Interfacial free energy of copper-antimony alloys

It was suspected that the brittleness of copper-antimony alloys is partly due to a low surface energy caused by segregation of antimony to interfaces in the Gibbs manner. In these experiments the surface and grain-boundary energies and the surface segregation were measured on pure copper and copper alloys containing 0.26, 0.57 and 0.78 at. % antimony. The surface energies were measured on these alloys in the form of wires in a helium atmosphere at 950 $^\circ$C and as similar results were obtained in a hydrogen atmosphere it was concluded that no serious unwanted surface contamination occurred. The grain-boundary energies were deduced from the surface energies by measuring the dihedral angles in an electron microscope. The surface energies were 1770, 980, 950 and 900 ergs/cm$^2$ and the grain-boundary energies 600, 290, 280 and 320 ergs/cm$^2$ in order of ascending antimony content. The creep rates of the wires in the surface energy experiments agreed to within a factor of $\frac{3}{2}$ with the rate calculated from Herring's equation for diffusion creep. The surface segregation was measured on copper and the 0.57 and 0.78 at. % antimony alloys after annealing and irradiating in order to detect antimony radioactively. Surface segregation of antimony was found in the two alloys in an amount equivalent to 0.37 monolayer of pure antimony. The surface composition and surface energies are shown to be consistent. Antimony does therefore drastically reduce the surface and grain boundary energies of copper by segregating in the Gibbs manner.