Relaxation process in quenched-in vacancies during annealing in B2FeAl single crystals

Coincidence Doppler broadening (CDB) technique and positron lifetime measurement were used to investigate the relaxation process in quenched-in vacancies during annealing in Fe-48mol%Al single crystals quenched from 1373 K The electron momentum curve of the as-quenched FeAl normalized by the pure Fe curve obtained from CDB was analogous to that of pure Al. After annealing at 673 K for 86.4 ks, the shape of the momentum curve became similar to that of pure Fe when normalized by pure Al. These results suggest that vacancies on Al-sublattice sites were newly created during relaxation of quenched-in vacancies. The CDB and the positron annihilation measurements show that positron trapping sites are constricted after annealing at 873 K for 60 s and 673 K for 86.4 ks, and retained vacancies migrate under these heat treatment conditions. It is suggested that these vacancies change into secondary defects having smaller open volumes than the vacancies, e.g., sessile dislocations, stacking fault tetrahedras and so on.