Precipitation hardening in Cu 1.81 wt % Be 0.28 wt % Co

Abstract

The structure of the precipitation hardening alloy Cu 1.81 wt % Be 0.28 wt % Co has been studied as a function of ageing temperature and time, by transmission electron microscopy. The continuous precipitation sequence found is: supersaturated solid solution → G.P. zones →γ′.

The G.P. zone is an ordered platelet precipitate, which is coherent on {100} matrix planes and is nucleated in very high densities (>10²⁴ m⁻³). The coherency stress fields, due to the misfit of the G.P. zone and matrix, overlap to produce a net matrix contrast along {110} 〈1ţ0〉, and give the characteristic “tweed” structure, which can be described by the kinematical theory of diffraction. The semi-coherentγ′ intermediate precipitate is nucleated by the G.P. zones and the transformation is characterized from the changes in the “arrowhead” structure produced in the electron diffraction patterns. No transformation ofγ′ to theγ equilibrium precipitate is found for the ageing times investigated.