ornl-tm-2724
DESCRIPTION
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- OAK RIDGE NATIONAL LABORATORY
operated by
UNION CARBIDE CORPORATION NUCLEAR DIVISION
for the U.S. ATOMIC ENERGY COMMISSION
ORNL- TM- 2724
COMPATIBILITY OF MOLYBDENUM-BASE ALLOY TZM,WITH
LiF-BeF ThF UF (68-20-1 1.7-0.3 mole %) at 1100% 2- 4- 4
J. W. Koger and A. P. Litman
NOTICE This document contains information of a preliminary nature and was prepared primarily for internal use a t the Oak Ridge National Laboratory. I t is subiect to revision or correction and therefore does not represent a final report.
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LEGAL NOTICE ~
This report was prepared as an account of Government sponsored work. Neither the United States,
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A. Makes any warranty or representation, expressed or implied, with respect to the accuracy,
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Assumes any l iabi l i t ies wi th respect to the use of, or for damages resulting from the use of
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O R N L T M - 2 7 2 4
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V
C o n t r a c t No. W-7405-eng- 26
METALS AND CERAMICS D I V I S I O N
COMPATIBILITY O F MOLYBDENUM-BASE ALLOY TZM WITH L i F - B e F * - T h F & - U F 4 (68-20-11.7-0.3 m o l e 4) at 1100°C
J. W. Koger and A. P. Litman
DECEMBER 1969
OAK RIDGE NATIONAL LABORATORY O a k R i d g e , Tennessee
operated by UNION CARBIDE CORPORATION
U.S. ATOMIC ENERGY COMMISSION f o r the
,
.
iii . CONTENTS
Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abstract 1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . 2
Results and Discussion . . . . . . . . . . . . . . . . . . . . . 3
S a l t Analysis . . . . . . . . . . . . . . . . . . . . . . . 3
Weight Changes . . . . . . . . . . . . . . . . . . . . . . 3
X-Ray Fluorescence and Microprobe Analysis . . . . . . . . 4
Microstructural Changes . . . . . . . . . . . . . . . . . . 4
Re cry s t a l l i z a t ion Strength . . . . . . . . . . . . . . . . . . . . . . . . . 8 Corrosion Reactions and Kinetics . . . . . . . . . . . . . 9
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 12
. . . . . . . . . . . . . . . . . . . . . 5
V COMPATIBILITY OF MOLYBDENUM-BASE ALLOY TZM WITH LiF-BeF2-ThF4-UF4 (68-20-11.7-0.3 mole %) at 1100" C
J. W . Koger and A. P. Litman
ABSTRACT
The TZM al loy (Mo-O.5% Ti-0.08% Zr-O.02$ C ) showed a very small amount of a t t ack by t h e fused f luor ide sal t (LiF-BeF2-ThF4-UF4, 68-20-11.7-0.3 mole %) at 1100" C for 1011 hr . Corrosion manifested i t s e l f as leaching of t i t an ium and possibly zirconium from t h e a l loy . The TZM a l l o y exposed t o t h e salt p a r t i a l l y r ec rys t a l l i zed , while t h a t exposed t o t h e vapor did not. w a s a t t r i b u t e d t o the removal of t i t an ium and zirconium. On t h e basis of t h i s s ing le t e s t t h e magnitude and mecha- nism of corrosion ind ica te no ser ious problems f o r long- term use of TZM i n t h e vacuum d i s t i l l a t i o n processing scheme f o r t h e Molten Sa l t Breeder Reactor. However, t h e s t rength propert ies of t h e TZM a l l o y would approach those of unalloyed molybdenum as salt exposure time increased; t h i s i s not considered a problem now.
This r ec rys t a l l i za t ion
INTRODUCTION
The current success of t h e Molten S a l t Reactor Experiment a t ORNL
has st imulated work on a thermal Molten S a l t Breeder Reactor (MSBR).'
One of t h e requirements for a successful MSBR s y s t e m w i l l be t h e con-
tinuous reconditioning of t h e fuel salt t o remove unwanted f i s s i o n prod-
uc ts .
i s vacuum d i s t i l l a t i o n . * and t h e remaining sal t would be d i s t i l l e d a t 1000°C and 2 t o r r .
d i luents of t he f u e l sa l t , l i th ium and beryll ium f luor ides , would d i s t i l
r ead i ly and leave behind the ra re-ear th and a lka l ine-ear th f i s s i o n
products.
and with some radioact ive salt from t h e E R E .
