Corrosion of metals and alloys -- Measurement of the electrochemical critical localized corrosion temperature (E-CLCT) for Ti alloys fabricated via the additive manufacturing method

This document specifies procedures for testing the resistance to localized corrosion of Ti alloys fabricated via additive manufacturing (AM) method. This document regulates the electrochemical critical localized corrosion temperature (E-CLCT) of the AM Ti materials for a comparative evaluation of resistance to localized corrosion.

Corrosion des métaux et alliages -- Mesurage de la température critique de la corrosion localisée électrochimique pour les alliages de Ti fabriqués à l'aide d'une méthode de fabrication additive

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Published
Publication Date
05-Aug-2020
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
13-Jul-2020
Completion Date
08-Jul-2020
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INTERNATIONAL ISO
STANDARD 22910
First edition
2020-08
Corrosion of metals and alloys —
Measurement of the electrochemical
critical localized corrosion
temperature (E-CLCT) for Ti
alloys fabricated via the additive
manufacturing method
Corrosion des métaux et alliages — Mesurage de la température
critique de la corrosion localisée électrochimique pour les alliages de
Ti fabriqués à l'aide d'une méthode de fabrication additive
Reference number
ISO 22910:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 22910:2020(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 22910:2020(E)
Contents Page

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

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

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

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

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

4 Main contents and limitations of existing standards ..................................................................................................... 1

4.1 Application coverage of ISO 17864 ....................................................................................................................................... 1

4.2 Limitations of ISO 17864 ............................................................................................................................................................... 1

4.3 Scope of ISO 18089.............................................................................................................................................................................. 2

4.4 Limitations of ISO 18089 ............................................................................................................................................................... 2

5 Principle ........................................................................................................................................................................................................................ 2

6 Apparatus ..................................................................................................................................................................................................................... 4

7 Test solutions ........................................................................................................................................................................................................... 6

8 Test specimens........................................................................................................................................................................................................ 6

9 Procedure..................................................................................................................................................................................................................... 6

9.1 Preparation of reference electrodes ..................................................................................................................................... 6

9.2 Preparation of Ti alloy specimen ............................................................................................................................................ 6

9.3 Preparation of solution .................................................................................................................................................................... 6

9.4 Setting up the E-CLCT test ......... .................................................................................................................................................... 6

9.5 Ending test .................................................................................................................................................................................................. 7

10 Evaluation of test results .............................................................................................................................................................................. 7

11 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Relationship between applied potential and localized corrosion of

AM Ti-alloys with temperature .............................................................................................................................................................. 9

Bibliography .............................................................................................................................................................................................................................10

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 22910:2020(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 156, Corrosion of metals and alloys.

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 22910:2020(E)
Introduction

Ti alloys such as Ti-6Al-4V are considered the most promising engineering materials. Due to a unique

combination of high strength-to-density ratio and increased mechanical and corrosion resistance,

their applications are growing in a wide range of industries, e.g. aerospace, automobile, marine and

biomedical fields.

Ti alloys are conventionally produced by wrought or cast processes, which are subtractive

manufacturing (SM) methods. The recent emergence of a new additive manufacturing (AM) method

known as “3D printing” has gained worldwide attention as a way to cut costs and improve efficiency for

small quantity, batch productions.

Additively manufactured Ti alloys are extensively investigated for their usage in aerospace and medical

applications. When AM is compared with conventional manufacturing, the buy-to-fly ratio is known

to be around 15:1 (conventional). In terms of mechanical viewpoints, both the strength and ductility

of Ti alloys such as Ti-6Al-4V fabricated via AM are comparable to or superior to those developed

via conventional manufacturing methods, because of their unique microstructure based on laser or

electron beam technologies. However, the characteristics of additively manufactured alloys are highly

dependent upon the geometric and processing conditions (and there are over 130 variables) such as

layer formation (imbedded or sprayed), size and quality of powder or wire, dimension, input energy,

layer orientation and surface conditions, and tolerance in the CAD process, which converts the data

into additive layers for building parts. The differences in layer orientation and the porosity generated

by crossing hatches during the layer-by-layer fabrication process can result in differences in both

mechanical and electrochemical properties in AM materials. Heat treatment controls the porosity or

the microstructure derived from rapid melting and quenching; however, it cannot eliminate interlayers,

which contribute to the differences in the mechanism of localized corrosion in AM materials. The

resistance to corrosion of Ti alloys produced via AM is similar to that of conventionally manufactured

Ti alloys. The mechanisms of corrosion also differ. Therefore, since the conventional testing methods

have shown limited ability for evaluation of those properties, the new test method measuring

electrochemical critical localized corrosion temperature (E-CLCT) has been developed to evaluate

pitting and crevice corrosion in alloys generated via AM. E-CLCT is defined as the lowest temperature

on the surface of the AM specimen on which localized corrosion to both pitting and crevice corrosion is

initiated under specified test conditions.

