Interfacial free energies and solute diffusivities from data on Ostwald ripening
Interface Science - Tập 3 - Trang 119-125
Tóm tắt
Using recent theoretical modifications of the kinetic constants characterizing Ostwald ripening, it is demonstrated that accurate values of the interfacial free energy, λ, and solute diffusivities, D, can be obtained from experimental data when the kinetics of particle growth are measured in conjunction with independent measurements of either the decrease of the matrix supersaturation or the increase in volume fraction with aging time. The accuracy of λ is limited only by the assumption that the matrix phase is an ideal solid solution, and is effectively independent of the influence of equilibrium volume fraction, Φ
e, on the kinetics of coarsening. Analyses of the available data on the coarsening of γ′-type (Ni3X) precipitates in binary Ni−Al, Ni−Si and Ni−Ti alloys yield values of λ=6.9±0.3, 10.2±3.0 and 13.0 mJ/m2, respectively, assuming ideal solution thermodynamics; a more realistic thermodynamic model for the Ni−Al solid solution raises the value of λ in Ni−Al alloys to 8.1±0.2 mJ/m2. Proportional increases probably obtain in the other two alloys. The accuracy with which D can be evaluated from comparable data depends theoretically on Φ
e. However, analyses of the same data yield values of D in very good agreement with the results of conventional diffusion experiments. This is consistent with the absence of an effect of Φ
e on the kinetics of Ostwald ripening in these alloys over the ranges of Φ
e investigated.
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