Diffusion of Ge in binary and ternary Al-(Si,Ge) solid-solution alloys

In this paper we report on the Ge-71 diffusion in Al-(Si,Ge) solid-solution alloys with seven different microalloying concentrations. The temperature, composition, and pressure dependence of diffusion and the pertaining activation enthalpies, enhancement factors, and activation volumes have been determined within the solid-solution phase field. The radiotracer method in combination with serial sectioning by microtome was employed in our experiments. Oxide hold-up effects of the isotope at the surface, which are often encountered in tracer diffusion studies of Al and of Al alloys, have been overcome either by sputter-cleaning of the diffusion samples before evaporating a thin Ge-71 layer or by implantation of Ge-71. Diffusion anneals were either performed at ambient pressure or in a high-pressure cell. Like in pure aluminium Ge is a 'normal' diffuser in both binary and ternary solid solutions. Its activation enthalpies are slightly smaller than those of self-diffusion of the Al solvent. Activation volumes of about one atomic volume are observed which are typical of vacancy-mediated diffusion of 'normal' foreign atoms in Al. Solute additions slightly enhance the Ge diffusivity in both binary and ternary solid solutions by similar amounts. The results are discussed together with literature data on the temperature and pressure dependence of the diffusion of various solute atoms in pure Al.