This document specifies a procedure for evaluation of the resistance to localized corrosion on the

AM alloys by measuring their E-CLCT, providing an efficient method for a qualitative evaluation or

comparison of corrosion properties between AM materials or their heats with altered process variables.

This test method demonstrates the quality of heat treatment, bonding integrities between layers, and

effective control of variables for AM materials, providing a qualitative tool for long-term application.

Furthermore, this document can extend its use from AM Ti-alloys to other AM alloys, such as Ni alloys

by modifying the concentration of test solutions or the applied potentials. This document also provides

important clues to evaluate other types of localized corrosion such as corrosion cracking and erosion-

corrosion. Related documents can be developed and followed up based on the results of this test.

© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 22910:2020(E)
Corrosion of metals and alloys — Measurement of the
electrochemical critical localized corrosion temperature
(E-CLCT) for Ti alloys fabricated via the additive
manufacturing method
1 Scope

This document specifies procedures for testing the resistance to localized corrosion of Ti alloys

fabricated via additive manufacturing (AM) method. This document regulates the electrochemical

critical localized corrosion temperature (E-CLCT) of the AM Ti materials for a comparative evaluation

of resistance to localized corrosion.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
electrochemical critical localized corrosion temperature
E-CLCT

lowest temperature on the surface of the AM Ti alloy specimen at which stable localized corrosion,

including both pitting and crevice corrosion, occurs under specified test conditions

3.2
temperature ramp rate
rate at which the surface temperature of the specimen increases during the test
4 Main contents and limitations of existing standards
4.1 Application coverage of ISO 17864

The test method in ISO 17864 determines the critical pitting temperature (CPT) using a potentiostatic

technique with a temperature scan. The current is monitored during the temperature scan, and CPT

is defined as the temperature at which the current increases rapidly, which for practical reasons is

defined as the temperature at which the current density exceeds 100 µA/cm for 60 s. Pitting on the

specimen is confirmed visually after the test.
4.2 Limitations of ISO 17864

ISO 17864 is useful to measure the resistance of pitting corrosion for stainless steel and related alloys.

This method applies to wrought or cast products. However, this method cannot be used for Ti alloys

© ISO 2020 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 22910:2020(E)

fabricated via AM, which are superior to stainless steels in terms of resistance to pitting, and fabricated

via SM. Therefore, it requires much higher potential and more aggressive corrosion environment.

4.3 Sc
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 22910
ISO/TC 156
Corrosion of metals and alloys —
Secretariat: SAC
Measurement of the electrochemical
Voting begins on:
2020­05­13 critical localized corrosion
temperature (E-CLCT) for Ti
Voting terminates on:
2020­07­08
alloys fabricated via the additive
manufacturing method
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 22910:2020(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
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 22910:2020(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 22910:2020(E)
Contents Page

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

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

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

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

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

4 Main contents and limitations of existing standards ..................................................................................................... 1

4.1 Application coverage of ISO 17864 ....................................................................................................................................... 1

4.2 Limitations of ISO 17864 ............................................................................................................................................................... 1

4.3 Scope of ISO 18089.............................................................................................................................................................................. 2

4.4 Limitations of ISO 18089 ............................................................................................................................................................... 2

5 Principle ........................................................................................................................................................................................................................ 2

6 Apparatus ..................................................................................................................................................................................................................... 4

7 Test solutions ........................................................................................................................................................................................................... 6

8 Test specimens........................................................................................................................................................................................................ 6

9 Procedure..................................................................................................................................................................................................................... 6

9.1 Preparation of reference electrodes ..................................................................................................................................... 6

9.2 Preparation of Ti alloy specimen ............................................................................................................................................ 6

9.3 Preparation of solution .................................................................................................................................................................... 6

9.4 Setting up the E­CLCT test ......... .................................................................................................................................................... 6

9.5 Ending test .................................................................................................................................................................................................. 7

10 Evaluation of test results .............................................................................................................................................................................. 7

11 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Relationship between applied potential and localized corrosion of

AM Ti-alloys with temperature .............................................................................................................................................................. 9

Bibliography .............................................................................................................................................................................................................................10

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 22910:2020(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 non­governmental, 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 156, Corrosion of metals and alloys.

