Effect of Nonequilibrium Defects Due to Phase Transformation on Diffusion in Beta Zirconium
Chelluri, Bhanumathi
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https://hdl.handle.net/2142/68649
Description
Title
Effect of Nonequilibrium Defects Due to Phase Transformation on Diffusion in Beta Zirconium
Author(s)
Chelluri, Bhanumathi
Issue Date
1981
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
The effect of the hcp(--->)bcc phase transformation on the anomalous diffusion characteristics of bcc zirconium has been investigated in this study. ('113)Sn and ('59)Fe tracers were used to typify the diffusing nature of self- and fast-diffusing atoms. A differential measurement of diffusion in two samples was carried out under very different preannealing conditions but otherwise identical states of diffusion time and temperature. In the first set of experiments, one of the samples was annealed for lengthy periods of time ((TURN) 20-30 hours) at premelting temperatures ((TURN) 1550(DEGREES)C) prior to diffusion (at lower temperature in the bcc phase). This was done in an attempt to decrease the defect concentration produced by the phase transformation. During the second set of experiments, the sample was cycled three times through the phase transformation temperature ((TURN) 890(DEGREES)C) (hcp(--->)bcc(--->)hcp(--->)bcc), with a view to enhance the defect density due to phase changes. In both sets of experiments, the second sample was raised to the diffusion temperature directly. The relative diffusivities of two samples were measured by serial sectioning and counting techniques. Appropriate correction methods were derived, for each set, to identify the proper interface because of the unique sectioning problems encountered.
Within errors, no significant difference in diffusivity was found for ('113)Sn diffusion for differing preannealing conditions. A small difference of ((TURN) 30%) was found for ('59)Fe diffusion, but this result was somewhat obscured by the non-Gaussian tracer profiles measured for this case. The results show that the anomalous diffusion behavior of bcc zirconium is not a result of excess defects introduced by the hcp(--->)bcc phase transformation.
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