Dl. Joslin et al., REACTION SYNTHESIS OF FE-AL ALLOYS, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 193, 1995, pp. 544-548
Reaction synthesis of several Fe-Al alloys has been observed in an eva
cuated quartz tube under a vacuum of 10(-4) Pa. The compositions studi
ed include 25, 30, 35.8, 45, and 54 at.% Al. Direct observation of the
progression of the reaction of compacts formed from 45 mu m Fe and 10
mu m Al powders revealed that an unusual ''two-stage'' rection exists
under these conditions. The occurrence of this two-stage reaction is
sensitive to the composition, density, and volume of the powder compac
t. The first stage, which lasts several seconds, starts at around 650
degrees C. After it passes through the powder compact, the temperature
continues to rise, and the second reaction begins at about 900 degree
s C. The second reaction reaches temperatures between 1250 and 1350 de
grees C. Electron microprobe analysis of samples quenched during the f
irst reaction stage revealed the presence of large amounts of FeAl3 to
gether with unalloyed Fe and small amounts of an aluminum-rich phase (
similar to 95 at.% Al). Samples allowed to react through the second st
age contained primarily FeAl and Fe3Al, with very small amounts of FeA
l2. The occurrence of the ''two-stage'' reaction is explained in terms
of thermodynamics and heat transfer.