Effect of external stress on discontinuous precipitation in a Cu-2.1 wt % Be alloy

The influence of an applied stress on discontinuous precipitation (DP) in a Cu-2.1 wt % Be alloy aged at 300 °C was examined. A compressive stress accelerates the growth of DP cells, which consist of lamellae of the precipitated γ phase and the solute-depleted α phase, but a tensile stress does not essentially change it. The cell growth rates along the loading direction under the compressive and tensile stress are identical to those along the direction perpendicular to the loading direction under the same stress. Both the compressive and tensile stresses have no influence on the incubation time to initiate DP. From measurements of the specimen length change and investigations of the distribution of γ variants in cells in a particular case, specific γ variants among crystallographically equivalent ones are found to be formed, depending on the sense of the applied stress. This result, together with the dependence of the cell growth rate on the sense of the applied stress, can be well understood through the interaction energy between the external stress and the misfit strains of discontinuous γ precipitates.