Microbeam analysis -- Electron backscatter diffraction -- Measurement of average grain size

This document describes procedures for measuring average grain size derived from a two-dimensional polished cross-section using electron backscatter diffraction (EBSD). This requires the measurement of orientation, misorientation and pattern quality factor as a function of position in the crystalline specimen[1]. The measurements in this document are made on two dimensional sections. The reader should note carefully the definitions used (3.3) which draw a distinction between the measured sectional grain sizes, and the mean grain size which can be derived from them that relates to the three dimensional grain size. NOTE 1 While conventional methods for grain size determination using optical microscopy are well-established, EBSD methods offer a number of advantages over these techniques, including increased spatial resolution and quantitative description of the orientation of the grains. NOTE 2 The method also lends itself to the measurement of the grain size of complex materials, for example those with a significant duplex content. NOTE 3 The reader is warned to interpret the results with care when attempting to investigate specimens with high levels of deformation.

Analyse par microfaisceaux -- Diffraction d'électrons rétrodiffusés -- Mesurage de la taille moyenne des grains

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INTERNATIONAL ISO
STANDARD 13067
Second edition
2020-07
Microbeam analysis — Electron
backscatter diffraction —
Measurement of average grain size
Analyse par microfaisceaux — Diffraction d'électrons rétrodiffusés —
Mesurage de la taille moyenne des grains
Reference number
ISO 13067:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 13067:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13067:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

3.1 Terminology associated with EBSD measurement of grain size .................................................................. 2

3.2 Terminology associated with grains and grain boundaries determined via EBSD ...................... 4

3.3 Terminology associated within grain size measurement ................................................................................... 5

3.4 Terminology associated with data correction and uncertainty of EBSD maps ............................... 6

4 Equipment for grain sizing by EBSD ................................................................................................................................................. 7

4.1 Hardware requirements ......... ......................................................................................................................................................... 7

4.2 Software requirements .................................................................................................................................................................... 7

5 Acquiring the map for grain sizing by EBSD ............................................................................................................................ 7

5.1 Specimen preparation ...................................................................................................................................................................... 7

5.2 Defining specimen axes ................................................................................................................................................................... 7

5.3 Stage positioning and calibration ........................................................................................................................................... 8

5.4 Linear calibration ................................................................................................................................................................................. 8

5.5 Preliminary examination ......... ....................................................................................................................................................... 8

5.6 Choice of step size ................................................................................................................................................................................ 8

[7][8]

5.7 Determination of the level of angular accuracy needed ......................................................................10

5.8 Choice of areas to be mapped and map size ...............................................................................................................10

5.9 Considerations when examining plastically deformed materials ............................................................11

6 Analytical procedure .....................................................................................................................................................................................11

6.1 Definition of boundaries ..............................................................................................................................................................11

6.1.1 Grain boundary angles .............................................................................................................................................11

6.1.2 Handling incomplete boundaries ...................................................................................................................12

6.1.3 Dealing with special boundaries .....................................................................................................................12

6.2 Post-acquisition treatment of raw data ..........................................................................................................................12

6.3 Data-cleaning steps ..........................................................................................................................................................................12

6.4 Measurement of sectional grain size .................................................................................................................................16

6.5 Calculation of average grain size ..........................................................................................................................................16

6.6 Representation of data ..................................................................................................................................................................17

7 Measurement uncertainty .......................................................................................................................................................................17

8 Reporting of analysis results ................................................................................................................................................................18

Annex A (informative) Grain size measurement ...................................................................................................................................20

Annex B (informative) Reproducibility...........................................................................................................................................................22

Bibliography .............................................................................................................................................................................................................................25

© ISO 2020 – All rights reserved iii
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ISO 13067:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 202, Microbeam analysis.

This second edition cancels and replaces the first edition (ISO 13067:2011), which has been technically

revised. The main changes compared to the previous edition are as follows:
— Data from a round robin (Annex B) have been used to:
— Include information on expected precision (Clause 7 and Annex B);
— Include more detail on sources of errors (Clause 7);

— Clarify statements on minimum numbers of grains measured (5.8) and acceptable clean up

procedures (6.3–6.3);

— Clarify the distinction between sectional grain size measured on a 2D section and average

grain size determined from some 2D measurements of grain sections which can be related by

stereology to the 3D grain size;

— Additionally, improvements have been made to the description of calculation of average values

(6.5) and representation of the data (6.6).

