Overview
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 in simulated biomedical solutions specifies a reproducible electrochemical method to evaluate resistance to localized corrosion of biomedical titanium (Ti) alloys made by additive manufacturing (AM). The standard defines how to measure the electrochemical critical localized corrosion potential (E-CLCP) in aqueous, simulated physiological fluids (e.g., Ringer, Hanks, saliva) to enable comparative assessment of AM Ti implants and components.
Key topics and technical requirements
- Purpose: Determine the highest potential at which repassivation occurs (E-CLCP) as an indicator of resistance to propagation of localized corrosion in AM Ti alloys.
- Test principles: Combines potentiodynamic, galvanostatic and potentiostatic polarization techniques; complements cyclic potentiodynamic polarization (CPP) and can be used for fine-tuning repassivation potential.
- Temperature control: Testing confined to human-body conditions - specimen surface temperature held at 37.0 °C ± 1 °C.
- Electrochemical equipment: Potentiostat capable of controlling potential within ±1 mV; upper voltage limit 9 V (terminate test if no localized corrosion up to 9 V).
- Electrodes and cell: Use of an external reference electrode (commonly saturated calomel electrode via a Luggin capillary), and a high‑purity platinum auxiliary electrode larger than the specimen area.
- Specimen requirements: Minimum exposed area example 10 mm × 10 mm × 1 mm; connections and holders must avoid introducing additional corrosion sites (coating/sealant allowed).
- Test solutions: Artificial physiological fluids selected by the end user (Ringer, Hanks, saliva).
- Reporting and evaluation: Procedural steps include electrode preparation, specimen set-up, polarization protocol and criteria for ending the test; annex provides correlation of E-CLCP with E-CLCT.
Applications and users
- Who uses it: Materials engineers, biomedical implant manufacturers, corrosion laboratories, regulatory testing bodies, and researchers assessing AM Ti alloys (e.g., Ti-6Al-4V) for implantable devices.
- Practical uses: Screening and comparing localized corrosion resistance of AM-produced biomedical components; quality control for implant manufacturing; preclinical evaluation of new AM processes or post-processing (heat treatment, surface finishing) to ensure biocompatibility and long-term corrosion performance.
Related standards
- ISO 22910 (electrochemical critical localized corrosion temperature - E-CLCT) is cited as a complementary method; ISO 4631 specifically introduces E-CLCP for biomedical AM Ti alloys at physiological temperature.
Keywords: ISO 4631:2023, E-CLCP, additive manufacturing, AM Ti alloys, localized corrosion, biomedical implants, potentiostat, cyclic potentiodynamic polarization.