ISO 4631:2023

Corrosion of metals and alloys — Measurement of the electrochemical critical localized corrosion potential (E-CLCP) for Ti alloys fabricated via additive manufacturing method in simulated biomedical solutions

This document specifies the procedures for testing the resistance to localized corrosion of biomedical Ti alloys fabricated via additive manufacturing (AM) method. This document defines the method of measuring the electrochemical critical localized corrosion potential (E-CLCP) of the AM Ti materials in aqueous environments, including biomedical solutions, for comparative evaluation of resistance to localized corrosion.

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General Information

• Status: Published
• Publication Date: 06-Nov-2023
• ICS: 77.060 - Corrosion of metals
• Technical Committee: ISO/TC 156 - Corrosion of metals and alloys
• Drafting Committee: ISO/TC 156/WG 11 - Electrochemical test methods
• Current Stage: 6060 - International Standard published
• Start Date: 07-Nov-2023
• Due Date: 04-Jan-2024
• Completion Date: 07-Nov-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 4631
First edition
2023-11
Corrosion of metals and alloys —
Measurement of the electrochemical
critical localized corrosion potential
(E-CLCP) for Ti alloys fabricated via
additive manufacturing method in
simulated biomedical solutions
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 1
5 Apparatus . 3
5.1 Potentiostat . 3
5.2 Heating bath with temperature controller . 3
5.3 Specimen holder and connections . 3
5.4 Test cell . 4
5.5 Auxiliary electrode and reference electrode . 4
6 Test solutions . 4
7 Test specimen . 4
8 Procedure .5
8.1 Preparation of reference electrodes . 5
8.2 Preparation of biomedical AM Ti alloy specimen . 5
8.3 Preparation of solution . 5
8.4 Setting up the E-CLCP test . 5
8.5 Ending test . 6
9 Examination and evaluation . 6
10 Test report . 7
Annex A (informative) Validity of the E-CLCP by the correlation between E-CLCP and
E-CLCT . 8
Bibliography . 9
iii
Foreword
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iv
Introduction
Ti alloys such as Ti-6Al-4V are considered to be the most promising biomedical materials. Due to a
unique combination of high strength, low modulus, lower density, and outstanding corrosion resistance,
their applications have become more widespread in a wide range of industries, e.g. aerospace,
automobile, marine and biomedical fields. Especially the medical grade Ti alloys are implanted
in patients worldwide every year and also have a significantly higher strength to weight ratio than
competing stainless steels. It is well established that Ti alloys have excellent corrosion resistance to
all body fluids and tissue and are thus completely biocompatible. These Ti alloys are conventionally
produced by wrought or cast processes which are the subtractive manufacturing (SM) methods, but
recently the new additive manufacturing (AM) method is emerging, called “3D printing”. This new
methodology has gained worldwide attention as a way to cut costs and improve efficiency. Comparing
SM with AM, the ratio of the mass of the starting, raw material to the mass of the final, finished part
can be as high as 20:1. In terms of mechanical view point, both strength and ductility of Ti alloys such
as Ti-6Al-4V fabricated by AM are comparable to or above their properties made by conventional
manufacturing methods, because of their unique microstructure. However, the resistance to corrosion
of Ti alloys produced by AM is still unknown, whether it is comparable to those of the conventionally
manufactured Ti alloys or not, because of their defects such as porosity, the formation of martensite
phase resulting from the rapid solidification, and directional difference with the stacking. Therefore,
the new standards should be made how to evaluate the resistance to localized corrosion on the stacked
alloys produced by AM methods. For this use, the measurement method such as electrochemical
critical localized corrosion temperature (E-CLCT) has been adopted as ISO 22910. However, at the
normal ranges of pH and temperatures corresponding to human body, the use of E-CLCT measurement
method should be limited because of the temperature scan during testing. Therefore, electrochemical
critical localized corrosion potential (E-CLCP) is newly introduced and proposed as a new criterion
for the evaluation of the resistance to the localized corrosion on the biomedical AM Ti alloys in human
body environments. This new test method is controlled by potentiostat through potentiodynamic –
galvanostatic-potentiostatic polarization processes and electrochemical polarization cell is used in the
artificial physiological fluids.
v
INTERNATIONAL STANDARD ISO 4631:2023(E)
Corrosion of metals and alloys — Measurement
of the electrochemical critical localized corrosion
potential (E-CLCP) for Ti alloys fabricated via additive
manufacturing method in simulated biomedical solutions
1 Scope
This document specifies the procedures for testing the resistance to localized corrosion of biomedical
Ti alloys fabricated via additive manufacturing (AM) method. This document defines the method of
measuring the electrochemical critical localized corrosion potential (E-CLCP) of the AM Ti materials
in aqueous environments, including biomedical solutions, for 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 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
electrochemical critical localized corrosion potential
E-CLCP
highest potential at which repassivation occurs, as indicator of the resistance to propagation of localized
corrosion of AM Ti alloy specimen
Note 1 to entry: The more noble the potential, the greater the resistance to localized corrosion.
3.2
cyclic potentiodynamic polarization
CPP
electrochemical test method to evaluate the resistance to propagation of localized corrosion through
the measurement of repassivation potential
3.3
electrochemical critical localized corrosion temperature
E-CLCT
lowest temperature on the surface of AM Ti alloy specimen at which stable propagating localized
corrosion occurs under specified test conditions
4 Principles
This test method specifies a determination of the electrochemical critical localized corrosion potential
(E-CLCP) for localized corrosion from the reciprocating anodic polarization of biomedical AM Ti alloys
in artificial physiological fluid environments. E-CLCP of AM Ti alloys is a criterion for the evaluation
of the resistance to localized corrosion on the biomedical AM Ti alloys in artificial human body
environments. This test method, which is a complement to the cyclic potentiodynamic polarization
(CPP), combines techniques such as potentiodynamic, galvanostatic, and potentistatic polarization
methods. CPP is used as first fast screening method while E-CLCP test method is used for fine-tuning
the repassivation potential for localized corrosion. Th
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