ASTM E2627-10
(Practice)Standard Practice for Determining Average Grain Size Using Electron Backscatter Diffraction (EBSD) in Fully Recrystallized Polycrystalline Materials
Standard Practice for Determining Average Grain Size Using Electron Backscatter Diffraction (EBSD) in Fully Recrystallized Polycrystalline Materials
SIGNIFICANCE AND USE
This practice provides a way to estimate the average grain size of polycrystalline materials. It is based on EBSD measurements of crystallographic orientation which are inherently quantitative in nature. This method has specific advantage over traditional optical grain size measurements in some materials, where it is difficult to find appropriate metallographic preparation procedures to adequately delineate grain boundaries.
SCOPE
1.1 This practice is used to determine grain size from measurements of grain areas from automated electron backscatter diffraction (EBSD) scans of polycrystalline materials.
1.2 The intent of this practice is to standardize operation of an automated EBSD instrument to measure ASTM G directly from crystal orientation. The guidelines and caveats of E112 apply here, but the focus of this standard is on EBSD practice.
1.3 This practice is only applicable to fully recrystallized materials.
1.4 This practice is applicable to any crystalline material which produces EBSD patterns of sufficient quality that a high percentage of the patterns can be reliably indexed using automated indexing software.
1.5 The practice is applicable to any type of grain structure or grain size distribution.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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Standards Content (Sample)
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Designation: E2627 − 10
StandardPractice for
Determining Average Grain Size Using Electron Backscatter
Diffraction (EBSD) in Fully Recrystallized Polycrystalline
Materials
This standard is issued under the fixed designation E2627; 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.
1. Scope E1181 Test Methods for Characterizing Duplex Grain Sizes
E1382 Test Methods for Determining Average Grain Size
1.1 This practice is used to determine grain size from
Using Semiautomatic and Automatic Image Analysis
measurements of grain areas from automated electron back-
scatter diffraction (EBSD) scans of polycrystalline materials.
3. Terminology
1.2 The intent of this practice is to standardize operation of
3.1 Definitions:
an automated EBSD instrument to measure ASTM G directly
3.1.1 cleanup—Post processing applied to EBSD scan data
from crystal orientation. The guidelines and caveats of E112
to reassign extraneous points in the scan grid to neighboring
apply here, but the focus of this standard is on EBSD practice.
points. The extraneous points are assumed to arise from
1.3 This practice is only applicable to fully recrystallized
non-indexed or misindexed EBSD patterns.
materials.
3.1.2 (crystallographic) orientation—The rotation required
1.4 This practice is applicable to any crystalline material
tobringtheprincipleaxesofacrystalintocoincidencewiththe
which produces EBSD patterns of sufficient quality that a high
principle axes assigned to a specimen. For example, in a rolled
percentage of the patterns can be reliably indexed using
material with cubic crystal symmetry, it is the set of rotations
automated indexing software.
required to bring the [100], [010] and [001] axes of the crystal
1.5 The practice is applicable to any type of grain structure
into coincidence with the rolling, transverse and normal
or grain size distribution.
directions of the specimen. Orientations may be described in
terms of various sets of angles, a matrix of direction cosines or
1.6 The values stated in SI units are to be regarded as
a rotation vector.
standard. No other units of measurement are included in this
standard.
3.1.3 electron backscatter diffraction (EBSD).—A crystal-
line specimen is placed in a scanning electron microscope
1.7 The values stated in inch-pound units are to be regarded
(SEM) at a high tilt angle (~70°). When a stationary electron
as standard. The values given in parentheses are mathematical
beam is positioned on a grain, the electrons are scattered in a
conversions to SI units that are provided for information only
small volume (typically 30nm in the tilt direction, 10nm in the
and are not considered standard.
transversedirectionand20nmindepthforafieldemissiongun
SEM and approximately an order of magnitude larger in the
2. Referenced Documents
2 lateral directions for a tungsten filament SEM). Electrons that
2.1 ASTM Standards:
satisfyBragg’slawarediffractedbackoutofthespecimen.The
E7 Terminology Relating to Metallography
diffracted electrons strike a phosphor screen (or alternatively a
E112 Test Methods for Determining Average Grain Size
YAG crystal) placed in the chamber. The colliding electrons
E766 Practice for Calibrating the Magnification of a Scan-
fluoresce the phosphor and produce a pattern. The pattern is
ning Electron Microscope
composed of a set of intersecting bands (Kikuchi lines). These
bands are indicative of the arrangement of crystal lattice planes
in the diffracting crystal volume. Assuming the material is of
This practice is under the jurisdiction of ASTM Committee E04 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray and
knowncrystalstructure,theorientationofthecrystalwithinthe
Electron Metallography.
diffracting volume can be determined.
