STRUCTURAL EVOLUTION OF MECHANICALLY ALLOYED TI-AL ALLOYS

Two titanium alloys with 24 and 50 at.% Al respectively, were mechanically alloyed in a steel vial with hardened steel balls using a Spex 8000 mixer-mill. The sequence of phases formed has been investigated by both X-ray diffraction and transmission electron microscopy. With increasing milling time a solid solution of aluminum in titanium, intermetallic Ti3Al, an amorphous phase and an f.c.c. crystalline phase formed sequentially. The formation of the amorphous phase has been rationalized in terms of Miedema's thermodynamic analysis. The results available on the f.c.c. phase suggest that this phase may be a titanium nitride formed by pick-up of nitrogen during milling and that it has not formed by the crystallization of the amorphous phase per se.