Variations of microstructure and tensile property of γ-TiAl alloys with 0-0.5 at% C additives

Alloy element carbon was added into a lamellar γ-TiAl alloy with a composition of Ti-47Al-2Nb-2Cr. The volume fraction of B2 phase decreased with the increase of carbon content. Most of carbon atoms were in solid solution state in the C-containing TiAl alloys and some fine carbide were dispersedly distributed in the lamellar matrix in case of 0.5 at% carbon additions. For the TiAl alloys containing carbon, the lattice parameters (i.e., a and c) and unit cell volume of α2 phase increased larger than those of γ phase due to higher solid solubility of carbon in the α2 phase. Incorporations of carbon refined the interlamellar spacing of the TiAl based alloys by promoting the nucleation of γ phase and suppressing the thickening of γ lath. The room temperature tensile properties of the TiAl based alloy were improved by the additions of carbon and the alloy with 0.2 at% C showed the highest tensile strength. The trans-lamellar was the major fracture mode. Besides, more excellent high temperature ductility was acquired for the C-doped TiAl alloys because parts of the lamellae displayed the features of ductile fracture. Presence of nano-twins in the C-containing TiAl alloys contributed to the higher high-temperature strength.