A study of vacancy-type defects in the B2-phase region of the Fe–Al system by positron annihilation method

Vacancy-type defects of B2-type intermetallic compound FeAl have been investigated as functions of composition ranging from 41.2 to 50.7 at.% Al and quenching temperature ranging from 610 to 1373 K by means of positron annihilation technique. At quenching temperatures lower than 873 K, both the mean positron lifetimes and S-parameters increase with increase in Al content. With increasing quenching temperature from 873 K, the S-parameters for 41.2, 49.0 and 50.7 at.% Al certainly increase. The results are discussed by considering changes in the defect type and the atom configuration around the vacancies. The composition dependence at lower quenching temperatures is explained partly as a change in the fractions of Fe-vacancies, VFe, and the di-vacancies on the Fe-sites, 2VFe, and partly as a change in the fraction of antisite Fe atoms, FeAl. The temperature dependence of the S-parameter is explained by change in defect type from di-vacancies, 2VFe, to different type of di-vacancies, VFeVAl, sitting on the nearest neighboring Fe and Al sites.