Determination of displacement threshold energies in pure Ti and in γ-TiAl alloys by electron irradiation

Abstract

Resistivity damage rates, determined during low-temperature electron irradiations in the energy range 0.3–2.5 MeV, were used for evaluating displacement threshold energies of titanium in high purity hcp titanium, and of titanium and aluminium in γ-TiAl intermetallic compounds. These parameters were deduced from a comparison of experimental displacement cross-section variations as a function of electron energy, with theoretical curves based on a displacement model for diatomic materials. The displacement energy of titanium in hcp titanium appears to depend on the electron energy. A threshold value of 21 ± 1 eV was obtained in the range 0.3–0.5 MeV, and a larger value of 30 ± 2 eV is determined in the range 0.5–2.5 MeV. In γ-TiAl, aluminium atoms are displaced first, with a threshold displacement energy (34 ± 2 eV) larger than the one of titanium atoms, and much higher than the value in pure aluminium. The displacement energy of Ti atoms is 28 ± 2 eV, close to the one obtained in pure titanium under similar conditions. These results were used for re-evaluating the Frenkel-pair resistivity of the stoichiometric TiAl compound.