Self-Diffusion in Bulk Metallic Glasses

We have studied self-diffusion in the bulk metallic glasses Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 and Zr 65 Cu 17.5 Ni 10 A1 7.5 by means of the radiotracer method. Diffusion of 63 Ni has been investigated as a function of temperature in both alloys and also as a function of hydrostatic pressure in Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 . With the isotope 95 Zr diffusion studies of the major component Zr were performed in Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 . The diffusivity of 95 Zr is much smaller than that of 63 Ni. The temperature dependence of 63 Ni self-diffusion into Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 and into Zr 65 Cu 17.5 Ni 10 A1 7.5 cannot be described by a single set of Arrhenius parameters, breaks in the Arrhenius curves are observed. We attribute the non-linear Arrhenius behaviour to the transition from the glassy to the supercooled liquid state. For the first time activation volumes of diffusion in a supercooled melt have been determined. From the pressure dependence of 63 Ni diffusion in Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 we get activation volumes around one mean atomic volume favouring a diffusion mechanism via vacancy-like defects.