffraction camera, which would introduce un-
calcite—a doubly refracting mineral used in the manufacture
desired electrostatic fields.
of polarizing prisms.
DISCUSSION—It is uniaxial negative and in the trigonal diversion of
¯
chemical potential—(µ or G ) the partial molar free energy
i i
the hexagonal system of crystals. Its indexes are ε=1.486, ω =1.658;
of component i, that is, the change in free energy of a
its hardness is 3 on the Mohr scale and specific gravity 2.711. (E175)
solution upon adding one mole of component i to an infinite
Canada balsam——see balsam, Canada. (E175)
amount of solution of given composition,
carbide—a compound of carbon with one or more elements, ¯
δG/δn 5 G 5 µ (4)
~ !
i T,P,n i i
1···
which, in customary formulation, are considered as being
where:
more positive than carbon.
G = Gibbs free energy, and
case—in a ferrous alloy, the outer portion that has been made th
n = number of moles of the i component.
i
harder than the inner portion (see core) as a result of altered
composition, or structure, or both, from treatments such as Chinese script eutectic—a configuration of eutectic
carburizing, nitriding, and induction hardening. constituents, found particularly in some cast alloys of
aluminum containing iron and silicon and in magnesium
cassette—a light-tight film or plate holder.
alloyscontainingsilicon,whichresemblesinappearancethe
characters in Chinese script.
cast replica—See replica.
cast structure—the structure, on a macroscopic or micro-
chlorine or volatile halide extraction—See extraction.
scopic scale, of a casting.
chromatic aberration—a defect in a lens or lens system as a
result of which the lens possesses different focal lengths for
cathode lens—a lens field terminated on one side by a surface
at zero potential (cathode) normal to the optic axis. A radiation of different wavelengths.
cathode lens occurs in any system in which a cathode is
Class I quaternary equilibrium—in a four-component
imaged by its own electron emission, be it thermionic,
system, the stable univariant coexistence of five phases, one
photoelectric, secondary, or field emission.
of which must disappear upon lowering the temperature or
cementite—a very hard and brittle compound of iron and pressure; for example, the quaternary eutectic equilibrium,
carbon corresponding to the empirical formula Fe C. It is L= α+ β+ γ+ δ.
E7−22
Class I quinary equilibrium—in a five-component system, associated bivariant equilibria below; for example,
the stable univariant coexistence of six phases, one of which L+ α+ β+ γ= δ+ ε.
must disappear upon lowering the temperature or pressure;
Class V quinary equilibrium—in a five-component system,
for example, the quinary eutectic equilibrium,
the stable univariant coexistence of six phases, one of which
L= α+ β+ γ+ σ+ ε.
must disappear upon increasing the temperature or pressure;
Class I ternary equilibrium—in a three-component system, for example, the quinary peritectic equilibrium,
L+ α+ β+ γ+ δ= ε.
the stable univariant coexistence of four phases, one of
which must disappear upon lowering the temperature or
Clausius-Clapeyron equation—the rate of change of the
pressure; for example, the ternary eutectic equilibrium,
pressure of a heterogeneous equilibrium with change of
L= α+ β+ δ.
temperature dP/dT is equal to the heat of transformation
from the low to the high temperature state ∆ Hv divided by
Class II quaternary equilibrium—in a four-component
system, the stable univariant coexistence of five phases, two the product of the absolute temperature of the equilibrium
and the volume change of the transformation T∆V:
of which appear in each of the three associated bivariant
equilibria at temperatures and pressures above, while the
dP/dT 5 ∆Hv/T∆V (5)
other three phases all occur in both of the associated
or,
bivariant equilibria below; for example,L+ α= β+ γ+ δ.
dlnP/dT'Hv/RT (6)
Class II quinary equilibrium—in a five-component system,
where R is the gas constant and the equilibrium is not
thestableunivariantcoexistenceofsixphases,twoofwhich
near a critical point.
appear in each of the four associated bivariant equilibria at
clear cross test—an experimental method for determining
temperatures and pressures above, while the other four
whichoftwoconceivabletwo-phaseequilibriaisreal;atthat
phases occur in both of the associated bivariant equilibria
composition at which the two conceivable two-phase fields
below; for example,L+ α= β+ γ+ δ+ ε.
cross, an alloy is brought to equilibrium and the phases
Class II ternary equilibrium—in a three-component system,
identified;thesameprinciplemaybeappliedtohigher-order
the stable univariant coexistence of four phases, two of
equilibria in higher-order systems.
which appear in both of the associated bivariant equilibria at
clear glass focusing screen—a glass screen polished on both
higher temperature and pressure, while the other two phases
sides and mounted for use in a camera, in lieu of photo-
occur in both bivariant equilibria below; for example,
sensitive material, for the purpose of establishing a plane on
L+ α= β+ γ.
which to focus an image prior to recording it.
Class III quaternary equilibrium—in a four-component
cleavage planes—that family of planes of a crystal along
system, the stable univariant coexistence of five phases,
which the crystal is easily split.
three of which appear in both of the associated bivariant
equilibria at temperatures and pressures above, while the
close packed—a geometric arrangement whereby a collection
othertwophasesoccurinallthreeoftheassociatedbivariant
of equally sized spheres (atoms) may be packed together in
equilibria below; for example,L+ α+ β= γ+ δ.
a minimum total volume.
Class III quinary equilibrium—in a five-component system,
coefficient of thermal expansion—changeinunitoflength(or
the stable univariant coexistence of six phases, three of
volume) accompanying a unit change of temperature, at a
which appear in all three of the associated bivariant equilib-
specified temperature.
riaattemperaturesandpressuresabove,whiletheotherthree
occurinallthreeoftheassociatedbivariantequilibriabelow;
coalescence—growthofgrainsattheexpenseoftheremainder
for example,L+ α+ β= γ+ δ+ ε. by absorption or the growth of a phase or particle at the
expenseoftheremainderbyabsorptionorbyreprecipitation.
Class III ternary equilibrium—inathree-componentsystem,
the stable univariant coexistence of four phases, one of coarse grains—grains either larger than normal for the par-
which must disappear at higher temperature or pressure; for
ticular wrought metal or alloy, or grains of such a size that a
example, the ternary peritectic equilibrium,L+ α+ β= γ. surface roughening, popularly known as “orange peel” or
“alligator skin,” is produced.
Class IV quaternary equilibrium—in a four-component
system, the stable univariant coexistence of five phases, one
coherent precipitate—a precipitated particle of a second
of which must disappear at higher temperature or pressure; phase, the lattice of which still maintains registry with the
for example, the quaternary peritectic equilibrium,
matrix lattice. Because the lattice spacings are usually
L+ α+ β+ γ= δ. different, strains usually exist at the interface.
