Quasielastic neutron scattering has been used to study atomic dynamics in liquid Cu. At small wave numbers q the intermediate scattering function is dominated by incoherent scattering contributions. From the decay of the quasielastic signal, self-diffusion coefficients D are obtained on an absolute scale. In a temperature range from 1370 to 1620 K, D values exhibit an Arrhenius-type temperature dependence and are significantly smaller than those from previous tracer experiments that are hampered by convective flow.

We report on investigations on the atomic dynamics and the static structure factors of binary ${\text{Ni}}_{36}{\text{Zr}}_{64}$ alloy melts. In order to undercool the melts deeply below the melting temperature and to avoid reactions with crucible materials, the liquids are containerlessly processed by the application of the electromagnetic levitation technique. This technique is combined with quasielastic neutron scattering at the time-of-flight spectrometer TOFTOF of the Munich research reactor (FRM II) and neutron diffraction at the diffractometer D20 of the Institut Laue-Langevin. Partial static structure factors of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ have been derived via isotopic substitution. The quasielastic neutron-scattering experiments indicate a large activation energy for Ni self-diffusion in liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ of 0.64 eV. This may result from a peculiar short-range order of the Ni-Zr melts that differs from the icosahedral short-range order that was previously found to prevail in most melts of pure metals and of metallic alloys with a small difference of the atomic radii of the components and that is characterized by a high nearest-neighbor coordination number of $⟨Z⟩\approx 13.9$, as found by elastic neutron scattering.

We use time-resolved x-ray radiography in order to monitor interdiffusion processes in~situ in liquid alloys. We measure temperature and composition dependent interdiffusion coefficients (DAlCu) in Al-rich Al-Cu melts. At constant temperature, DAlCu only exhibits a weak dependence of the alloy composition. As compared to self-diffusion, interdiffusion is enhanced by a factor of about 3. Our results demonstrate that it is not possible to express interdiffusion in terms of self-diffusion and thermodynamic driving forces.

EPJ Web of Conferences, open-access proceedings in physics and related sciences

We studied structural relaxation in the bulk metallic glass forming alloy ${\mathrm{Zr}}_{46.8}{\mathrm{Ti}}_{8.2}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ on different timescales and length scales, with emphasis on the supercooled liquid state. Using x-ray photon correlation spectroscopy, we determined the microscopic structural relaxation time covering timescales of more than two decades in the supercooled liquid region, down to the subsecond regime. Upon heating across the glass transition, the intermediate scattering function changes from a compressed to a stretched decay, with a smooth transition in the stretching exponent and characteristic relaxation time. In the supercooled liquid state, the macroscopic and microscopic relaxation time and the melt viscosity all exhibit the same temperature dependence. This points to a relaxation mechanism via intrinsic structural relaxation of the majority component Zr, with its microscopic timescale controlling both the stress relaxation and viscous flow of the melt.

With incoherent quasielastic neutron scattering self-diffusion coefficients in pure iron, and iron-carbon alloys containing 8.7 at% and 16.9 at% carbon have been measured. At the melting point in liquid iron is m² s⁻¹. For the close-to-eutectic Fe_83.1C_16.9 composition m² s⁻¹ at T K. Contradicting conclusions drawn from literature values of tracer diffusion experiments the addition of carbon has only a minor effect on the iron mobility: at a given temperature the self-diffusion coefficient in Fe_83.1C_16.9 is only 10% larger than in liquid iron, although mixing has a drastic effect on liquidus temperature and phase behavior.