The temporal evolution of ordered γ'(L12)-precipitates precipitating in a disordered γ(f.c.c.) matrix is studied in extensive detail for a Al at.% alloy aged at 823 K (550 o C), for times ranging from 0.08 to 4096 h. Three-dimensional atom-probe tomography (3-D APT) results are compared to monovacancy-mediated lattice-kinetic Monte Carlo (LKMC1) simulations on a rigid lattice, which include monovacancy-solute binding energies through 4 th nearest-neighbor distances, for the same mean composition and aging temperature. The temporal evolution of the measured values of the mean radius, , number density, aluminum supersaturations, and volume fraction of the γ'(L12)-precipitates are compared to the predictions of a modified version of the Lifshitz-Slyozov-Wagner coarsening model due to Calderon, Voorhees et al. The resulting experimental rate constants are used to calculate the Gibbs interfacial free-energy between the γ(f.c.c.)-and γ'(L12)-phases, which enter the model, using data from two thermodynamic databases, and its value is compared to all extant values dating from 1966. The diffusion coefficient for coarsening is calculated utilizing the same rate constants and compared to all archival diffusivities, not determined from coarsening experiments, and is demonstrated to be the inter-diffusivity, , of Ni and Al. The monovacancy-mediated LKMC1 simulation results are in good agreement with our 3-D APT data. It is demonstrated that the compositional interfacial width, for the {100} interface, between the γ(f.c.c.)-and γ'(L12)-phases, decreases continuously with increasing aging time and , both for the 3-D APT results and monovacancy-mediated LKMC1 simulations, in disagreement with an ansatz intrinsic to the so-called trans-interface diffusion-controlled coarsening model, which assumes the exact opposite trend for binary alloys. | P a g e

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