Class IV quinary equilibrium—in a five-component system, coherent scattering—a kind of X-ray electron scattering in
thestableunivariantcoexistenceofsixphases,fourofwhich which the phase of the scattered beam has a definite (not
appearinbothassociatedbivariantequilibriaattemperatures random) relation to the phase of the incident beam. Also
and pressures above, while the other two occur in all four called unmodified scattering.
E7−22
cold-cathode gun—an electron gun in which electrons pro- composition—the quantity of each of the components of a
duced in a gas discharge are accelerated through a small mixture; usually expressed in terms of the weight
aperture in the anode. percentage, or the atomic percentage of each of the compo-
nents in the mixture.
cold junction—See reference junction.
coldjunctioncorrection—See reference junction correction.
Compton scattering—X-ray scattering by atoms in which the
cold worked structure—a microstructure resulting from plas- scattered beam has, relative to the incident beam, a longer
ticdeformationofametaloralloybelowitsrecrystallization
wavelength and a random phase relationship. Also called
temperature. incoherent or modified scattering.
collimation—the operation of controlling a beam of radiation
condensed system—apuresubstance,ormixture,atapressure
so that its rays are as nearly parallel as possible.
and temperature such that the vapor phase does not exist.
collodion replica— See replica.
condenser—a term applied to lenses or mirrors designed to
color film—aphotographicfilmconsistingofseveralemulsion
collect, control, and concentrate radiation in an illumination
layers,wheretheindividuallayersselectivelyrecordvarious
system.
wavelengths of light.
condenser, Abbe—originally a two-lens substage condenser
color temperature—the temperature of a blackbody in de-
combination designed by Ernst Abbe.
grees Kelvin (K). In photography, the apparent temperature
DISCUSSION—It lacks chromatic correction though designed for a
in K of a luminous source which may be measured by its minimum of spherical aberration and has only a very low-angle
aplanaticcone.Itmayberatedwithanumericalapertureashighas1.3.
emission ratio of blue to red light.
(E175)
column, electron microscope—the assembly of gun, lenses,
and specimen, viewing and plate chambers. condenser aperture— See aperture.
condenser, darkfield—a condenser forming a hollow cone of
columnar structure—a macro- or microstructure character-
light with its apex (or focal point) in the plane of the
ized by elongated grains whose long axes are parallel, for
specimen.
example, to solidification direction, electroplated direction,
DISCUSSION—When used with an objective having a numerical
etc.
aperture lower than the minimum numerical aperture of the hollow
cone, only light deviated by the specimen enters the objective. Objects
coma—a lens aberration occurring in that part of the image
are seen as bright images against a dark background. (E175)
field that is some distance from the principal axis of the
system. It results from different magnification in the various
condenser, darkfield, bispheric—a darkfield condenser con-
lens zones.
sisting of a convex spherical reflector mounted concentric
DISCUSSION—Extra-axial object points appear as short comet-like
with a larger concave reflector.
images with the brighter small head toward the center of the field
DISCUSSION—The rays are formed into a diverging cone by the
(positive coma) or away from the center (negative coma). (E175)
convex reflector. The annular concave reflector then forms a hollow
converging cone which is focused on the subject. See condenser,
comparison standard—a standard micrograph or a series of
darkfield. (E175)
micrographs, usually taken at 75 or 100 diameters, or a
suitable equivalent built into the eyepiece and used to
condenser lens—adeviceusedtofocusradiationinornearthe
determine grain size by direct comparison with the image.
plane of the object.
compensating eyepiece—onedesignedforusewithobjectives
condenser, darkfield, paraboloid—a darkfield condenser
such as apochromats, the lateral chromatic aberration of
consisting of a reflecting surface in the form of a segment of
which is undercorrected.
a paraboloid of revolution.
DISCUSSION—Parallel rays entering the condenser around the periph-
compensating lead wires—wires leading from a thermo-
ery of the central stop are reflected from the curved surfaces and
couple to the voltage-measuring instrument. These wires
converge at the focus of the paraboloid. See condenser, darkfield.
must be of such compositions that they will generate an emf
(E175)
equivalent to the emf generated by the reference junction of
condenser, variable-focus—essentially anAbbe condenser in
the couple.
whichtheupperlenselementisfixedandthelowermovable.
complex silicate inclusions—a general term describing sili-
DISCUSSION—The lower lens may be used to focus the illumination
cate inclusions containing visible constituents besides the
between the elements so that it emerges from the stationary lens as a
silicate matrix. An example would be corundum or spinel
large diameter parallel bundle. The field of low-power objectives may
thus be filled without removing the top element. At the opposite
crystals occurring in a silicate matrix in steel.
extreme it can be adjusted to have a numerical aperture as high as 1.3.
component—one of the independently variable substances by
(E175)
means of which the composition of each phase of a system
of heterogeneous equilibrium may be described completely; congruent transformation—an isothermal, or isobaric, phase
usually an element, or a compound that remains undissoci- changeinwhichbothofthephasesconcernedhavethesame
ated throughout the range of temperature and pressure composition throughout the process; the order of a system
concerned. becomes unary at a composition of congruency.
E7−22
conjugate phases—those states of matter of unique composi- particle) resulting from non-equilibrium growth which oc-
tion which coexist at equilibrium at a single point in curs over a range of temperatures or compositions.
temperature and pressure; for example, the two coexisting
corona shield—a smooth, rounded metal covering placed
phases of a two-phase equilibrium.
around exposed high-voltage components to prevent electri-
conjugate planes—two planes of an optical system such that
cal discharge.
one is the image of the other.
counter—a device for the measurement of radiation intensity
constituent—a phase, or combination of phases, which occurs
by means of an electrical triggering principle (Geiger-
in a characteristic configuration in an alloy micro-structure.
