There are continous and discontinuous precipitations in alloys. Cu-In
and Al Zn alloys belong to have discontinuous precipitation phenomena.
The study of the discontinuous precipitation at high pressure might
give a better undestanding on precipitation phenomena. During
discontinuous precipitation, nodules (cells) usually grow from grain
boundaries and incoherent interfaces migrate (nodule reaction or
cellar reaction) to the inside of grains. A lamellar structure of two
phases appears after interface migration. One of the purpose of this
presentation, is to make clear the factors which control the
discontinuous precipitation in the two alloys. Cu-9at%In and
Al-20.3at%Zn alloys were prepared. The Cu-9at% alloy was solution
treated from 923K in water with ice, and the Al-20.3at%Zn alloy was
done 673K in water with ice. After aging at high pressure, SEM
structures were obtained from aged alloys. The discontinuous
precipitate growth velocity G was obtained from the time dependence of
the discontinuous precipitate cell width. Otherwise, the lamellar
spacing was measured too. The discontinuous growth velocity is a
function of the drivibg force, grain boundary diffusion coefficient,
lamellar spacing and interface thickness. From the dependencies of
these facore on pressure, the grain boundary diffusion and interface
thickness control the discontinuous precipitation phenomena at high
pressure.

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