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/FDIS 22910:2020(E)
Introduction

Ti alloys such as Ti-6Al-4V are considered the most promising engineering materials. Due to a unique

combination of high strength-to-density ratio and increased mechanical and corrosion resistance,

their applications are growing in a wide range of industries, e.g. aerospace, automobile, marine and

biomedical fields.

Ti alloys are conventionally produced by wrought or cast processes, which are subtractive

manufacturing (SM) methods. The recent emergence of a new additive manufacturing (AM) method

known as “3D printing” has gained worldwide attention as a way to cut costs and improve efficiency for

small quantity, batch productions.

Additively manufactured Ti alloys are extensively investigated for their usage in aerospace and medical

applications. When AM is compared with conventional manufacturing, the buy-to-fly ratio is known

to be around 15:1 (conventional). In terms of mechanical viewpoints, both the strength and ductility

of Ti alloys such as Ti-6Al-4V fabricated via AM are comparable to or superior to those developed

via conventional manufacturing methods, because of their unique microstructure based on laser or

electron beam technologies. However, the characteristics of additively manufactured alloys are highly

dependent upon the geometric and processing conditions (and there are over 130 variables) such as

layer formation (imbedded or sprayed), size and quality of powder or wire, dimension, input energy,

layer orientation and surface conditions, and tolerance in the CAD process, which converts the data

into additive layers for building parts. The differences in layer orientation and the porosity generated

by crossing hatches during the layer-by-layer fabrication process can result in differences in both

mechanical and electrochemical properties in AM materials. Heat treatment controls the porosity or

the microstructure derived from rapid melting and quenching; however, it cannot eliminate interlayers,

which contribute to the differences in the mechanism of localized corrosion in AM materials. The

resistance to corrosion of Ti alloys produced via AM is similar to that of conventionally manufactured

Ti alloys. The mechanisms of corrosion also differ. Therefore, since the conventional testing methods

have shown limited ability for evaluation of those properties, the new test method measuring

electrochemical critical localized corrosion temperature (E­CLCT) has been developed to evaluate

pitting and crevice corrosion in alloys generated via AM. E-CLCT is defined as the lowest temperature

on the surface of the AM specimen on which localized corrosion to both pitting and crevice corrosion is

initiated under specified test conditions.

This document specifies a procedure for evaluation of the resistance to localized corrosion on the

AM alloys by measuring their E-CLCT, providing an efficient method for a qualitative evaluation or

comparison of corrosion properties between AM materials or their heats with altered process variables.

This test method demonstrates the quality of heat treatment, bonding integrities between layers, and

effective control of variables for AM materials, providing a qualitative tool for long-term application.

Furthermore, this document can extend its use from AM Ti-alloys to other AM alloys, such as Ni alloys

by modifying the concentration of test solutions or the applied potentials. This document also provides

important clues to evaluate other types of localized corrosion such as corrosion cracking and erosion-

corrosion. Related documents can be developed and followed up based on the results of this test.

© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 22910:2020(E)
Corrosion of metals and alloys — Measurement of the
electrochemical critical localized corrosion temperature
(E-CLCT) for Ti alloys fabricated via the additive
manufacturing method
1 Scope

This document specifies procedures for testing the resistance to localized corrosion of Ti alloys

fabricated via additive manufacturing (AM) method. This document regulates the electrochemical

critical localized corrosion temperature (E­CLCT) of the AM Ti materials for a comparative evaluation

of resistance to localized corrosion.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
electrochemical critical localized corrosion temperature
E-CLCT

lowest temperature on the surface of the AM Ti alloy specimen at which stable localized corrosion,

including both pitting and crevice corrosion, occurs under specified test conditions

3.2
temperature ramp rate
rate at which the surface temperature of the specimen increases during the test
4 Main contents and limitations of existing standards
4.1 Application coverage of ISO 17864

The test method in ISO 17864 determines the critical pitting temperature (CPT) using a potentiostatic

technique with a temperature scan. The current is monitored during the temperature scan, and CPT

is defined as the temperature at which the current increases rapidly, which for practical reasons is

defined as the temperature at which the current density exceeds 100 µA/cm for 60 s. Pitting on the

specimen is confirmed visually after the test.
4.2 Limitations of ISO 17864

ISO 17864 is useful to measure the resistance of pitting corrosion for stainless steel and related alloys.

This method applies to wrought or cast products. However, this method cannot be used for Ti alloys

© ISO 2020 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO/FDIS 22910:2020(E)
fabricated via
...

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