On the Order-Disorder Transformation of the Alloys of Iron and Cobalt

The specific heat of 17 alloys in the range of α solid solution of iron and cobalt system has been measured. It has been found that there are 3 maximum portions on the curve of temperature of the maximum of specific heat against concentration, besides one corresponding to the transformation of FeCo superstructure ; the 3 portions extend over the concentration ranges of 20 to 29, 34.6 to 66 and 66 to 78 per cent of cobalt, respectively. The maximum portion in the range of 34.6 to 66 per cent of cobalt has been already found by S. Kaya and H. Sato and is considered by the present investigators to be due to a lattice transformation of FeCo superstructure. The other maximum portions, in the ranges of 20 to 29 and 66 to 78 per cent of cobalt, are considered to be due to the existence of superstructures of Fe_3Co and FeCo_3, respectively