A p o s s i b i l i t y under study f o r one s t e p of t h e salt reprocessing
Uranium would be s t r ipped from t h e f u e l sa l t ,
The
This process has been demonstrated i n laboratory experiments
'M. W. Rosenthal -- et al., MSR Program Semiann. Progr. Rept. Aug. 31,
2J. R. Hightower and L. E. McNeese, MSR Program Semiann. Frogr. Rept.
- 1968, ORNL-4344, pp. 53-108.
Aug. 31, 1968, ORNL-4344, pp. 306-308.
2
The s t rength and corrosion res i s tance required of a container
mater ia l fo r t h e high-temperature vacuum d i s t i l l a t i o n s t e p eliminate
most conventional a l loys from consideration. Our preliminary survey
disclosed t h a t ce r t a in re f rac tory a l loys , p a r t i c u l a r l y molybdenum-base
mater ia ls , may be su i t ab le fo r t h i s spec ia l service. The a l l o y TZM (Mo-O.5% Ti4.08’$ Zl-o .O2$ C ) w a s se lec ted f o r an i n i t i a l experiment
because it is s t ronger and usua l ly m r e fabr icable than pure molybdenum.
Accordingly, t h e experiment reported here provides a preliminary t e s t of
t h e compatibi l i ty of TZM a l l o y with a t y p i c a l f e r t i l e - f i s s i l e salt
(LiF-BeF2-ThF4-UF4, 68-20-11.7-0.3 mole $) at 1100°C.
st rong candidate f o r t h e s ing le- f lu id MSBR now being designed.
were spec i f i ca l ly conducted t o determine t h e s t rength proper t ies of TZM
a l loy , but conditions caused by t h e exposure t o t h e sa l t t h a t could
a f f ec t t he s t rength were noted.
This salt i s a
No t e s t s
EXPERIMENTAL PROCEDURE
The experimental system used f o r t h i s study consis ted of a simple
capsule fabr ica ted of cold-worked TZM a l loy , containing specimens of
t h e same a l loy , and shown i n Fig. 1. Note t h a t t h e specimens were
located i n the sal t , at the salt-vapor in te r face , and i n t h e vapor. The
pu r i f i ed sal t (60 g) w a s supplied by t h e Fluoride Processing Group of
t h e Reactor Chemistry Division. Pur i f ica t ion involved sparging with an
HF-Hz mixture at 600°C t o remove oxides and su l f ides and s t r ipp ing with
H 2 at 790°C t o remove meta l l ic impurit ies.
consis ts of introducing t h e f luoride salt i n t o t h e capsule, welding t h e
t e s t capsule, and sea l ing t h e outer Inconel pro tec t ive container, was
ca r r i ed out i n an inert-gas atmosphere charriber containing argon purer
than 99.995%.
The loading operation, which
After being t e s t e d i n t h e pos i t ion shown i n Fig. 1 f o r 1011 h r a t
llOO°C, t h e capsule w a s removed f r o m t h e furnace, inverted t o keep t h e
specimens out of t h e sal t , and quenched i n l i q u i d nitrogen t o r e t a i n
high-temperature corrosion products. Af’ter t e s t , weight changes of t he
specimens were determined, t he salt was analyzed for impuri t ies , and t h e
specimens and capsules were analyzed by x-ray fluorescence and examined
metallographically.
3
O R N L - D W G 69-10034
Fig. 1. Schematic Drawing of Corrosion Test Capsule Used t o Study Compatibility of TZM Alloy with a Fused Fluoride S a l t .
RESULTS AND DISCUSSION
S a l t Analys is
~ 1.625 in 0.88 in.
/0.125- in. WALL INCONEL PROTECTIVE CONTAINER
_, 0.040 -in. WALL T Z M CAPSULE
- -00 .004- in . TANTALUM FOIL L INER
,-ARGON /’
L i F- Be F2 -Th 5 - U F4 SALT (68 - 20 - 11.7 - 0.3 MOLE % )
-TZM SPECIMEN (0.30 in.x 1.0 in. x 0.02 in.)
Concentrations of t h e const i tuents of t h e salt and i t s impuri t ies
before and a f t e r t e s t a r e given i n Table 1. During t h e experiment
t i tanium, zirconium, and chromium concentrations i n t h e sa l t increased
and t h a t of i ron decreased. The t i t an ium and zirconium a r e in t en t iona l
a l loy ing addi t ions, but chromium i s an unwanted impurity.
