Ductility Improvement of Direct-Cast Gamma TiAl-Based Alloy Sheet

Abstract

ABSTRACTFor improving the room temperature tensile ductility of direct-cast gamma TiAl sheets without affecting their high-temperature strength, direct sheet casting with T1B2 particle dispersion is employed and conducted. The T1B2 addition and rapid cooling results in the formation of a fine equiaxed grain microstructure with an average grain size of ∼10μm, contributing to the increase in the room temperature ductility to 2.1% with the high-temperature tensile strength kept at about 200MPa. This improvement of room-temperature ductility is attributable to the following fact. The high oxygen content of this material, about 2500wt. ppm, is not harmful to the tensile ductility when the oxygen is in the solid solution of the 0:2 lamellar phase or in oxide particles, which are fine enough not to cause brittleness to the matrix. From these findings, a principle is proposed that oxygen is not harmful to the ductility of gamma TiAl when its microstructure containing oxygen is fine enough.