Interdiffusion and Kirkendall effect in Cu—In alloys

Interdiffusion coefficients, [Dbar], in Cu-rich Cu—In solid solutions containing less than 7 at.% In have been determined by Matano's method in the temperature range 949–1119 K using semi-infinite diffusion couples consisting of pure Cu and Cu—In alloys with Kirkendall markers. From the interdiffusion coefficient and the Kirkendall marker shift, the intrinsic diffusion coefficients of In and Cu, D In, and D cu, have been determined for the compositions at the marker positions, 0·9, 1·7, 2·9 and 4·6 at.% In. The intrinsic diffusion coefficients in dilute alloys containing less than 2 at.% In have been determined by Heumann's method using thin-plate couples. In both types of the couples (semi-infinite and thin plate), it has been found that the Kirkendall marker moves towards the In-rich side and that the ratio of D In/D cu is about three. Using the values of the tracer diffusion coefficients of In and Cu in pure Cu and the value of the intrinsic diffusion coefficient of Cu extrapolated to the infinite dilution of In, the vacancy flow factor, that is, the ratio of the phenomenological coefficients at infinite dilution of In in the flux equations (L cuIn/L InIn)N In = 0, at 1005 and 1089 K has been calculated to be −0·71(+ 0·13, − 0·14) and −0·57(+ 0·10, −0·11) respectively. The large negative value of the vacancy flow factor suggests that the jumps of a vacancy neighbouring an In atom are highly correlated with the jumps of the In atom in Cu.