Interdiffusion and Kirkendall Effect in Cu–Sn Alloys

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Abstract
Interdiffusion coefficients in copper-rich copper-tin solid solutions containing up to 6 at% of Sn have been determined by Matano’s analysis in the temperature range between 973 and 1101 K using semi-infinite couples with Kirkendall markers consisting of pure copper and Cu–Sn alloys. An anomalously large Kirkendall effect reported by several authors has been shown to be an overestimation resulting from the disregard for the large difference in partial molar volumes between Cu and Sn in the alloy. Using the data on the interdiffusion coefficient, the marker shift, the partial molar volumes and Darken’s relation, the intrinsic diffusion coefficients, DSn, and DCu, in the Cu-alloys containing 0.9, 1.7, 3.1 and 4.9 at% of Sn have been determined, and the ratio of DSn⁄DCu has been found to be about three. In addition to the above experiments with semi-infinite couples, the intrinsic diffusion coefficients in the Cu-alloys containing 0.6, 1.4, 2.6 and 3.5 at% of Sn at 1089 K have been determined by Heumann’s method using finite thin plate couples. Using the tracer diffusion data in pure Cu and the value of DCu in the infinite dilution of Sn evaluated from the detailed concentration dependence of DCu thus obtained, the vacancy flow factor which is expressed by the ratio of the phenomenological coefficients of flux equations in the infinite dilution of Sn, (LCuSn⁄LSnSn)NSn=0, at 1014 and 1089 K, has been estimated to be −1.06−0.24+0.18 and −0.84−0.13+0.12, respectively. Such a negative large ratio suggests that the jump between a tin atom and a vacancy in copper is strongly correlated.

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