Multi-Metal Interfacial Heterogeneity: How It Impacts Corrosion
Corrosion, or the dissolution of a material due to exposure to a given active environment, is an irreversible effect that affects all engineering materials, leading to unexpected failures and economic losses. Of particular concern is the corrosion of multi-component materials, such as multi-metal systems, which complicate the definition of the corrosion process and can lead to diffused localized attack. In this paper, we address the concept of multi-metal interfacial heterogeneity (MMIH), the observation that two metals can interdiffuse when in contact, which leads to complex patterns of corrosion progression.
The cause of MMIH is related to the interface stability between two metallic elements and their relative diffusion behavior. When two metals are in contact with one another, they create a “grain boundary” or a boundary between the materials having different chemical composition and electronic structure. If the interface between the two metals is sufficiently stable, then theMMIH phenomenon can occur. In this case, interdiffusion will occur between the two metallic elements and a third immiscible element may be formed at the interfaces that has unique properties compared to the original two materials.
Examples of this phenomenon are seen in the form of galvanic series. Galvanic series are potential differences between metals that are observed when two metals are placed into contact with each other. This potential difference is significant because it is directly proportional to the propensity of metal assimilation and corrosion. Most metals that possess a low potential difference tend to corrode more readily when they are placed in contact with a metal of higher potential. For example, aluminum and zinc create an aluminum-zinc grab when they are placed in contact with each other and this gallivanting effect results in increased corrosion of the aluminum due to increased interdiffusional forces.
The MMIH phenomenon can also lead to an increased corrosion rate at or near the grain boundaries of the material due to the chemical interactions taking place at the interface. As already mentioned, when two metals are in contact with each other, unique patterns of corrosion can develop which can lead to accelerated corroded areas. This subsequently can lead to localized failure and detriment of the material. Therefore, a thorough understanding of MMIH and its associated corrosion profile is necessary to avoid corrosion-related material failure.
The MMIH phenomenon is a complex process and current studies are attempting to develop a better understanding as to how different parameters, such as temperature, pH, and mechanical strain, when combined, affect the corrosion behavior at the multi-metal interfaces. In conclusion, we can see that understanding the impact of MMIH on corrosion is of utmost importance, particularly in the case of multi-metal systems, so that the best protection strategies can be implemented to reduce the risk of corrosion-related failures.
