ISO 23703:2022

INTERNATIONAL ISO
STANDARD 23703
First edition
2022-01
Microbeam analysis — Guidelines
for misorientation analysis to assess
mechanical damage of austenitic
stainless steel by electron backscatter
diffraction (EBSD)
Analyse par microfaisceaux — Lignes directrices relatives à
l'analyse des défauts d'orientation pour l'évaluation des dommages
mécaniques de l'acier inoxydable austénitique par diffraction
d'électrons rétrodiffusés (EBSD)
Reference number
ISO 23703:2022(E)
© ISO 2022

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ISO 23703:2022(E)
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© ISO 2022
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Published in Switzerland
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ISO 23703:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 4
5 Equipment for EBSD measurement . 4
6 Preparation . 4
6.1 Calibration . 4
6.2 Specimen preparation . 5
7 Measurement procedures .6
7.1 Setting SEM operating conditions . 6
7.1.1 Accelerating voltage . 6
7.1.2 Probe current . 6
7.1.3 Magnification observation . 6
7.1.4 Working distance . 6
7.1.5 Focus . 6
7.2 Setting the EBSD measurement conditions . 6
7.2.1 Background correction . 6
7.2.2 Binning . 7
7.2.3 Pattern averaging . 7
7.2.4 Hough transform . 7
7.2.5 Measurement area . 7
7.2.6 Step size . 7
7.2.7 Scanning grid . 8
8 Calculation of misorientation .8
8.1 Defining grains . 8
8.1.1 General . 8
8.1.2 Setting the misorientation to define grains . 8
8.1.3 Setting of minimum grain size . 8
8.1.4 Caution . 8
8.2 Data screening . 8
8.2.1 Evaluation of reliability of measured data . 8
8.2.2 Treatment of blank pixels . 9
8.3 Calculation of misorientation parameters . 9
9 Material damage assessment .11
9.1 General . 11
9.2 Misorientation parameter for qualitative assessments .12
9.3 Misorientation parameter for quantitative assessments .12
10 Report .12
Annex A (informative) Round robin crystal orientation measurement for damage
assessment .15
Bibliography .25
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ISO 23703:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 202, Microbeam analysis.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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ISO 23703:2022(E)
Introduction
Mechanical damage such as creep or fatigue, in engineering materials can be assessed by misorientation
analysis using electron backscatter diffraction (EBSD) technique. The EBSD technique measures
crystal orientation of sample surface by indexing EBSD patterns which are acquired by scanning its
surface with electron beam in a scanning electron microscope (SEM). It can give orientation maps and
misorientation maps. To determine the degree of damage induced in the materials, the misorientations
calculated from the mapping data are qualified by various parameters such as the local misorientation,
which is an averaged misorientation between neighbouring measurement points, and intra-grain
misorientations, which is an averaged misorientation between the reference orientation assigned to
each crystal grain and measurement points inside the grain. These misorientation parameters correlate
well with the degree of mechanical damage caused by deformation, fatigue and/or creep. Therefore, the
magnitude of the material damage can be estimated using the correlation curve which represents the
relationship between the misorientation parameters and the degree of the damage (hereafter called
correlation curve).
In the EBSD measurement, the crystal orientation is identified through electron beam illumination to
the material surface, acquisition of the EBSD pattern by an image detector, and then crystal orientation
identification by indexing of the EBSD patterns. It was shown that the point to point accuracy of the
crystal orientation measurement is about 0,05° to 0,5°. The misorientation parameters vary depending
on SEM conditions, observation conditions, EBSD pattern acquisition conditions and crystal orientation
identification conditions. Several measurement parameters are determined for calculating the
misorientation parameters. In particular, the local misorientation greatly depends on the distance
between the measurement points (step size). Furthermore, the accuracy of the crystal orientation
measurement and the definition of the misorientation parameters may depend on the hardware and
software used for the measurement and analysis. There are several venders of commercial EBSD
measurement and analysis systems. The correlation curve obtained for a certain condition using a
certain measurement system is not always comparable with other master curve obtained with different
conditions or systems. Therefore, it is necessary to have a standard to measure comparable master
curves to show the degree of mechanical damage by using any EBSD systems.
