The Influence of Heat Treatement on Point Defect Concetration in Fe-Al and Fe-Al-Cr systems

FeAl alloys of nominal Al content 28, 38 and 45 at.% and Fe28Al5Cr with minor alloying elements added to improve their application properties are studied by positron annihilation lifetime analysis. The lifetime spectra of samples FeXAl with X ≥ 38 (both quenched and cooled with furnace) are described by a single lifetime component related to the saturated positron trapping by quenched-in vacancies of concentration much higher than 100 ppm. A very strong dependence of retained vacancy concentration on the rate of cooling is shown for Fe28Al and Fe28Al5Cr alloys. After quenching, the concentration is of the order of 10–4 whereas in samples slowly cooled it is reduced to 10–5. The chromium addition to Fe28Al5Cr dismisses the vacancies concentration in comparison to the concentration in Fe28Al after the same heat treatment