ANOMALOUS DIFFUSION OF FE IN LIQUID AL MEASURED BY THE PULSED-LASER TECHNIQUE

The diffusivity of Fe and Cu in liquid Al was measured by using a nano second-duration pulsed laser to melt thin Al films ion implanted with solute. The thin film geometry eliminates convection in the melt durin g the experiment. The time-dependent electrical conductance and optica l reflectance of the Al film during melting were measured to determine the melt duration, allowing the diffusivity to be calculated based on the one-dimensional broadening of an ion-implanted solute depth profi le. The measured diffusivity of Cu is about three times that of Fe, wh ich is consistent with Turnbull's cluster model for liquid Al-Fe. The diffusion coefficients measured for both Fe and Cu changed very little as the peak concentration decreased with time, implying little or no concentration dependence. The temperature dependence of the diffusivit y was examined by using heat-flow simulations to extract temperature i nformation from the transient conductance data. Our results for Fe dif fusion in liquid Al are consistent, within experimental uncertainties, with extrapolations of Ejima's data to lower temperatures, but we obs erve Cu diffusivities approximately twice as large as would be expecte d from extrapolations of Ejima's data.