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 13067:2020(E)
Introduction

The mechanical and electromagnetic properties of engineering materials are strongly influenced

by their crystal grain size and distribution. For example, strength, toughness and hardness are

all important engineering properties that are strongly influenced by these parameters. Both bulk

materials and thin films, even as narrow two-dimensional structures, are influenced by grain size. For

this reason, it is important to have standard methods for its measurement with commonly used and

agreed terminology. This document describes procedures for measuring average grain size from maps

of local orientation measurements using electron backscatter diffraction.
© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 13067:2020(E)
Microbeam analysis — Electron backscatter diffraction —
Measurement of average grain size
1 Scope

This document describes procedures for measuring average grain size derived from a two-dimensional

polished cross-section using electron backscatter diffraction (EBSD). This requires the measurement

of orientation, misorientation and pattern quality factor as a function of position in the crystalline

[1]

specimen . The measurements in this document are made on two dimensional sections. The reader

should note carefully the definitions used (3.3) which draw a distinction between the measured

sectional grain sizes, and the mean grain size which can be derived from them that relates to the three

dimensional grain size.

NOTE 1 While conventional methods for grain size determination using optical microscopy are well-

established, EBSD methods offer a number of advantages over these techniques, including increased spatial

resolution and quantitative description of the orientation of the grains.

NOTE 2 The method also lends itself to the measurement of the grain size of complex materials, for example

those with a significant duplex content.

NOTE 3 The reader is warned to interpret the results with care when attempting to investigate specimens

with high levels of deformation.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 16700, Microbeam analysis — Scanning electron microscopy — Guidelines for calibrating image

magnification

ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

ISO 23833, Microbeam analysis — Electron probe microanalysis (EPMA) — Vocabulary

ISO 24173, Microbeam analysis — Guidelines for orientation measurement using electron backscatter

diffraction
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 24173 and ISO 23833 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2020 – All rights reserved 1
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ISO 13067:2020(E)
3.1 Terminology associated with EBSD measurement of grain size
3.1.1
step size

distance between adjacent points from which individual EBSD patterns are acquired during collection

of data for an EBSD map
3.1.2
pixel
picture element

smallest area of an EBSD map, with the dimensions of the step size (3.1.1), to which is assigned the

result of a single orientation (3.1.3) measurement made by stopping the beam at a point at the centre of

that area
3.1.3
orientation

mathematical description of the angular relationship between the crystal axes of the analysis point and

a reference frame, usually the specimen axes
[SOURCE: ISO 24173:2009, 3.16, modified to include different reference frames.]
3.1.4
indexed

meets the predetermined threshold for reliability for the orientation (3.1.3) of a pixel (3.1.2) calculated

from the EBSD pattern acquired for that pixel
3.1.5
indexing reliability

numerical value that indicates the confidence/reliability that the indexing software places in an

automatic analysis

Note 1 to entry: This parameter varies between EBSD manufacturers, but can include:

a) the average difference between the experimentally determined angles between diffracting planes and those

angles calculated for the orientation determined by EBSD software;

b) the difference between the number of triplets (intersections of three Kikuchi bands) in the EBSD pattern

matched by the chosen orientation and the next best possible solution, divided by the total number of

triplets.
3.1.6
orientation map
crystal orientation map

map-like display of pixels (3.1.2) derived from the sequential measurement of crystal orientation (3.1.3)

at each point in a grid [see Figures 1 b) to 1 f)] showing the crystallographic relationship between the

pixels and the reference frame
[SOURCE: ISO 24173:2009, 3.17, modified to include reference to examples.]
3.1.7
pattern quality

measure of the sharpness of the diffraction bands or the range of contrast within a diffraction pattern

Note 1 to entry: Different terms are used in different commercial software packages, including, for example,

band contrast, band slope and image quality.
2 © ISO 2020 – All rights reserved
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ISO 13067:2020(E)
3.1.8
pattern quality map

map-like display of pixels (3.1.2) derived from the sequential collection of EBSD patterns at each point

in a grid [see Figure 1 a)] showing the pattern quality (3.1.7) of the individual pixels

Note 1 to entry: Since measures of pattern quality can change at features such as grain boundaries and with

orientation, the pattern quality map can give an indication of grain shape and size.

Note 2 to entry: Pattern quality maps can also indicate areas of heavy deformation and inadequate preparation,

such as residual scratches.

Note 3 to entry: Small particles and features also contribute to the pattern quality map.

3.1.9
pseudosymmetry

potential for an EBSD pattern to be indexed in several different ways due to internal similarities within

the EBSD pattern

Note 1 to entry: Pseudosymmetry is a problem with some crystal orientations, usually when a main zone axis is

in the centre of the pattern. Typical cases are a {0001} pole for a hexagonal structure and a <111> pole for a cubic

structure.

