3-DIMENSIONAL CHARACTERIZATION AND MODELING OF SPINODALLY DECOMPOSED IRON-CHROMIUM ALLOYS

The iron-chromium system has a spinodal region within which a random solid solution is thermodynamically unstable with respect to small composition fluctuations. The resulting decomposition yields Cr-enriched alpha' and Fe-rich alpha phases forming complex and often interconnected morphologies. The resultant physical properties of the alloy are dependent on the scale and morphology of the microstructure and the amplitude of composition fluctuations. In this paper, the results of a series of thermally aged Fe-Cr specimens that have been analyzed with the position sensitive atom probe (POSAP) are compared with the results from a Monte Carlo simulation of the decomposition process. The resulting microstructures have been analyzed in terms of scale, composition amplitude and morphology. The scale has been measured by an autocorrelation analysis and the composition amplitude calculated from an analysis of the frequency distribution of block compositions. New morphological analysis techniques based on the measurement of a fractal dimension, and counting the number of handles within the microstructure, have been applied to characterize the detailed morphology on a subnanometre scale.