Ultrafine fully-lamellar structures in two-phase γ-TiAl alloys

Special ultrafine fully-lamellar microstructures have been found recently in γ-TiAl alloys with 46-48 at.% Al, when they are processed or heat-treated above the α-transus temperature (T_α) Hot-extrusion above T_α also produces a refined colony or grain size. Refined-colony/ultrafine-lamellar (RC/UL) microstructures produce an excellent combination of room-temperature ductility and high-temperature strength in Ti-47Al-2Cr-2Nb (at.%) alloys. UL structures generally have an average interlamellar spacing of 100-200 nm, and have regularly alternating γ and α₂ lamellea, such that they are dominated by γ/α₂ interfaces with relatively few γ/γ twin boundaries. The focus of this study is how variations in processing parameters or alloy composition affect formation of the UL structure, particularly the α₂ component.