This document describes measurement procedures and conditions and definitions of misorientation
parameters independent on the measurement system in order to assess damage of austenitic stainless
steel precisely.
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INTERNATIONAL STANDARD ISO 23703:2022(E)
Microbeam analysis — Guidelines for misorientation
analysis to assess mechanical damage of austenitic
stainless steel by electron backscatter diffraction (EBSD)
1 Scope
This document describes the guidelines for misorientation analysis to assess mechanical damage
such as fatigue and creep induced by plastic and/or creep deformation for metallic materials by using
electron backscatter diffraction (EBSD) technique. This international standard defines misorientation
parameters and specifies measurement conditions for such mechanical damage assessment. This
document is recommended to evaluate mechanical damage of austenitic stainless steel, which is widely
used for various components of power plants and other facilities.
In this document, the mechanical damage refers to the damage which causes the fracture of structural
materials due to external overload, fatigue and creep; excepting the chemical and thermal damages
themselves.
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 24173:2009, Microbeam analysis — Guidelines for orientation measurement using electron backscatter
diffraction
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
area averaged intra-grain misorientation
average of intra grain misorientation of all pixels in the measurement area
3.2
area averaged local misorientation
average of local misorientation of all pixels in the measurement area
3.3
blank point
non-indexed point (pixel) due to insufficient quality of the EBSD pattern
Note 1 to entry: This can occur for a variety of reasons, such as insufficient specimen surface condition, dust or
contamination on the specimen surface, overlapping patterns at the grain boundary, a poor-quality pattern due
to the effects of strain, or if the pattern is from an unanticipated phase.
Note 2 to entry: See ISO 13067:2020, 3.4.2 for definition of non-indexing.
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ISO 23703:2022(E)
3.4
electron backscatter diffraction
EBSD
diffraction process that arises between the backscattered electrons and the crystal planes in a highly
tilted crystalline specimen when illuminated by a stationary incident electron beam
[SOURCE: ISO 24173:2009, 3.7]
3.5
electron backscatter diffraction pattern
EBSD pattern
Kikuchi pattern like electron diffraction pattern which is generated on a phosphor screen or
photographic film by backscatter diffracted electrons in a SEM
Note 1 to entry: A specimen is generally tilted to 70 degrees to get better quality of the diffraction pattern.
[SOURCE: ISO 24173:2009, 3.8, modified — The definition has been modified.]
3.6
grain averaged intra-grain misorientation
one value for each grain by averaging intra grain misorientations
3.7
grain averaged local misorientation
average of local misorientation of all pixels in a grain
3.8
grain boundary
lines between grains in an EBSD orientation map
Note 1 to entry: Grains are defined by grouping connected neighbour pixels which misorientation is less than the
specified tolerance angle.
[SOURCE: ISO 13067:2020, 3.2.1, modified — The definition has been modified.]
3.9
Hough transform
mathematical transformation of image processing techniques, which converts a line in an image to a
point
Note 1 to entry: This allows automated detection of bands in an EBSD pattern.
Note 2 to entry: In EBSD, a linear Hough transform is used to identify the position and orientation of the Kikuchi
bands in each EBSD pattern, which enables the EBSD pattern to be indexed. Each Kikuchi band is identified as a
bright spot in Hough space. The Hough transform is essentially a special case of the Radon transform. Generally,
the Hough transform is for binary images, and the Radon transform is for grey-level images.
[SOURCE: ISO 24173:2009, 3.12, modified — The definition has been modified.]
3.10
indexing reliability
numerical value that indicates the confidence/reliability of indexing result which indexing software
place in automatic analysis procedure
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.
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ISO 23703:2022(E)
3.11
intra-grain misorientation
misorientation of each pixel with the average orientation of the grain
Note 1 to entry: See Figure 3.
Note 2 to entry: A map that displays the deviation of a pixel to a reference orientation
3.12
local misorientation
average misorientation between the measured pixel (P ) and neighbouring pixels
1
Note 1 to entry: See Figure 2.
