Concurrent emergence of Hume-Rothery phases in Cu-8.6% Sn alloy annealed at 573 K

Precipitating phases in a supersaturated Cu-8.6 at.% Sn alloy annealed at 573 K have been studied by using transmission electron microscopy. Three Hume-Rothery (HR) phases, δ, ζ and ε were identified in the α matrix, each with distinct morphologies. The δ phase emerges in the form of rhombic precipitates inside grains with an orientation relationship (OR): (110)_δ//(111)_α, [111] _δ//[110]_α. The ζ phase emerges both inside grains and at grain boundaries. Frequently observed OR is (1010) _ζ//(111)_α, [1210]_ζ//[112] _α. Intragranular ζ particles consistently satisfy this OR; while it is proposed that a cellular morphology, whose details have been reported separately, develops only when this condition is satisfied for ζ precipitates at grain boundaries. The ε phase emerges along {111} _α planes inside grains with a planar morphology. These plates exhibit two types of ORs: (010)_ε//(111)_α, [100]_ε//[110]_α. and (001)_ε// (111)_α, [100]_ε//[110]_α. and. The latter is the OR, reported for the same alloy annealed at 593 K. These findings are discussed from the viewpoints of the layer structures of the respective HR phases. It was shown that both the atomic configuration and interlayer spacing of the δ and ζ phases match well with {111} _α, while the ε phase cannot satisfy these two conditions simultaneously, resulting in one of the two ORs.