Note 2 to entry: Structures such as high-symmetry tetragonal crystals with an axial ratio, c/a, αpproximately

equal to 1 are also likely to exhibit pseudosymmetry in EBSD patterns.
[SOURCE: ISO 24173:2009, 3.22]
3.1.10
misorientation

rotation, often defined by an angle/axis pair, required to rotate one set of crystal axes into coincidence

with the other set of crystal axes, given two crystal orientations (3.1.3)
3.1.11
disorientation

due to crystal symmetry, there can be several axis/angle pairs which represent the same misorientation,

in which case the one having the smallest angle is called the disorientation

Note 1 to entry: For most crystal symmetries, there are multiple symmetrically equivalent axes for the

disorientation with the smallest misorientation angle.

Note 2 to entry: Misorientation and disorientation are terms which are often used interchangeably. Disorientation

is the more rigorous term here, but misorientation is the more frequently used.
3.1.12
forescatter imaging
orientation contrast produced from electrons which channel out of the specimen

Note 1 to entry: Other contrast mechanisms such as composition can also affect the contrast obtained.

3.1.13
electron-channelling contrast imaging
ECCI
orientation contrast produced from electrons which channel into the specimen
3.1.14
barrel distortion

difference in lateral magnification between the central and peripheral areas of an image such that the

lateral magnification is less at the periphery

Note 1 to entry: A square object in the centre of the field appears barrel-shaped (i.e. with convex sides).

[SOURCE: ISO 10934-1:2002, 2.4.5.1]
© ISO 2020 – All rights reserved 3
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ISO 13067:2020(E)
3.1.15
pincushion distortion

difference in lateral magnification between the central and peripheral areas of an image such that the

lateral magnification is greater at the periphery

Note 1 to entry: A square object in the centre of the field appears cushion-shaped (i.e. with concave edges).

[SOURCE: ISO 10934-1:2002, 2.4.5.2]
3.2 Terminology associated with grains and grain boundaries determined via EBSD
3.2.1
grain boundary

line separating adjacent regions of points in an EBSD orientation map with disorientation (3.1.11) across

the line greater than a minimum angle chosen to define the grain boundaries
3.2.2
grain

region of points with similar orientation (3.1.3) (within a tolerance), completely enclosed by grain

boundaries (3.2.1) and greater than the minimum size defined to exclude isolated (often badly indexed

(3.1.4)) points as small grains
3.2.3
sub-grain boundary

line separating adjacent regions of points in a grain (3.2.2) with a difference in orientation (3.1.2) across

the line smaller than that defining a grain (3.2.2) but greater than that defining a sub-grain (3.2.4)

Note 1 to entry: Effectively, sub-grain boundaries are grain boundaries with a smaller misorientation limit than

that defining a grain boundary. These boundaries can have a characteristic linear appearance and exhibit a

characteristic misorientation.
3.2.4
sub-grain

region of points with similar orientation completely enclosed by boundaries greater than the minimum

sub-grain boundary (3.2.3) angle
3.2.5
special boundary

boundary between two grains (3.2.2) having a special orientation (3.1.3) relationship within a tolerance

associated with identifying them in orientation maps (3.1.6)
3.2.6
twin boundary

particular case of a special boundary (3.2.5) between crystals oriented with respect to one another

according to some symmetry rule, in which the boundary itself is planar and is a characteristic

crystallographic plane (for both crystals) and, frequently, one crystal is the mirror image of the other

Note 1 to entry: For example, in face-centred-cubic structures, the characteristic misorientation defining a

common twin can be described as a 60° rotation about the <111> axis with the boundary plane normal to the

rotation axis.
3.2.7
recrystallized grains

new set of undeformed grains (3.2.2) formed by consuming deformed grains through nucleation and

growth processes

Note 1 to entry: Measurements of misorientation within grains by EBSD can be used to distinguish between

deformed and undeformed grains.
4 © ISO 2020 – All rights reserved
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ISO 13067:2020(E)
3.2.8
phase

physically homogeneous volume in a material having the same crystal structure and chemical

composition
3.3 Terminology associated within grain size measurement

There are a variety of ways of representing average grain size. This subclause outlines some of the

more common terms used, and the reader is referred to Annex A for more details about other terms,

about the standards available and about the applicability of methods for particular grain shapes and

distributions.
3.3.1
3D grain size

three-dimensional size of a grain (3.2.2) or crystal within a polycrystalline material, measured as

a volume

Note 1 to entry: In a strict stereological definition, just the term grain size is sufficient to denote this value, but

it is recommended to use the full description 3D grain size to avoid confusion with the sectional grain size (3.3.8)

which is often shortened to grain size as well.
3.3.2
average grain size

value determined from a two dimensional measurement which is related to the average three

dimensional size of a collection of grains or crystals forming a polycrystalline material by stereological

[2]
relationships . It can be reported as one or more of the following measurements:
a) average area
b) average diameter determined from average area
c) average linear intercept length
3.3.3
line intercept

distance between the points at which a straight line crossing a grain intersects the grain boundary

(3.2.1) on each side
[15]
Note 1 to entry: See ASTM E112 for more details.
3.3.4
equivalent circle diameter
circle

diameter of the circle with an area equivalent to the grain section area, given by:

1/2
D = (4A/π)
circle
where A is the area of the grain (3.2.2)
[15]
Note 1 to entry: The ASTM grain size number, G, is given by :
G = −6,64log D − 2,95
10 circle
where D is measured in mm.
circle
© ISO 2020 – All rights reserved 5
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ISO 13067:2020(E)
3.3.5
Feret diameter

perpendicular distance between two parallel lines drawn in a given direction tangential to the

perimeter of an object on opposite sides of the object
Note 1 to entry: It is also known as the calliper diameter.

