Diffusion of Tin in a Solid Solution of the Copper–Tin System

Electron probe microanalysis (EPMA) has been used to obtain concentration curves and calculate the bulk diffusion coefficients of Sn in solid solutions of the copper–tin system in a tin concentration range of less than 13.9% weight (7.96 at %) and temperature range from 500 to 650°C. Diffusion couples are made from pure Cu (99.995%) and a two-component alloy of Cu with chemically pure Sn by direct alloying metallic Cu with Sn in an Ar–H2 atmosphere at 1100°C for 2 h. Diffusion coefficients were calculated using the Matano–Boltzmann and Grube methods from the upper part of the concentration curve (from 6 to 8 at % (D1)) and the lower part (from 2 at % to zero (D2)). It is shown that Sn diffusion coefficients in a concentrated solution were several times greater than Sn diffusion coefficients in dilute solution. Both values of diffusion activation energy, especially the second, coincide with isotope data on Sn diffusion in a pure copper (187 kJ/mol). A qualitative interpretation is proposed of the effect of accelerating the diffusion of tin in a concentrated solid solution of the copper–tin system.