Müller).
constitutional diagram—graphical representation of the
coupler, color—a substance capable of reacting with the
compositions, temperatures, pressures or combinations
oxidation product of a color-forming developer to produce a
thereof at which the heterogeneous equilibria of an alloy
colored dye image.
system occur; also called “phase diagram,” or “equilibrium
critical curve—in a binary, or higher order, phase diagram, a
diagram.”
line along which the phases of a heterogeneous equilibrium
continuous phase—the phase forming the matrix or back-
become identical.
ground in which other phases may be dispersed as isolated
critical illumination—see illumination, critical. (E175)
units.
critical point—in a phase diagram, that specific value of
continuous spectrum (X-rays)—the polychromatic radiation
composition, temperature, pressure or combinations thereof
given off by the target of an X-ray tube, containing all
at which the phases of a heterogeneous equilibrium become
wavelengthsaboveacertainminimumvaluecalledtheshort
identical. (See also transformation temperature.)
wave length limit.
critical pressure—that pressure above which the liquid and
contrast enhancement (electron optics)—animprovementin
vapor states are no longer distinguishable.
electron image contrast by the use of an objective aperture
diaphragm, shadow casting, or other means.
critical surface—in a ternary, or higher order, phase diagram,
contrast perception—the ability to differentiate various com- the area upon which the phases in equilibrium become
identical.
ponentsoftheobjectstructurebydifferentintensitylevelsin
the image.
critical temperature—that temperature above which the va-
contrast, photographic—the word contrast has been used in por phase cannot be condensed to liquid by an increase in
many different senses in connection with various photo- pressure.
graphic characteristics; there are different types of photo-
cross direction—one of three mutually perpendicular direc-
graphic contrast and different methods of measuring it. It is
tions used to define a worked material, specifically that
frequently used to designate the magnitude of the density
direction in the plane of working which is at right angles to
difference resulting from a given exposure difference. (For
the direction of maximum elongation.
another use, see gamma.)
crystal—a solid composed of atoms, ions, or molecules
conversion, hardness—the exchange of a hardness number
arranged in a pattern which is periodic in three dimensions.
determined by one method for an equivalent hardness
number of a different scale.
crystal, birefringent——a pertaining to the use of a micro-
scope. (E175)
cooling curve—graphical representation of the course of
temperature fall of a chemical mixture as a function of time
crystal analysis—a method for determining crystal structure,
commonly exhibiting more or less abrupt changes of rate at,
for example, the size and shape of the unit cell and the
or near, those temperatures at which phase changes begin;
location of all atoms within the unit cell.
used in finding the temperatures at which phase changes
crystallite—a crystalline grain not bounded by habit planes.
occur. Occasionally, some property or function other than
time may be used; for example, thermal expansion.
crystal system—one of seven groups into which all crystals
may be divided; triclinic, monoclinic, orthorhombic,
cooling rate—the average slope of the time-temperature curve
hexagonal, rhombohedral, tetragonal, and cubic.
taken over a specified time and temperature interval.
cube texture—a texture found in wrought metals in the cubic
core—(1) case hardening—interior portion of unaltered
system, in which nearly all the crystal grains have a plane of
composition, or microstructure, or both, of a case-hardened
the type (100) parallel or nearly parallel to the plane of
steel article.
working and a direction of the type [001] parallel or nearly
(2) clad products—the central portion of a multilayer com-
parallel to the direction of elongation.
posite metallic material.
coring—avariablecompositionbetweenthecenterandoutside cubic—having three mutually perpendicular axes of equal
of a unit of structure, (such as a dendrite, grain, carbide length.
E7−22
cupping—the condition sometimes occurring in heavily cold deformation lines—thin bands or lines produced in grains of
worked rods and wires, in which the outside fibers are still some metals, particularly those of face-centered cubic
intact and the central zone has failed in a series of cup-and- structure, by cold working; they are not removed by repol-
cone fractures. ishing and re-etching.
degree of freedom—inheterogeneousequilibrium,anexternal
Curie point—that temperature above which a substance be-
variablethatmaybeadjustedindependentlywithoutcausing
comes paramagnetic.
a change of state; the external variables usually considered
curvature of field—a property of a lens that causes the image
are: temperature, pressure, and concentration parameters
of a plane to be focused into a curved surface instead of a
numbering one less than the order of the system.
plane.
delta ferrite—designation commonly assigned to delta iron
darkfield condenser—see condenser, darkfield. (E175)
containing alloying elements in solid solution. Small
amounts of carbon and large amounts of other alloying
darkfield illumination—the illumination of an object such
elementsmarkedlyaffectthehigh-and-low-temperaturelimit
that it appears illuminated with the surrounding field dark.
of equilibrium.
This results from illuminating the object with rays of
sufficient obliquity so that none can enter the objective
delta iron (δ Fe)—solid phase of pure iron which is stable at
directly. As applied to electron microscopy, the image is
temperatures between 1400 and 1539°C and possesses the
formed using only electrons scattered by the object.
body-centered cubic lattice. Strictly, there is no difference
between delta and alpha iron.
dashpot—a hydraulic cylinder device with a controlled leak
designed to eliminate impact loading of mechanisms. Hard-
denatured alcohol—ethyl alcohol containing an addition of a
ness testers may employ a dashpot to bring an indenter into
poisonous substance, making it unfit for human consump-
contactwithaspecimenwithoutimpactorotherdisturbance.
tion.
dead-weight loading—a method of loading in which a weight dendrites—crystals, usually formed during solidification or
is supported solely by the specimen and has no other
sublimation, which are characterized by a tree-like pattern
mechanical connection to the testing machine. In hardness composed of many branches; pine-tree or fir-tree crystals.
testing, the weight is supported by the indenter.
densitometer—an instrument which measures the relationship
between incident light and transmitted or reflected light and,
Debye ring—a continuous circle, concentric about the unde-
viated beam, produced by monochromatic X-ray diffraction using a logarithmic scale, gives a numerical measurement
that corresponds to a material’s opacity or a film’s photo-
from a randomly oriented crystalline powder.An analogous
effect is obtained with electron diffraction. graphic density.
density (film)—transmission density is the common logarithm
Deby
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E7 − 17 E7 − 22
Standard Terminology Relating to
Metallography
This standard is issued under the fixed designation E7; 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
1.1 This standard covers the definition of terms, acronyms, and symbols used in ASTM documents related to the field of
metallography and metallographic testing. Terms that are only relevant to a particular standard or that are adequately defined in
a general dictionary are not defined in this terminology standard.
1.2 This standard includes terminology used in metallographic areas, such as, but not limited to: light microscopy, microinden-
tation hardness testing, specimen preparation, x-ray and electron metallography, quantitative metallography, photomicrography,
and determination of grain size and inclusion content.
1.3 This standard may be of use to individuals utilizing standards of Committee E04 as well as by those in need of a general
reference source for terminology in the field of metallography.
2. Referenced Documents
2.1 ASTM Standards:
E45 Test Methods for Determining the Inclusion Content of Steel
E80 Recommended Practice for Dilatometric Analysis of Metallic Materials; Replaced by E 228 (Withdrawn 1986)
E112 Test Methods for Determining Average Grain Size
E175 Terminology of Microscopy (Withdrawn 2019)
E1122 Practice for Obtaining JK Inclusion Ratings Using Automatic Image Analysis (Withdrawn 2006)
3. Significance and Use
3.1 Standards of Committee E04 consist of test methods, practices, and guides developed to ensure proper and uniform testing in
the field of metallography. In order for one to properly use and interpret these standards, the terminology used in these standards
must be understood.
