Sub-microstructure titanium aluminide obtained by crystallization of mechanically alloyed amorphous

A submicrostructure titanium aluminide was obtained by crystallization of the amorphous Ti50at%Al powders, which were prepared by highenergy milling in a planetary ball milling system for up to 100h. The Xray diffraction, differential thermal analysis techniques and scanning electron microscope were used to characterize the structure evolution during the milling and the process of crystallization. Results show that, after 60h milling, aluminum completely dissolved into titanium to form an Ti(Al) hcp supersaturated solid solution, and at the same time a small amount of amorphous phase was produced. When the milling time was increased to 100h, the Ti(Al) hcp supersaturated solid solution disappeared, and only amorphous phase was left.The milling process can be describe by: Ti+Al→Ti(Al) hcp→Amorphous. Crystallization occurs at the process of decency during hot pressing, and the crystallization process can be describe by: Amorphous→disordered α (hcp)→ordered γTiAl phase(+ ordered α2Ti3Al phase). The disordered α phase is a metastable phase during this process, and with increased temperature and longer annealed time, the transformation of α→ γ(α2) occurs. From the micrograph of the hotpressed γTiAl phase, it is supposed that the transformation may be a massive transformation.