THE BALANCE OF MECHANICAL AND ENVIRONMENTAL PROPERTIES OF A MULTIELEMENT NIOBIUM-NIOBIUM SILICIDE-BASED IN-SITU COMPOSITE

This article describes room-temperature and high-temperature mechanica l properties, as well as oxidation behavior, of a niobium-niobium sili cide based in situ composite directionally solidified from a Nb-Ti-Hf- Cr-Al-Si alloy. Room-temperature fracture toughness, high-temperature tensile strength (up to 1200 degrees C), and tensile creep rupture (11 00 degrees C) data are described. The composite shows an excellent bal ance of high- and low-temperature mechanical properties with promising environmental resistance at temperatures above 1000 degrees C. The co mposite microstructures and phase chemistries are also described. Samp les were prepared using directional solidification in order to generat e an aligned composite of a Nb-based solid solution with Nb3Si- and Nb 5Si3-type silicides. The high-temperature mechanical properties and ox idation behavior are also compared with the most recent Ni-based super alloys. This composite represents an excellent basis for the developme nt of advanced Nb-based intermetallic matrix composites that offer imp roved properties over Ni-based superalloys at temperatures in excess o f 1000 degrees C.