3.2 The terms used in the field of metallography have precise definitions. The terminology and its proper usage must be completely
understood in order to adequately communicate in this field. In this respect, this standard is also a general source of terminology
relating to the field of metallography facilitating the transfer of information within the field.
This terminology is under the jurisdiction of ASTM Committee E04 on Metallography and are the direct responsibility of Subcommittee E04.02 on Terminology.
Current edition approved June 1, 2017Oct. 1, 2022. Published July 2017October 2022. Originally approved in 1926. Last previous edition approved 20152017 as
E7 –15. –17. DOI: 10.1520/E0007-17.10.1520/E0007-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E7 − 22
4. Terminology
Abbe condenser—see condenser, Abbe. (E175)
aberration—any error that results in image degradation. Such errors may be chromatic, spherical, astigmatic, comatic,
distortion, or curvature of field; and can result from design or execution, or both. (E175)
absorption—the decrease in intensity which radiation undergoes during its passage through matter when the ratio of transmitted
or reflected luminous flux to incident is less than 1.
absorption coefficient—specific factor characteristic of a substance on which its absorption radiation depends. The rate of
decrease of the natural logarithm of the intensity of a parallel beam per unit distance traversed in a substance. For X-rays, the
linear absorption coefficient is the natural logarithm of the ratio of the incident intensity of an X-ray beam incident on unit
thickness of an absorbing material to the intensity of the beam transmitted. If I is the incident intensity of a beam of X-rays,
e
I the transmitted intensity, and X the thickness of the absorbing material, then:
t
I 5 I exp 2μX (1)
~ !
t e
Here μ is the linear absorption coefficient. The mass absorption coefficient is given by μ/ρ where ρ is the density.
absorption edge—an abrupt change in absorption coefficient at a particular wavelength. The absorption coefficient is always
larger on the short wavelength side of the absorption edge.
absorption limit—See absorption edge.
accelerating potential—a relatively high voltage applied between the cathode and anode of an electron gun to accelerate
electrons.
achromatic—literally, color-free. A lens or prism is said to be achromatic when corrected for two colors. The remaining color
seen in an image formed by such a lens is said to be secondary chromatic aberration. See apochromatic objective
achromatic objective—an objective that is corrected chromatically for two colors, and spherically for one, usually in the
yellow-green part of the spectrum.
achromatic objective lens—an objective lens with longitudinal chromatic correction for green and blue, and spherical
chromatic correction for green. Note—Lens should be used with a green filter.
acid extraction—See extraction.
air-lock—an intermediate enclosed chamber of a vacuum or pressure system through which an object may be passed without
materially changing the vacuum or pressure of the system.
airy disk—the image of a bright point object, as focused by a lens system.
DISCUSSION—
With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the
reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the center
to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving
power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is
a factor limiting the resolution of a well corrected optical system. (E175)
alignment—a mechanical or electrical adjustment of the components of an optical device in such a way that the path of the
radiating beam coincides with the optical axis or other predetermined path in the system. In electron optics there are three general
types:
(1) magnetic alignment—an alignment of the electron optical axis of the electron microscope such that the image rotates
about a point in the center of the viewing screen when the current flowing through a lens is varied.
E7 − 22
(2) mechanical alignment—a method of aligning the geometrical axis of the electron microscope by relative physical
movement of the components, usually as a step preceding either magnetic or voltage alignment.
(3) voltage alignment—a condition of alignment of an electron microscope such that the image expands or contracts
symmetrically about the center of the viewing screen when the accelerating voltage is changed.
allotriomorphic crystal—a crystal whose lattice structure is normal, but whose outward shape is imperfect since it is
determined to some extent by the surroundings; the grains in a metallic aggregate are allotriomorphic crystals.
alloy system—a complete series of compositions produced by mixing in all proportions any group of two, or more, components,
at least one of which is a metal.
alpha brass—a solid solution phase of one or more alloying elements in copper and having the same crystal lattice as copper.
alpha iron (Fe)—solid phase of pure iron which is stable at temperatures below 910°C and possesses the body-centered cubic
lattice. It is ferro-magnetic below 768°C.
amplifier—a negative lens, used in lieu of an eyepiece, to project under magnification the image formed by an objective. The
amplifier is especially designed for flatness of field and should be used with an apochromatic objective.
ampliphan eyepiece— See amplifier.
analyzer—an optical device, capable of producing plane polarized light, used for detecting the state of polarization.
angle of reflection: ( 1)reflection —the angle between the reflected beam and the normal to the reflecting surface.
(2) diffraction—the angle between the diffracted beam and the diffracting planes.
−8
Angstrom unit (abbreviation) = A,Å , orA. U—a unit of length equal to 10 cm. This is the standard unit of measurement in
X-ray crystallography.
angular aperture—See aperture, optical.
anisotropic (replaces anisotropy)—having different values for a property, in different directions.
annealing-twin bands— See twin bands.
anode aperture—See aperture.
anvil—the base on which objects for hardness test are placed.
anvil effect—the effect caused by use of too high a load or when testing the hardness of too thin a specimen, resulting in a bulge
or shiny spot on the under side of the specimen.
aperture, angular—the angle between the most divergent rays that can pass through a lens to form the image of an object
(E175)
aperture, effective—the diameter of the entrance pupil; it is the apparent diameter of the limiting aperture measured from the
front. (E175)
aperture, electron:—
anode aperture— the opening in the accelerating voltage anode shield of the electron gun through which the electrons must pass
to illuminate or irradiate the specimen.
E7 − 22
condenser aperture—an opening in the condenser lens controlling the number of electrons entering the lens and the angular
aperture of the illuminating beam. The angular aperture can also be controlled by the condenser lens current.
physical objective aperture—a metal diaphragm, centrally pierced with a small hole, used to limit the cone of electrons accepted
by the objective lens. This improves image contrast since highly scattered electrons are prevented from arriving at the Gaussian
image plane and therefore can not contribute to background fog.
aperture, optical—the working diameter of a lens or a mirror.
angular aperture— the angle between the most divergent rays which can pass through a lens to form the image of an object.
aplanatic—corrected for spherical aberration and coma. (E175)
aperture diaphragm—a device to define the aperture.
apochromatic objective—an objective with longitudinal chromatic correction for red, green and blue, and spherical chromatic
correction for green and blue. This is the best choice for high resolution or color photomicrography.
arcing—in electron diffraction, the production of segments of circular patterns, indicating a departure from completely random
orientation of the crystals of the specimen.
arrest—that portion of a cooling curve in which temperature is invariant with time (for example, thermal or eutectic arrest).
artifact—a false microstructural feature that is not an actual characteristic of the specimen; it may be present as a result of
improper or inadequate preparation, handling methods, or optical conditions for viewing.
ascending fork point—in a ternary phase diagram, the configuration at the convergence of the three bivariant curves upon each
of the four phases associated in Class II univariant equilibrium; for example, the union of two ascending liquidus surface valleys
to form one ascending liquidus surface valley.
aspect ratio—the length-to-width ratio of a microstructural feature in a two-dimensional plane.
asterism—a lengthening of diffraction spots usually in the radial direction.
astigmatism—a defect in a lens or optical system which causes rays in one plane parallel to the optical axis to focus at a distance
different from those in the plane at right angles to it.