Weight Changes
The specimens exposed t o t h e sal t showed small (0.5 mg/cm2) weight
gains, and t h e one exposed t o the vapor did not change weight measurably.
Table 1. Chemical Analysis of Fe r t i l e -F i s s i l e S a l t Exposed t o TZM Alloy Capsule f o r 1011 h r at 1100°C (2010°F)
Content, w t $ Constituent Before After Before After
Content, ppm Constituent
Mo < 5 < 10 L i 6.71 7.01 Zr 37 134 Be 2.65 2.55 T i 74 151 Th 43.1 42.6 Fe 80 38 U 1.75 1.93 C r 20 97 F 45.5 45.7 0 58 < 50 H20 40 70
X-Ray Fluorescence and Microprobe Analysis
Table 2 gives t h e concentrations of t h e major elements i n the TZM
Iron a l l o y as determined by x-ray fluorescence before and a f t e r t e s t .
w a s found on the surface and probably caused a major port ion of t h e
weight gains, but no quant i ta t ive value w a s obtained. S igni f icant ly ,
t h e quant i ta t ive analysis shows a decrease i n t i t an ium concentration,
no s ign i f i can t change i n zirconium concentration, and a corresponding
increase i n t h e concentration of molybdenum a f t e r exposure t o t h e salt .
Care must be taken i n in te rpre t ing these r e s u l t s , s ince the s e n s i t i v i t y
of t h e fluorescence analysis i s questionable a t these low concentrations
and i ron w a s deposited over t h e surface. The e lec t ron microprobe
analysis showed 0.3% T i on t h e surface and 0.5$ T i i n t h e matrix.
zirconium content w a s about ‘2.1% i n a l l portions of t h e specimen.
changes at t h e l e v e l of O.l$ a re beyond the l i m i t of detect ion of t h e
instrument.
concentration of ce r t a in a l loy ing elements i n t h e sal t and a r e i n accord
with t h e proposed corrosion mechanism(s). (See Corrosion Reactions and
Kinetics. )
The
Any
Hawever, these r e s u l t s agree reasonably with t h e increase i n
Microstructural Changes
Figure 2(a) shows t h e t y p i c a l cold-worked s t ruc tu re of t h e specimens
and capsule before t e s t . This f igure i s a l s o t y p i c a l of t h e specimen Y
5
Table 2. Concentration of Alloying Elements i n TZM Alloy Specimen Before and After Exposure t o a Fe r t i l e -F i s s i l e S a l t a t 1100°C
f o r 1011 hr , as Determined by X-Ray Fluorescence Analysis"
Sample Analyzed Content. w t % Mo Z r T i
Untested a l l o y
Exposed specimens i n vapor a t i n t e r f ace i n salt
99.4 0.08 0.5
99.8 0.08 0.1 99.87 0.09 0.04 99.90 0.0% 0.013
a The analysis disclosed subs t an t i a l i ron on t h e a l l o y surface a f t e r t e s t , but i ron w a s not considered i n determining t h e quanti- t i e s above.
exposed t o t h e vapor, where no microstructural change occurred. An
unetched specimen, Fig. 2 (b) , exposed t o t h e sal t shows no a t t a c k a t t h e
surface. The same specimen etched, Fig. 2 ( c ) , shows r ec rys t a l l i za t ion
for a maximum depth of about 0.004 in . Examination of t h i s specimen at
a lower magnification, Fig. 2 (d ) , shows t h a t both surfaces r ec rys t a l l i zed
as t h e r e s u l t of t e s t . The inside capsule w a l l a l so r ec rys t a l l i zed i n
t h e same manner.
Recrss t a l l iza t ion
In view of t h e microstructural and chemical changes induced i n t h e
TZM a l l o y by t h i s t e s t , we compared reported r ec rys t a l l i za t ion tempera-
t u r e s fo r molybdenum and TZM a l l o y (Table 3) .
above and from general metal lurgical considerations t h a t an increase i n
annealing tlme from 1 h r t o severa l thousand hours should lower t h e
r ec rys t a l l i za t ion temperature of TZM a l l o y only 100 t o 200°C.
the presence of as l i t t l e as 0.01% of a foreign element i n s o l i d solut ion
can r a i s e t h e r ec rys t a l l i za t ion temperature as much as severa l hundred
degrees. Conversely, t he removal of a l loying const i tuents would f r e e
It i s c l ea r from t h e
Moreover
3R. E. Reed-Hill, Physical Metallurgy Principles , V a n Nostrand, Princeton, N. J . , 1964, p. 198.
