Structural evolution in mechanically alloyed Al-Fe powders |
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Authors: | D K Mukhopadhyay C Suryanarayana F H FROES |
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Affiliation: | (1) Institute for Materials and Advanced Processes, University of Idaho, 83844-3026 Moscow, ID |
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Abstract: | The structural evolution in mechanically alloyed binary aluminum-iron powder mixtures containing 1, 4, 7.3, 10.7, and 25 at.
pct Fe was investigated using X-ray diffraction (XRD) and electron microscopic techniques. The constitution (number and identity
of phases present), microstructure (crystal size, particle size), and transformation behavior of the powders on annealing
were studied. The solid solubility of Fe in Al has been extended up to at least 4.5 at. pct, which is close to that observed
using rapid solidification (RS) (4.4 at. pct), compared with the equilibrium value of 0.025 at. pct Fe at room temperature.
Nanometer-sized grains were observed in as-milled crystalline powders in all compositions. Increasing the ball-to-powder weight
ratio (BPR) resulted in a faster rate of decrease of crystal size. A fully amorphous phase was obtained in the Al-25 at. pct
Fe composition, and a mixed amorphous phase plus solid solution of Fe in Al was developed in the Al-10.7 at. pct Fe alloy,
agreeing well with the predictions made using the semiempirical Miedema model. Heat treatment of the mechanically alloyed
powders containing the supersaturated solid solution or the amorphous phase resulted in the formation of the Al3Fe intermetallic in all but the Al-25 at. pct Fe powders. In the Al-25 at. pct Fe powder, formation of nanocrystalline Al5Fe2 was observed directly by milling. Electron microscope studies of the shock-consolidated mechanically alloyed Al-10.7 and
25 at. pct Fe powders indicated that nanometer-sized grains were retained after compaction. |
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