  The temporal evolution of ordered gamma-prime(L12)-precipitates and the
compositional trajectories during phase-separation of the
gamma(face-centered-cubic(f.c.c.)) and gamma-prime(L12)-phases are studied in a
Ni-0.10Al-0.085Cr-0.02Re(mole-fraction) superalloy, utilizing atom-probe
tomography, transmission electron microscopy, and the Philippe-Voorhees (PV)
coarsening model. As the gamma-prime(L12)-precipitates grow, the excesses of
Ni, Cr and Re, and depletion of Al in the gamma(f.c.c.)-matrix develop as a
result of diffusional fluxes crossing gamma(f.c.c.)/gamma-prime(L12)
heterophase interfaces. The coupling effects on diffusional fluxes was
introduced (PV coarsening model) in terms of the diffusion tensor, D, and the
second-derivative tensor of the molar Gibbs free energies, G", obtained
employing Thermo-Calc and DICTRA calculations. The Gibbs interfacial free
energies are (6.9 +- 1.4) mJ/m2 with all terms in D and G", which changes to
(18.9 +- 2.1) mJ/m2, (37.7 +- 3.3) mJ/m2, and (-7.5 +- 1.2) mJ/m2 without
including the off-diagonal terms in D, G", and both D and G", respectively. The
experimental APT compositional trajectories are displayed and compared with the
PV model in a partial quaternary phase-diagram, employing a tetrahedron. The
compositional trajectories measured by APT exhibit curvilinear behavior in the
nucleation and growth regimes, which become vectors, moving simultaneously
toward the gamma(f.c.c.) and gamma-prime(L12) conjugate solvus-surfaces, for
the quasi-stationary coarsening regime. The compositional trajectories are
compared to the PV model with and without the off-diagonal terms in D and G".
The directions including the off-diagonal terms in D and G" tensors are
consistent with the APT experimental data.
