Microstructures and tensile properties of as-cast iron-aluminide alloys

Room-temperature tensile properties of as-cast Fe{sub 3}Al, Fe{sub 3}Al with chromium, and Fe{sub 3}Al-based FA-129 alloy have been investigated. Tensile properties have been obtained in air in the as-cast condition for all three alloys. Samples of FA-129 alloy have also been tested in oxygen and water vapor environments, and after homogenization at 700, 900, and 1200C. Transmission electron microscopy has been used to characterize ordered phases and optical metallography and scanning electron microscopy have been used to characterize the microstructure and fracture morphology. Tensile properties in the as-cast condition exhibited an environmental effect; tensile ductilities in an oxygen atmosphere were greater than those obtained in laboratory air. Homogenized samples of FA-129 alloy exhibited almost twice the ductility of the as-cast condition. Results indicate that the low ductility of as-cast Fe{sub 3}Al-based alloys may be related to the relatively large grain size in the as-cast condition and the presence of the DO{sub 3} ordered phase. Microstructural characterization of the homogenized samples and comparison of the as-cast and homogenized microstructures may provide a clue to the poor ductility in the as-cast condition.