OSTWALD RIPENING IN CONCENTRATED ALLOYS

The temporal power laws describing the coarsening process in a concent rated nonideal solid solution are derived. It is shown that the interf acial energy sigma can be determined in such a system from measurement s of the coarsening kinetics, if an isothermal stress-free two-phase m ixture is assumed. In the derivation, a modified Gibbs-Thomson equatio n is used and the effects of nonideal solution thermodynamics and nonz ero solubilities of solute in each phase on the flux conservation cond ition at the interface am taken into account. The resulting rate const ant is then used to analyze the coarsening process of N3Al precipitate s in a homogeneus Ni-Al matrix. A model for the solution thermodynamic s of the matrix phase is used to compute the various thermodynamic fac tors and phase compositions necessary to evaluate the rate constant. T he resulting value of sigma is approximately an order of magnitude sma ller than that derived on the basis of the assumptions used in the cla ssical theory by Lifshitz and Slyozov, and Wagner. However, it is poss ible to extract only an approximate value of sigma from the experiment al data due to an unfortunately large uncertainty in the value of the interdiffusion coefficient present during the coarsening experiments.