The diffusion behavior in single-crystal Ni-based superalloys critically influences microstructural stability and high-temperature performance, yet quantitative kinetic data for Re-containing systems remain limited. In this work, the interdiffusion behavior of the Ni-Re-Mo system in the FCC_A1 solid solution was investigated at 1373-1473 K through high-throughput diffusion experiments and calculations. Interdiffusivities were independently determined by the Matano-Kirkaldy (M-K) method and the numerical inverse method (NIM), with the two approaches yielding mutually consistent results. The results show that the main interdiffusivity of Re is approximately one order of magnitude lower than that of Mo, consistent with its higher melting point and activation energy. Moreover, Mo exhibits a pronounced negative composition dependence, with its interdiffusivity decreasing as the Mo concentration increases. Based on the experimentally determined interdiffusivities and existing thermodynamic descriptions, atomic mobility parameters were further evaluated and optimized within the CALPHAD framework. Simulated composition profiles and diffusion paths based on the presently obtained parameters agree well with experimental measurements. The established mobility description was further used to analyze the composition dependence of Arrhenius parameters. Overall, this study provides a consistent kinetic description of diffusion in the Ni-Re-Mo system, contributing to improved predictive modelling of Re-containing single-crystal Ni-based superalloys.
The alloys in the Cu-Ni-Mn system exhibit exceptional properties of high strength and high thermal conductivity. Among them, the prominent solid-solution strengthening effect of Cu-based and Ni-based alloys makes them highly promising candidates for applications in aerospace, marine engineering, medical devices, electronic equipment, and auto parts. In this work, the thermal conductivity of the Cu-Ni-Mn system was evaluated by the CALPHAD (CALculation of PHAse Diagrams) method, and the corresponding parameters for the pure element, binary and ternary systems were obtained. The model using these parameters exhibit good consistency with the experimental data, which indicates that the CALPHAD-type model for thermal conductivity is valid and suitable for predicting the thermal conductivity of the Cu-Ni-Mn system. This work is helpful for predicting the thermal conductivity of Cu-Ni-Mn system during the industrial production process and improving production efficiency.
For the chosen thermodynamic model, the topology of the phase diagram depends on the thermodynamic parameters of the elements and the selected interaction energy parameters. A systematic variation of the energy parameters can reveal the nature of the phase diagrams obtained under the given conditions. In the present study, the quasi-chemical solution model, which accounts for short range order parameter up to the pair cluster, is adopted for the solid phase, while the regular solution model is used for the liquid phase. Using these solution models, the boundaries of the interaction energy parameters that result in various invariant reactions are calculated for the model system. The regions bounded by these boundaries are referred to as domains. This methodology is applied to the Cu-Ir system. The invariant reaction data obtained from these domains are used to train an artificial neural network model to predict the interaction energy parameters. The phase diagram obtained from the predicted values shows a good agreement with the experimental data. Thus, this methodology provides intelligent initial interaction parameters for the optimization process using experimental data.
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.
The increasing demand for efficient solid-state hydrogen storage materials has stimulated significant interest in hydrogen-rich double perovskite hydrides due to their structural versatility and tunable physicochemical properties. In this work, the structural, electronic, optical, and hydrogen-storage properties of Na2NiH6 and K2NiH6 were investigated using density functional theory (DFT) within the GGA-PBE and HSE06 frameworks. Structural stability was confirmed by Goldschmidt tolerance factors (t = 0.91 for Na2NiH6 and t = 0.96 for K2NiH6), negative formation energies, phonon dispersion calculations, and ab initio molecular dynamics simulations at 400 K. Formation energies of-0.182 and-0.196 eV/atom indicate thermodynamic stability for Na2NiH6 and K2NiH6, respectively. Both compounds exhibit indirect semiconducting behavior with HSE06 band gaps of 3.17 eV and 1.33 eV. Optical calculations reveal strong ultraviolet absorption for Na2NiH6, whereas K2NiH6 displays enhanced activity in the visible region. Regarding hydrogen storage, Na2NiH6 achieves a gravimetric capacity of 5.46 wt% and a volumetric density of 79.86 g H2 L-1, while K2NiH6 reaches 4.23 wt% and 65.75 g H2 L-1. Estimated desorption temperatures of 403 K and 432 K suggest favorable intermediate thermodynamic stability. Overall, Na2NiH6 offers the best balance between storage capacity and hydrogen release, whereas K2NiH6 exhibits superior visible-light optoelectronic performance.
