Localized Corrosion Currents from Graphite/Aluminum and Welded SiC/Al Metal Matrix Composites.
Abstract
Scanning vibrating electrode techniques (SVET) have been used to study corrosion in Gr/Al and SiC/Al metal matrix composites. This new technique uses vibrating probes to measure localized ionic currents with spatial and current resolutions on the order of 15 to 20 micrometers and 5nA/sq.cm, respectively. Thus, it is now possible to measure corrosion currents resulting from individual local cell activity on a scale closely related to many microstructural features of the composites. The relative severity of pits and crevices associated with the corrosion process. The observations demonstrate that corrosion effects from metallurgical variations due to welding to SiC/Al can be detected and areas of accelerated corrosion activity delineated. The observations of the corroding Gr/Al specimen imply that the corrosion rate of the composite in the absence of flaws would depend upon the catalytic properties of the graphite in promoting or retarding the oxygen reduction reaction as well as the rate of diffusion of o2 to the surface. Both the exchange current density for the reaction and the Tafel constant would affect the oxygen reduction reaction rate. Thus, the corrosion rate in the absence of flaws might be improved by additions of poisions to the fiber to retard the oxygen reduction reaction on graphite. The fact that an increase in the anodic current streaming from the flaws was detected indicates that the interface and crevice corrosion is important. Originator key words include: Corrosion, Galvanic couple, Electrochemistry.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 28, 1985
- Accession Number
- ADA150988
Entities
People
- C. R. Crowe
Organizations
- United States Naval Research Laboratory