Diffusion coefficients and atomic mobilities in fcc Ag-Ge and Cu-Ge alloys: Experiment and modeling

The comprehensive investigations regarding the diffusion behaviors for Ag-Ge and Cu-Ge solders play key roles in their design and application. However, the diffusion behaviors in fcc Ag-Ge and Cu-Ge binary systems have not been carried out. To fill this gap, their diffusion characteristics were studied in this work based on the measured composition profiles of diffusion couples prepared for fcc Ag/Ag-Ge diffusion couples annealed at 873, 923 and 973 K as well as fcc Cu/Cu-Ge diffusion couples annealed at 1023, 1073 and 1123 K. On the basis of measured composition profiles, the composition-dependent interdiffusivities were calculated by the numerical inverse method incorporated in CALTPP (CALculation of ThermoPhysical Properties) program, which agree well with the ones calculated by the classic Sauer-Freise method. Besides, the atomic mobilities in fcc Ag-Ge and Cu-Ge alloys were assessed based on the diffusivities obtained from the literature and this work. Comparisons between model-predicted diffusion characteristics (viz. composition profiles and interdiffusivities) and experimental ones further validate the reliability of the presently obtained atomic mobilities. Insights gained in this work are of scientific significance and practical benefit for designing new Ge-bearing Ag and Cu solers.