EFFECTS OF THERMOMECHANICAL TREATMENT AND AL CONTENT ON THE MICROSTRUCTURE AND ROOM-TEMPERATURE DUCTILITY IN GAMMA+ALPHA(2) TYPE BINARY TITANIUM ALUMINIDES

Thermo-mechanical treatment conditions have been investigated on gamma+alpha(2) type titanium aluminides to obtain a uniformly fine grained structure which is expected to exhibit a high ductility at room temperature. A higher working reduction, followed by a heat treatment at the temperature at which volume fractions of the gamma and alpha phases are equal to each other is required to obtain the fine duplex microstructure consisting of the equi-axed gamma and lamellar grains. The room temperature tensile elongation in such fine duplex microstructures strongly depends on the volume fraction of the alpha(2) phase. A higher Al content results in a high tensile elongation, especially 7.8% in the stoichiometric composition where small amount of alpha(2) are contained. The maximum elongation of 7.8% is substantially higher than those formerly reported.