Positron lifetimes were measured in B2 intermetallic compounds, Co100-xAlx (x = 46.9 to 54.1), which had been water-quenched, air- or furnace-cooled from high temperatures. The positron mean lifetime depended entirely upon the composition, regardless of the cooling rate, and increased steadily from 161 to 180ps as the Al concentration was increased from 46.9 to 54.1at%. Water-quenched Co53.1Al46.9 was isochronally annealed for 900s successively at 25K intervals up to 1073K. Its positron lifetime remained unchanged by the annealing. The results clearly showed that vacancies were not only formed at Co sites, but also at Al sites, and the total vacancy concentration was greater than 10-4 in both Co-rich and Al-rich CoAl. It was also found that the population ratio of Al vacancies to Co vacancies increased gradually with Co concentration, and the number of Al vacancies was comparable to that of Co vacancies in the vicinity of the stoichiometric composition.
Positron Lifetime Study of Defect Structures in B2 Ordered Co-Al Alloys. H.Araki, T.Mimura, P.Chalermkarnnon, M.Mizuno, Y.Shirai: Materials Transactions, 2002, 43, 1498-501