ASTM grain size number— See grain size.
athermal—not isothermal, with changing rather than constant temperature conditions.
atomic replica—See replica.
atomic scattering factor—the ratio of the amplitude of the wave scattered by an atom to that scattered by a single electron.
Symbol = f.
austenite—a face-centered cubic solid solution of carbon or other elements in gamma iron.
austenite grain size—the grain size which exists or existed in austenite at a given temperature. See Test Methods E112.
autographic dilatometer—a dilatometer that automatically records instantaneous and continuous changes in dimensions and
some other controlled variable such as temperature or time.
E7 − 22
autographic pyrometer— See pyrometer.
automatic image analysis—the separation and quantitative evaluation of an image into its elements with or without operator
interaction. It includes the enhancement, detection, and quantification of the features contained in an image through the use of
optical, geometrical, and stereological parameters and a computer program. Image analysis data output can provide individual
measurements on each separate feature (feature specific) or totals for all features of a particular type in the field (field specific).
automatic image analyzer—a device which can be programmed to detect and measure features of interest in an image. It may
include accessories such as automatic focus and an automatic traversing stage to permit unattended operation.
average coefficient of cubical expansion— average change in unit volume of a substance per unit change in temperature over
a specified range of temperature.
average coefficient of linear expansion— average change in unit length of a body per unit change in temperature over a
specified range of temperature.
average coefficient of thermal expansion— general term. (See also average coefficient of cubical expansion and average
coefficient of linear expansion.)
average grain diameter— See grain size.
axial ratio—the ratio of the length of one axis to that of another (for example, c/a) or the continued ratio of three axes (for
example, a:b:c).
axis (crystal)—the edge of the unit cell of a space lattice. Any one axis of any one lattice is defined, in length and direction,
with respect to the other axes of that lattice.
axis, optical—the line formed by the coinciding principal axes of a series of optical elements comprising an optical system. It
is the line passing through the centers of curvature of the optical surfaces. (E175)
axis, optic—the direction, or directions in an anisotropic crystal along which light is not doubly refracted. (E175)
Babo’s law—the vapor pressure over a liquid solvent is lowered approximately in proportion to the quantity of a nonvolatile
solute dissolved in the liquid.
backing film—a film used as auxiliary support for the thin replica or specimen-supporting film.
back reflection—the diffraction of X-rays at a Bragg angle approaching 90°.
bainite—upper, lower, intermediate— metastable microstructure or microstructures resulting from the transformation of
austenite at temperatures between those which produce pearlite and martensite. These structures may be formed on continuous
(slow) cooling if the transformation rate of austenite to pearlite is much slower than that of austenite to bainite. Ordinarily, these
structures may be formed isothermally at temperatures within the above range by quenching austenite to a desired temperature
and holding for a period of time necessary for transformation to occur. If the transformation temperature is just below that at
which the finest pearlite is formed, the bainite (upper bainite) has a feathery appearance. If the transformation temperature is
just above that at which martensite is produced, the bainite (lower bainite) is acicular, resembling slightly tempered martensite.
At the higher resolution of the electron microscope, upper bainite is observed to consist of plates of cementite in a matrix of
ferrite. These discontinuous carbide plates tend to have parallel orientation in the direction of the longer dimension of the bainite
areas. Lower bainite consists of ferrite needles containing carbide platelets in parallel array cross-striating each needle axis at
an angle of about 60°. Intermediate bainite resembles upper bainite; however, the carbides are smaller and more randomly
oriented.
E7 − 22
balsam, Canada——a resin from the balsam fir Abies balsamea.
DISCUSSION—
Dissolved in xylene, toluene, or benzene it is used as a mountant for permanent microscopical preparations. Its refractive index may vary from 1.530
to 1.545 and its softening point from room temperature to 100°C, these properties varying with age and solvent content. If impure it discolors with
age. (E175)
band—in electron diffraction, a broad intensity maximum with sharp edges.
banded structure (banding)—alternate bands parallel with the direction of working resulting from the elongation of segregated
areas.
barrel distortion— See distortion.
basal plane—that plane of a hexagonal or tetragonal crystal which is perpendicular to the axis of highest symmetry. Its Miller
indices are (0001) or (001), respectively.
bellows length—the distance from the eyepiece to the photosensitive material or viewing screen in a photomicrographic
apparatus.
Bertrand lens—an auxiliary removable lens in the body of a microscope, used to examine images in the back focal plane of
the objective, for example, interference figures with polarized light.
beta structure—structurally analogous body-centered cubic phases (similar to beta brass), or electron compounds, that have
ratios of 3 valence electrons to 2 atoms.
biased gun—an electron gun in which there is a bias voltage on the cathode cap. (See also self-biased gun.)
bifilar eyepiece—a Filar eyepiece with motion in two mutually perpendicular directions.
bi-modal grain size distribution—a condition where the distribution of individual grain areas or intercept lengths, converted
to ASTM grain size numbers (based on the area percent or length percent per G class) exhibits two peaks.
binary alloy—any specific composition in a binary system.
binary system—the complete series of compositions produced by mixing a pair of components in all proportions.
binodal curve—in a two-dimensional phase diagram, a continuous line consisting of both of the pair of conjugate boundaries
of a two-phase equilibrium and which join, without inflection, at a critical point. See miscibility gap.
birefringent—having more than one refractive index. Such materials exhibit alternately bright and dark reflections at 45°
intervals during a 360° rotation with plane-polarized light. (See also anisotropic.)
bivariant equilibrium—a stable state among a number of phases equal to the number of components in a system and in which
any two of the external variables (temperature, pressure, or concentrations) may be varied, at will, without necessarily causing
a change in the number of phases; sometimes called divariant equilibrium.
bisectrix, acute—in biaxial crystals, that principal axis of the ellipsoid of indexes which bisects the smaller angle between the
optic axes. (E175)
E7 − 22
bisectrix, obtuse—in biaxial crystals, that principal axis of the ellipsoid of indexes which bisects the larger angle between the
optic axes. (E175)
blowholes—a hole produced in a casting by gas which was trapped during solidification.