Note 2 to entry: Different variants of the Feret diameter are used. For example, the Feret diameter can be

measured in the vertical and horizontal directions or in any two directions at right angles to each other.

3.3.6
grain shape

property whose value is determined by fitting an ellipse round the grain (3.2.2) and measuring the

aspect ratio, i.e. the ratio of the length of minor axis to the length of the major axis

Note 1 to entry: It is sometimes referred to as grain elongation.
Note 2 to entry: The value lies in the range 0 to 1.

Note 3 to entry: There are several ways of fitting the ellipse round the grain, and different methods can result in

small differences in the measured aspect ratio.
3.3.7
grain shape orientation

angle between the major axis of an ellipse fitted round the grain (3.2.2) and the horizontal direction,

usually measured counter clockwise
3.3.8
sectional grain size

two-dimensional size of a planar cross section through a grain (3.2.2), reported as

a) the area of the cross section
b) a diameter (see circle equivalent diameter (3.3.4) or Feret diameter (3.3.5))

Note 1 to entry: This is often shortened to grain size in common parlance, but can lead to confusion with the 3D

grain size (3.3.1).
Note 2 to entry: This is equivalent to the term projected grain size.
3.4 Terminology associated with data correction and uncertainty of EBSD maps
3.4.1
misindexing

assigning an incorrect orientation (3.1.3) or phase (3.2.8) to the measured EBSD pattern

Note 1 to entry: This can occur for a number of reasons, e.g. pseudosymmetry effects, attempting to index a poor

pattern or attempting to index a pattern from an unanticipated phase for which the indexing software is not

configured.
3.4.2
non-indexing

non-assignment of an orientation (3.1.3) due to insufficient quality of the EBSD pattern

Note 1 to entry: This can occur for a variety of reasons, such as roughness of the specimen, dust on the specimen,

overlapping patterns at the grain boundary, a poor-quality pattern due to the effects of strain, or the pattern is

from an unanticipated phase.
6 © ISO 2020 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 13067:2020(E)
3.4.3
data cleaning

process chosen to accommodate non-indexed (3.4.2) and misindexed (3.4.1) data within the map, using

a given set of parameters, typically based on the characteristics (orientation (3.1.3), phase (3.2.8)) of a

certain number of nearest neighbours

Note 1 to entry: A wide range of terms (not necessarily mathematically precise) is used in the various

commercially available software packages for different data-cleaning operations, including noise reduction,

extrapolation, dilation and erosion.
Note 2 to entry: See Figures 1 b) to 1 f).
4 Equipment for grain sizing by EBSD
4.1 Hardware requirements

The reader is referred to ISO 24173 for equipment needed to acquire electron backscatter patterns,

index the patterns (determine the orientation) and either step the beam across the specimen surface or,

less commonly, step the stage, keeping the beam stationary to acquire a map.
4.2 Software requirements

4.2.1 The software shall allow the orientation data (or other parameters, such as pattern quality

derived from each diffraction pattern) to be displayed as a map.

4.2.2 The software shall correct misindexed pixels or fill in non-indexed pixels (see 6.2 and 6.3).

4.2.3 The software shall use orientation data to define the positions of boundaries in accordance with

the criteria selected.

4.2.4 The software shall identify grains as regions of connected pixels from the set of boundary points

and measure grain size parameters. Special treatment may be applied to grains that intercept the map

edges, e.g. removal or weighting.
5 Acquiring the map for grain sizing by EBSD
5.1 Specimen preparation

In order to achieve a high degree of indexing of individual pixels (a high indexing hit rate), it is necessary

to produce a surface finish which produces EBSD patterns of sufficient quality to be indexed reliably.

The criteria used for indexing reliability shall be defined and reported by the user.

The surface preparation method adopted will be dependent on the material and also on its condition

e.g. metallurgical heat treatment. The reader should refer to standard texts on polishing and etching

and ISO 24173:2009, Annex B. Over-etching of grain boundaries should be avoided since it leads to

increased numbers of non- and mis-indexed points and to low index reliability at the grain boundaries.

