Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 39 of 47
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This concept is relatively unexplored as yet and should be augmented with work
with other alloys and other heat treating methods. It should be advantageous,
for instance, to explore in actual irradiation tests the response of different
transformation products. It would also seem desirable to confirm these patterns
of behavior with induction heating as opposed to salt bath heating.
STUDIES OF URANIUM STRUCTURES BY TRANSMISSION ELECTRON MICROSCOPY
The introduction of alloys to uranium fuel had made it possible to control
uranium grain size by mechanisms that appeared to be reasonably well understood.
Certain combinations of such alloys had also enhanced the performance under
irradiation, but there had been no- clear evidence of what the direct cause of
this benefit might be. It appeared highly likely that the presence of a
precipitate of some optimum particle size and distribution played a major
factor in providing resistance to swelling but specific evidence of why this
was beneficial was lacking. There had been hypotheses, however, that- swelling
might be due to the accumulation of dislocation motions within the uranium
structure and that perhaps this accumulation could be halted by the presence of
very fine precipitates which could serve to pin these dislocations in place and
prevent further motion. It was from the point of view of attempting to explore
this concept that studies with the-transmission electron microscope were under-
A considerable amount of time.was necessary to gain skill in'the preparation of
the extremely thin foils necessary for transmission of an electron beam as well
as to achieve an understanding of the types of data which the microscope makes,
available. Correct interpretation of the X-ray diffraction patterns as
influenced by orientation of the sample, for instance, required appreciable
experience before the lattice planes could be identified with confidence.
Problems of residual stress giving rise to extinction bands in the transmission
pictures were also troublesome at first since these obscured much of the >
information that would otherwise have been available in the picture. Ultimately,
however, techniques were successfully devised which permitted the creation of
extremely thin foils and the delineation of aspects of structure in amazingly
fine detail. A
Studies of Uranium Compound Precipitates
Before undertaking the more difficult task of learning how to observe
dislocation motion, it was useful in gaining experience with the microscope to
conduct studies of the size, shape, orientation, and location within the
lattice -of various uranium compound precipitates. As a part-of this effort,
the precipitation mechanisms of U3Si in alpha uranium were studied with alloys
containing 330, 530, and 1500 ppm of silicon, respectively.29 These materials-
were solution treated in the beta phase and after quenching were annealed for
various lengths of time in the high alpha temperature range. The microscope-
revealed that annealing for up to 300 hours at 500*C. showed no-visible
precipitates (at 21,500X), although many dislocations were visible Annealing
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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/m1/39/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.