Phase equilibria in the Fe-Co binary system

alpha (A2)/gamma (A1) phase equilibria of the Fe-Co system between 400 and 800degreesC were determined by means of lattice parameter measurement using thin film specimens. Bulk specimens were also analyzed to compare the extent of attainment to the equilibrium. The thin film technique was found to be greatly advantageous for obtaining the phase equilibria at lower temperatures where solid-state reactions are too slow to reach the equilibrium state in the conventional methods using bulk specimens. It was confirmed that the alpha + gamma two-phase region extends below the temperature at which the alpha (A2)/alpha' (B2) transus meets the alpha/alpha + gamma boundary. Thermodynamic analysis was also conducted by taking the magnetic and chemical ordering contributions of the B2 structure into account, findings of which confirmed the extension of the alpha + gamma two-phase region below the alpha/alpha' ordering temperature. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.