' I n *

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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,

nor the Commission, nor any person acting on k h a l f of the Commission:

A. Makes any warranty or representation, expressed or implied, with respect to the accuracy,

completeness, or usefulness of the information contained in th is report, or that the use of

any information, apparatus, method, or process disclosed in th is report may not infringe

privately awned rights; or

Assumes any l iabi l i t ies wi th respect to the use of, or for damages resulting from the use of

any information, apparatus, method, or process disclosed in thio report.

As used in the above, "person acting on behalf of the Commission" includes any employee or

contractor of the Commission. or employee of such contractor, to the extent that such employes

or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuont t o h is employment or contract wi th the Commission,

or h is employment wi th such contractor.

6.

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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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