ASTM E2627-13(2019)

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: E2627 − 13 (Reapproved 2019)
Standard Practice 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice is used to determine grain size from
E7 Terminology Relating to Metallography
measurements of grain areas from automated electron back-
E112 Test Methods for Determining Average Grain Size
scatter diffraction (EBSD) scans of polycrystalline materials.
E177 Practice for Use of the Terms Precision and Bias in
1.2 The intent of this practice is to standardize operation of
ASTM Test Methods
an automated EBSD instrument to measure ASTM G directly
E691 Practice for Conducting an Interlaboratory Study to
from crystal orientation. The guidelines and caveats of E112
Determine the Precision of a Test Method
apply here, but the focus of this standard is on EBSD practice.
E766 Practice for Calibrating the Magnification of a Scan-
ning Electron Microscope
1.3 This practice is only applicable to fully recrystallized
E1181 Test Methods for Characterizing Duplex Grain Sizes
materials.
E1382 Test Methods for Determining Average Grain Size
1.4 This practice is applicable to any crystalline material
Using Semiautomatic and Automatic Image Analysis
which produces EBSD patterns of sufficient quality that a high
percentage of the patterns can be reliably indexed using 3. Terminology
automated indexing software.
3.1 Definitions:
3.1.1 cleanup—Post processing applied to EBSD scan data
1.5 The practice is applicable to any type of grain structure
to reassign extraneous points in the scan grid to neighboring
or grain size distribution.
points. The extraneous points are assumed to arise from
1.6 The values stated in SI units are to be regarded as
non-indexed or misindexed EBSD patterns.
standard. No other units of measurement are included in this
3.1.2 (crystallographic) orientation—The rotation required
standard.
tobringtheprincipleaxesofacrystalintocoincidencewiththe
1.7 This standard does not purport to address all of the principle axes assigned to a specimen. For example, in a rolled
safety concerns, if any, associated with its use. It is the material with cubic crystal symmetry, it is the set of rotations
responsibility of the user of this standard to establish appro- required to bring the [100], [010] and [001] axes of the crystal
into coincidence with the rolling, transverse and normal
priate safety, health, and environmental practices and deter-
directions of the specimen. Orientations may be described in
mine the applicability of regulatory limitations prior to use.
terms of various sets of angles, a matrix of direction cosines or
1.8 This international standard was developed in accor-
a rotation vector.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 3.1.3 electron backscatter diffraction (EBSD)—Acrystalline
specimenisplacedinascanningelectronmicroscope(SEM)at
Development of International Standards, Guides and Recom-
a high tilt angle (~70°). When a stationary electron beam is
mendations issued by the World Trade Organization Technical
positioned on a grain, the electrons are scattered in a small
Barriers to Trade (TBT) Committee.
volume (typically 30nm in the tilt direction, 10nm in the
transversedirectionand20nmindepthforafieldemissiongun
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
Electron Metallography. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2019. Published December 2019. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2010. Last previous edition approved in 2013 as E2627–13. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2627–13R19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2627 − 13 (2019)
SEM and approximately an order of magnitude larger in the materials, where it is difficult to find appropriate metallo-
lateral directions for a tungsten filament SEM). Electrons that graphic preparation procedures to adequately delineate grain
satisfyBragg’slawarediffractedbackoutofthespecimen.The boundaries.
diffracted electrons strike a phosphor screen (or alternatively a
6. Apparatus
YAG crystal) placed in the chamber. The colliding electrons
fluoresce the phosphor and produce a pattern. The pattern is
6.1 An electron backscatter diffraction (EBSD) system
composed of a set of intersecting bands (Kikuchi lines). These
mounted on a Scanning Electron Microscope (SEM) is used.
bands are indicative of the arrangement of crystal lattice planes
The EBSD system is constituted by a low-light sensitive video
in the diffracting crystal volume. Assuming the material is of
camera (typically a charge-coupled device or CCD camera).
knowncrystalstructure,theorientationofthecrystalwithinthe
The camera images a medium for detecting the diffracted
diffracting volume can be determined.
electrons such as a phosphor screen or YAG crystal. EBSD
patterns formed on the detecting medium are imaged using the
3.1.4 EBSD pattern—AnEBSDpatterniscomposedofaset
camera and transmitted to a computer.
of intersecting bands. The geometrical arrangement of these
bands is indicative of the crystallographic orientation of the
6.2 Software capable of reliably indexing an EBSD pattern
crystal lattice within the diffraction volume.
to determine the crystallographic orientation from the EBSD
pattern is needed. The computer and resident software should
3.1.5 EBSD scan—Under computer control, the beam of the
be capable of rapid collection of orientation data from EBSD
SEM is moved to a point on the specimen, an EBSD pattern
patterns.
captured and indexed to determine the crystallographic orien-
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
points on a regular scan grid.
3.1.6 grain—In EBSD, grains have a specific meaning.
They are defined as a group of similarly oriented neighboring
7. Hazards
pointsonthescangrid.Thegroupissurroundedbyaperimeter
7.1 There are no hazards specific to this test method.
where misorientation across that perimeter exceeds a specified
However, SEM operators should be familiar with safe SEM
tolerance value.
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)
8. Sampling and Test Specimens
required to bring one crystal lattice into coincidence with a
second crystal lattice.
8.1 Specimens should be selected to represent average
conditions within a heat lot, treatment lot, or product, or to
3.1.9 misorientation tolerance—If the angular difference
assess variations anticipated across or along a product or
betweentwoneighboringpixelsislessthanthistolerancevalue
component, depending on the nature of the material being
then they are assumed to belong to the same grain.
tested and the purpose of the study. Sampling location and
3.1.10 orientation Map—Each point in the scan grid is
frequency can be based upon agreements between the manu-
assigned a color according to its orientation. This forms an
facturers and the users.
image showing the microstructure.
8.2 Specimens should not be taken from areas affected by
3.1.11 step size (∆)—–The distance between neighboring
shearing, burning, or other processes that will alter the grain
points on the scan grid.
structure.
8.3 The surface to be polished should be large enough in
4. Summary of Practice
area to permit measurement of at least five fields at the desired
4.1 An EBSD scan is performed on a specimen, post-
magnification.
processing routines are applied to the scan data, and the
individual points of the scan are grouped into grains according
9. Specimen Preparation
to their orientation. Average grain size is determined from the
9.1 It is important to follow good metallographic prepara-
field average of grain areas based on the number of points in
tion procedures for successful EBSD work. EBSD is a surface
the EBSD map and the step size.
sensitive technique. The surface should be free from deforma-
tion and have minimal topography. Careful mechanical polish-
5. Significance and Use
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
E2627 − 13 (2019)
indexed. The grain boundaries are delineated by processing of measured. Exclude grains with point counts less than 100. For
the orientation measurement data. each grain with P exceeding 100 calculate the corresponding
i
area, A. For scan data measured on a regular square grid, the
i
10. Preparation of Apparatus
area of a grain, A, is equal to the number of points in the grain
i
multiplied by the square of the step size:
10.1 Good practices should be used in the operation of both
the SEM and EBSD systems. Particular attention should be A 5 P ∆ (1)
i i
For data collected on a regular hexagonal grid, the area of a
given to geometric alignment of the specimen surface with the
grain, A, is equal to the number of points in the grain multi-
assumed measurement plane (typically 70° from the horizon- i
plied by the square of the step size, ∆ multiplied by the
tal). Misalignments can e
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