If necessary, the specimen may be coated with a thin conductive coating (such as carbon) to prevent

charging and electron beam drift and thus avoid distortion of the image.
5.2 Defining specimen axes

If the specimen is known to be strongly textured, e.g. from thermomechanical processing, the axes of

the specimen shall be identified prior to preparation for EBSD such that EBSD measurements can be

related to these axes. These axes are usually related to the rolling direction (for metals), to a growth

direction (e.g., in thin films) or to a principal applied stress.
© ISO 2020 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO 13067:2020(E)
5.3 Stage positioning and calibration

The procedures set out in ISO 24173 shall be followed. The specimen shall be fixed to the scanning

electron microscope (SEM) stage in the desired orientation with the specimen axes relative to the stage

axes and imaged at a working distance at which the SEM and EBSD image magnifications have been

calibrated and at which the EBSD system itself has been calibrated to index diffraction patterns.

The purpose of
...

FINAL
INTERNATIONAL ISO/FDIS
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STANDARD 13067
ISO/TC 202
Microbeam analysis — Electron
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backscatter diffraction —
Voting begins on:
2020­03­23 Measurement of average grain size
Voting terminates on:
Analyse par microfaisceaux — Diffraction d'électrons rétrodiffusés —
2020­05­18
Mesurage de la taille moyenne des grains
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 13067:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
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NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 13067:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 13067:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

3.1 Terminology associated with EBSD measurement of grain size .................................................................. 2

3.2 Terminology associated with grains and grain boundaries determined via EBSD ...................... 4

3.3 Terminology associated within grain size measurement ................................................................................... 5

3.4 Terminology associated with data correction and uncertainty of EBSD maps ............................... 6

4 Equipment for grain sizing by EBSD ................................................................................................................................................. 7

4.1 Hardware requirements ......... ......................................................................................................................................................... 7

4.2 Software requirements .................................................................................................................................................................... 7

5 Acquiring the map for grain sizing by EBSD ............................................................................................................................ 7

5.1 Specimen preparation ...................................................................................................................................................................... 7

5.2 Defining specimen axes ................................................................................................................................................................... 7

5.3 Stage positioning and calibration ........................................................................................................................................... 8

5.4 Linear calibration ................................................................................................................................................................................. 8

5.5 Preliminary examination ......... ....................................................................................................................................................... 8

5.6 Choice of step size ................................................................................................................................................................................ 8

[7][8]

5.7 Determination of the level of angular accuracy needed ......................................................................10

5.8 Choice of areas to be mapped and map size ...............................................................................................................10

5.9 Considerations when examining plastically deformed materials ............................................................11

6 Analytical procedure .....................................................................................................................................................................................11

6.1 Definition of boundaries ..............................................................................................................................................................11

6.1.1 Grain boundary angles .............................................................................................................................................11

6.1.2 Handling incomplete boundaries ...................................................................................................................12

6.1.3 Dealing with special boundaries .....................................................................................................................12

6.2 Post-acquisition treatment of raw data ..........................................................................................................................12

6.3 Data­cleaning steps ..........................................................................................................................................................................12

6.4 Measurement of sectional grain size .................................................................................................................................16

6.5 Calculation of average grain size ..........................................................................................................................................16

6.6 Representation of data ..................................................................................................................................................................17

7 Measurement uncertainty .......................................................................................................................................................................17

8 Reporting of analysis results ................................................................................................................................................................18

Annex A (informative) Grain size measurement ...................................................................................................................................20

Annex B (informative) Reproducibility...........................................................................................................................................................22

Bibliography .............................................................................................................................................................................................................................25

© ISO 2020 – All rights reserved iii
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ISO/FDIS 13067:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

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expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 202, Microbeam analysis.

This second edition cancels and replaces the first edition (ISO 13067:2011), which has been technically

revised. The main changes compared to the previous edition are as follows:
— Data from a round robin (Annex B) have been used to:
— Include information on expected precision (Clause 7 and Annex B);
— Include more detail on sources of errors (Clause 7);

— Clarify statements on minimum numbers of grains measured (5.8) and acceptable clean up

procedures (6.3–6.3);

— Clarify the distinction between sectional grain size measured on a 2D section and average

grain size determined from some 2D measurements of grain sections which can be related by

stereology to the 3D grain size;

— Additionally, improvements have been made to the description of calculation of average values

(6.5) and representation of the data (6.6).

