Void formation during the reactive diffusion of Ti and Al foils, to produce TiAl intermetallic sheets having oriented lamellae, was studied by using optical microscopy, scanning electron microscopy and EDX. Many rows of coarse voids were observed at the mid-plane of the initial Al foils after heating (630C, 10h). It was concluded that the voids formed via the condensation of excess vacancies which were generated due to the difference in diffusivities of Al and Ti in the Al region. The difference arose because Al had a reasonable solubility in Ti, while Ti had almost no solubility in Al. The voids moved during migration of the interface between Al and Al3Ti. Migration ended when the interface encountered the same type of interface, coming from the other side, at the center of the initial Al foil. Therefore, the voids existed in the form of rows at the mid-plane sites of the initial Al foils.

Void Formation by the Reactive Diffusion of Titanium and Aluminium Foils. H.Fukutomi, M.Nakamura, T.Suzuki, S.Takagi, S.Kikuchi: Materials Transactions, 2000, 41[9], 1244-6