6
Fig. 2. TZM Alloy Exposed t o Ferti le-Fissile Salt , LiF-BeF2-ThF4-UF4 (68-20-11.7-0.3 mole $) for 1011 hr at l lOO°C. (a) Typical cold-worked structure of capsule and specimens before t e s t ; a lso the structure of the specimen exposed t o the vapor during t e s t . 50Ox. Etchant : H20, H202, H2S04* (b) &-polished capsule and specimen exposed t o salt.
and specimen exposed t o salt. 50Ox. Etchant: H20, H202, Specimen exposed t o salt. 1OOx. Etchant : H20, H202, H2SO4.
500x.
7
Table 3. Recrystal l izat ion Behavior of Wrought, Stress- Relieved, Unalloyed Molybdenum and TZM Alloy
. Temperature Time Percent
Reference ( " C ) (hr ) Recrys t a l l i z a t ion
Unalloyed Mo 1130 1 100 a
TZM 560 4400 0 b
TZM 1100 1 0 a
TZM 1160 4400 85 b
TZM 1250 4400 100 b
TZM 1390 1 100 a
%. A. Wilcox, p. 26 i n Refractory Metal Alloys, Metallurgy and Technology, ed. by I. Machlin, R. T. Begley, and E. D. Weisert, Plenum Press; New York, 1968.
bD. H. Jans en, Fue Is and Materials Development Program Quart. Progr. Rept. Sept. 30, 1968, ORNL-4350, pp. 107-111, and pr iva te communi ca t ion.
t h e grain boundaries and allow them t o move t o form new gra ins .
t he enhanced r ec rys t a l l i za t ion (lower r ec rys t a l l i za t ion temperature) i n
t h e samples and capsule of t h i s experiment i s due pr imari ly t o t h e
removal of t h e t i t an ium and possibly zirconium f r o m t h e molybdenum
matrix. This i s fur ther subs tan t ia ted by t h e lack of r ec rys t a l l i za t ion
i n t h e samples exposed t o t h e vapor, where t h e composition changed much
l e s s .
Thus,
The addi t ion of carbon and one or more group IV-A elements t o
molybdenum grea t ly increases t h e r e c r y s t a l l i z a t i o n temperature.
carbon removal from the a l l o y should likewise change r ec rys t a l l i za t ion
behavior. However, carbon analyses show no difference (about 0.035% C
i n each) between exposed and unexposed TZM samples, s o t h i s e f f ec t i s
very small or absent. Although carbon mass t ranspor t is comon i n
l i q u i d metal systems, espec ia l ly a l k a l i metals, it i s not considered a
problem i n fused f luor ide systems.
Thus,
W 'W. H. Chang, A Study of t h e Influence of Heat Treatment on Micro-
s t ruc tu re and Properties of Refractory Alloys, ASD-TDR-62-211 (Apri l 1962).
8
Strength
The molybdenum-base TZM a l l o y i s about t he bes t documented refrac-
t o r y a l l o y i n which base metal s t rength i s improved by p rec ip i t a t ion
hardening.
of t i tanium and zirconium as wel l as by cold working, and i t s ul t imate
t e n s i l e s t rength i s double or t r i p l e t h a t of unalloyed molybdenum. The
100-hr rupture s t rength of TZM at 1100°C i s a l s o much grea te r than t h a t
of molybdenum.5
commercial a l loys and many ref rac tory a l loys , it i s usua l ly much eas i e r
t o work than unalloyed molybdenum. Thus, as an engineering mater ia l TZM
has many advantages over molybdenum.
This a l l o y i s strengthened by t h e formation of f i n e carbides
Although TZM i s much m r e d i f f i c u l t t o f ab r i ca t e than
Comparing t h e s t rength and d u c t i l i t y o f wrought, s t ress - re l ieved ,
and r ec rys t a l l i zed TZM, Wilcox -- e t a L 6 noted a s ign i f i can t increase i n
y i e ld and ul t imate s t rengths due t o working a t t e s t temperatures of 1200
t o 1300°C.
the re w a s r e l a t i v e l y l i t t l e difference i n t h e mater ia ls . However, at
l l O O ° C , t he temperature of our capsule t e s t , Wilcox's r ec rys t a l l i zed
a l l o y had much lower s t rength than t h e wrought a l loy .
a s t ress - re l ieved TZM a l l o y f o r conditions given i n t h i s experiment
should a l s o be considered.
