Solid-solid diffusion couples assembled with disks of copper, tin and intermetallics (Cu 3 Sn and Cu 6 Sn 5 ) were employed to investigate the Kirkendall effect in the copper-tin system at the temperature of 200°C. In the Cu(99.9%)/Sn diffusion couple, inert alumina particles used as markers were identified in the Cu 6 Sn 5 phase, while microvoids were observed at the Cu/Cu 3 Sn interface. The Cu(99.9%)/Sn and Cu(99.9%)/Cu 6 Sn 5 diffusion couples annealed at 200°C for 10 days were analyzed for intrinsic diffusion coefficients of Cu and Sn in the Cu 6 Sn 5 and Cu 3 Sn phases, respectively with due consideration of changes in molar volume. Interdiffusion, integrated and effective interdiffusion coefficients were also calculated for the intermetallic phases. Diffusion couples annealed at 125-400°C for various times were analyzed for the kinetic parameters such as growth rate constants and activation energies for the formation of Cu 3 Sn and Cu 6 Sn 5 phases. Uncertainties in the calculated intrinsic diffusivities of Cu and Sn arise mainly from the non-planar morphologies of the interfaces and the non-planar distribution of the markers. Intrinsic diffusion coefficients based on average locations of the marker plane indicate that Cu is the faster diffusing component than Sn in both the Cu 3 Sn and Cu 6 Sn 5 phases.

Concentration profiles that develop in a ternary diffusion couple during an isothermal anneal can be analyzed directly for average ternary interdiffusion coefficients. A new analysis is presented for the determination of average values for the main and cross-interdiffusion coefficients over selected regions in the diffusion zone from an integration of interdiffusion fluxes, which are calculated directly from experimental concentration profiles. The analysis is applied to selected isothermal diffusion couples investigated with ␣ (fcc) Cu-Ni-Zn alloys at 775 ЊC, ␤ (bcc) Fe-Ni-Al alloys at 1000 ЊC, and ␥ (fcc) Ni-Cr-Al alloys at 1100 ЊC. Average ternary interdiffusion coefficients treated as constants are calculated over composition ranges on either side of the Matano plane and examined for the diffusional interactions among the diffusing components. The ternary interdiffusion coefficients determined from the new analysis are observed to be consistent with those determined by the Boltzmann-Matano analysis at selected compositions in the diffusion zone. The ternary interdiffusion coefficients are also employed in analytical solutions based on error functions for the generation of concentration profiles for the selected diffusion couples. The generated profiles are a good representation of the experimental profiles including those exhibiting uphill diffusion or zero-flux plane (ZFP) development for the individual components. Uncertainties in the values of the interdiffusion coefficients calculated on the basis of the new analysis are found to be minimal.

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Solid-solid diffusion couples assembled with disks of Mo and Si were annealed at selected temperatures, over the temperature range from 900 ЊC to 1350 ЊC, for the development of diffusion structure and determination of interdiffusion coefficients for the silicides of Mo. Layers of MoSi 2 and Mo 5 Si 3 were observed to form in the diffusion zone; the MoSi 2 layer was one to two orders of magnitude larger in thickness than the Mo 5 Si 3 layer. The MoSi 2 layer developed a columnar microstructure with evidence of texture and preferential growth of grains in the direction of diffusion. The Si-to-Mo ratio, determined by microprobe analysis across the thickness of the MoSi 2 layer, varied within the approximate range from 1.9 to 2.0. From the concentration profiles, integrated interdiffusion coefficients as well as energies of activation for interdiffusion were determined for the silicide layers. On the basis of the observed stoichiometric range for the MoSi 2 phase, average values of the interdiffusion coefficients were also estimated. Relations are derived between the growth-rate constant and the integrated interdiffusion coefficient for the MoSi 2 phase. The evaluated activation energies for interdiffusion in the MoSi 2 and Mo 5 Si 3 phases are 130 ‫ע‬ 20 and 210 ‫ע‬ 10 kJ/mol, respectively.

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