Hi,
I recently did the plasma electrolytic oxidation coatings on Ti6Al4V and Ti6Al7Nb. When it comes to potentiodynamic tests - they're getting stuck because of the curve is below 0 current density and the polarization resistance is about 1,5 MOhm. The curve is reversed compared to that for normal tests. When I took my multimeter - it show that the coating don't conduct the electricity into the metal. Does it means that the corrosion cannot take place on that coating?
Best regards
The behavior you described regarding the potentiodynamic tests and the inability of the coatings to conduct electricity suggests that the PEO (Plasma Electrolytic Oxidation) coatings on Ti6Al4V and Ti6A17Nb are acting as insulating layers. This means that the coatings are not allowing the passage of electrical current, which can impede the occurrence of certain electrochemical processes, including corrosion.
Corrosion is an electrochemical reaction that typically occurs when a conductive path exists for the flow of electrons. In the case of metals, this involves the transfer of electrons from anodic areas (where corrosion occurs) to cathodic areas (where reduction reactions take place). However, if an insulating coating is present, it can prevent the flow of electrons and hinder the corrosion process.
The PEO process often forms thick, porous oxide layers on the surface of the metal substrate. These oxide layers can have insulating properties due to their composition and structure. While the PEO coatings can provide excellent protection against corrosion by acting as a barrier, they can also limit the access of electrolyte and prevent the formation of the conductive path necessary for electrochemical reactions.
It's important to note that the behavior of PEO coatings can vary depending on various factors, including the specific process parameters, coating thickness, composition, and morphology. In some cases, PEO coatings may exhibit partial conductivity due to the presence of defects, cracks, or pores, which can allow limited electron flow and potentially lead to localized corrosion. However, in your case, it seems that the coatings are predominantly insulating and providing effective corrosion resistance.
To assess the corrosion resistance of the PEO coatings, it may be more appropriate to use techniques such as electrochemical impedance spectroscopy (EIS) or potentiostatic polarization tests, which can provide insights into the coating's ability to inhibit corrosion under specific conditions. These techniques can help evaluate the barrier properties and long-term performance of the PEO coatings, taking into account factors such as the presence of defects and the stability of the oxide layer.
It's worth mentioning that the behavior of PEO coatings can be influenced by the specific characteristics of the substrate material, the electrolyte composition, and the process parameters used during the PEO treatment. Therefore, further investigation and characterization of the coatings may be necessary to fully understand their conductivity and corrosion resistance properties.
Grzegorz
What sort of coating did you apply on Ti-alloys mentioned in your question and what was the purpose for applying the coating? Is it to prevent corrosion and are Ti-alloys used as an implant in the human body?
Dr. K
It is used to make stronger connection between bone and metallic implant because of porosity on its surface.
Best regards
- Badges
- Science topic
- Similar topics
- Methodology
- Research Methodology
- Research Papers