Coarsening of iron precipitate particles in copper-iron alloys

Transmission electron microscopy has been used to measure the average sizes during coarsening of spherical alpha -Fe and gamma -Fe precipitates in Cu- 1.0 mass%Fe and Cu-2.0 mass%Fe alloys aged at 873, 923 and 973 K, and elect ric resistivity has been used to measure the depletion of Fe concentration in the Cu matrix with aging time t. The growth kinetics of alpha -Fe and ga mma -Fe precipitates obeys t(1/3) kinetics, as predicted by the Lifshitz-Sl yozov-Wagner theory. The kinetics of the reduction of Fe concentration for alpha -Fe and gamma -Fe precipitates is consistent with the predicted t(-1/ 3) time law. The equilibrium solubilities of Fe in the matrix at the alpha -Fe/Cu interface are smaller than those at the gamma -Fe/Cu interface. The former and latter values are in good agreement with those previously report ed by Tammann and Oelsen, and Andersen and Kingsbury, respectively. The val ues of the Fe/Cu interface energy rand volume diffusion coefficient D have been independently derived from the data on coarsening. The value of Gamma for the incoherent alpha -Fe/Cu interface is estimated to be 0.52 J/m(2), a nd two times as large as the coherent gamma -Fe/Cu interface energy, 0.25 J /m2, which is nearly consistent with values previously reported. The pre-ex ponential factor and activation energy for diffusion of Fe in Cu are determ ined to be 1.05 x 10(-4) m(2)/s and 213 kJ/mol, respectively.