OSTWALD RIPENING IN CONCENTRATED ALLOYS

The temporal power laws describing the coarsening process in a concentrated nonideal solid solution are derived. It is shown that the interfacial energy sigma can be determined in such a system from measurements of the coarsening kinetics, if an isothermal stress-free two-phase mixture is assumed. In the derivation, a modified Gibbs-Thomson equation is used and the effects of nonideal solution thermodynamics and nonzero solubilities of solute in each phase on the flux conservation condition at the interface am taken into account. The resulting rate constant is then used to analyze the coarsening process of N3Al precipitates in a homogeneus Ni-Al matrix. A model for the solution thermodynamics of the matrix phase is used to compute the various thermodynamic factors and phase compositions necessary to evaluate the rate constant. The resulting value of sigma is approximately an order of magnitude smaller than that derived on the basis of the assumptions used in the classical theory by Lifshitz and Slyozov, and Wagner. However, it is possible to extract only an approximate value of sigma from the experimental data due to an unfortunately large uncertainty in the value of the interdiffusion coefficient present during the coarsening experiments.