Iron and nickel aluminide composites

Iron and nickel aluminide intermetallics are not only oxidation and corrosi on resistant, but also thermodynamically compatible with a wide range of ce ramics. This makes them suitable as the matrix for a wide range of composit e systems. Among the composites evaluated to date are combinations of FeAl or Ni3Al with WC, TiC, SiC, TiB2, and Al2O3, With ceramic volume fractions ranging from (5 to 90%. A variety of processing techniques has been employe d, but conventional liquid phase sintering and pressureless melt infiltrati on appear to be the most successful ones. Recently, a novel one-step melt i nfiltration procedure has been developed to fabricate composites with ceram ic volume fractions approaching 90%. Room temperature flexure strengths as high as 1.8 GPa have been obtained. Both FeAl and Ni3Al composites exhibit fracture toughnesses similar to those of WC/Co. It is found that sufficient ly thin (< 2 mu m) ligaments of FeAl tend to fracture in a ductile manner. The absence of cleavage fracture in these thin ligaments is due to the unav ailability of sufficiently long dislocation pile-ups for nucleating cleavag e cracks. In addition to the mechanical properties of FeAl and Ni3Al compos ites, other properties of interest such as wear and corrosion resistance ar e briefly discussed. The properties of FeAl and Ni3Al composites are seen t o complement each other and may be of interest in those applications where WC/Co composites have limitations.