Intrinsic and Interdiffusion in Cu-Sn System

Solid-solid diffusion couples assembled with disks of copper, tin and intermetallics (Cu3Sn and Cu6Sn5) 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 Cu6Sn5 phase, while microvoids were observed at the Cu/Cu3Sn interface. The Cu(99.9%)/Sn and Cu(99.9%)/Cu6Sn5 diffusion couples annealed at 200 °C for 10 days were analyzed for intrinsic diffusion coefficients of Cu and Sn in the Cu6Sn5 and Cu3Sn 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 Cu3Sn and Cu6Sn5 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 Cu3Sn and Cu6Sn5 phases.

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