ISO/DIS 23703

Microbeam analysis -- Guideline for misorientation analysis to assess mechanical damage of austenitic stainless steel by electron backscatter diffraction (EBSD)

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DRAFT INTERNATIONAL STANDARD
ISO/DIS 23703
ISO/TC 202 Secretariat: SAC
Voting begins on: Voting terminates on:
2021-03-24 2021-06-16
Microbeam analysis — Guideline for misorientation
analysis to assess mechanical damage of austenitic
stainless steel by electron backscatter diffraction (EBSD)
ICS: 71.040.99
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
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ISO/DIS 23703:2021(E)
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ISO/DIS 23703:2021(E)
Contents Page

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

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

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

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

3 Abbreviations........................................................................................................................................................................................................... 1

4 Terms and definitions ..................................................................................................................................................................................... 1

5 Equipment for EBSD measurement .................................................................................................................................................. 4

6 Preparation ................................................................................................................................................................................................................ 4

6.1 Calibration ................................................................................................................................................................................................. 4

6.2 Specimen preparation ..................................................................................................................................................................... 4

7 Measurement procedures ........................................................................................................................................................................... 5

7.1 Setting SEM operating conditions ......................................................................................................................................... 5

7.1.1 Accelerating Voltage .................................................................................................................................................... 5

7.1.2 Probe current .................................................................................................................................................................... 5

7.1.3 Magnification Observation ..................................................................................................................................... 5

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 .................................................................................................................................................................................... 6

7.2.3 Pattern averaging ........................................................................................................................................................... 6

7.2.4 Hough transform ............................................................................................................................................................ 6

7.2.5 Measurement area ........................................................................................................................................................ 7

7.2.6 Step size ...................................................................... ............................................................................................................ 7

7.2.7 Scanning grid ..................................................................................................................................................................... 7

8 Calculation of misorientation ................................................................................................................................................................. 7

8.1 Defining grains ....................................................................................................................................................................................... 7

8.1.1 Setting the misorientation to define grains ............................................................................................. 7

8.1.2 Setting of minimum grain size. ........................................................................................................................... 7

8.1.3 Caution .................................................................................................................................................................................... 8

8.2 Date screening ......................................................................................................................................................................................... 8

8.2.1 Evaluation of reliability of measured data; ............................................................................................... 8

8.2.2 Treatment of blank pixels ........................................................................................................................................ 8

8.3 Calculation of Misorientation parameters ...................................................................................................................... 8

9 Material damage assessment ...............................................................................................................................................................10

9.1 General ........................................................................................................................................................................................................10

9.2 Misorientation parameter for qualitative assessments ....................................................................................10

9.3 Misorientation parameter for quantitative assessments ................................................................................11

10 Record ...........................................................................................................................................................................................................................11

Annex A Round robin crystal orientation measurement for damage assessment ..........................................14

Bibliography .............................................................................................................................................................................................................................24

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ISO/DIS 23703:2021(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

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

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The committee responsible for this document is ISO/TC 202.
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ISO/DIS 23703:2021(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 accuracy of the crystal orientation

measurement is about 0.1–1.0°. 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 will be necessary to have a standard to measure comparable master curves to show the

degree of mechanical damage by using any EBSD systems.

This International Standard 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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ISO/DIS 23703:2021(E)
© ISO 2021 – All rights reserved vii
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DRAFT INTERNATIONAL STANDARD ISO/DIS 23703:2021(E)
Microbeam analysis — Guideline for misorientation
analysis to assess mechanical damage of austenitic
stainless steel by electron backscatter diffraction (EBSD)
1 Scope

This document describes the guideline 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

standard 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 means 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 referenced documents are indispensable for the application 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 13067, Microbeam analysis — Electron backscatter diffraction — Measurement of average grain size

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

diffraction
3 Abbreviations
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
4 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
4.1
area averaged intra-grain misorientation
average of intra grain misorientation of all pixels in the measurement area
4.2
area averaged local misorientation
average of local misorientation of all pixels in the measurement area
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4.3
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.
See 3.4.2 of ISO13067: 2011 for definition of non-indexing.
4.4
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: ISO24173: 2009, 3.7]
4.5
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 SEMA specimen is generally tilted to 70

degrees to get better quality of the diffraction pattern.
[SOURCE: ISO24173: 2009, 3.8]
4.6
grain averaged intra-grain misorientation
one value for each grain by averaging intra grain misorientations
4.7
grain averaged local misorientation
average of local misorientation of all pixels in a grain
4.8
grain boundary
lines between grains in an EBSD orientation map

Grains are defined by grouping connected neighbour pixels which misorientation is less than the

specified tolerance angle.
[SOURCE: ISO13067: 2011, 3.2.1]
4.9
Hough transform

mathematical transformation of image processing techniques, which converts a line in an image to a

point. This allows automated detection of bands in an EBSD pattern.