Note 2 to entry: When the misorientation between the measured pixel (P ) and neighbour pixel exceeds the
2
threshold angle like the measured pixels at the grain boundary as shown in Figure 2, these pixels are excluded
from the misorientation calculation.
3.13
master curve
correlation curve obtained experimentally between misorientation parameter and mechanical damage
degree
Note 1 to entry: It is used to estimate damage degree quantitatively.
3.14
minimum grain size
number of pixels required to constitute a grain
Note 1 to entry: If the sum number of measurements constituting a grain are less than this value then the grain
is excluded.
3.15
misorientation
angle/axis pair, required to rotate one set of crystal axes into coincidence with the other set of crystal
axes for the given two crystal orientations
Note 1 to entry: The smallest angle used here.
3.16
misorientation parameter
parameter calculated from misorientation such as “local misorientation”, “intra-grain misorientation”
Note 1 to entry: It is classified as 3 groups; parameter for each pixel, grain or area.
3.17
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.
3.18
pixel
smallest area of an EBSD map, with the dimensions of the step size, to which is assigned the result of a
single orientation measurement made by stopping the beam at a point at the centre of that area
[SOURCE: ISO 13067:2020, 3.1.2]
Note 1 to entry: This is different from "camera pixels".
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ISO 23703:2022(E)
3.19
scanning grid
pattern of spacing of measurement points
Note 1 to entry: A regular hexagonal grid or a regular square grid is adopted generally. A hexagonal (square) grid
means that the individual points making up the scan area are situated on a hexagonal (or square) array.
3.20
step size
distance between adjacent points from which individual EBSD patterns are acquired during collection
of data for an EBSD map
[SOURCE: ISO 13067:2020, 3.1.1]
4 Abbreviated terms
CCD charge coupled device
CMOS complementary metal-oxide semiconductor
EBSD electron backscatter diffraction
EBSP electron backscatter diffraction pattern
SEM scanning electron microscope/microscopy
WD working distance
5 Equipment for EBSD measurement
See ISO 24173:2009, Clause 4.
5.1 SEM, EPMA or FIB instrument, fitted with an electron column and including controls for beam
position, stage, focus and magnification.
5.2 Accessories, for detecting and indexing electron backscatter diffraction patterns, including:
5.2.1 Phosphorescent (“phosphor”) screen, which is fluoresced by electrons from the specimen to
form the diffraction pattern.
5.2.3 Image acquisition device, with low light sensitivity, for viewing the diffraction pattern
produced on the screen.
5.2.4 Computer, with image processing, computer-aided pattern indexing, data storage and data
processing, and SEM beam (or stage) control to allow mapping.
NOTE Modern systems generally use charge-coupled devices (CCDs) or complementary metal-oxide
semiconductor (CMOS).
6 Preparation
6.1 Calibration
The procedures described in ISO 24173 shall be followed.
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ISO 23703:2022(E)
6.2 Specimen preparation
The areas chosen for examination shall be representative of location of interest, and, if there is variation
with position in the specimen, the positions examined shall be recorded in relation to the specimen
geometry.
The procedures set out in ISO 24173:2009, Annex B shall be followed.
For specimen preparation for EBSD analysis, the following equipment can be required (depending on
the types of specimen to be prepared, ISO 24173:2009, Annex B):
— cutting and mounting equipment;
— mechanical grinding and polishing equipment;
— electrolytic polisher;
— ultrasonic cleaner;
— ion-sputtering equipment; and
— coating equipment.
It should also be considered to avoid any phase transformation during specimen preparation.
Undesired damage on the specimen surface shall be removed carefully. In order to obtain the desired
damage-free surface for misorientation analysis, final polishing using colloidal silica or electro-
polishing is effective. If scratches remain on the surface, they cause larger misorientation as shown in
Figure 1
a)  Pattern quality map b)  Local misorientation map
Key
1 scratches
Figure 1 — Example of remaining scratches
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ISO 23703:2022(E)
7 Measurement procedures
7.1 Setting SEM operating conditions
7.1.1 Accelerating voltage
Accelerating voltage ranging between 10 kV and 20 kV is recommended to get reasonable EBSD
patterns. Increasing the accelerating voltage may result in increasing beam spread in the specimen,
and hence make the spatial resolution worse. It depends on the specimen Z number, but in most cases,
there is no merit to use higher accelerating voltage more than 20 kV with recent high sensitivity image
detectors.
