Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 34 of 47
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size throughout the entire cross section of the core blank. Frequencies as low
as.60 cycles per second were tested, but a corresponding extension of the fine-
grained region was not achieved nor did any of the frequencies employed show a
difference in degree of preferred orientation after quenching.28
Polygonization of Beta-Quenched Structures
The recrystallization possible by alpha annealing of uranium metal drastically
quenched from the beta phase has been mentioned previously.4 This effect
observed in Jominy end-quenched specimens gave an equiaxed structure in the
cross section but columnar grain shapes in the longitudinal section. It seemed
possible, however, that this anisotropy arose from the very special stress
condition induced by the end quench and that with a different stress pattern, a
recrystallization perhaps could be achieved without the occurrence of columnar-
type grains. A further interest in possible grain refinement by alpha
annealing grew out of studies of vacuum heat treatment as a means of removing
hydrogen from the uranium lattice. It appeared possible that a double benefit
could be achieved by a vacuum anneal at a proper alpha temperature in which
both hydrogen removal and refinement of the grain size would be the outcome.
A sequence of studies8,15,39,4:,41,4,47,48,49,54 has shown that a change in'
grain size can indeed be accomplished by an alpha anneal following the beta
heat treatment. It is not certain whether this change in structure should be
called recrystallization or polygonization since while there is a reduction in
grain size, it is not in the sense of nucleating a submicroscopic array of
grains which then grow with time at temperature. The behavior during
polygonization responds to a number of influences as follows:
1. The rate of polygonization increases as the temperature of the alpha
annealing treatment is raised.
2. The cooling rate during the transformation from beta to alpha
influences the rate of polygonization in the subsequent annealing
treatment with more rapid rates of cooling, providing more rapid rates
of polygonization. There also appears to be a critical cooling rate
below which no polygonization will occur in a following annealing
3. Alloy -additions to the uranium tend to retard the polygonization rate;
for instance, 150 ppm Fe and 100 ppm Si is sufficient to prolong the
time for polygonization.by a full order of magnitude.
4. The mode of poly onization varies with the alloy content. In dilute
uranium alloys, 'he polygonization begins at the O.D. surface and
proceeds toward the center in, a uniform progression. In relatively
pure dingot, however, polygonization will initiate at the O.D. and
then take place at random throughout the cross section.
5. The-refinement in grain size produced by polygonization appears to be
greater -if'the--annealing-temperature is in the high alpha range
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Fellows, J. A. Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966., report, January 1, 1966; Weldon Spring, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1033773/m1/34/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.