Two-Phase Microstructures of α-Fe–Al Alloys in the K-State

Abstract

Electron diffraction and microscopy have been utilized to investigate the Fe–Al system up to 20 at.-% A1. It is found that alloys at and above 10 at.-% Al aged at low temperatures consist of two phases, as indicated by coherent-particle strain-contrast images and by electron diffraction. At 15·5 at.-% A1 and above the particles are identified as the α₁ phase, exhibiting DO₃-type structure. Thus, the so-called K-state and other abnormal properties attributed previously to short-range order in these alloys are associated with very small ordered particles (≤50 Å in dia.). Outside the conventional two-phase field, growth of these particles is limited.