The precipitation processes in a Cu–0.9 mass%Be alloy single crystal containing only G.P. zones parallel to the matrix (001)
α plane have been studied by high-resolution transmission electron microscopy. The precipitation sequence found is: G.P. zones→γ″→γ′
I→γ
I+γ′→γ. The γ″ phase has a two-layer structure of Be atoms separated by a matrix layer parallel to (001)
α, and a body-centered tetragonal (bct) lattice. The γ′
I phase consisting of five to ten Be-layers is body-centered monoclinic. The γ
I phase continuously transforms from the G.P. zones via γ″ and γ′
I. The heterogeneous formation of γ′ occurs on the γ
I phase. The γ
I or γ′ phase is bct with
a=
b=0.254 nm and
c=0.352 nm or
a=0.254 nm and
b=
c=0.268 nm. The γ″, γ′
I or γ
I phase aligns with the matrix according to the Bain orientation relationship. The plate-shaped γ′ precipitates have the (1\\bar1\\bar2)
α habit plane and the orientation relationship, (1\\bar1\\bar2)
α||(0\\bar1\\bar2)
γ′; [110]
α||[100]
γ′ (OR I), or the (1\\bar13)
α habit plane and the orientation relationship, (1\\bar13)
α||(0\\bar13)
γ′; [110]
α||[100]
γ′ (OR II). The structure of γ′ successively changes into that of the γ phase with
a=0.280 nm for OR I or 0.268 nm for OR II. The γ precipitates of OR I and OR II are elongated along approximately [1\\bar11]
α and [3\\bar3\\bar2]
α, which are in good agreement with the invariant-line directions.
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