The orientation relationships and interfaces of θ-Al2Cu/Cu and γ2-Al4Cu9/Cu and the formation sequence of θ-Al2Cu and γ2-Al4Cu9 at the Cu/Al interface

The orientation relationships and interfacial planes of the theta (θ)-Al2Cu/Cu and gamma2 (γ2)-Al4Cu9/Cu interfaces formed on the Cu (001) and (111) surfaces have been studied by transmission electron microscopy (TEM). Epitaxial thin Cu films are grown on the single-crystal NaCl surfaces and then Al is evaporated to form θ-Al2Cu and γ2-Al4Cu9. Results showed that the θ-Al2Cu first formed and then the γ2-Al4Cu9 formed. The orientation relationships at the Al/Cu interface were found: (1) [110]θ//[111]Cu (zone axis) and ( 1 ¯ 10 ) θ // ( 1 ¯ 1 ¯ 2 ) Cu on the (111)Cu surface, (2) the (110)γ2 surface is the interface with both the Cu (001) and (111) surfaces with a common orientation relationship of ( 1 ¯ 11 ) γ2// ( 1 1 ¯ 0 ) Cu, and (3) [110]θ//[110]γ2 (zone axis) and ( 1 ¯ 10 ) θ// ( 1 ¯ 1 2 ¯ ) γ2 on the (111)Cu surface. The θ/Cu, γ2/Cu, and γ2/θ interfaces were further analyzed. The γ2-Al4Cu9 phase has good orientation relationships to Cu and therefore low interfacial energies. In addition, the energy of formation of γ2-Al4Cu9 is about 1.2 times than that of eta (η)-AlCu. Therefore γ2-Al4Cu9 nucleates first after θ-Al2Cu.