Misorientation dependence of discontinuous precipitation reaction at [001] twist boundaries in a Cu-0.75 mass% be alloy

The discontinuous precipitation (DP) at [001] twist boundaries has been studied as a function of the misorientation angle in Cu-0.75 mass% Be alloy bicrystals aged at 523 to 723 K. The formation and growth of DP at [001] symmetric tilt boundaries in bicrystals of the same alloy take place more easily than those at [001] twist boundaries. Both the incubation period for cell formation and the cell growth rate at a boundary exhibit a good correlation with the energy of the boundary. Lower-energy boundaries have a longer incubation period and a slower growth rate. A kinetic analysis of DP using the models of Turnbull, and Petermann and Hornbogen has yielded grain boundary diffusion data. The activation energy Q(b) of boundary diffusion vs misorientation curve displays several peaks and the positions of these peaks agree with those of cusps in the boundary energy vs misorientation curve. The higher the boundary energy, the more easily the boundary diffusion occurs with a smaller value of Qb.