Note 1 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: ISO24173: 2009, 3.12]
4.10
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;
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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.
4.11
intra-grain misorientation

misorientation of each pixel with the average orientation of the grain (see Figure 8.2)A map that

displays the deviation of a pixel to a reference orientation
4.12
local misorientation

average misorientation between the measured pixel (P1) and neighbouring pixels (see Figure 8.1)When

the misorientation between the measured pixel (P2) and neighbour pixel exceeds the threshold angle

like the measured pixels at the grain boundary as shown in Fig. 8.1, these pixels are excluded from the

misorientation calculation.
4.13
master curve

correlation curve obtained experimentally between misorientation parameter and mechanical damage

degreeIt is used to estimate damage degree quantitatively.
4.14
minimum grain size

Once the grain grouping algorithm has completed, if the sum number of measurements constituting a

grain are less than this value then the grain is excluded.
4.15
misorientation

given two crystal orientations, 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. The smallest

angle used here.
4.16
misorientation parameter

general term indicates parameter calculated from misorientation such as “local misorientation”, “intra-

grain misorientation”It is classified as 3 groups; parameter for each pixel, grain or area.

4.17
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.
4.18
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 center of that area

[SOURCE: ISO13067: 2011, 3.1.2]
Note 1 to entry: This is different from ‘camera pixels’.
4.19
scanning grid

A regular hexagonal grid or a regular square grid is adopted generally. A hexagonal (square) grid means

the individual points making up the scan area a situated on a hexagonal (or square) array.

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4.20
step size

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

of data for an EBSD map
[SOURCE: ISO13067: 2011, 3.1.1]
5 Equipment for EBSD measurement
See 4 of ISO24173: 2009.

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:

Phosphorescent (“phosphor”) screen, which is fluoresced by electrons from the specimen to form the

diffraction pattern.

Image acquisition device, with low light sensitivity, for viewing the diffraction pattern produced on

the screen.

Computer, with image processing, computer-aided pattern indexing, data storage and data processing,

and SEM beam (or stage) control to allow mapping.

NOTE 1 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.
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 Annex B of ISO 24173 shall be followed.

For specimen preparation for EBSD analysis, the following equipment might be required (depending on

the types of specimen to be prepared — see Annex B of ISO 24173): cutting and mounting equipment,

mechanical grinding and polishing equipment, electrolytic polisher, ultrasonic cleaner, ion-sputtering

equipment and coating equipment.

It is also needed to be considered to avoid any phase transformation during specimen preparation.

Undesired damage on the specimen surface must be removed carefully. In order to obtain the desired

damage-free surface for misorientation analysis, final polishing using colloidal silica is effective. If

scratches remain on the surface, they cause larger misorientation as shown in Fig. 6.1

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(a) Pattern quality map, (b) Local misorientation map
Figure 6.1 — Example of remaining scratches
7 Measurement procedures
7.1 Setting SEM operating conditions
7.1.1 Accelerating Voltage

Accelerating voltage ranging between 15 kV and 30 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 20kV with recent high sensitivity image

detectors.
See 5.3.1 of ISO24173: 2009.
7.1.2 Probe current

Increasing the probe current will increase 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. So it allows shorter

camera exposure time, namely faster mapping.
See 5.3.1 of ISO24173: 2009.
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.

NOTE 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 10µm.
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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 center of the phosphor

screen. It is set at around 15mm in general case, but it can be changed depending on each SEM/EBSD

system configuration. Short working distances will generally improve the spatial resolution of EBSD

measurements, although additional care has to be paid to avoid collisions between the specimen and

the pole-piece or the backscatter detector (if present).
See 5.3.2 of ISO24173: 2009.
7.1.5 Focus

EBSD measurement will be done with a highly tilted specimen in a SEM. So the focus can vary depending

on the beam position on the specimen (focus ISO24173). The dynamic focus is recommended to be used

to avoid the out of focus condition at upper and lower of measurement area.
See also 5.3 of ISO24173: 2009.
7.2 Setting the EBSD measurement conditions
7.2.1 Background correction

EBSD patterns generally have a bright center and become much darker near the corners. The brightness

of raw EBSD pattern images decrease seriously in the surrounding area. Background correction should

be used to make the “raw” EBSD pattern image into ones with more uniform brightness across its whole

area with better local contrast.
See 5.3.6 of ISO24173: 2009.
7.2.2 Binning

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

may 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 5.3.4 of ISO24173: 2009.

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 5.3.5 of ISO24173: 2009.
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

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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 5.3.7 of ISO24173: 2009.
7.2.5 Measurement area

It is recommended to include reasonable number of grains, it is expected more than 100 grains as noted

in 7.1.3, in the measurement area to evaluate the average status of polycrystalline materials. If the

measurement area becomes larger, then the time for measurement becomes longer. In this case, it may

be needed to consider about the stability of SEM’s such as the beam drift or specimen drift.

7.2.6 Step size
This depends on the type of speci
...