The effects of diffusional couplings on compositional trajectories and interfacial free energies during phase separation in a quaternary Ni-Al-Cr-Re model superalloy

The temporal evolution of ordered γ′(L12)-precipitates and the compositional trajectories during phase-separation γ(face-centered-cubic (f.c.c.))- γ′(L12)-phases are studied in a Ni–0.10Al-0.085Cr-0.02Re (mole-fraction) superalloy, utilizing atom-probe tomography, transmission electron microscopy, Philippe-Voorhees (PV) coarsening model. As grow, excesses Ni, Cr Re, depletion Al γ(f.c.c.)-matrix develop because diffusional fluxes crossing γ(f.c.c.)/γ′(L12) heterophase interfaces. coupling effects on introduced (PV model) terms diffusion tensor, D, second-derivative tensor molar Gibbs free energies, G″, obtained employing Thermo-Calc DICTRA calculations. interfacial σγ/γ′, (6.9 ± 1.4) mJ/m2 with all D which changes to (18.9 2.1) mJ/m2, (37.7 3.3) (-7.5 1.2) when not including off-diagonal both respectively. experimental APT displayed compared PV model partial quaternary phase-diagram, tetrahedron. measured by exhibit curvilinear behavior nucleation growth regimes, t < 16 h, become vectors, moving simultaneously toward γ(f.c.c.) γ′(L12) conjugate solvus-surfaces, for quasi-stationary regime, ≥ h. h without G″. directions, G″tensors, consistent data.