Calorimetric Studies of Superlattice in Fe-Co-Cr Alloys

The specific heat of Fe1Co1−xCrx alloys in b.c.c. range has been measured by a modified Sykes method. The critical temperature of the order-disorder transformation falls rapidly with the Cr content and this tendency is consistent with the simple theory of superlattice in ternary alloys based on the Bragg-Williams approximation. In the Co-rich range, the 550°C anomaly of Fe1Co1 alloy extends up to the b.c.c.-h.c.p. phase boundary keeping its temperature constant. Another anomaly is found in ternary alloys of the same composition range at temperatures between 630°C and 660°C. In the Cr-rich range, an anomaly is found. This appears to correspond with the 570°C anomaly of Fe1Cr1 alloys, but the temperature of this anomaly is found to rise with the increasing Co content.