Metal-matrix composites galvanic corrosion

H. Ding, H. Hihara, Galvanic corrosion in metal-matrix composites containing semiconducting constituents, J. Electrochem. Soc. 156 (2009) C422-C427. 

Hihara, L. H. Eind Latanision, R. M., "Suppressing Galvanic Corrosion in Graphite/Aluminum Metal-Matrix Composites, Corrosion Science, Vol. 34, No. 4, 1993, pp. 655-665. 

Hihara L H and Kondepudi P K (1993), The galvanic corrosion of SiC monofilament/ZEi41 Mg metal-matrix composite in 0.5M NaN03 , Corrosion Science, 34, 1761-1772. 

Figure 1. Evans diagram for estimating the galvanic current density. The bimetallic electrode consists of a carbon fibre embedded in a 6061 aluminium alloy (metal matrix composites). Two galvanic regimes can be reached as function of the aeration of the corrosive media. This analysis does not take into account the spatial distribution of the carbon fibers in the metallic matrix (see Fig. 12). Reprinted with permission from/nrernahono/Mafen-alsReviews, 39 (1994) 245.Copyright 1994 Maney Publishing. ...

In contrast, carbon fibres are inert under normal service temperatures they are usually considered insensitive to moisture and only little affected by alkaline environments. Therefore, apparent degradations of carbon fibre-reinforced composite are in general exclusively due to the interaction between the matrix and the environment. Besides, it is of note that galvanic corrosion may occur if CFRP composites are adventitiously placed in contact with metal elements, which usually contributes to accelerated corrosion of the metal components (Tavakkolizadeh and Saadatmanesh, 2001). 

Carbon itself has been successfully used as a biomaterial. Carbon based fibers used in composites are known to be inert in aqueous (even seawater) environments, however they do not have a track record in the biomaterials setting. In vitro studies by Kovacs [1993] disclose substantial electrochemical activity of carbon fiber composites in an aqueous environment. If such composites are placed near a metallic implant, galvanic corrosion is a possibiHty. Composite materials with a polymer matrix absorb water when placed in a hydrated environment such as the body. Moisture acts as a plasticizer of the matrix and shifts the glass transition temperature towards lower values [Delasi and Whiteside, 1978], hence a reduction in stifihess and an increase in mechanical damping. Water immersion of a graphite epoxy... 

---