Combined segregation of silver and tin from the surface of Cu-Ag-Sn ternary alloys

The study of Cu-Ag-Sn ternary alloys by the methods of temperature-programmed desorption (TPD) and statistical modeling is сarried out. The results of the TPD experiment on the combined surface segregation of Ag and Sn atoms in dilute solutions of silver and tin in copper in polycrystalline and liquid states are presented. It was found out that the desorption of particles from the surface of the alloy occurs from regions enriched with this component. In addition, the silver atoms form, in the main, slightly layered islets. Data are also provided for computer simulation of the surface of these alloys by the Monte Carlo method in combination with the embedded atom method (EAM). Using the EAM method, it was possible to avoid a priori assumptions about the composition and structure of the alloy surface. Simulation showed that the binding energy of surface atoms is close to the experimental activation energies of thermal desorption for Cu and Ag atoms. But there is a significant difference for tin atoms. Secondly, in the modeling for the solid state of the Cu$_{98}$Ag$_1$Sn$_1$ alloy, the surface concentrations of $\Theta_{\mathrm{Ag}} \approx\Theta_{\mathrm{Sn}} = 30$ at.%, which for Ag atoms are close to the results of the TPD experiment. In the melt, the degree of surface segregation is reduced to $8$ at.% Ag and $14$ at.% Sn. Both the TPD experiment and the simulation give an excess of $10$ to $30$ times the surface concentrations of Ag and Sn over bulk values, both in the solid and in the liquid state of the alloy. Third, computer models reveal surface structures in the form of zigzag chains of Sn atoms, which alternate with chains of Ag atoms. The profiles of tin concentrations in alloys confirm the hypothesis of a two-layered character of segregation of tin.