Vacancy Formation in Fe-Al of B2 and DO₃Alloys

Abstract

The positron lifetime spectroscopy is employed to study vacancy formation in intermetallic phases of DO3 and B2 structures from Fe-Al system as a function of Al concentration, ternary additive (Cr) and their thermal treatment. Lifetime spectra were fitted en block by a simple trapping model encoded directly to the software (computer program LT-9). In the investigated range of Al concentration (28, 38, 42, and 45 at%) only two types of defects are found. In DO3 region a single type of defects (characterized by positron lifetime 1 = 170 2 ps) is detected and indicated as vacancies in the Fe sublattice (VFe). In B2 region a small amount of an additional type of defects (characterized by positron lifetime 2 = 214 13 ps) appears. Supposedly, these are vacancies in Al sublattice (V Al ). For Fe28Al and Fe28Al5Cr samples changes in V Fe concentration are determined as a function of the sample composition, annealing time at 1000 C and quenching the samples to air and oil. The defect concentration increases with increase in Al content. For FeAl with Al above 38 at%, the total concentration of defects is so high that positrons are exclusively trapped by defects. Therefore the concentrations V Al and V Fe cannot be determined separately. However, the ratio of V Al concentration to VFe concentration is estimated as a function of Al content.