Atomic diffusion in liquid alloys

The mechanisms of atomic diffusion in metallic melts are elucidated by various experimental techniques and molecular dynamics (MD) computer simulation, as well as by the mode coupling theory (MCT) of the glass transition. Self-diffusion experiments in the bulk metallic glassformer Pd40Ni10Cu30P20 performed under microgravity conditions on FOTON M2 and in the lab show that self-diffusion is controlled by the effective packing of the atoms. The temperature dependence of Ni-self diffusion as measured by quasielastic neutron scattering (QNS) can be described by a power law, as predicted by MCT. The relation between self- and interdiffusion is studied for an A180Ni20 melt. Results from MD simulations are in good agreement with the Ni-self- and interdiffusion coefficients obtained from QNS and the long-capillary (LC) technique. The detailed information provided by the MD simulation reveals why the interdiffusion coefficient is up to a factor 5 larger than the self-diffusion coefficient. The relation between self-diffusion and interdiffusion is further studied for Zr2Ni by a combination of neutron diffraction and calculations in the framework of MCT. Comparisons to MCT calculations for hard spheres shed light onto the relation between chemical short-range order and diffusive mass transport.