MICROSTRUCTURE OF GUINIER-PRESTON ZONES IN AL-AG

An Al-3 at.% Ag single crystal aged for 4 h at 413 K to produce Guinie r-Preston zones (eta-zones) was investigated by diffuse wide-angle X-r ay and small-angle neutron scattering. Based on the separated short-ra nge order scattering, model crystals were generated. The zones in the model crystal have an average Ag concentration of (80 +/- 10) at.% Ag. The same result is obtained by applying the same procedure to a previ ously measured state with epsilon-zones (Al-3 at.% Ag aged at 453 K fo r 4 min). For both types of zone, Ag concentrations range from (70-75) at.% in the core to (85-90) at.% in the shell. No signs of long-range order are detected within the epsilon- and eta-zones. Thus, a distinc tion (suggested by previous investigators) of two different states for Guinier-Preston zones in Al-Ag seems no longer compelling.