ORNL-4191 - the Molten Salt Energy Technologies Web Site

time what the effective diffusivities of titanium
will be in the alloy at 1100 to 1400°F, because
at these lower temperatures short-circuit diffusion
paths become an important factor in the materia1
transport. Since we currently have no estimate of
this latter contribution to the net diffusivity for
titanium, we must extend our diffusion measure-
ments to lower temperatures before concluding
what the expected behavior would be under reactor
operating condil ions.
18.8. HASTELLOY N-TELLURIUM
COMPATIBILITY
C. E. Sessions
The compatibility of IJastelloy N with fission
products in the MSRE is of concern, since the
strength and ductility of the structural material
could be reduced after prolonged exposure at ele-
vated temperatures. Consideration as to which
of the products imight be detrimental to the strength
of the alloy revealed that tellurium was a poten-
tially troublesome element. Tellurium is in the
same periodic series as sulfur, a known detrimental
element in nickel-base alloys.
'Yo evaluate the possible effects of tellurium on
Hastelloy N, several tensile samples were vapor
plated with tellurium and then heat treated in
quartz capsules to allow interdiffusion of the tel-
lurium with the alloy. Also, several samples were
233
vapor coated with tellurium and then coated with
an outer layer of pure nickel in order to reduce
the vaporization of the tellurium during subsequent
heat treatments.
After heat treatment of the coated samples, the
specimens were tensile tested at either room tem-
perature or 1200°F using a strain rate of 0 05
min-'. Table 18.4 lists the test conditions and
results for 12 samples of Ilastelloy N. No effect
of the tellurium coating on the ductility of Hastel-
loy N was found at either test temperature. At
1200"F, the ductility following the various treat-
ments ranged from 20 to 34% elongation, which
is within the range normally obtained in the ab-
sence of tellurium. At room temperature the duc-
tility was in the range 52 to 57%, which again is
normal.
Metallographic examination of the specimens
was made after testing to evaluate the interaction
of tellurium with Hastelloy N. A representative
area on the shoulder of one sample is shown in
Fig. 18 19. Irregular surface protuberances are
evident in a localized region of the edge of the
tIastelloy N. 'The gray phase around the protu-
berances is tellurium metal that remained on the
sample after mechanical testing in air at room
temperature. The roughness of the Hastelloy N
specimens resulted from corrosive interaction of
the vapor or liquid tellurium during the heat treat-
ment. At higher magnifications it is evident that
a slight amount of grain-boundary penetration of
the tellurium into the Hastelloy N had taken place.
Table 18.4. Tensile Properties of Tellurium-Hastelloy N Compatibility Studies"
Maximum
Sample Coating Anne a ling
Technique Temperature
(OF)
Tellurium in 2012 24 7 5
capsule with 2012 24 1200
spec iinen 2012 150 75
Anne a ling Test Yield T ota 1
Time Tempera turf Strength Elongation
(hr) (OF) (psi) (%)
2012 150 1200
Vapor coated with 1652 100 75
tellurium and 1652 100 1200
nickel
Vapor coated with 1472 100 75
tellurium 1472 100 1200
-~
aTested at a strain rate of 0.05 minC1
49,100
31,300
49,800
37,000
53,2 00
36,700
52,800
40.500
57
22
57
20
52
27
54
34