Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 37 of 47
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some superiority in impact strength compared to those water quenched, thus
tending to confirm the susceptibility of these types of cores- to form micro-
cracks during the beta quench. The difference, however, was not of a magnitude
to suggest that a change in heat treatment would eliminate the possibility for
transverse fracture. The general conclusion might be drawn, in fact, that the
impact properties did not appear to offer a characterization of specimen
composition or thermal or mechanical history that was particularly meaningful.51
Tensile tests were performed over the same temperature-range using a standard
tensile specimen. These showed the expected range in properties with low -
ductility at low temperature and fairly'constant levels of high ductility above
+200*F. Included in these tests was a range of iron compositions which showed
that with increasing iron the ductility was definitely reduced. The data
suggested, in fact, that above 200 ppm iron, the uranium fuel might be
characterized as being essentially brittle at all alpha temperatures. Other
than this particular correlation with alloy content, however, there did not
appear to be a significant difference in mechanical properties which would
explain slug failures.
At a later date the prospect of producing centrifugally cast core blanks made
it appropriate to undertake a specific examination of the tensile properties of
cast material as influenced by heat treatment and temperature of testing.
Special test equipment was provided to permit these tests to be carried out in
vacuum with the ability to adjust the load sensitively and record the
elongation as the test proceeded. A small-size sample was used (1/4-inch O.D.
by 1-inch gauge length) to permit its preparation from the wall section of a
centrifugally cast tube.3o,62,e3
Initial samples were prepared from centrifugal castings that had been poured in
the Laboratory from induction melted metal of a nominal composition of 175 ppm
Fe, 325 ppm Si. Tensile testing was performed over the range of 25 C. to 600 c.
The strength varied inversely with the temperature, whereas both elongation and
reduction of area increased to a marked degree with a plateau at a little under
20% E in the range of 150-350*c. The low ductility at low temperature may have
been caused by the high carbon (1200 ppm) from the recycled scrap used in the
melting charge and high hydrogen (18 ppm) from a salt bath treatment in the
gamma phase prior to fi-nal beta treatment before machining. There were thus
many nonmetallic particles which could affect the mechanical properties since
they tended to rupture under stress and to form a path for generation ofcracks
as deformation proceeded. The data, therefore, should be viewed with
reservations. Unfortunately, there has not been available time or manpower to
repeat this work at a favorable carbon and hydrogen level,
Time-Temperature-Transformation (TTT) Diagrams
Growing experience with the more highly alloyed fuel compositions being studied
for use at Savannah River made it desirable to explore thoroughly the trans-
formation characteristics of the various alloy types. Work at other sites had
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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/m1/37/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.