Concentration dependence of interdiffusion in aluminum-rich Al-Cu melts

We present measurements and ab initio molecular dynamic simulations of interdiffusion in aluminum-rich Al-Cu melts for concentrations up to 30 at. % copper. To obtain accurate data, a combination of x-ray radiography and shear-cell technique is used, including an experiment in microgravity. Interdiffusion coefficients between 5.3 and $3.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{2}/\mathrm{s}$ at 973 K are found experimentally with a slight decrease with increasing Cu concentration. Results from ab initio molecular dynamic simulation at 1000 K show a decrease of interdiffusion coefficients with the same slope at slightly higher values. Using Darken's equation to discuss the relation between self-diffusion and interdiffusion, we find the cross-correlation term $S$ to be around unity by simulation and experiment.