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/FDIS 13067:2020(E)
Introduction

The mechanical and electromagnetic properties of engineering materials are strongly influenced

by their crystal grain size and distribution. For example, strength, toughness and hardness are

all important engineering properties that are strongly influenced by these parameters. Both bulk

materials and thin films, even as narrow two-dimensional structures, are influenced by grain size. For

this reason, it is important to have standard methods for its measurement with commonly used and

agreed terminology. This document describes procedures for measuring average grain size from maps

of local orientation measurements using electron backscatter diffraction.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 13067:2020(E)
Microbeam analysis — Electron backscatter diffraction —
Measurement of average grain size
1 Scope

This document describes procedures for measuring average grain size derived from a two­dimensional

polished cross-section using electron backscatter diffraction (EBSD). This requires the measurement

of orientation, misorientation and pattern quality factor as a function of position in the crystalline

[1]

specimen . The measurements in this document are made on two dimensional sections. The reader

should note carefully the definitions used (3.3) which draw a distinction between the measured

sectional grain sizes, and the mean grain size which can be derived from them that relates to the three

dimensional grain size.

NOTE 1 While conventional methods for grain size determination using optical microscopy are well-

established, EBSD methods offer a number of advantages over these techniques, including increased spatial

resolution and quantitative description of the orientation of the grains.

NOTE 2 The method also lends itself to the measurement of the grain size of complex materials, for example

those with a significant duplex content.

NOTE 3 The reader is warned to interpret the results with care when attempting to investigate specimens

with high levels of deformation.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 16700, Microbeam analysis — Scanning electron microscopy — Guidelines for calibrating image

magnification

ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

ISO 23833, Microbeam analysis — Electron probe microanalysis (EPMA) — Vocabulary

ISO 24173:2009, Microbeam analysis — Guidelines for orientation measurement using electron backscatter

diffraction
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 24173 and ISO 23833 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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ISO/FDIS 13067:2020(E)
3.1 Terminology associated with EBSD measurement of grain size
3.1.1
step size

distance between adjacent points from which individual EBSD patterns are acquired during collection

of data for an EBSD map
3.1.2
pixel
picture element

smallest area of an EBSD map, with the dimensions of the step size (3.1.1), to which is assigned the

result of a single orientation (3.1.3) measurement made by stopping the beam at a point at the centre of

that area
3.1.3
orientation

mathematical description of the angular relationship between the crystal axes of the analysis point and

a reference frame, usually the specimen axes
[SOURCE: ISO 24173:2009, 3.16, modified to include different reference frames.]
3.1.4
indexed

meets the predetermined threshold for reliability for the orientation (3.1.3) of a pixel (3.1.2) calculated

from the EBSD pattern acquired for that pixel
3.1.5
indexing reliability

numerical value that indicates the confidence/reliability that the indexing software places in an

automatic analysis

Note 1 to entry: This parameter varies between EBSD manufacturers, but can include:

a) the average difference between the experimentally determined angles between diffracting planes and those

angles calculated for the orientation determined by EBSD software;

b) the difference between the number of triplets (intersections of three Kikuchi bands) in the EBSD pattern

matched by the chosen orientation and the next best possible solution, divided by the total number of

triplets.
3.1.6
orientation map
crystal orientation map

map-like display of pixels (3.1.2) derived from the sequential measurement of crystal orientation (3.1.3)

at each point in a grid [see Figures 1 b) to 1 f)] showing the crystallographic relationship between the

pixels and the reference frame
[SOURCE: ISO 24173:2009, 3.17, modified to include reference to examples.]
3.1.7
pattern quality

measure of the sharpness of the diffraction bands or the range of contrast within a diffraction pattern

Note 1 to entry: Different terms are used in different commercial software packages, including, for example,

band contrast, band slope and image quality.
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ISO/FDIS 13067:2020(E)
3.1.8
pattern quality map

map-like display of pixels (3.1.2) derived from the sequential collection of EBSD patterns at each point

in a grid [see Figure 1 a)] showing the pattern quality (3.1.7) of the individual pixels

Note 1 to entry: Since measures of pattern quality can change at features such as grain boundaries and with

orientation, the pattern quality map can give an indication of grain shape and size.

Note 2 to entry: Pattern quality maps can also indicate areas of heavy deformation and inadequate preparation,

such as residual scratches.

Note 3 to entry: Small particles and features also contribute to the pattern quality map.

3.1.9
pseudosymmetry

potential for an EBSD pattern to be indexed in several different ways due to internal similarities within

the EBSD pattern

Note 1 to entry: Pseudosymmetry is a problem with some crystal orientations, usually when a main zone axis is

in the centre of the pattern. Typical cases are a {0001} pole for a hexagonal structure and a <111> pole for a cubic

structure.

Note 2 to entry: Structures such as high-symmetry tetragonal crystals with an axial ratio, c/a, αpproximately

equal to 1 are also likely to exhibit pseudosymmetry in EBSD patterns.
[SOURCE: ISO 24173:2009, 3.22]
3.1.10
misorientation

given two crystal orientations (3.1.3), the misorientation is the rotation, often defined by an angle/axis

pair, required to rotate one set of crystal axes into coincidence with the other set of crystal axes

3.1.11
disorientation

due to crystal symmetry, there can be several axis/angle pairs which represent the same misorientation,

in which case the one having the smallest angle is called the disorientation

Note 1 to entry: For most crystal symmetries, there are multiple symmetrically equivalent axes for the

disorientation with the smallest misorientation angle.

