A theoretical treatment of atomic configurations found in some iron-aluminum solid solutions

Abstract

Theoretical calculations have been carried out for the two ordering phases which occur in the FeAl system. The statistical treatment involves first and second neighbor interaction parameters as well as a magnetic interaction between first neighbor iron atoms. The phase diagram, and the amount and type of long range order for slowly cooled alloys are calculated. Further calculations include short range order for the disordered phase at three compositions and two temperatures. As expected, short range order increases as a critical temperature is approached either in composition or in temperature. In each case, a comparison is made with experiment. The magnetic interaction gives a closer approach to experimental results. However, the three-constant-model does not give complete agreement. To quantitatively describe the asymmetry of the Fe 3Al loop, the rapid rise in the FeAl boundary, the rapid decline in Curie temperature and the short range order coefficients, it was necessary to postulate rapid changes in the first neighbor interaction parameters within the range 20–30 at. per cent aluminum. These effects are concurrent with the rapid decline in magnetic saturation.