Atom Probe Analysis of Solute Clustering above a Miscibility Gap

At temperatures just above a miscibility gap, spatially small but large amplitude solute fluctuations or clusters are predicted. These clusters may be retained in the solution upon quenching to a lower temperature and may influence subsequent decomposition kinetics. A model has been developed which quantitatively predicts the shape of composition histograms as a function of temperature and composition. At high temperatures, the model predicts a binomial-shaped composition distribution indicative of a random dispersion of solute, whereas at temperatures just above the miscibility gap, a broadening of the distribution is expected signifying solute clustering. Experimental histograms measured in an Fe-45at.%Cr alloy were found to obey the predictions of the thermodynamic model.