ORNL-1771 - Oak Ridge National Laboratory

PERIOD ENDING SEPTEMBER IO, 1954
0,004
I_
: 0
6,
0.002
I_
0.003 -
X
u
z-
3.004 -
Fig. 6.8. lnconel Exposed to Static Rubidium for '100 hr ot 1650OF. Note decarburization in attacked
area. Specimen nickel plated after test to protect edge. Etched with glyceria regia.
cent sodium and some oxygen contamination. Ad-
ditional static tests are under way with triple-
distilled rubidium, and an Inconel thermal convection
loop is being operated with boiling rubidium, Fig.
6.9. This loop has now operated for several hundred
hours without difficulty.
Carburization of Inconel by Sodium
It is well known that sodium, in addition to de-
carburizing metals, can, in some cases, carburize
them if the carbon concentration in the sodium is
sufficiently high. Therefore, an attempt is being
made to determine whether small additions of carbon
would prevent decarburization of lnconel specimens
during long-time creep tests in contact with sodium
at elevated temperatures. A-nickel containers are
being used for static tests so that the ratio of
lnconel surface area to sodium volume! will be
small. The maximum solubility of carbon in nickel
at 1500°F is approximately 0.1%, and therefore the
carburization of the nickel Containers in these
tests is very slight. The A-nickel used for the
containers was found by analysis to contain only
0.05% carbon.
The ratio of the lnconel surface to the sodium
volume in the tests performed to date was 0.76.
The lnconel specimens used were 0.049-in. sheet
reduced to 0.015 in. by cold rolling, and they were
annealed for 2 hr at 1650°F. The carbon additions
(1, 5, and 10 wt %) were made to the sodium in the
form of small lumps of reactor-grade graphite.
The nickel containers were loaded with the ln-
conet specimens, the graphite, and the sodium in a
dry box in o purified helium atmosphere and sealed
under vacuum, As shown in Table 6.4 and Fig.
6.10, all the specimens were very heavily carburized
and extremely brittle after exposure for 100 hr at
1500'F. Also, they were partly covered with a
89