A t 1550°C a f t e r r ec rys t a l l i za t ion of t h e wrought sample
Thus, t h e use of
Although TZM would general ly be favored over molybdenum f o r t h e
previous reasons, through t h e loss of i t s al loying elements ( t i tanium
and zirconium) during exposure t o t h e fused f luor ide salt t h e composi-
t i o n and the s t rength propert ies of t he cold-worked TZM approach those
of unalloyed r ec rys t a l l i zed molybdenum. Although unalloyed molybdenum
or r ec rys t a l l i zed TZM i s weaker than t h e i n i t i a l cold-worked mater ia l ,
t h e s t rength of t h e exposed mater ia l would probably be ample f o r t h e
loads proposed i n t h e lvlSBR vacuum d i s t i l l a t i o n system.
t h e depleted TZM i s used, it should be t e s t e d t o more ca re fu l ly define
However, before
5T. E. Tietz and J. W. Wilson, Behavior and Propert ies of Refractory Metals, Stanford University Press, Cal i fornia , 1965, pp. 156-205.
6B. A. Wilcox, A. Gi lber t , and B. C. Allen, Intermediate Temperature Duc t i l i t y and Strength of Tungsten and Molybdenum TZM, AFMETR-66-89 (Apri l 1966).
9
t h e s t rength propert ies of t h e r ec rys t a l l i zed material .
t rade-off with these mechanical property changes is , of course, t h a t
pure molybdenum i s more r e s i s t a n t than T Z M t o t he f luor ide salts of
i n t e r e s t t o t h e MSRP.
system with TZM while others accrue from the "conversion" of TZM t o
molybdenum during t h e f luor ide salt exposure.
An advantageous
Thus, severa l benef i t s come from fabr ica t ing the
Corrosion Reactions and Kinetics
In f luor ide salt systems one of the major corrosion react ions i s
t h e oxidation of one of t he const i tuents of the container a l l o y by t h e
reduction of a l e s s s t ab le impurity metal f luor ide i n i t i a l l y i n t h e salt ,?
f o r example
The reduced metal subs t i t u t e s f o r t h e oxidized metal on t h e container
mater ia l .
involving t h e strong reducing agents t i tanium and zirconium:
This type of react ion apparently occurred i n our experiment
Z r + 2FeF2 --3 ZrFL + 2Fe . ( 3 )
The reported* free energy changes for the react ions shown by
(1) , (2), and (3) a re s t rongly negative, and Eqs . Eqs.
(3) seem t o be indicated by t h e r e s u l t s reported above.
t h e i ron metal t h a t formed i n these react ions deposited i n t h i n layers on
t h e container and specimens.
( 2 ) and possibly
A s noted e a r l i e r ,
7W. R. Grimes, G. M. Watson, J. H. DeVan, and R. B. Evans, "Radio-Tracer Techniques i n t he Study of Corrosion by Molten Fluorides ," pp. 559-574 i n Conference on t h e Use-of Radioisotopes i n t h e Physical Sciences and Industry, September 6-17, 1960, Proceedings, Vol. 111, In terna t iona l Atomic Energy Agency, Vienna, 1962.
'A. Glassner, The Thermochemical Properties of t h e Oxides, Fluorides, and Chlorides t o 2500"K, ARE5750 (1957).
10
Alternat ively the f u e l salt corrosion react ions i n which UF4 i s
reduced t o UF3 a l s o may have occurred t o remove t i t an ium and zirconium
from t h e a l loy :
However, no data w
a r e avai lable .
t h which t o determine t h e extent of L e s e react ions
Assuming t h a t t h e removal of t h e elements from t h e TZM was control led
by so l id - s t a t e diffusion, one can ca lcu la te f r o m t h e increase of t h e
t i tanium and zirconium i n the salt t h e apparent d i f fus ion coef f ic ien ts of
t i t an ium and zirconium i n t h e TZM a l loy . Fromthese one can estimate the
amount of those mater ia ls that would be removed at d i f f e ren t times and
temperatures.
analysis i s correct and t h a t t h e instruments involved i n t h e fluorescence
and microprobe analyses a r e not s u f f i c i e n t l y sens i t i ve t o measure t h e
mvement of t h e zirconium.
