The galvanic interaction between metals and carbon fiber/polymer matrix composite degrades not only the metals but the composite itself. The objective of this study was to investigate if the fiber type influenced either the mechanism or form of damage. Two different composites were examined. Both have same epoxy matrix, 3501-6 epoxy, but contain different carbon fibers, either AS4 or IM6. The surfaces of the composite materials were exposed to 0.5 N NaCl solution to simulate sea water at open circuit condition or cathodic potentials to simulate galvanic coupling of metals. Electrochemical impedance spectroscopy (EIS) was employed to monitor changes in the behavior of the composites. Modeling of experimental data indicated that the parameter, Rp, representing the polymer resistance decreased with increasing time of exposure for both open circuit conditions and applied cathodic potentials. The value of Rp also decreased with increasingly cathodic applied potentials. This suggested that a damage process for the polymer involving increased access of solution to the carbon fibers. SEM examination showed that cracks and polymer separations on the exposed but not on the unexposed surfaces. The fiber type did not appear to influence the damage mechanism in this study.

Experimental results show that when carbon fiber/epoxy resin composite materials are joined with high-strength titanium alloys, aluminum alloys, lCrl8Ni9Ti stainless steel, or other structural materials, galvanic corrosion and crevice corrosion take place on the contact boundaries. This corrosion is primarily determined by the electrochemical properties of the materials. It is also related to the materials' mutual coupling situation, treatment technology, and environmental conditions. Galvanic corrosion is affected by the coupled materials' static energy of corrosion (Ecorr), galvanic currents, and other dynamic closed-circuit properties. In a 3.5% NaCl solution, materials' electrochemical properties and treatment techniques tended to have similar effects on galvanic corrosion and crevice corrosion. When soaking weight loss methods, salt spray methods, and crevice corrosion methods were used to test couples of CFRM with anodized titanium alloys or couples of CFRM with hot water-sealed or chromate-sealed aluminum alloys, the materials were proved to be stable and satisfactory for the needs of engineering applications. (MM).

Using potentiodynamic polarization and electrochemical impedance techniques, the electrochemical behavior of carbon-fiber/polyetheretherketone (C/PEEK) composite material was studied primarily in lactated Ringer's solution with and without a stable, fast reacting redox couple (0.01M K4[Fe(CN)6] + 0.01M K3[Fe(CN)6]), at 37°C. For comparison, the spontaneous passivation of stainless steel 316L, Co-Cr-Mo alloy, and Ti-6Al-4V was also investigated in these electrolytes. It was found that the rate of total electrochemical interaction (corrosion + electron exchange) between a spontaneously passivated metal and the environment can be considerably smaller than the rate of simple electron exchange between the carbon-fiber composite and the environment. Considering the excellent biocompatibility of carbon, this finding seems to indicate the important role of protective passive films on metals, rather than the clinical significance of higher electron exchange rates in general. When the protective passive layer on the metals is damaged or removed mechanically, the undesirable effect of substantially increased corrosion rates can be observed, particularly in environments with low redox activity. While galvanic corrosion may also occur between the mechanically depassivated and the passive sites of implant metal surfaces, more considerable galvanic corrosion can be expected if the metal undergoing fretting wear is in contact with a carbon-fiber composite, depending on the anodic/cathodic surface area ratio and on the redox properties of the environment. Additionally, the repassivation of the damaged metal surface may not take place effectively. Being the most susceptible to localized corrosion, stainless steel 316L, even in the passivated condition, may show accelrated pitting corrosion if coupled with carbon-fiber composites.

Carbon fiber reinforced silicon carbide matrix composites (C/SiC) are a ceramic matrix composite (CMC) material that offers benefits for use in a wide range of high temperature structural applications. However the susceptibility of the carbon fibers to degradation in oxidizing environments has hindered the material's use in certain applications requiring long lives under oxidizing conditions. The susceptibility of carbon fibers to oxidation will be discussed as well as the enhancement (improvement in oxidation resistance) of C/SiC materials. Thermogravimetric analysis of carbon fibers shows susceptibility to oxidation in two distinct kinetic regimes. However, in the thermogravimetric (wt. loss) analysis of unstressed, unenhanced, seal coated C/SiC coupons, the two regimes were not observed due to crack closure and matrix effects, which inhibited the oxidation process. Stressed oxidation (creep rupture) tests put the material under a stress, which is a more realistic condition for many applications. In stressed oxidation tests, the two oxidation kinetics regimes were observed. These tests can provide better insight into how the material will perform in applications involving stress. Stressed oxidation of enhanced materials containing oxidation inhibitors showed significantly improved lives at the specific test conditions considered, although there was susceptibility to oxidation at intermediate temperatures.

Interface tailoring in carbon fiber-polymer composites by means of electrochemical polymerization has been investigated. It was expected that fiber-matrix adhesion and composite mechanical properties can be modified by the electrochemical formation of polymer layers of varying structure and properties on carbon fibers prior to their incorporation in a polymer matrix. Techniques were developed first for producing thin polymer coatings on carbon fibers by using the latter as electrodes in an electrolytic cell containing the monomer. Composite specimens were prepared by the incorporation of the coated fibers in an epoxy matrix. It was demonstrated that, in fact, the effect of the surface treatment on the interfacial properties of the resulting composite was manifested in variations of the measured interlaminar shear and impact strengths of the composite specimens. The increase in interlaminar shear was considered to be the result of improved fiber-matrix adhesion when compared to composite specimens prepared from untreated carbon fibers. The corresponding reversed trend in impact strength values was attributed to the effect of excessive fiber-matrix adhesion in causing brittle failure of the composite. It was significant, when in exception to this general trend, it was also found that both interlaminar shear and impact strengths could simultaneously be increased.

Estimating possible damage to electrical/electronic equipment.

Degradation of the Carbon Fiber/Vinylester (CF/VE) polymer matrix composites due to different electrochemical interactions when exposed to seawater or at high temperature had been experimentally investigated. Water uptake behavior of composite specimen was examined based on weight gain measurement. Three point bending test was performed to quantify the mechanical degradation of composite immersed in seawater with different environmental and electrochemical interactions. Finally, Electrochemical Impedance Spectroscopy (EIS) was used to better understanding of the degradation process in CF/VE composite produced by interactions between electrochemical and different environmental conditions. A detailed equivalent circuit analysis by using EIS spectra is also presented in an attempt to elucidate the degradation phenomenon in composites.