High resolution electron microscopy of metastable precipitates in a Cu-7.8 at% Be alloy

It is known that three metastable phases, the G.P. zone, the γ double-prime and the γ' phase precipitate in Cu-rich, Cu-Be alloys prior to the precipitation of the stable γ (CuBe) phase. In addition, a precursor to the G.P. zone was reported in the as-quenched state by Rioja and Laughlin, Koo et al. and Koo and Cohen, which is described as ''equiaxed'' or ''ellipsoidal'' Be clusters. There is little known about the phases ability to dissolve to form the following next phase or to continuously transform to the next, except for the formation of the γ double-prime by a stacking of the G.P. zones. The authors of this study have recently suggested, based on the results of a calorimetric study of Cu-Be alloys, that the structure of the G.P. zones and the γ double-prime gradually change with aging toward that of γ double-prime and the γ', respectively. The high resolution electron microscopy (HREM) is considered to be a suitable method for examining the structural changes in these precipitates. Therefore, in the present study, the precipitates formed in the Cu-Be alloy are observed in detail by HREM to clarify the relationship between their structures