Diffusion of iron in Mg 60Ni 25Nd 15 amorphous alloys with a wide supercooled liquid region

Abstract

Impurity diffusion of 59Fe in Mg 60Ni 25Nd 15 amorphous alloys with a wide supercooled liquid region has been investigated over the temperature range from 407 to 469 K. Concentration depth profiles of the radioisotope 59Fe in Mg 60Ni 25Nd 15 supercooled liquid and amorphous alloy have been measured by an ion beam sputter-sectioning technique. The temperature dependence of the impurity diffusivity of Fe in Mg 60Ni 25Nd 15 supercooled liquid (446–469 K) and amorphous alloy (407–438 K) is expressed as respectively D(supercooled) = 2.0 × 10 −10 exp (−53.3 ± 3.5 kJ mol −1/ RT)m 2s −1 and D(amorphous) = 7.7 × 10 3 exp (−164.0 ± 19.4 kJ mol −1/ RT) m 2 s −1 The temperature dependence of Fe diffusivities in the supercooled liquid region is less significant than that in the amorphous phase; the activation energy for diffusion in the supercooled liquid region is much smaller than that in the amorphous alloy by a factor of 3. Such a temperature dependence is consistent with results of viscosity measurement.