Nonequilibrium Alloying of Aluminum for Improving the Corrosion Resistance ofGraphite-Reinforced Metal Matrix Composites

摘要

High modulus graphite (Gr) reinforced metal matrix composites (MMCs) offer a widevariety of attractive properties including: high specific modulus and strength (E/p and UTS/p), tailorable or zero coefficient of thermal expansion (CTE), and high thermal conductivity. Using Al as the matrix metal results in a reduction of the final density of the composite with high elastic modulus and excellent strength in the fiber direction. Unfortunately, MMCs, especially Gr reinforced composites, are extremely susceptible to corrosion with severe attack in chloride-containing environments occurring in as little time as several weeks for Gr/Al composites. The overall objective of this research is to determine whether improving the inherent passivity of the matrix metal in a Gr/Al composite can alleviate, or at least minimize, galvanic corrosion between the graphite and the matrix metal. This galvanic corrosion is currently the limiting factor in utilization of these composites. Our research focuses on the unique properties of sputter deposited alloys. With sputter deposition it is possible to significantly increase the solubility of passivity enhancing species, thus dramatically improving their corrosion resistance. The approach being undertaken is to develop alloy systems capable of minimizing galvanic degradation of the composite. An essential step in this process is identification of alloy compositions which maintain enhanced passivity after processing into the bulk composite. Our earlier work indicated that Al-Mo alloys provide the best combination of thermal stability, corrosion resistance, and alloy density. This paper will address the thermal stability and corrosion resistance of selected compositions of Al-Mo and Al-Mg-Mo alloys.