Processing and Characterization of Niobium Aluminide-Based Composites

摘要

Many ordered intermetallic compounds exhibit attractive properties for hightemperature structural aerospace applications. These materials provide an alternative to and surpass the performance of existing high temperature superalloys and ceramics. High melting point, low density, high strength, and relatively good corrosion resistance are the attractive properties that have led to the current thrust of research in these materials. However, the major obstacles limiting the use of these materials are their low ductility and toughness at room temperature and poor creep resistance at elevated temperatures. Previous studies have shown that micro and macro-alloying of several systems lead to improvements in low temperature ductility and toughness, while the use of suitable ceramic reinforcements lead to increases in creep resistance. However, the reinforcements of the composites are not protected from reaction with the matrix at elevated temperatures. Thus, they do not have appropriate microstructures for thermal stability and are likely to have poor creep resistance at elevated temperatures. In this investigation a novel approach has been devised to address both low and high temperature problems by the incorporation of 'treated' refractory metal and ceramic reinforcements into a niobium aluminide matrix. The 'treated' ductile phase is to improve room temperature toughness and the 'treated' ceramic phase is to improve creep resistance. The 'treatment', an oxide layer produced on the reinforcements (niobium and silicon carbide whiskers) by elevated temperature exposure, is to protect them from reacting with the matrix materials during hot pressing or subsequent use at elevated temperatures. (MM).