ENTHALPY OF FORMATION OF THE AL0.63CU0.25FE0.12 ICOSAHEDRAL PHASE

In order to establish, on a thermodynamic basis, whether the icosahedral (i) phase is a ground state of the Al-Cu-Fe system, the determination of the enthalpy of formation of the binary and ternary crystalline phases in the vicinity of the i phase was undertaken by solution calorimetry. A high-temperature microcalorimeter was used and measurements were performed in an aluminium bath at 976 K. The results of the determination of the enthalpy of formation at 298 K of Al0.67Cu0.33 (theta phase), Al0.75Fe0.25 (lambda phase), Al0.70Cu0.20Fe0.10 (omega phase) and Al0.63Cu0.25Fe0.12 (i phase) are reported in this paper. The values for omega and i phases are of the same order of magnitude, but as long as the heats of formation of the beta and PHI crystalline phases [4] have not been determined, no definitive conclusion can be drawn on the respective stabilities of the various phases in this part of the Al-Cu-Fe phase diagram.