The decomposition kinetics of Al-1 at% Ag at 413 K studied by HREM

Starting from a partly decomposed as-quenched state, the further decomposition kinetics of Al-1 at% Ag at 413 K is traced by means of HREM. Precipitates with less than 1 nm in diameter still give rise to strong contrast. The development of the mean radius of the precipitates exhibits the features predicted by a numerical nucleation and growth decomposition model due to Kampmann and Wagner. It turns out, however, that this model is not applicable to Al-1 at% Ag at 413 K because it assumes a deterministic diffusional growth. But the role of thermal fluctuations must also be incorporated in order to understand the experimental results. Based on this idea, a nucleation rate of precipitates is estimated from the evolution of their mean radii. The result supports the classical nucleation theory.