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

Published

Author(s)

Carelyn E. Campbell, Sung-Il Baik, Zugang Mao, Qingqiang Ren, Chuan Zhang, BiCheng Zhou, Ronald D. Noebe, David N. Seidman, Fei Xue

Abstract

The temporal evolution of ordered γ′(L12)-precipitates and the compositional trajectories during phase-separation of the γ(face-centered-cubic (f.c.c.))- and γ′(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 γ′(L12)-precipitates grow, the excesses of Ni, Cr and Re, and depletion of Al in the γ(f.c.c.)-matrix develop because of diffusional fluxes crossing the γ(f.c.c.)/γ′(L12) heterophase interfaces. The coupling effects on diffusional fluxes are 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, sigma^(gamma/gamma prime) , 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 when not 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 partial tetrahedron. The compositional trajectories measured by APT exhibit curvilinear behavior in the nucleation and growth regimes, t < 16 h, which become vectors, moving simultaneously toward the γ(f.c.c.) and γ′(L12) conjugate solvus-surfaces, for the quasi-stationary coarsening regime, t ≥ 16 h. The compositional trajectories for t ≥ 16 h 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 the D and G'' tensors, are consistent with the APT experimental data.
Citation
ACTA Materialia

Keywords

Ni-based superalloys, Rhenium, Atom-probe tomography, Coarsening, Diffusion tensor, Philippe-Voorhees (PV) model, Transmission electron microscopy

Citation

Campbell, C. , Baik, S. , Mao, Z. , Ren, Q. , Zhang, C. , Zhou, B. , Noebe, R. , Seidman, D. and Xue, F. (2022), The effects of diffusional couplings on compositional trajectories and interfacial free energies during phase separation in a quaternary Ni-Al-Cr-Re model superalloy, ACTA Materialia, [online], https://doi.org/10.1016/j.actamat.2022.118020, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=928146 (Accessed May 25, 2024)

Issues

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Created August 1, 2022, Updated January 18, 2023