An electron microscopy study of continuous ordering and phase separation in iron-rich iron-aluminum alloys

Abstract

The discrepancy between two recent phase diagram determinations of the Fe-Al system is resolved experimentally. Both diagrams are correct, but-one is a metastable coherent phase diagram. The iron-aluminum system possesses a tricritical point where a line of [lambda]- transitions ends at a miscibility gap at about 23 atom percent aluminum and 615°C. Rules of general applicability governing phase separation within the miscibility gap are developed. Application of the rules to the iron-aluminum system results in detailed predictions about the mechanisms of decomposition and their sequences in this system. Electron microscopy is used to study the reactions experimentally and the results are in agreement with theoretical predictions.