Abstract
Ostwald ripening of Co precipitates in Cu-Co alloys aged at 873 K was investigated by electron microscopic observation. Radii of the individual precipitated particles were measured from their strain contrasts, and the rate of increase of the mean radius and the relative size distribution were obtained. The size distributions of Co precipitates n Cu-Co alloys are sharp and symmetric, and they do not agree with the theoretical predictions by Lifshitz-Slyozov-Wagner (LSW) and Ardell. The distribution becomes somewhat broad for the large mean concentration, or for the large volume fraction of the precipitates of the alloy, in qualitative agreement with Ardell’s theory. The rate of increase of the mean radius is proportional to the cube root of the aging time, and almost independent of the mean concentration of the alloy in contradiction to the prediction by Ardell. With the increase of the aging time, the shape of the distribution changes slowly, implying that the observed coarsening process of Cu-Co alloy is not in a steady state as assumed in LSW and Ardell’s theory.
