Misorientation dependence of discontinuous precipitation in Cu-Be alloy bicrystals

Abstract

The boundary-dependent discontinuous precipitation (DP) for various [001] symmetric tilt boundaries in Cu–5.2 at% Be alloy bicrystals has been examined in the temperature range 523–698 K. The precipitate phase maintains a constant interlamellar spacing under isothermal growth conditions. The interlamellar spacing increases with an increase in temperature. The incubation period τ to initiate DP and cell growth rate for DP against misorientation angle diagrams show local peaks and cusps at the same misorientation angles. The positions of the peaks and cusps agree with those of cusps in the boundary energy against misorientation diagram. The formation and growth of DP occur more easily at higher-energy boundaries. A detailed kinetic analysis of the experimental data using the models by Turnbull and Petermann–Hornbogen has enabled the determination of the grain-boundary diffusivity of Be along each boundary in the temperature range studied. A close correlation is found between the diffusivity and the energy of boundaries. A higher-energy boundary has a higher diffusivity with a smaller activation energy and a smaller pre-exponential factor.