In regard t o t h e zirconium removal, we f e e l t h a t t h e salt
The t o t a l amount of mater ia l , Mt, t h a t d i f fuses from t h e a l l o y held
under isothermal conditions w i t h a zero surface concentration i s given
by
where
C O = t h e concentration of t h e d i f fus ing element,
D = t h e d i f fus ion coef f ic ien t , and
t = t h e time.
We calculated D = 1.2 x
2 . 9 x
f o r chromium removal, as i t s concentration f luc tua ted from sample t o
sample and we could not assume that it w a s d i s t r ibu ted homogeneously
through the a l loy .
cm2/sec f o r t i t an ium i n TZM and
cm2/sec f o r zirconium i n TZM at 1100°C. We d i d not ca lcu la te
9J. Crank, The Mathematics of Diff is ion, Clarendon Press, Oxford, England, 1956, p. 11.
v
J
W
11
The expression
t - X2/D , (7)
where X i s t h e dis tance of composition change, i s very usefu l i n calcu-
l a t i n g approximately whether t he composition has changed appreciably by
d i f fus ion under a given s e t of circumstances.
l a t e t h e time required f o r appreciable removal - concentration between
the i n i t i a l and ul t imate concentrations - of t h e d i f fus ing element a t a
ce r t a in dis tance from t h e surface.
For example, we can calcu-
From the calculated diffusion coef f ic ien ts and t h e experimental
time of 1011 h r , we f i n d t h e depths of removal of t i tanium and zirconium,
respect ively, a r e 0.0008 and 0.0040 in . Since the microstructures shuw
r e c r y s t a l l i z a t i o n f o r a dis tance of about 0.004 i n . , we may assume t h a t
t h e calculated d i f fus ion coef f ic ien t f o r zirconium may be more accurate
than t h a t f o r t i t an ium - t h a t i s , t h e salt analysis for t h e t i tanium may
be somewhat i n e r ro r . Extrapolation of t h e calculated values shows t h a t
it would require 4000 hr t o r e c r y s t a l l i z e an addi t iona l 0.004 in. of
material . This i l l u s t r a t e s t h e decrease of t h e corrosion r a t e with time
and t h e general usefulness of TZM a l l o y f o r MSR reprocessing service.
C ONC LUS IONS
1. This t e s t shawed negl ig ib le corrosion of t h e TZM a l l o y by t h e
fused fluoride sal t (LiF-BeFz-ThF4-UF4, 68-20-11.7-0.3 mole ’$) at 1100°C
f o r over 1000 hr .
2. Corrosion manifested i tself as leaching of t i t an ium and possibly
zirconium from the a l loy . FeF2 i n i t i a l l y present i n t h e salt oxidized
t h e al loying elements t o f luorides dissolved i n t h e salt bath. The i ron
metal r e su l t i ng from t h e react ion deposited i n t h i n layers on t h e speci-
mens and container.
2.9 x
We found t h a t DTi and DZr were 1 . 2 x cm2/sec, respect ively, a t 1100°C i n t h e a l loy .
The TZM a l l o y exposed t o t h e salt p a r t i a l l y r ec rys t a l l i zed ,
and
3.
while t h e TZM a l l o y simultaneously exposed t o t h e vapor did not.
r ec rys t a l l i za t ion w a s a t t r i b u t e d t o t h e removal of t i t an ium and zirconium.
This
12
4. On t h e bas is of t h i s s ing le t e s t , t h e magnitude and mechanism
of corrosion indicate no ser ious problems for long-term use of TZM a l l o y
i n t h e IGBR vacuum d i s t i l l a t i o n processing scheme.
propert ies of t h e TZM a l l o y would approach those of unalloyed molybdenum
as salt exposure time increased.
However, t h e s t rength
ACKNOWLFEMENTS
It i s our pleasure t o acknowledge t h e ass i s tance of F. D. Harvey,
E. J. Lawrence, and J. B. Ph i l l i p s with these experiments. We a r e a l s o
indebted t o J. R. DiStefano, W. 0. H a r m s , and H. E. McCoy, Jr., f o r t h e i r
constructive review of t he manuscript.
Thanks a l s o go t o H. R. Gaddis of the Metallography Group,
H a r r i s Dunn and other members of t h e Analytical Chemistry Division, t h e
Graphic Arts Department, and the Metals and Ceramics Division Reports
Office f o r invaluable ass is tance.
13
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