1 1 1
body-centered—having an atom (or group of atoms) separated by a translation of ⁄2, ⁄2, ⁄2 from a similar atom (or group of
atoms). The number of atoms in a body-centered cell must be a multiple of two.
boiling pressure—at a specified temperature, the pressure at which a liquid and its vapor are in equilibrium.
boiling temperature—at a specified pressure, the temperature at which a liquid and its vapor are in equilibrium.
bonded abrasive disk—a rigid support surface with an abrasive, typically diamond, bonded to the surface by a ceramic, resin,
or metal based material.
boundary grain—in the Jeffries’ method for grain size measurement, a grain that is intersected by the boundary of the standard
area and is, therefore, counted only as one-half grain. (See also Jeffries’ Method.)
Bragg angle—the angle between the incident beam and the lattice planes considered.
Bragg equation:—
nλ5 2dsinθ (2)
where:
n = order of reflection,
λ = wavelength of X-rays,
d = distance between lattice planes, and
θ = Bragg angle.
Bragg method—a method of X-ray diffraction in which a single crystal is mounted on a spectrometer with a crystal face parallel
to the axis of the instrument.
Braun’s law—the ratio of the solubility change with pressure, temperature being constant, (δ X/δP)T, to the solubility change
with temperature, pressure being constant, (δ X/δT)P, is equal to the negative of the product of the absolute temperature, T, and
the (fictitious) volume change (Δv) which accompanies the solution of 1 g·molecular weight of the solute in an infinitely large
quantity of the saturated solution at T degrees, divided by the amount of heat, Q, developed in the process:
~δX/δP!T/~δX δT!P 52T·Δv/Q (3)
brightfield illumination— for reflected light, the illumination which causes specularly reflected surfaces normal to the axis of
a microscope to appear bright. For transmission electron microscopy, the illumination of an object so that it appears on a bright
background.
burning (burnt, burned)—a term applied to metal which has been permanently damaged by having been heated to a
temperature close to or within the melting range. This results in a structure exhibiting incipient melting or intergranular
oxidation.
calibration—1) the act or process of determining the relationship between a set of standard units of measure and the output of
an instrument or test procedure,
E7 − 22
2) the graphical or mathematical relationship relating the desired property (expressed in a standard unit of measure such as
micrometers or Kg/mm ) to the instrument output (instrument units such as filar divisions or pixels).
caliper diameter (Feret’s diameter)—the length of a line normal to two parallel lines, tangent to opposite edges of a phase or
object.
calcite—a doubly refracting mineral used in the manufacture of polarizing prisms.
DISCUSSION—
It is uniaxial negative and in the trigonal diversion of the hexagonal system of crystals. Its indexes are ε = 1.486, ω = 1.658; its hardness is 3 on the
Mohr scale and specific gravity 2.711. (E175)
Canada balsam——see balsam, Canada. (E175)
carbide—a compound of carbon with one or more elements, which, in customary formulation, are considered as being more
positive than carbon.
case—in a ferrous alloy, the outer portion that has been made harder than the inner portion (see core) as a result of altered
composition, or structure, or both, from treatments such as carburizing, nitriding, and induction hardening.
cassette—a light-tight film or plate holder.
cast replica—See replica.
cast structure—the structure, on a macroscopic or microscopic scale, of a casting.
cathode lens—a lens field terminated on one side by a surface at zero potential (cathode) normal to the optic axis. A cathode
lens occurs in any system in which a cathode is imaged by its own electron emission, be it thermionic, photoelectric, secondary,
or field emission.
cementite—a very hard and brittle compound of iron and carbon corresponding to the empirical formula Fe C. It is commonly
known as iron carbide and possesses an orthorhombic lattice. In “plain-carbon steels” some of the iron atoms in the cementite
lattice are replaced by manganese, and in “alloy steels” by other elements such as chromium or tungsten. Cementite will often
appear as distinct lamellae or as spheroids or globules of varying size in hypo-eutectoid steels. Cementite is in metastable
equilibrium and has a tendency to decompose into iron and graphite, although the reaction rate is very slow.
central pencil—a bundle of rays originating in the axis with an angular aperture equal to the effective aperture of the lens. These
rays pass through the lens aperture and contribute to the formation of the image.
certified reference material—a reference material, the composition or properties of which are certified by a recognized
standardizing agency or group. Typically such a material is accompanied by documentation (certificate).
characteristic curve—the curve showing the relationship between exposure and resulting density in a photographic image. It
is usually plotted as the density against the log exposure. Called also the “H and D curve” and the “sensitometric curve.”
characteristic radiation—X-radiation of a particular set of wavelengths, produced by and characteristic of a particular element
used as a target whenever its excitation potential is exceeded.
charge neutralizer gun—an electron gun used to dissipate the charges which tend to build up on specimen surfaces, within an
electron-diffraction camera, which would introduce undesired electrostatic fields.
E7 − 22
chemical potential—(μ or G¯ ) the partial molar free energy of component i, that is, the change in free energy of a solution
i i
upon adding one mole of component i to an infinite amount of solution of given composition,
¯
δG/δn 5 G 5 μ (4)
~ !
i T,P,n i i
1···
where:
G = Gibbs free energy, and
th
n = number of moles of the i component.
i
Chinese script eutectic—a configuration of eutectic constituents, found particularly in some cast alloys of aluminum containing
iron and silicon and in magnesium alloys containing silicon, which resembles in appearance the characters in Chinese script.
chlorine or volatile halide extraction—See extraction.
chromatic aberration—a defect in a lens or lens system as a result of which the lens possesses different focal lengths for
radiation of different wavelengths.
Class I quaternary equilibrium—in a four-component system, the stable univariant coexistence of five phases, one of which
must disappear upon lowering the temperature or pressure; for example, the quaternary eutectic equilibrium, L = α + β + γ + δ.
Class I quinary equilibrium—in a five-component system, the stable univariant coexistence of six phases, one of which must
disappear upon lowering the temperature or pressure; for example, the quinary eutectic equilibrium, L = α + β + γ + σ + ε.
Class I ternary equilibrium—in a three-component system, the stable univariant coexistence of four phases, one of which must
disappear upon lowering the temperature or pressure; for example, the ternary eutectic equilibrium, L = α + β + δ.
Class II quaternary equilibrium—in a four-component system, the stable univariant coexistence of five phases, two of which
appear in each of the three associated bivariant equilibria at temperatures and pressures above, while the other three phases all
occur in both of the associated bivariant equilibria below; for example, L + α = β + γ + δ.
Class II quinary equilibrium—in a five-component system, the stable univariant coexistence of six phases, two of which
appear in each of the four associated bivariant equilibria at temperatures and pressures above, while the other four phases occur
in both of the associated bivariant equilibria below; for example, L + α = β + γ + δ + ε.
Class II ternary equilibrium—in a three-component system, the stable univariant coexistence of four phases, two of which
appear in both of the associated bivariant equilibria at higher temperature and pressure, while the other two phases occur in both
bivariant equilibria below; for example, L + α = β + γ.
