Synthesis of titanium aluminide coatings on aluminum and titanium surfaces by mechanical alloying and subsequent annealing

Intermetallic Ti-Al-based coatings were synthesized by mechanical alloying in a vibratory ball mill and subsequent annealing. A titanium layer was deposited on aluminum specimens and an aluminum layer and aluminum-titanium mixture were deposited on titanium specimens. Under the effect of milling balls, powder particles deposit at the substrates, forming layers that have a very good cohesion with the substrate. During subsequent heating, diffusion layers on the basis of titanium-aluminum phases are synthesized as a result of the chemical interaction between titanium and aluminum. In the case of titanium layer deposited on aluminum, the temperature interval of transformations is 600–650°C; first, a Ti₃Al₅-based phase is formed; then, as diffusion saturation with Al increases, an Al₂Ti-based layer appears; and finally, the Al₃Ti compound is formed. The reaction rates depend on the temperature and the duration of annealing. On titanium with a (Ti + Al) layer deposited on its surface, the Al₃Ti, Al₂Ti, TiAl, and Ti₃Al compounds are formed in a temperature interval of 600–900°C. In the case of deposition a homogeneous aluminum layer on titanium, only Al₃Ti and Ti₃Al phases were observed after annealing.