Preparation, Microstructure And Properties Of Mechanical Alloying TiAl Composites

Mechanical alloying of Ti-X%(X=30.0,44.7,70.0)Al and Ti-Al-W,Ti-Al-La-Ce,Ti-Al-La,Ti-Al-Ce have been performed in a high energy plant ball after different milling times. We have studied the structure of alloy powders by X-ray diffraction. The particle size of some specimens are analyzed by scanning electron microscopy. And we have used other means to analyze of TiAl alloying which is added of w and thulium: differential thermal analysis and transmission electron microscopy et al.It was revealed that Ti-Al composite powders with alternative Ti and Al lamellar structure could be obtained by milling of elemental Ti and Al powder mixture. With the milling time increasing, the lamellar structure of the Ti-Al composite powders becomes thinner and more uniform. Although the compactibility of the Ti-Al composite powders decreases due to the increasing of hardening degree resulted by MA, the composite powder billet with high relative density can be obtained by performing ,high sintering and die compacting at cold-state. Diffusion reaction of the Ti-Al composite powder billet was performed at solid state. The microstructures of the reacted billet have been analyzed by XRD,EPS, SEM and optical microscopy. It was found that MA could accelerate the diffusion reaction between Ti and Al, and the Ti-Al, and the Ti-Al composite powders could be completely transformed into TiAl and Ti3Al at solid state. Also, it was found that, by being sintered further at higher temperature, the TiAl-based alloy material with almost full density has been obtained from the reacted billet, it means that temperature is very important.And the results also show that the effect of the addition W, La, Ce on the microstructure and mechanical properties for TiAl alloy was studied: after 20 hour of MA with Ti-Al-W,W was dissolved in Ti and Al completely, lattice constant of Ti phase is decrease when the time of MA increase. Also the layer of TiO₂ formed on surface, the second layer of Al₂O₃ and interior Al₂O₃ densification continuity and have protectionability, so which can improve oxidation resistance. Which can also improve bending strength at room temperature.It was shown that addition of 0.5% La in the TiAl alloys may remarkably increase the intension and ductility. But addition of Ce in the TiAl alloys can descent intension and not more much of improvement of ductility. The microstructure of the samples both before and after compression test were analyzed with OM and TEM in details, deformation behaviour and strengthening mechanism of the studied alloys were discussed.