Ostwald ripening of spherical Fe particles in Cu-Fe alloys

The coarsening of spherical n -Fe and f -Fe precipitate particles in Cu-Fe alloys aged at 600, 650 and 700C has been studied by measuring both the particle size by transmission electron microscopy and the Fe concentration in the Cu matrix by electric resistivity. The average size of n -Fe and f -Fe particles increases with ageing time t as t 1/3, as predicted by the Lifshitz-Slyozov-Wagner theory. The kinetics of the depletion of supersaturation with t for n -Fe and f -Fe particles are consistent with the predicted t -1/3 time law. The solubilities of Fe in equilibrium with a n -Fe particle of infinite size are greater than those in equilibrium with an f -Fe particle of infinite size. The Fe-Cu interface energy and the diffusivity of Fe in Cu have been independently derived from the data on coarsening. The coherent n -Fe-Cu interface energy is estimated to be 0.25Jm -2, and the incoherent f -Fe-Cu interface energy 0.52Jm -2 . The preexponential factor and activation energy for diffusion are found to be 9.75 10 -5 m 2 s -1 and 213kJmol -1 respectively.