The positron lifetime spectra of Ti50Al50, Ti50Al48Cr2 and Ti50Al48Sn2 alloys were analyzed. The experimental results showed that the electron densities in bulk and grain boundary of binary TiAl alloy were lower than that of pure Al and Ti metals. The addition of Cr atoms to TiAl results in the increase of the electron density in bulk and grain boundary of the alloy. Cr atom could provide more free electrons than Ti or Al atom to participate in metallic bonds in the alloy. However, the addition of Sn to TiAl alloy has the opposite effect in comparison with Cr addition. It was suggested that replacing the Al (or Ti) atoms in TiAl alloy by using metallic elements with a bulk positron lifetime lower than that of pure Al (or Ti) metal may increase the free electron density and produce a good effect on room temperature ductility and vice versa.

Effects of Cr and Sn on Defects and Electron Densities in TiAl Alloys. W.Deng, Y.Y.Huang, D.H.Wu, M.Z.Cao, L.Y.Xiong: Materials Letters, 2002, 56[4], 593-6