See ISO 24173:2009, 5.3.1.
7.1.2 Probe current
Increasing the probe current increases the number of electrons contributing to the diffraction pattern
and it will give brighter EBSD patterns. This improves the signal/noise ration of the EBSD patterns
resulting in better band detection and better orientation determination. Therefore, it allows shorter
camera exposure time, namely faster mapping.
See ISO 24173:2009, 5.3.1.
7.1.3 Magnification observation
Depending on the observation’s purpose, it is recommended that the measurement area is nearly equal
to the observation area because of that the effective probe diameter depends on SEM’s magnification.
The measurement area should be set to include more than about 100 grains to avoid effects of individual
grains becoming too large. Therefore, the magnification should be set between 300 and 500 times in
case of that the grain size (diameter) is about couple of 10 µm.
7.1.4 Working distance
The ideal working distance for EBSD is the working distance at which the brightest region of the raw
EBSD pattern (i.e. without background correction) becomes nearly at the centre of the phosphor screen.
It is set at around 15 mm in general case, but it can be changed depending on each SEM/EBSD system
configuration. Short working distances generally improve the spatial resolution of EBSD measurements,
although additional care shall be paid to avoid collisions between the specimen and the pole-piece or
the backscatter detector (if present).
See ISO 24173:2009, 5.3.2.
7.1.5 Focus
EBSD measurement will be done with a highly tilted specimen in a SEM. Therefore, the focus can vary
depending on the beam position on the specimen (see ISO 24173). The dynamic focus is recommended
to be used to avoid the out of focus condition at upper and lower of measurement area.
See also ISO 24173:2009, 5.3.
7.2 Setting the EBSD measurement conditions
7.2.1 Background correction
EBSD patterns generally have a bright centre and become much darker near the corners. The brightness
of raw EBSD pattern images decrease seriously in the surrounding area. Background correction should
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ISO 23703:2022(E)
be used to make the “raw” EBSD pattern image into ones with more uniform brightness across its whole
area with better local contrast.
See ISO 24173:2009, 5.3.6.
7.2.2 Binning
The number of camera pixels, which form EBSD pattern image acquired through an image detector can
be adjusted by binning setting. If the image size becomes smaller, it means binning is set larger. Then
the time required for measurement becomes shorter, though the accuracy of orientation measurement
can become lower in general. Large binning does not always get the faster measurement speed either,
because of that the measurement speed is sometimes limited by the image processing speed or data
transfer speed. The accuracy of orientation measurement for distinguishing about 0,5˚ orientation
difference, can be acquired by setting the binning to the image size between 100 × 100 and 200 × 200
camera pixels.
See ISO 24173:2009, 5.3.4.
NOTE The binning is applicable to CCDs cameras and not applicable to CMOS cameras.
7.2.3 Pattern averaging
Quality of EBSD pattern image can be improved by averaging patterns collected more than one frame
at the same measurement point. However, the pattern averaging makes the measurement speed slower
a lot. For this reason, it is recommended to increase the probe current to acquire the same quality of
EBSD patterns, instead of using pattern averaging. The quality of EBSD pattern is also controlled by
adjusting the binning size and the gain of the image detector.
See ISO 24173:2009, 5.3.5.
7.2.4 Hough transform
Band detection during EBSD refers to the automatic detection of Kikuchi bands in an EBSP via use of
a Hough transform. Hough transformation technique is used to extract bands from an EBSD pattern
acquired by an image detector. A suitable set of Hough transformation parameters should be set
depending on the features of EBSD patterns. These parameters may affect to the speed and the accuracy
of Hough transformation calculation.
See ISO 24173:2009, 5.3.7.
7.2.5 Measurement area
It is recomme
...