Microstructure evolution through thermomechanical treatment and its effects on room temperature ductility in TiAl based alloys

Microstructural evolution through thermomechanical treatments consisting of forging and subsequent heat treatment have been studied on binary TiAl based alloys to obtain an optimum polycrystalline microstructure performing high ductility at ambient temperature. Room temperature ductility strongly depends on the Al content and the best composition lies close to the stoichiometric composition which can minimize the final volume of {alpha}{sub 2} phase having less ductility than {gamma} phase. The microstructural dependence of room temperature ductility is also remarkable and the uniform microstructure consisting of relatively fine grains in the duplex mode of {gamma} and lamellar grains, exhibited significantly high ductility at room temperature. The attainment of the above microstructure in Ti-49.9at%Al produced the best value of more than 7% in tensile elongation with low proof stress, although the fracture mode still remained brittle. It was concluded that to minimize the amount of {alpha}{sub 2} phase, in grain form or as a part of lamella, is an essential and effective approach for the improvement of room temperature ductility in polycrystalline TiAl based alloys.