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Mechanisms of formation of Al4Cu9 during mechanical alloying: An experimental study.

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Title: Mechanisms of formation of Al4Cu9 during mechanical alloying: An experimental study.
Authors: Besson, R.1, Avettand-Fènoël, M.-N.1, Thuinet, L.1, Kwon, J.1, Addad, A.1, Roussel, P.2, Legris, A.1
Source: Acta Materialia. Apr2015, Vol. 87, p216-224. 9p.
Subjects: Mechanical alloying, Aluminum-copper alloys, Surface morphology, Milling (Metalwork), Chemical equilibrium, Nucleation
Abstract: In spite of its complex structure, the Cu-rich γ 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. γ 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 θ-Al 2 Cu expected for this composition is detected only for longer times (90 h). Whereas the early formation of γ 1 suggests that its nucleation should occur at Al/Cu interfaces, direct visualization reveals the presence of γ 1 crystallites within Cu-rich zones. The thermal instability of MA-formed γ 1 -Al 4 Cu 9 is evidenced, this phase evolving towards θ-Al 2 Cu at temperatures lower than those predicted for equilibrium conditions. These observations indicate that γ 1 -Al 4 Cu 9 may be able to form through non-thermally activated mechanisms. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:In spite of its complex structure, the Cu-rich γ 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. γ 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 θ-Al 2 Cu expected for this composition is detected only for longer times (90 h). Whereas the early formation of γ 1 suggests that its nucleation should occur at Al/Cu interfaces, direct visualization reveals the presence of γ 1 crystallites within Cu-rich zones. The thermal instability of MA-formed γ 1 -Al 4 Cu 9 is evidenced, this phase evolving towards θ-Al 2 Cu at temperatures lower than those predicted for equilibrium conditions. These observations indicate that γ 1 -Al 4 Cu 9 may be able to form through non-thermally activated mechanisms. [ABSTRACT FROM AUTHOR]
ISSN:13596454
DOI:10.1016/j.actamat.2014.12.050