An AP-FIM study on metastable phases in AlAg binary alloy

The morphology and chemical composition of metastable phases in an Al-5.72at.% Ag alloy have been investigated by means of atom-probe field ion microscopy. It was found that the η G.P. zones formed by aging at 413 K have an average solute concentration of 45.8 ± 0.7 at.% Ag. the present data on zone size and interparticle distance were found to be consistent with data determined by small-angle X-ray scattering. When the specimen was aged at 436 K for 60 ks, both ε{lunate} G.P. zones and γ′ metastable phase were observed simultaneously. The solute concentration of ε{lunate} zones was determined to be 35.7 ± 0.2 at.% Ag. The γ′ phase was a plate-like precipitate lying on the {111} matrix plane, and its solute concentration was 33.3 ± 1.5 at.% Ag and its thickness was in the range of 2.3-7.0 nm. By combining the present data with other results certain pending questions on the structures of metastable phases in this alloy have been successfully solved.