An x-ray study of diffusion in the Cu-Ag system

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Abstract
The interdiffusion coefficients for both solid phases of the Ag‐Cu system have been determined from x‐ray diffraction and electron microprobe data. Specimens containing 3.2 μm of Ag on a (111) ‐oriented Cu crystal were used for the x‐ray studies, while a 15‐μm deposit of Ag was used for the probe specimens. Composition profiles for each phase were obtained from the x‐ray intensity bands and a new iterative one‐dimensional model was applied to determine the composition‐dependent diffusion coefficients. The average diffusion coefficients for both phases are nearly equal at about 10−10 cm2/sec at 750 °C, the diffusion temperature. Also, the solubility for the Ag‐rich phase is about three times the solubility for the Cu‐rich phase. These conditions result in interface reversal, i.e., the interface first moves into the substrate and later moves toward the free surface. Structural damage resulting from atomic diffusion was found to be much smaller for the Ag‐Cu system than for other single‐phase Cu‐base specimens that have been examined. Both crystal misorientation (tilt) and subgrains are formed as a result of diffusion. The subgrain shape in the plating depends upon the ratio of the thickness to the initial grain size of the plating.