PROCESSING OF FE3AL AND FEAL ALLOYS BY REACTION SYNTHESIS

The effects of powder particle size, alloy composition, and reaction atmosphere on reaction synthesis of binary Fe-Al alloys were studied. Reactions were observed in an open (air) furnace, under static vacuum (in an evacuated quartz tube) and in a dynamic vacuum furnace. Reactions occurring in the open furnace and in the evacuated quartz tube were recorded using high-speed video equipment. High-speed videotapes of reaction synthesis of compacts formed from 45 mu m Fe and 10 mu m Al particles reacted in air and under static vacuum revealed that an unusual 'two-stage' reaction exists in this system under these conditions. Compacts formed from 9 mu m Fe and 3 mu m Al powder particles do not exhibit 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 900 degrees C, reaching temperatures between 1250 and 1350 degrees C. The progress of the reaction to the second stage is sensitive to the alloy composition and reaction atmosphere. The reaction behavior is explained in terms of thermodynamics and heat transfer, which control the delicate balance between heat accumulation and heat loss during reaction synthesis.