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

Special ultrafine fully-lamellar microstructures have been found recently in gamma-TiAl alloys with 46-48 at.% Al, when they are processed or heat-treated above the alpha-transus temperature (T-alpha). Hot-extrusion above T-alpha also produces a refined colony or grain size. Refined-colony/ultrafine-lamellar(RC/U) 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 gamma and alpha(2) lamellea, such that they are dominated by gamma/alpha(2) interfaces with relatively few gamma/gamma twin boundaries. The focus of this study is how variations in processing parameters or alloy composition affect formation of the UL structure, particularly the alpha(2) component.