Diffusion in Zr-based glass forming melts
In simple metallic melts, which are supposed to be in equilibrium, dynamic asymmetry and thus large differences in diffusivities of the constituents are not expected. For instance, on the previous investigation in multicomponent Pd-based glass forming melts, diffusivities of all components merge into one single temperature dependence, and the majority component Pd obeys Stokes-Einstein (SE) relation in the whole temperature range; from the stable melt down to the glass transition temperature. It is interesting to check whether these results are generally accepted also for another class of metallic glass formers, e.g. Zr-based glass formers. Therefore, simultaneous radiotracer diffusion experiments of Co-57 and Zr-95 in the melt of multicomponent system,Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy 4), and of the simpler systems, Zr64Ni36 , Zr36Ni64 and Zr60Ni25Al15 above their respective liquidus temperature, Tl , are performed. From these experiments, the effects of component complexity on the atomic diffusion in the melt can be understood. Additionally, from the experimental results of the simpler systems, the atomic diffusion in the multicomponent Zr-based systems, as well as the effects of packing density and chemical short range order (CSRO) on the atomic diffusion, can also be explained. The results in multicomponent Vit. 4 melt show that Zr diffusivity differs significantly from the diffusivities of the smaller components by a factor of 4 at its Tl, although it obeys SE relation. On the other hand, the Co and Zr diffusivities ratio in the melt of the simpler Zr-based systems is the same as the component diffusivities ratio in simple metallic and Pd-based melts, although it increases sequentially from Zr64Ni36 to Zr60Ni25Al15 and Zr36Ni64. These results suggest that in multicomponent Vit.4, Zr atoms enter energy-landscape-controlled regime and behave solid-like already at least 150 K above its Tl. Additionally, although the diffusion in the simpler system of Zr-based melts is similar to the simple metallic melts, the results show the effects of packing density and CSRO on the atomic iffusion.
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