High-throughput determination of diffusivity and atomic mobility in fcc Ni-Fe-Nb alloys

The Ni-Fe-Nb ternary system is a critical subsystem in Ni-based superalloys, yet systematic studies on diffusion kinetics in its fcc (face-centered cubic) phase remain limited. In this work, twelve ternary fcc Ni-Fe-Nb diffusion couples were prepared and annealed at 1273, 1373, and 1473 K. The corresponding composition profiles were determined using EPMA (Electron Probe MicroAnalysis). Based on the presently measured composition profiles along with thermodynamic descriptions, the interdiffusivities and atomic mobility parameters of the fcc Ni-Fe-Nb system were evaluated and optimized using the CALTPP (CALculation of ThermoPhysical Properties) software, which employs a high-throughput NIM (Numerical Inverse Method). The optimized parameters accurately reproduce the measured composition profiles and diffusion paths. To validate the reliability of the evaluated mobility parameters, the interdiffusivities calculated by the NIM were compared with those determined by the traditional M − K (Matano-Kirkaldy) method, which provides the reliable diffusion coefficients at the intersection point of two ternary diffusion couples. The relative deviations between the two methods are within 26.5% for all interdiffusivities, confirming the reliability of the present NIM-based assessment. The present work reveals that Nb diffuses more rapidly than Fe in the Ni-rich fcc matrix. Finally, by integrating the optimized mobility parameters with the thermodynamic description, composition-dependent, three-dimensional surfaces of interdiffusivities, activation energies, and pre-exponential factors were predicted. This work provides a reliable set of kinetic parameters for the fcc Ni-Fe-Nb phase, which are crucial for understanding microstructural evolution and optimizing Ni-based superalloys.