MICROSTRUCTURE-PROPERTY CORRELATIONS IN RAPID-SOLIDIFICATION PROCESSED IRON-ALUMINUM-SILICON ALLOYS

Alloys of the iron-aluminum-silicon system are potential candidates for high temperature applications because of their good oxidation resistance and good strength. However utilization has been limited because of their poor ductility. In this study Fe-Al, Fe-Si and Fe-Al-Si alloys were prepared by rapid-solidification processing of powders and subsequent consolidation by hot extrusion/hot-isostatic-pressing. Titanium and boron in small quantities were added to the melt to obtain a fine dispersion of titanium boride particles in the alloys. The tensile properties of the alloys were determined at room temperature and at 1000(DEGREES)F (811 K). The alloys exhibited good mechanical properties, three of the alloys had yield strengths greater than 200 ksi (1.4 GPa) at room temperature. This was a significant improvement over the properties of alloys of similiar composition prepared by conventional ingot metallurgy techniques. A substantial improvement in ductility was also observed. The tensile properties at 1000(DEGREES)F (811 K) were also superior to the ingot metallurgy alloys.;Another new class of alloys were prepared by mixing powders of two different compositions and then consolidating the mixture. A softer, more ductile powder was chosen as the matrix material and small quantities of harder powders were added to this and consolidated. The properties of these "Blended Alloys" varied with blend composition in a similiar way as the properties of the dual-phase steels vary with martensite content. In addition the properties of the blended alloys also vary with heat treatment, thus making them versatile alloys.;Transmission electron microscopy of all the extruded alloys revealed fine elogated grains of average length of 2.0 microns and width of 0.5 microns. Titanium boride particles of average size 0.03 microns were distributed uniformly. This microstructure was stable upto a temperature 1800(DEGREES)F (1255 K). The fine grain size and the titanium boride particles contributed to the improvement in properties.