PROCESSING OF FE3AL AND FEAL ALLOYS BY REACTION SYNTHESIS

The effects of powder particle size, alloy composition, and reaction a tmosphere on reaction synthesis of binary Fe-Al alloys were studied. R eactions were observed in an open (air) furnace, under static vacuum ( in an evacuated quartz tube) and in a dynamic vacuum furnace. Reaction s occurring in the open furnace and in the evacuated quartz tube were recorded using high-speed video equipment. High-speed videotapes of re action synthesis of compacts formed from 45 mu m Fe and 10 mu m Al par ticles reacted in air and under static vacuum revealed that an unusual 'two-stage' reaction exists in this system under these conditions. Co mpacts formed from 9 mu m Fe and 3 mu m Al powder particles do not exh ibit a two-stage reaction under any of the conditions examined in this work. The first stage of the two-stage reaction lasts several seconds and starts at round 650 degrees C. The second stage begins at about 9 00 degrees C, reaching temperatures between 1250 and 1350 degrees C. T he progress of the reaction to the second stage is sensitive to the al loy composition and reaction atmosphere. The reaction behavior is expl ained in terms of thermodynamics and heat transfer, which control the delicate balance between heat accumulation and heat loss during reacti on synthesis.