Radiation-induced defects in electron-irradiated beta-TiAl compounds: The effect of composition

The radiation damage produced at 21 K by 2.5 MeV electrons, and the subsequent recovery have been investigated for gamma-TiAl intermetallic compounds (50-54.5 at.% Al) by means of residual electrical resistivity measurements, with particular emphasis on the effects of the composition and fluence. The resistivity damage rate was much higher for the alloys than for a simultaneously irradiated nickel reference sample. Disordering contributes only a small fraction (8-15%) to the resistivity damage. The analysis of the dominant defect contribution led to Frenkel-pair resistivity values of approximate to 60 mu Omega cm/%, larger than those for pure Al or Ti, and nearly independent of the composition. The recovery of the damage was characterized by two main stages. The temperature of the first one (approximate to 81 K) is independent of the composition: it was assigned to close-pair recombination, and to the migration and annihilation of self-interstitials. The second main one (approximate to 444 K, for the stoichiometric compound) has a temperature which depends on the fluence and on the composition. It corresponds to the migration and elimination of vacancies. An activation enthalpy of 1.55 +/- 0.16 eV was estimated for this stage for stoichiometric TiAl. Its shift to higher temperatures with increasing aluminium content indicates a reduction in the vacancy mobility.