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

Vacancy-type defects of B2-type intermetallic compound FeAl have been inves tigated as functions of composition ranging from 41.2 to 50.7 at.% Al and q uenching temperature ranging from 610 to 1373 K by means of positron annihi lation 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 co nsidering changes in the defect type and the atom configuration around the vacancies. The composition dependence at lower quenching temperatures is ex plained partly as a change in the fractions of Fe-vacancies, V-Fe, and the di-vacancies on the Fe-sites, 2V(Fe), and partly as a change in the fractio n of antisite Fe atoms, Fe-Al. The temperature dependence of the S-paramete r is explained by change in defect type from di-vacancies, 2V(Fe), to diffe rent type of di-vacancies, VFeVAl, sitting on the nearest neighboring Fe an d Al sites. (C)2001 Elsevier Science Ltd. All rights reserved.