AC Impedance Analysis of Corrosion Fatigue in Naval Aircraft Alloys.
Abstract
The objective of this program is to develop rapid electrochemical methods for evaluating the susceptibility of Naval aircraft materials to corrosion fatigue (CF). A fatigue admittance method that evaluates the coupling of the modulated stress intensity factor to electrochemical reaction kinetics has been developed. In addition, phase sensitive detection of the crack tip displacement allows continuous measurement of the CF rate as a function of time and potential. Application of fatigue admittance analysis to the CF of Al 7075-T73 demonstrates that the crack tip of the material in aerated 0.5 M NaCI is anodic to the noncluded surface of the material. Injection of a corrosion inhibitor (DNBM) into the crack tip decreases the extent to the anodic polarization of the crack tip and decrease the electrochemical rate of oxidation in the crack tip by a factor of 100. The role of aqueous and organic phase dichromate, nitrite, borate and molydbate (DNBM) on the CF rate of 4340 steel in 0.5 Sodium Chloride has also been evaluated. The organic complex DNBM when injected in the crack tip reduces the crack growth rate by a factor of 10. The aqueous inhibitors at a concentration level of 0.01 M show only small influences on the open CF rate, but 0.01 M borate reduces the cathodically aerated CF. The molybdate and dichromate inhibitors at the 0.01 M level appear to show the anodic reaction in the crack tip. The maximum load has a dominating influence on the electrochemical kinetics in the crack tip.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1987
- Accession Number
- ADA190822
Entities
People
- F. Mansfield
- M. Kendig