Configuration and the recovery of defects in TiAl intermetallic compounds studied by positron annihilation

Defects of doped and neutron-irradiated TiAl alloys were investigated using positron annihilation lifetime and coincidence doppler broadening spectroscopies. In doped alloys, niobium additions replaced some atoms in the lattice, which maintains the ordered structure as undoped, while silicon additions induced Ti vacancies. After neutron irradiation, a number of vacancy-type defects were introduced, including some large vacancies, which can be congregated and hardly be eliminated by annealing at temperature above 1000 K. The vacancy-type defects in (Ti51Al49)98Si2 began to migrate at 452 K, which is lower than in Ti51Al49 alloy. This probably resulted from vacancies induced by the addition of silicon, which facilitated atom migration and decreased initial recovery temperature.