High-temperature positron lifetime measurements, together with the modelling of defect formation in the framework of nearest-neighbor pair bonds, were carried out. Appreciable increases in the positron lifetime were observed in Ti65.6Al34.4 and Ti77.1Al22.9, at temperatures above 1200K. Here, thermal vacancy concentrations were expected to be above the detection limit for positron annihilation. Features of the positron spectra were attributed to the fast de-trapping and re-trapping of positrons at vacancies, due to a low positron-vacancy binding energy. From these results, vacancy formation enthalpies of 1.55 and 1.8eV were deduced for Ti65.6Al34.4 and Ti77.1Al22.9, respectively.

Thermal Vacancy Formation and Positron–Vacancy Interaction in Ti3Al at high Temperatures. R.Würschum, E.A.Kümmerle, K.Badura-Gergen, A.Seeger, C.Herzig, H.E.Schaefer: Journal of Applied Physics, 1996, 80[2], 724-8