Corrosion of Aircraft Materials: Correlation Between Nanometer Scale and Macroscopic Structural Damage Parameters

The structures of aircraft onen suffer from corrosion especially in humid, hot, polluted areas, and near to marine environnents. CoiTosion nay shorten the aircraft's sevice life, increase naintenance and repair costs, and even cause structural failures. Therefore, there is a critical need to develop and inplement instruments able to perforn nondestructive evaluation (NDE) of hidden corrosion and material degradation with a high degree of accuracy, sensitivity, and versatitlity. Thus, the understanding of the fundamental chenust^ of corrosion is essential. The pu^ose of the work outlined in this proposal is to develop a fundamental research project focused on understanding coiTosion initiation in aircraft metallic materials at the nanonieter scale and to relate it with nacroscopic properties of the material. The proposed approach is to use: (l) scanning tunneling microscopy (STM) to study in situ corrosion initiation and to identify surface regions where corrosion is most likely to occur; (2) impedance spectroscopy to detect changes in the impedance properties of the material due to corrosion. The effect of atmospheric pollutants on the coiTosion process will be investigate. Phase I will provide the basis for the developnent of a NDE probe for the evaluation of hidden corrosion on aircraft structures ion Phase II.