Class III quaternary equilibrium—in a four-component system, the stable univariant coexistence of five phases, three of
which appear in both of the associated bivariant equilibria at temperatures and pressures above, while the other two phases occur
in all three of the associated bivariant equilibria below; for example, L + α + β = γ + δ.
Class III quinary equilibrium—in a five-component system, the stable univariant coexistence of six phases, three of which
appear in all three of the associated bivariant equilibria at temperatures and pressures above, while the other three occur in all
three of the associated bivariant equilibria below; for example, L + α + β = γ + δ + ε.
Class III ternary equilibrium—in a three-component system, the stable univariant coexistence of four phases, one of which
must disappear at higher temperature or pressure; for example, the ternary peritectic equilibrium, L + α + β = γ.
E7 − 22
Class IV quaternary equilibrium—in a four-component system, the stable univariant coexistence of five phases, one of which
must disappear at higher temperature or pressure; for example, the quaternary peritectic equilibrium, L + α + β + γ = δ.
Class IV quinary equilibrium—in a five-component system, the stable univariant coexistence of six phases, four of which
appear in both associated bivariant equilibria at temperatures and pressures above, while the other two occur in all four
associated bivariant equilibria below; for example, L + α + β + γ = δ + ε.
Class V quinary equilibrium—in a five-component system, the stable univariant coexistence of six phases, one of which must
disappear upon increasing the temperature or pressure; for example, the quinary peritectic equilibrium, L + α + β + γ + δ = ε.
Clausius-Clapeyron equation—the rate of change of the pressure of a heterogeneous equilibrium with change of temperature
dP/dT is equal to the heat of transformation from the low to the high temperature state Δ Hv divided by the product of the
absolute temperature of the equilibrium and the volume change of the transformation TΔV:
dP/dT 5 ΔHv/TΔV (5)
or,
dlnP/dT'Hv/RT (6)
where R is the gas constant and the equilibrium is not near a critical point.
clear cross test—an experimental method for determining which of two conceivable two-phase equilibria is real; at that
composition at which the two conceivable two-phase fields cross, an alloy is brought to equilibrium and the phases identified;
the same principle may be applied to higher-order equilibria in higher-order systems.
clear glass focusing screen—a glass screen polished on both sides and mounted for use in a camera, in lieu of photo-sensitive
material, for the purpose of establishing a plane on which to focus an image prior to recording it.
cleavage planes—that family of planes of a crystal along which the crystal is easily split.
close packed—a geometric arrangement whereby a collection of equally sized spheres (atoms) may be packed together in a
minimum total volume.
coefficient of thermal expansion—change in unit of length (or volume) accompanying a unit change of temperature, at a
specified temperature.
coalescence—growth of grains at the expense of the remainder by absorption or the growth of a phase or particle at the expense
of the remainder by absorption or by reprecipitation.
coarse grains—grains either larger than normal for the particular wrought metal or alloy, or grains of such a size that a surface
roughening, popularly known as “orange peel” or “alligator skin,” is produced.
coherent precipitate—a precipitated particle of a second phase, the lattice of which still maintains registry with the matrix
lattice. Because the lattice spacings are usually different, strains usually exist at the interface.
coherent scattering—a kind of X-ray electron scattering in which the phase of the scattered beam has a definite (not random)
relation to the phase of the incident beam. Also called unmodified scattering.
cold-cathode gun—an electron gun in which electrons produced in a gas discharge are accelerated through a small aperture in
the anode.
cold junction—See reference junction.
E7 − 22
cold junction correction— See reference junction correction.
cold worked structure—a microstructure resulting from plastic deformation of a metal or alloy below its recrystallization
temperature.
collimation—the operation of controlling a beam of radiation so that its rays are as nearly parallel as possible.
collodion replica— See replica.
color film—a photographic film consisting of several emulsion layers, where the individual layers selectively record various
wavelengths of light.
color temperature—the temperature of a blackbody in degrees Kelvin (K). In photography, the apparent temperature in K of
a luminous source which may be measured by its emission ratio of blue to red light.
column, electron microscope—the assembly of gun, lenses, and specimen, viewing and plate chambers.
columnar structure—a macro- or microstructure characterized by elongated grains whose long axes are parallel, for example,
to solidification direction, electroplated direction, etc.
coma—a lens aberration occurring in that part of the image field that is some distance from the principal axis of the system.
It results from different magnification in the various lens zones.
DISCUSSION—
Extra-axial object points appear as short comet-like images with the brighter small head toward the center of the field (positive coma) or away from
the center (negative coma). (E175)
comparison standard—a standard micrograph or a series of micrographs, usually taken at 75 or 100 diameters, or a suitable
equivalent built into the eyepiece and used to determine grain size by direct comparison with the image.
compensating eyepiece—one designed for use with objectives such as apochromats, the lateral chromatic aberration of which
is undercorrected.
compensating lead wires—wires leading from a thermocouple to the voltage-measuring instrument. These wires must be of
such compositions that they will generate an emf equivalent to the emf generated by the reference junction of the couple.
complex silicate inclusions—a general term describing silicate inclusions containing visible constituents besides the silicate
matrix. An example would be corundum or spinel crystals occurring in a silicate matrix in steel.
component—one of the independently variable substances by means of which the composition of each phase of a system of
heterogeneous equilibrium may be described completely; usually an element, or a compound that remains undissociated
throughout the range of temperature and pressure concerned.
composition—the quantity of each of the components of a mixture; usually expressed in terms of the weight percentage, or the
atomic percentage of each of the components in the mixture.
Compton scattering—X-ray scattering by atoms in which the scattered beam has, relative to the incident beam, a longer
wavelength and a random phase relationship. Also called incoherent or modified scattering.
condensed system—a pure substance, or mixture, at a pressure and temperature such that the vapor phase does not exist.
E7 − 22
condenser—a term applied to lenses or mirrors designed to collect, control, and concentrate radiation in an illumination system.
condenser, Abbe—originally a two-lens substage condenser combination designed by Ernst Abbe.
DISCUSSION—
It lacks chromatic correction though designed for a minimum of spherical aberration and has only a very low-angle aplanatic cone. It may be rated
with a numerical aperture as high as 1.3. (E175)
condenser aperture— See aperture.
condenser, darkfield—a condenser forming a hollow cone of light with its apex (or focal point) in the plane of the specimen.
DISCUSSION—
When used with an objective having a numerical aperture lower than the minimum numerical aperture of the hollow cone, only light deviated by the
specimen enters the objective. Objects are seen as bright images against a dark background. (E175)
condenser, darkfield, bispheric—a darkfield condenser consisting of a convex spherical reflector mounted concentric with a
larger concave reflector.
