Microstructure and Ductility of TiAl Alloys Modified by Cr Additions

Abstract

The effects of Cr additions to TiAl-base alloys have been investigated, using both consolidated rapid-solidification materials and wrought ingot materials. The composition ranges studied are 0-4 at% Cr and 44-54 at%Al. It was found that Cr additions do not affect the deformation behavior of single-phase γ alloys. However, they significantly enhance the plasticity of Al-lean duplex alloys, which contain grains of single-phase γ and grains of lamellar γ/α₂. Plastic elongations of [til.gif] 4% were measured in wrought Ti-46Al-2Cr at room temperature. Other Cr effects on the microstructure, phase stability, and site occupancy were characterized and correlated to the observed mechanical behavior. It was concluded that the ductilization effect of Cr is partially due to its ability to occupy Al lattice sites and modify the Ti-Al bond. It is also partially due to its ability to promote twin formation, by modifying the Al partitioning and therefore the γ/α₂ volume ratio in the lamellar regions.