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In the smelting process of large castings, the addition of deoxidiser is bound to introduce other elements, such as Al and Ti. This research investigates the influence of Al and Ti on the precipitation behaviour of the γ" phase in cast alloy 625. The results showed that Al and Ti can improve the supersaturation of Nb in inter-dendritic zones during long-term aging. Furthermore, Al and Ti atoms replace partial Nb atoms in the γ" phase and promote the precipitation and growth of γ", which lead to an increase in strength at high temperatures. [ABSTRACT FROM AUTHOR]

The influence of prior cold work (90% reduction) on the length change and precipitation behaviour of a Cu-1.8wt%Be-0.2wt%Co alloy aged at 320°C up to 350 h has been investigated. The alloy gradually expands to a maximum and then contracts during ageing. The maximum expansion is attributable to both the expansion due to the loss of Be solute atoms and the contraction due to precipitation of the [image omitted], γI, γm and γ' phases. The subsequent contraction results from the decrease in amounts of the [image omitted] and γm phases and the increase in amount of the γ' phase. The new-found γm phase, consisting of alternate Be and Cu matrix layers parallel to the matrix {001}α, is body-centred monoclinic with a = b = 0.263 nm and c = 0.279 nm and α = 83°, and aligns with the matrix according to the Bain orientation relationship. The Guinier-Preston (GP) zone transforms continuously to the γm or γI phase via γ'' and [image omitted]. The transformation from the GP zone to γ' via γ'', [image omitted] and γI is retarded in comparison with that for the un-deformed alloy. [ABSTRACT FROM AUTHOR]