DISCUSSION—
The rays are formed into a diverging cone by the convex reflector. The annular concave reflector then forms a hollow converging cone which is focused
on the subject. See condenser, darkfield. (E175)
condenser lens—a device used to focus radiation in or near the plane of the object.
condenser, darkfield, paraboloid—a darkfield condenser consisting of a reflecting surface in the form of a segment of a
paraboloid of revolution.
DISCUSSION—
Parallel rays entering the condenser around the periphery of the central stop are reflected from the curved surfaces and converge at the focus of the
paraboloid. See condenser, darkfield. (E175)
condenser, variable-focus—essentially an Abbe condenser in which the upper lens element is fixed and the lower movable.
DISCUSSION—
The lower lens may be used to focus the illumination between the elements so that it emerges from the stationary lens as a large diameter parallel
bundle. The field of low-power objectives may thus be filled without removing the top element. At the opposite extreme it can be adjusted to have
a numerical aperture as high as 1.3. (E175)
congruent transformation—an isothermal, or isobaric, phase change in which both of the phases concerned have the same
composition throughout the process; the order of a system becomes unary at a composition of congruency.
conjugate phases—those states of matter of unique composition which coexist at equilibrium at a single point in temperature
and pressure; for example, the two coexisting phases of a two-phase equilibrium.
conjugate planes—two planes of an optical system such that one is the image of the other.
constituent—a phase, or combination of phases, which occurs in a characteristic configuration in an alloy micro-structure.
constitutional diagram—graphical representation of the compositions, temperatures, pressures or combinations thereof at
which the heterogeneous equilibria of an alloy system occur; also called “phase diagram,” or “equilibrium diagram.”
continuous phase—the phase forming the matrix or background in which other phases may be dispersed as isolated units.
continuous spectrum (X-rays)—the polychromatic radiation given off by the target of an X-ray tube, containing all
wavelengths above a certain minimum value called the short wave length limit.
E7 − 22
contrast enhancement (electron optics)— an improvement in electron image contrast by the use of an objective aperture
diaphragm, shadow casting, or other means.
contrast perception—the ability to differentiate various components of the object structure by different intensity levels in the
image.
contrast, photographic—the word contrast has been used in many different senses in connection with various photographic
characteristics; there are different types of photographic contrast and different methods of measuring it. It is frequently used to
designate the magnitude of the density difference resulting from a given exposure difference. (For another use, see gamma.)
conversion, hardness—the exchange of a hardness number determined by one method for an equivalent hardness number of
a different scale.
cooling curve—graphical representation of the course of temperature fall of a chemical mixture as a function of time commonly
exhibiting more or less abrupt changes of rate at, or near, those temperatures at which phase changes begin; used in finding the
temperatures at which phase changes occur. Occasionally, some property or function other than time may be used; for example,
thermal expansion.
cooling rate—the average slope of the time-temperature curve taken over a specified time and temperature interval.
core—(1) case hardening—interior portion of unaltered composition, or microstructure, or both, of a case-hardened steel article.
(2) clad products—the central portion of a multilayer composite metallic material.
coring—a variable composition between the center and outside of a unit of structure, (such as a dendrite, grain, carbide particle)
resulting from non-equilibrium growth which occurs over a range of temperatures or compositions.
corona shield—a smooth, rounded metal covering placed around exposed high-voltage components to prevent electrical
discharge.
counter—a device for the measurement of radiation intensity by means of an electrical triggering principle (Geiger-Müller).
coupler, color—a substance capable of reacting with the oxidation product of a color-forming developer to produce a colored
dye image.
critical curve—in a binary, or higher order, phase diagram, a line along which the phases of a heterogeneous equilibrium
become identical.
critical illumination—see illumination, critical. (E175)
critical point—in a phase diagram, that specific value of composition, temperature, pressure or combinations thereof at which
the phases of a heterogeneous equilibrium become identical. (See also transformation temperature.)
critical pressure—that pressure above which the liquid and vapor states are no longer distinguishable.
critical surface—in a ternary, or higher order, phase diagram, the area upon which the phases in equilibrium become identical.
critical temperature—that temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure.
E7 − 22
cross direction—one of three mutually perpendicular directions used to define a worked material, specifically that direction in
the plane of working which is at right angles to the direction of maximum elongation.
crystal—a solid composed of atoms, ions, or molecules arranged in a pattern which is periodic in three dimensions.
crystal, birefringent——a pertaining to the use of a microscope. (E175)
crystal analysis—a method for determining crystal structure, for example, the size and shape of the unit cell and the location
of all atoms within the unit cell.
crystallite—a crystalline grain not bounded by habit planes.
crystal system—one of seven groups into which all crystals may be divided; triclinic, monoclinic, orthorhombic, hexagonal,
rhombohedral, tetragonal, and cubic.
cube texture—a texture found in wrought metals in the cubic system, in which nearly all the crystal grains have a plane of the
type (100) parallel or nearly parallel to the plane of working and a direction of the type [001] parallel or nearly parallel to the
direction of elongation.
cubic—having three mutually perpendicular axes of equal length.
cupping—the condition sometimes occurring in heavily cold worked rods and wires, in which the outside fibers are still intact
and the central zone has failed in a series of cup-and-cone fractures.
Curie point—that temperature above which a substance becomes paramagnetic.
curvature of field—a property of a lens that causes the image of a plane to be focused into a curved surface instead of a plane.
darkfield condenser—see condenser, darkfield. (E175)
darkfield illumination—the illumination of an object such that it appears illuminated with the surrounding field dark. This
results from illuminating the object with rays of sufficient obliquity so that none can enter the objective directly. As applied to
electron microscopy, the image is formed using only electrons scattered by the object.
dashpot—a hydraulic cylinder device with a controlled leak designed to eliminate impact loading of mechanisms. Hardness
testers may employ a dashpot to bring an indenter into contact with a specimen without impact or other disturbance.
dead-weight loading—a method of loading in which a weight is supported solely by the specimen and has no other mechanical
connection to the testing machine. In hardness testing, the weight is supported by the indenter.
Debye ring—a continuous circle, concentric about the undeviated beam, produced by monochromatic X-ray diffraction from a
randomly oriented crystalline powder. An analogous effect is obtained with electron diffraction.
Debye-Scherrer method—a method of X-ray diffraction employing monochromatic radiation and a polycrystalline specimen
mounted on the axis of a cylindrical strip of film. (See powder method.)
decarburization—loss of carbon from the surface of a carbon containing alloy due to a reaction with one or more chemical
substances in a medium that contacts the surface. Decarburization may be either (1) partial, that is, where carbon content is less
E7 − 22
than the unaffected inte
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