Grain-boundary diffusion and segregation of gold in copper: Investigation in the type-B and type-C kinetic regimes.

Abstract

Grain-boundary (GB) impurity diffusion of Au in Cu has been investigated by the radiotracer serial-sectioning technique using the $^{195}\mathrm{Au}$ isotope with high specific activity. Measurements in the temperature ranges 618 to 1036 K and 450 to 526 K were carried out in Harrison's type-B and type-C regimes, respectively. In the type-B regime, the product P=${\mathit{sD}}_{\mathrm{GB}}$\ensuremath{\delta} was determined (s being the segregation factor, ${\mathit{D}}_{\mathrm{GB}}$ the GB-diffusion coefficient, \ensuremath{\delta} the GB width), while in the type-C regime ${\mathit{D}}_{\mathrm{GB}}$ values were measured directly. Combining the obtained P and ${\mathit{D}}_{\mathrm{GB}}$ values and assuming \ensuremath{\delta}=0.5 nm, the Au GB-segregation factor was evaluated. From the temperature dependence of s, the segregation enthalpy ${\mathit{H}}_{\mathit{s}}$=-9.7 kJ ${\mathrm{mol}}^{\mathrm{\ensuremath{-}}1}$ has been obtained. GB self-diffusion in Cu in the type-B regime has also been studied by the same experimental technique using the tracer $^{64}\mathrm{Cu}$. The obtained ${\mathit{D}}_{\mathrm{GB}}$=P/\ensuremath{\delta} values for self-diffusion are systematically larger than ${\mathit{D}}_{\mathrm{GB}}$ values for Au in Cu, whereas for lattice diffusion the opposite interrelation holds. This observation is discussed in terms of a trapping of Au atoms during impurity GB diffusion.