On the Nature of the K-state in the System of Iron and Aluminium

The electrical resistivity and the thermal expansion were measured with the iron-aluminium alloys containing 9.75 to 11.66 weight per cent aluminium which were subjected to the isothermal treatment at temperatures between 200°C and 300°C or cooled to −183°C from the quenched state, the K-state and the Fe3Al-ordered state. It was found that the alloys containing more than 10.65 per cent aluminium, which exhibit the characteristics of the K-state at room temperature, transformed into the Fe3Al phase after passing through the K-state during the isothermal treatment. Further, it was also observed that the amount of the K-state in the alloys containing 10.5 to 10.9 per cent aluminium decreased at −183°C, and the alloys with more than 10.9 per cent aluminium showed the characteristics of the Fe3Al phase at that temperature. Therefore, it can be concluded that the K-state observed at room temperature is essentially of the Fe3Al superstructure. However, the alloys containing less than 10.5 per cent aluminium retained the K-state even at −183°C. The difference in the nature between the alloys containing more and less than 10.5 per cent aluminium remains to be clarified.