The influence of an applied stress on discontinuous precipitation (DP) has been investigated for a Cu-5 wt. pct. Ag alloy aged at 573 K. A tensile stress enhances the growth of DP cells in both the loading direction (LD) and transverse direction (TD), but the cell growth rate in the TD, v CT , is faster than that in the LD, v CL . A compressive stress suppresses the cell growth in the TD, but does not significantly influence it in the LD. The tensile or compressive stress tends to produce discontinuous silver precipitates elongated in a <110> direction of the copper matrix in a DP cell, nearly perpendicular to or parallel to the LD. This result, along with the dependence of the cell growth rate on the sense of the applied stress, can be understood through the interaction energy between the external stress and the misfit strains of silverprecipitates. An analysis of length-change measurement results has enabled estimation of the ratio of the growth rate of silver precipitates in the TD, v PT , to that in the LD, v PL , under tension or compression. The estimated values of v PT / v PL are in good agreement with the values of v CT / v CL , experimentally obtained, indicating that the anisotropy of the cell growth rate is determined by the growth behavior of silver precipitates.-3 -
Abstract. The influence of an external stress on the nucleation and growth of disk-shaped G.P. zones has been investigated for a Cu-1.2wt%Be-0.1wt%Co alloy aged at 220 C. A compressive stress applied in the [001] direction during aging preferentially accelerates the nucleation and growth of the G.P. zones perpendicular to the [001] axis, whereas a tensile stress does not significantly affect those of G.P. zones. The promotion of the nucleation and growth of the G.P. zones perpendicular to the compressive-stress axis can be well understood through the interaction energy between the applied stress and the misfit strains of G.P. zones. The critical diameter of the disk-shaped G.P. zone nucleus was estimated as about 1.3 nm from evaluation of the interaction energy.
The effects of an applied tensile stress on the growth rate and morphology of discontinuous precipitation (DP) product have been studied for a Cu-5wt%Ag alloy aged at 300 C. The DP cell consists of lamellae of the rod-shaped Ag precipitates and solute-depleted Cu matrix. The tensile stress accelerates the growth of DP cells along both the loading direction (LD) and transverse direction (TD) but the cell growth rate along the TD is faster than that along the LD. Transmission electron microscopy has revealed that the tensile stress is apt to produce the Ag precipitates elongated in a <110> direction nearly perpendicular to the LD in a cell, irrespective of the cell growth direction. The observed morphology of the Ag precipitates and the promotion of the cell growth, namely precipitate growth under tension can be understood through the interaction energy between the external stress and the misfit strains of precipitate. The growth of Ag precipitates toward the direction perpendicular to the LD explains the faster cell growth along the TD.
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