CHANGE IN VOLUME ON ORDERING OF FeCo SUPERLATTICE ALLOYS.

Thermal expansion of FeCo alloys in the b c c range have been measured. The volume changes due to the ordering of 30 - 70 at% Co alloys decrease at the order-disorder transition temperature T//c, and the expansivities of these alloys decrease as the long-range order parameter increases. The mean expansivities of the order 25 - 70 at% Co alloys are less than those of the disordered ones in the temperature range from 100 to 200 degree C. The volume change due to the ordering at room temperature decreases in 27. 5 - 33. 3 at% Co and increases in 40 - 70 at% Co. The volume increase due to the ordering at room temperature of the 40 - 70 at% Co alloys is more affected by the decrease of the expansivity than the contraction due to the ordering.