Electrical Transport During Phase Transformation in Metallic Glasses

Citation

Schulz, Robert (1984) Electrical Transport During Phase Transformation in Metallic Glasses. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/yxsm-vx37. https://resolver.caltech.edu/CaltechETD:etd-01252007-153245

Abstract

Electrical resistivity measurements have been used as a primary tool to study relaxation phenomena and high temperature structural transformations in metallic glasses. We will try to correlate, throughout this work, the resistivity behavior with structural measurements from high and low angle X-ray scattering, transmission electron microscopy, Mossbauer experiments and low temperature superconductivity measurements to get a better understanding of the scattering mechanism during the phase transformation. We will distinguish between topological relaxation and chemical relaxation and in this latter case, emphasis will be given to phase separation. Three systems will be discussed extensively. Amorphous Cu_100-xZr_x around the equiatomic composition, (Mo_0.6Ru_0.4)_100-xB_x for boron concentrations ranging from x = 14 to x = 22 and (Zr_1-xHf_x)₆₂Ni₃₈ across the concentration range. We will show that upon annealing at temperature above 300°C, Cu₅₀Zr₅₀ phase separates into two amorphous phases of concentration close to CuZr₂ and Cu₁₀Zr₇. During the phase separation an anomalous resistivity behavior, similar to the one observed during the early stage of Guinier-Preston zones formation in crystalline alloys is seen. In Mo-Ru-B alloys, the nonlinear behavior in resistivity is correlated with the presence of a peak in the small angle X-ray intensity and is explained in term of spinodal decomposition caused by the diffusion of boron in the amorphous matrix. In (Zr_1-xHf_x)₆₂Ni₃₈, an exothermic transformation which gives rise to an increase in resistivity but no resolvable Bragg peaks in the high angle X-ray pattern is investigated in detail. The applicability of the Ziman formalism to successfully explain the behavior of the resistivity in all these cases is questioned and an alternative approach, based on d-band conduction, is proposed. New ways of understanding transport phenomena during structural relaxation in metallic glasses follow from these discussions.

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