Void formation by the reactive diffusion of titanium and aluminum foils

In order to understand the mechanism of void formation in the reactive diff usion based process using titanium and aluminum foils developed to produce TiAl intermetallic sheets with oriented lamellae, microstructure analysis w as conducted by optical microscopy, scanning electron microscopy and EDX. M any rows of coarse voids were observed at the mid-plane of the starting alu minum foils after the heating at 630 degreesC for 36ks. It is concluded tha t the voids were formed by the condensation of excess vacancies which were generated by the difference of diffusivities between aluminum and titanium in the aluminum region due to the limitation imposed by the phase diagram. Aluminum has an enough solubility in titanium while titanium has almost no solubility in aluminum. The voids move with the migration of the interface between Al and Al3Ti. The migration ends when the interface faces the same kind of interface coming from another side at the center of the starting al uminum foil. Hence the voids exist in the form of rows at the mid-plane sit es of the starting aluminum foils.