Reaction synthesis and processing of nickel and iron aluminides

Composites of nickel and iron aluminides were obtained by hot-pressing and hot-extrusion of a blended mixture of nickel and aluminum or iron and aluminum with ceramic phases such as TiC, ZrO2, and Al2O3. Aluminides were analyzed by X-ray diffraction technique to determine the phase structures of the materials, and optical and scanning electron microscopic techniques were used to determine the grain sizes of the aluminides and dispersion of ceramics. Tensile properties such as 0.2% yield strength, ultimate tensile strength, total elongation, and reduction in area were measured on button-head and sheet specimens of nickel and iron aluminides and their composites at room and elevated temperatures in air at a strain rate of 1.2 x 10(-3)s(-1). Tensile properties of Fe-8 wt % Al alloys obtained by partial mechanical alloying followed by combustion synthesis compare extremely well with the oxide-dispersed alloys of iron. Iron aluminides of FeAl and their composites, based on Fe-24 wt % Al obtained by hot-pressing of iron and aluminum powders with or without ceramic phases, exhibited full densities and uniform grain sizes. The 0.2% yield strengths, tensile strengths, and tensile elongations of FeAl and their composites, based on hot-pressing of elemental powders, exhibited excellent mechanical properties as compared to the mechanical properties of FeAl alloys obtained by hot-extrusion of water-atomized powders. Iron aluminides were also obtained by hot-extrusion of iron and aluminum powders at extrusion temperatures of 950, 1000, and 1100 degrees C.