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

• Published in: Acta materialia Vol. 87; pp. 216 - 224
• Main Authors: Besson, R., Avettand-Fènoël, M.-N., Thuinet, L., Kwon, J., Addad, A., Roussel, P., Legris, A.
• Format: Journal Article
• Language: English
• Published: Elsevier 01.04.2015
• Subjects: Aluminum base alloys; Chemical Sciences; Copper; Crystallites; Equilibrium conditions; Formations; Inorganic chemistry; Mechanical alloying; Nucleation; Visualization
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2014.12.050

In spite of its complex structure, the Cu-rich gamma 1-Al4Cu9 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-25at.% Cu mixtures produced by mechanical alloying (MA) was performed. Strong morphological changes are found to occur for moderate milling times. gamma 1-Al4Cu9 is formed during the early milling steps (5.5h), its volume fraction increasing continuously with milling time, while the equilibrium [thetas]-Al2Cu expected for this composition is detected only for longer times (90h). Whereas the early formation of gamma 1 suggests that its nucleation should occur at Al/Cu interfaces, direct visualization reveals the presence of gamma 1 crystallites within Cu-rich zones. The thermal instability of MA-formed gamma 1-Al4Cu9 is evidenced, this phase evolving towards [thetas]-Al2Cu at temperatures lower than those predicted for equilibrium conditions. These observations indicate that gamma 1-Al4Cu9 may be able to form through non-thermally activated mechanisms.