Interface diffusion in eutectic Pb-Sn solder

Interface diffusion of Pb-210 and Sn-113 radioactive tracers in oriented Pb-62 wt% Sn eutectic specimens showing lamellar structure has been measured. The product of the interface diffusion coefficient and the width, delta D-i, shows an Arrhenius relationship below 400 K. The values of the Arrhenius parameters, ei and delta D degrees(i), for the Pb-210 and Sn-113 tracers are 84.8 kJ/mol, 7 x 10(-10) m(3)/s and 77 kJ/mol, 7 x 10(-12) m(3)/s, respectively. An interface energy of 150 mJ/m(2) has been computed from the diffusion measurements. Above 400 Ii, the values of delta D-i deviate from the Arrhenius relationship and rise steeply so that they finally merge with the diffusion data in grain boundaries in polycrystalline Pb and Pb-Sn alloys measured earlier. These effects are concomitant with the changes in the microstructure upon annealing where the Ph and Sn phases separate to form equiaxed grains. The importance of diffusion in nearly coherent Pb-Sn interfaces in its plastic deformation processes is discussed. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.