Mechanisms of formation of Al4Cu9 during mechanical alloying: An experimental study (original) (raw)
In spite of its complex structure, the Cu-rich c 1-Al 4 Cu 9 compound is frequently observed in Al-Cu processing. In order to better understand the intriguing formation of this compound, a thorough experimental study of Al-25 at.% Cu mixtures produced by mechanical alloying (MA) was performed. Strong morphological changes are found to occur for moderate milling times. c 1-Al 4 Cu 9 is formed during the early milling steps (5.5 h), its volume fraction increasing continuously with milling time, while the equilibrium h-Al 2 Cu expected for this composition is detected only for longer times (90 h). Whereas the early formation of c 1 suggests that its nucleation should occur at Al/Cu interfaces, direct visualization reveals the presence of c 1 crystallites within Cu-rich zones. The thermal instability of MA-formed c 1-Al 4 Cu 9 is evidenced, this phase evolving towards h-Al 2 Cu at temperatures lower than those predicted for equilibrium conditions. These observations indicate that c 1-Al 4 Cu 9 may be able to form through nonthermally activated mechanisms.
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