Diffusion and the thermal stability of amorphous copper-zirconium
Stelter, Eric Carl
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https://hdl.handle.net/2142/25295
Description
Title
Diffusion and the thermal stability of amorphous copper-zirconium
Author(s)
Stelter, Eric Carl
Issue Date
1985
Doctoral Committee Chair(s)
Lazarus, David
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
amorphous copper-zirconium
diffusion
thermal relaxation
melt-spinning under vacuum
Auger electron spectrometry (AES)
Rutherford backscattering spectrometry (RBS)
Language
en
Abstract
Measurements have been made of diffusion and thermal relaxation
in amorphous CU50Zr50. Samples were prepared by melt-spinning under vacuum. Diffusion measurements were made over the temperature range from 317 to 385 C, using Ag and Au as substitutional impurities, by means of Auger electron spectrometry (AES) and Rutherford backscattering spectrometry
(RBS). Thermal measurements were made by differential scanning calorimetry (DSC) up to 550 C. The diffusion coefficients of Ag and Au in amorphous
CU50zr50 are found to be somewhat higher than, but very close in magnitude to the coefficient of self-diffusion in crystalline Cu at the same temperatures. The activation energies for diffusion in the amorphous alloy are 0.72 to 1.55 ev/atom, much closer to the activation energy for self-diffusion in liquid Cu, 0.42 eV/atom, than that for the crystalline solid,
2.19 eV/atom. The mechanism for diffusion in the amorphous metal is presumably quite different from the monovacancy mechanism dominant in the crystalline solid.
The pre-exponential terms are found to be extremely small, on the order of 10-10 to 10-11 cm2/sec for Ag diffusion. This indicates that diffusion in amorphous Cu50Zr 50 may
involve an extended defect of 10 or more atoms. Analysis of the data in terms of the free-volume model also lends strength to this conclusion and indicates that the glass is composed of liquid-like clusters of 15 to 20 atoms.
The initial stage of relaxation in amorphous CuZr occurs with a spectrum of activation energies. The lowest activation energy involved, 0.78 eV/atom, is almost identical to the average activation energy of Ag diffusion in the glass, 0.77 eV/atom, indicating that relaxation occurs primarily through diffusion.
The activation energy of crystallization, determined by Kissinger's method, is 3.10 eV/atom. The large difference, on the order of 2.3 eV/atom, between the activation energies of crystallization and diffusion is attributed to the energy required to nucleate the crystalline phase.
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