Evaluation of mechanical and metallurgical properties of Fe/sub 3/Al-based aluminides

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Abstract
A study is being conducted to develop aluminide alloys based on Fe/sub 3/Al with an optimum combination of strength, ductility, and corrosion resistance for use as hot components in advanced fossil energy conversion systems. Three phases of the study have been planned: (1) Fe-Al base compositions will be prepared for preliminary studies and evaluation of potential for further alloy development; (2) two of the base alloys will be used in the development and characterization of the properties of ternary and quaternary alloys; and (3) based on the results of those two phases of the study, alloys will be selected for preparation and characterization of large heats. Studies will include the fabricability, microstructures, tensile properties, oxidation and sulfidation resistance, and weldability of Fe/sub 3/Al-based alloys to which a fine dispersion of TiB/sub 2/ particles has been added for grain refinement. This report summarizes the results of the first phase of this study and discusses our plans for future work. Alloys of Fe-24, 25, 26, 27, 28, and 30 at. % Al (all with 0.5 wt % TiB/sub 2/) were chosen as base alloys. All six compositions were easily fabricated and exhibited excellent oxidation and corrosion properties. Negligible weight changes were observedmore » after 500 h in air-oxidation tests at temperatures to 1000/sup 0/C. Similar results occurred in sulfidation tests conducted at 871/sup 0/C for 168 h. Resistance to oxidizing and sulfidizing environments is a result of the formation of a self-protecting oxide layer at low oxygen pressures. The tensile strengths of the six base alloys were shown to be higher than those of type 316 stainless steel at temperatures below 760/sup 0/C and those of modified 9Cr-1Mo steel at temperatures above 550/sup 0/C. Preliminary weldability studies indicate that the alloys with higher aluminum content develop fewer cracks in the fusion and heat-affected zones. 16 refs., 10 figs., 6 tabs. « less

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