Note 2 to entry: Misorientation and disorientation are terms which are often used interchangeably. Disorientation

is the more rigorous term here, but misorientation is the more frequently used.
3.1.12
forescatter imaging
orientation contrast produced from electrons which channel out of the specimen

Note 1 to entry: Other contrast mechanisms such as composition can also affect the contrast obtained

3.1.13
electron-channelling contrast imaging
ECCI
orientation contrast produced from electrons which channel into the specimen
3.1.14
barrel distortion

difference in lateral magnification between the central and peripheral areas of an image such that the

lateral magnification is less at the periphery

Note 1 to entry: A square object in the centre of the field appears barrel-shaped (i.e. with convex sides).

[SOURCE: ISO 10934­1:2002, 2.4.5.1]
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ISO/FDIS 13067:2020(E)
3.1.15
pincushion distortion

difference in lateral magnification between the central and peripheral areas of an image such that the

lateral magnification is greater at the periphery

Note 1 to entry: A square object in the centre of the field appears cushion-shaped (i.e. with concave edges).

[SOURCE: ISO 10934­1:2002, 2.4.5.2]
3.2 Terminology associated with grains and grain boundaries determined via EBSD
3.2.1
grain boundary

line separating adjacent regions of points in an EBSD orientation map with disorientation (3.1.11) across

the line greater than a minimum angle chosen to define the grain boundaries
3.2.2
grain

region of points with similar orientation (3.1.3) (within a tolerance), completely enclosed by grain

boundaries (3.2.1) and greater than the minimum size defined to exclude isolated (often badly indexed

(3.1.4)) points as small grains
3.2.3
sub-grain boundary

line separating adjacent regions of points in a grain (3.2.2) with a difference in orientation (3.1.2) across

the line smaller than that defining a grain (3.2.2) but greater than that defining a sub-grain (3.2.4)

Note 1 to entry: Effectively, sub-grain boundaries are grain boundaries with a smaller misorientation limit than

that defining a grain boundary. These boundaries can have a characteristic linear appearance and exhibit a

characteristic misorientation.
3.2.4
sub-grain

region of points with similar orientation completely enclosed by boundaries greater than the minimum

sub-grain boundary (3.2.3) angle
3.2.5
special boundary

boundary between two grains (3.2.2) having a special orientation (3.1.3) relationship within a tolerance

associated with identifying them in orientation maps (3.1.6)
3.2.6
twin boundary

particular case of a special boundary (3.2.5) between crystals oriented with respect to one another

according to some symmetry rule, in which the boundary itself is planar and is a characteristic

crystallographic plane (for both crystals) and, frequently, one crystal is the mirror image of the other

Note 1 to entry: For example, in face-centred-cubic structures, the characteristic misorientation defining a

common twin can be described as a 60° rotation about the <111> axis with the boundary plane normal to the

rotation axis.
3.2.7
recrystallized grains

new set of undeformed grains (3.2.2) formed by consuming deformed grains through nucleation and

growth processes

Note 1 to entry: Measurements of misorientation within grains by EBSD can be used to distinguish between

deformed and undeformed grains.
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ISO/FDIS 13067:2020(E)
3.2.8
phase

physically homogeneous volume in a material having the same crystal structure and chemical

composition
3.3 Terminology associated within grain size measurement

There are a variety of ways of representing average grain size. This subclause outlines some of the

more common terms used, and the reader is referred to Annex A for more details about other terms,

about the standards available and about the applicability of methods for particular grain shapes and

distributions.
3.3.1
3D grain size

three­dimensional size of a grain (3.2.2) or crystal within a polycrystalline material, measured as

a volume

Note 1 to entry: In a strict stereological definition, just the term grain size is sufficient to denote this value, but

it is recommended to use the full description 3D grain size to avoid confusion with the sectional grain size (3.3.8)

which is often shortened to grain size as well.
3.3.2
average grain size

value determined from a two dimensional measurement which is related to the average three

dimensional size of a collection of grains or crystals forming a polycrystalline material by stereological

[2]
relationships . It can be reported as one or more of the following measurements:
a) average area
b) average diameter determined from average area
c) average linear intercept length
3.3.3
line intercept

distance between the points at which a straight line crossing a grain intersects the grain boundary

(3.2.1) on each side
[15]
Note 1 to entry: See ASTM E112 for more details.
3.3.4
equivalent circle diameter
circle

diameter of the circle with an area equivalent to the grain section area, given by:

1/2
D = (4A/π)
circle
where A is the area of the grain (3.2.2)
[15]
Note 1 to entry: The ASTM grain size number, G, is given by :
G = −6,64log D − 2,95
10 circle
where D is measured in mm.
circle
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ISO/FDIS 13067:2020(E)
3.3.5
Feret diameter

perpendicular distance between two parallel lines drawn in a given direction tangential to the

perimeter of an object on opposite sides of the object
Note 1 to entry: It is also known as the calliper diameter.

