THERMODYNAMIC AND MAGNETIC-PROPERTIES OF METASTABLE FEXCU100-X SOLID-SOLUTIONS FORMED BY MECHANICAL ALLOYING

Metastable solid solutions of Fe and Cu, which are immiscible in equilibrium, have been formed using high-energy ball milling of elemental powder mixtures. Single-phase face-centered-cubic (fcc) solid solution was obtained for 0 < x less-than-or-equal-to 60, and body-entered-cubic (bcc) solid solution for 75 less-than-or-equal-to x < 100. The transition from fcc to bcc occurred near x = 70, where a mixture of fcc and bcc phases was obtained. The enthalpy of transformation to equilibrium was measured using differential scanning calorimetry. The average atomic volume of the phases exhibits a positive deviation from Vegard's law, in qualitative agreement with the large positive enthalpy of mixing in this system. The magnetic moments and Curie temperatures for the metastable solid solutions have been determined and compared with those reported for Fe-Cu alloys formed by vapor deposition. Calculations of the formation enthalpy (DELTAH) and free energy (DELTAG) have been performed based on CALPHAD data, with corrections based on our magnetization measurements. The calculated DELTAG results are used to explain the observed fcc-bcc transition under polymorphous constraints.