Effects of Cr and Sn on defects and electron densities in TiAl alloys

摘要

Positron lifetime spectra of Ti_(50)Al_(50), Ti_(50)Al_(48)Cr_2 and Ti_(50)Al_(48)Sn_2 alloys have been analyzed. The experimental results show that the electron densities in bulk and grain boundary of binary TiAl alloy are 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 can 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 is 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.