Note 2 to entry: Different variants of the Feret diameter are used. For example, the Feret diameter can be

measured in the vertical and horizontal directions or in any two directions at right angles to each other.

3.3.6
grain shape

property whose value is determined by fitting an ellipse round the grain (3.2.2) and measuring the

aspect ratio, i.e. the ratio of the length of minor axis to the length of the major axis

Note 1 to entry: It is sometimes referred to as grain elongation.
Note 2 to entry: The value lies in the range 0 to 1.

Note 3 to entry: There are several ways of fitting the ellipse round the grain, and different methods can result in

small differences in the measured aspect ratio.
3.3.7
grain shape orientation

angle between the major axis of an ellipse fitted round the grain (3.2.2) and the horizontal direction,

usually measured counter clockwise
3.3.8
sectional grain size

two­dimensional size of a planar cross section through a grain (3.2.2), reported as

a) the area of the cross section
b) a diameter (see circle equivalent diameter (3.3.4) or Feret diameter (3.3.5))

Note 1 to entry: this is often shortened to grain size in common parlance, but can lead to confusion with the 3D

grain size (3.3.1).
Note 2 to entry: this is equivalent to the term projected grain size.
3.4 Terminology associated with data correction and uncertainty of EBSD maps
3.4.1
misindexing

assigning an incorrect orientation (3.1.3) or phase (3.2.8) to the measured EBSD pattern

Note 1 to entry: This can occur for a number of reasons, e.g. pseudosymmetry effects, attempting to index a poor

pattern or attempting to index a pattern from an unanticipated phase for which the indexing software is not

configured.
3.4.2
non-indexing

non­assignment of an orientation (3.1.3) due to insufficient quality of the EBSD pattern

Note 1 to entry: This can occur for a variety of reasons, such as roughness of the specimen, dust on the specimen,

overlapping patterns at the grain boundary, a poor-quality pattern due to the effects of strain, or the pattern is

from an unanticipated phase.
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ISO/FDIS 13067:2020(E)
3.4.3
data cleaning

process chosen to accommodate non-indexed (3.4.2) and misindexed (3.4.1) data within the map, using

a given set of parameters, typically based on the characteristics (orientation (3.1.3), phase (3.2.8)) of a

certain number of nearest neighbours (see Figures 1 b) to 1 f))

Note 1 to entry: A wide range of terms (not necessarily mathematically precise) is used in the various

commercially available software packages for different data-cleaning operations, including noise reduction,

extrapolation, dilation and erosion.
4 Equipment for grain sizing by EBSD
4.1 Hardware requirements

The reader is referred to ISO 24173 for equipment needed to acquire electron backscatter patterns,

index the patterns (determine the orientation) and either step the beam across the specimen surface or,

less commonly, step the stage, keeping the beam stationary to acquire a map.
4.2 Software requirements

4.2.1 The software shall allow the orientation data (or other parameters, such as pattern quality

derived from each diffraction pattern) to be displayed as a map.

4.2.2 The software shall correct misindexed pixels or fill in non-indexed pixels (see 6.2 and 6.3).

4.2.3 The software shall use orientation data to define the positions of boundaries in accordance with

the criteria selected.

4.2.4 The software shall identify grains as regions of connected pixels from the set of boundary points

and measure grain size parameters. Special treatment may be applied to grains that intercept the map

edges, e.g. removal or weighting.
5 Acquiring the map for grain sizing by EBSD
5.1 Specimen preparation

In order to achieve a high degree of indexing of individual pixels (a high indexing hit rate), it is necessary

to produce a surface finish which produces EBSD patterns of sufficient quality to be indexed reliably.

The criteria used for indexing reliability shall be defined and reported by the user.

The surface preparation method adopted will be dependent on the material and also on its condition

e.g. metallurgical heat treatment. The reader should refer to standard texts on polishing and etching

and Annex B of ISO 24173:2009. Over-etching of grain boundaries should be avoided since it leads to

increased numbers of non- and mis-indexed points and to low index reliability at the grain boundaries.

If necessary, the specimen may be coated with a thin conductive coating (such as carbon) to prevent

charging and electron beam drift and thus avoid distortion of the image.
5.2 Defining specimen axes

If the specimen is known to be strongly textured, e.g. from thermomechanical processing, the axes of

the specimen shall be identified prior to preparation for EBSD such that EBSD measurements can be

related to these axes. These axes are usually related to the ro
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