Transmission Electron Microscopic Study on the "K-State" in Iron-Aluminium Alloys

Transmission electron microscopy and diffraction study and electrical re-sistivity measurement of iron-aluminium alloys containing 17.87 to 21.54 at.% aluminium have revealed the nature of the "K-state" in this alloy system. It has been conclusively demonstrated by the observations of dark field images that the so-called "K-state", which appears on annealing at a low temperature after quenching from a high temperature, is characterized by the inhomogeneous formation of very small Fe_3Al type ordered particles of 20～30 A in diameter in the matrix α-solid solution. The specimens slowly cooled from a high temperature and isothermally annealed have also been examined to compare the structures with those showing the "K-state". A discussion on the equilibrium phase diagram of the iron-aluminium solid solution is given