ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
lnconel and the molybdenum, ln a second series of
experiments the rolling temperature was reduced to
lOOO"e3, with reductions of 40% per pass and a
total reduction of 85% in thickness. The lower
rolling temperature reduced the tendency for inter-
metallic compounds to dorm at the interface. Bonding
was achieved by using nickel as the intermediate
layer, and evidences of intermetallic compounds
were found only by metallographic examination at
high magnifications. The find thickness of the
composite was 0,010 in. of molybdenum on 0.040 in.
of Inconel. In future experiments with this com-
bination, the maximum ratio of molybdenum to Inconel
wi tkout the directional properties of wrought
molybdenum wi II be determined,
All the composites mentioned above were suc-
cessfully reduced from 4-in. blanks to 21/2-in. cups
by the "Guerin" forming process (male parts of die
are hard rubber) at room temperature. Attempts to
deep draw the composites are to be made.
Si ma- F'ho se A! lays
For the continuing study of sigma-phase alloy
corrosion by liquid lead (cf. Sec, 6, "Corrosion
Research"), some additional tubing was made. Two
ingots of a 48.2% Cs-51.8% Fe alloy and two ingots
of o 45% Fe-40% G-1% Ni alloy were vacwum
cast into l>,-in.-dia ingots 6 in, long. These ingots
were then hot rolled in an air atmosphere at 1250°C
to rod in. in diameter. After annealing at 11Qo"C
for 2 hr and quenching, the rod was readily machin-
able into tubing.
The transformation from the ferrite to the sigma
phase will be accomplished by aging at 1425°F.
Two of the tubes (Fe-Cr) were cold swaged 12% so
that the effect of cold swaging on the distribution
of the sigma phase could be determined,
oron Carbide Shielding
The experimental fabrication of b-in.-thick shield
pieces by warm pressing boron carbide bonded with
copper or silver has been discontinued in favor of
the fabrication of pieces molded with nonmetallic
bonding material by cold pressing followed by
sintering to develop the desired properties. Non-
metallic bonding materials that would be suitable
from nuclear considerations and would be stable at
the expected service temperature include sodium
silicate, silica, silicon nitride, and boric oxide.
Arrangements are being made to secure samples of
these materials for compatibility tests with lncanel
under operating cot~ditions,
1 24
The density of the proposed shield pieces is to
be about 1.8 to 1.9 g/cm3 of R,C, equivalent to 1.4
to 1.5 g/crn3 of boron. They would be molded in
the form of equilateral triangles or diamond shapes,
2 to 3 in. on a side, so as fa cover a sphere with
an integral number of pieces.
Additional tests of the compatibil ity of lnconel
with pure boron carbide are being made. Previous
tests indicated the formation of a diffusion layer
5 mils thick in a 100-hr test at the operating temper-
ature of 1500°F.
Twelve tubular fuel elements are being prepared
for further drawing experiments at Superior Tube
Company. 'they are being assembled with high-
fired UO, inathe 30- to 55-p particle size range, as
well as with very fine UO,, and with prealloyed
and elemental stainless steel and iron core matrixes.
Plans are cilso being made to try hot swaging of
the tubes in an attempt to reduce stringer formation
in the cores by reducing the amount of cold working.
Hot swaging on a mandrel may prove to be suc-
cessful if bonding to the mandrel can be prevented
by an oxide scale or coating.
METALLOGRAPHIC EXAMINAPIOH OF A
FL UO RiDE-YO-SODIUM HEAT E XCMWNG E R
R. 9. Gray P. Patriarca
G. M. Slaughter
Meta I lurgy Division
The fluoride-to-sodium intermediate heat ex-
changer, which in a life test failed after 1680 hr in
cyclic service in the temperature range 1080 to
1500"F, was examined metaIlographically. All the
tube-to-header joints were manually heliarc welded,
and tests showed the heat exchanger to be heliuni
leak-tight before assembly into the test rig.
Visual examination indicated the presence of 19
fissures in the tube-to-headcr welds in two of the
three adjacent headers at the hot sodium inlet end.
The probable progressive propagotinn of these
fissures is shown in Figs. 7.14, 7.15, and 7,16.
The fissure shown in Fige 7.16 probably extends to
the surface of the weld. If so, there BWS ~1 leak in
the system at this point. It seems likely that dif-
ferential thermal expansion betwcrn the tubes and
the casing caused stress concentrations at the
roots of the tube-to-header welds. These stress
concentrations wou Id tend to propagate cracks
through the welds in the course of thermnl cycling,