In this study synthesis and formation mechanism of nanocrystalline TiAl intermetallic compounds and nanocomposites by mechanical alloying subsequent heat treatment were investigated. The powder particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and microhardness measurements. The results showed that milling of Ti 50 Al 50 powder mixture led to the formation of amorphous phase followed by the formation of an supersaturated Ti(Al) solid solution. Annealing of amorphous as well as supersaturated Ti(Al) solid solution structure separately resulted in the formation of nanocrystalline TiAl. The transition of the supersaturated Ti(Al) solid solution into the equilibrium TiAl intermetallic during annealing proceeds through an intermediate stage in which a metastable fcc phase forms. In-situ TiAl-Al 2 O 3 nanocomposites was synthesis by mechanical alloying of Ti, Al and TiO 2 powder mixture. Formation of nanocomposites was found to be graduate. The results showed that the formation mechanism depends on initial powder mixture composition. Mechanical alloying of Al-TiO 2 powder mixture led to the formation of disorder TiAl matrix nanocomposite reinforced by Al 2 O 3 particles. Subsequent heating led to the transition of disordered TiAl to ordered one. Increasing the Ti powder in initial powder mixture changed the formation mechanism of nanocomposites