Current edition approved April 1, 2010. Published May 2010. DOI10.1520/
E2627.
3.1.4 EBSD pattern—AnEBSDpatterniscomposedofaset
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
of intersecting bands. The geometrical arrangement of these
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
bands is indicative of the crystallographic orientation of the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. crystal lattice within the diffraction volume.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2627 − 10
3.1.5 EBSD scan—Under computer control, the beam of the pattern is needed. The computer and resident software should
SEM is moved to a point on the specimen, an EBSD pattern be capable of rapid collection of orientation data from EBSD
captured and indexed to determine the crystallographic orien- patterns.
tation at the beam location.This process is repeated for a set of
6.3 ElectronicsandsoftwaretocontrolthebeamintheSEM
points lying on a regular grid.
(or the stage, or both) are required to collect orientation data at
3.1.6 grain—In EBSD, grains have a specific meaning.
points on a regular scan grid.
They are defined as a group of similarly oriented neighboring
7. Hazards
pointsonthescangrid.Thegroupissurroundedbyaperimeter
where misorientation across that perimeter exceeds a specified
7.1 There are no hazards specific to this test method.
tolerance value.
However, SEM operators should be familiar with safe SEM
operatingprocedurestopreventexposuretoXraysandcoming
3.1.7 indexing—The process of identifying the crystallo-
in contact with the high voltages inherent to SEMs. Care
graphic orientation of the crystal lattice associated with an
should also be exercised in preparing specimens for EBSD as
EBSDpatterngeneratedbytheinteractionoftheelectronbeam
is the case for specimen preparation for light and electron
with that lattice.
microscopy.
3.1.8 misorientation —The set of rotations (Euler angles)
required to bring one crystal lattice into coincidence with a
8. Sampling and Test Specimens
second crystal lattice.
8.1 Specimens should be selected to represent average
3.1.9 misorientation tolerance—If the angular difference
conditions within a heat lot, treatment lot, or product, or to
betweentwoneighboringpixelsislessthanthistolerancevalue
assess variations anticipated across or along a product or
then they are assumed to belong to the same grain.
component, depending on the nature of the material being
3.1.10 orientation Map—Each point in the scan grid is
tested and the purpose of the study. Sampling location and
assigned a color according to its orientation. This forms an frequency can be based upon agreements between the manu-
image showing the microstructure.
facturers and the users.
3.1.11 step size (∆)—–The distance between neighboring
8.2 Specimens should not be taken from areas affected by
points on the scan grid.
shearing, burning, or other processes that will alter the grain
structure.
4. Summary of Practice
8.3 The surface to be polished should be large enough in
area to permit measurement of at least five fields at the desired
4.1 An EBSD scan is performed on a specimen, post-
processing routines are applied to the scan data, and the magnification.
individual points of the scan are grouped into grains according
9. Specimen Preparation
to their orientation. Average grain size is determined from the
field average of grain areas based on the number of points in
9.1 It is important to follow good metallographic prepara-
the EBSD map and the step size.
tion procedures for successful EBSD work. EBSD is a surface
sensitive technique. The surface should be free from deforma-
5. Significance and Use
tion and have minimal topography. Careful mechanical polish-
ing or electropolishing, or both should be performed on
5.1 This practice provides a way to estimate the average
specimen surfaces. However, as compared with preparing
grain size of polycrystalline materials. It is based on EBSD
specimens for grain size measurements based on optical
measurements of crystallographic orientation which are inher-
microscopy, the surface should not be etched or treated to
ently quantitative in nature. This method has specific advan-
produce relief to delineate grain boundaries. This would be
tage over traditional optical grain size measurements in some
disadvantageous for obtaining EBSD patterns that can be
materials, where it is difficult to find appropriate metallo-
indexed. The grain boundaries are delineated by processing of
graphic preparation procedures to adequately delineate grain
the orientation measurement data.
boundaries.
10. Preparation of Apparatus
6. Apparatus
10.1 Good practices should be used in the operation of both
6.1 An electron backscatter diffraction (EBSD) system
the SEM and EBSD systems. Particular attention should be
mounted on a Scanning Electron Microscope (SEM) is used.
given to geometric alignment of the specimen surface with the
The EBSD system is constituted by a low-light sensitive video
assumed measurement plane (typically 70° from the horizon-
camera (typically a charg
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