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https://ntrs.nasa.gov/search.jsp?R=19660010241 2018-09-30T11:27:44+00:00Z

t' BNWL-196

UC-25, Metals, Ceramics, and Materials

FIRST TID-4500 UNRESTRICTED ,

@ISTRIBUTION MADE EDITION

A STUDY OF TUNGSTEN-TECHNETIUM ALLOYS OCTOBER 1, 1965JANUARY 1, 1966

The Staff of Metallurgy Development Section Reactor and Materials Technology Department

Sponsored by the National Aeronautics and Space Administration Project Management at Washington, D.C.

J. W. Maltz, Office of Advanced Research and Technology

* January 3, 1966

PACIFIC NORTHWEST LABORATORY RICHLAND, WASHINGTON

I . ii 1

P r e v i o u s Q u a r t e r l y P r o g r e s s R e p o r t s i n t h i s s e r i e s :

HW-83550

HW-84309

HW-84550

B N W L - 1 4 1 B N W L - 1 4 2

BNWL-162

A p r i l 1 , 1 9 6 4 - J u l y 1, 1964

J u l y 1, 1 9 6 4 - O c t o b e r 1 , 1964

O c t o b e r 1, 1 9 6 4 - J a n u a r y 1 , 1965 J a n u a r y 1, 1 9 6 5 - A p r i l 1 , 1965 A p r i l 1, 1 9 6 5 - J u l y 1, 1 9 6 5

J u l y 1, 1 9 6 5 - O c t o b e r 1, 1965

.

P r i n t e d i n USA. P r i c e $ 1 . 0 0 . A v a i l a b l e f r o m t h e C l e a r i n g h o u s e f o r F e d e r a l S c i e n x i f i c a n d T e c h n i c a l I n f o r m a t i o n ,

N a t i o n a l B u r e a u o f S t a n d a r d s , U.S. D e p a r t m e n t o f Commerce,

S p r i n g f i e l d , V i r g i n i a

1 BNWL-196

QUARTERLY PROGRESS REPORT A STUDY OF TUNGSTEN-TECHNETIUM ALLOYS

OCTOBER 1, 1 9 6 5 - J A N U A R Y 1, 1966

I N T R O D U C T I O N

T e c h n e t i u m i s a s i s t e r e l e m e n t t o rhen ium a n d h a s many

p r o p e r t i e s t h a t a r e s i m i l a r t o rhen ium. I t i s p r e d i c t e d t h a t

t e c h n e t i u m w i l l have a b o u t t h e same e f f e c t s on t u n g s t e n as r h e - nium i n r e g a r d t o i n c r e a s e i n w o r k a b i l i t y , l o w e r e d d u c t i l e - t o - b r i t t l e t r a n s i t i o n t e m p e r a t u r e , a n d improved d u c t i l i t y .

The o b j e c t i v e s o f t h e c u r r e n t work a r e t o r e c o v e r t e c h n e - t i u m f rom f i s s i o n p r o d u c t wastes a t H a n f o r d a n d r e d u c e t o

p u r i f i e d m e t a l ; p r e p a r e W-TC a l l o y s c o n t a i n i n g up t o 50 a t . % Tc; f a b r i c a t e t h e a l l o y i n g o t s t o s h e e t s t o c k , a s s e s s i n g t h e e f f e c t o f t e c h n e t i u m on w o r k a b i l i t y ; and p e r f o r m m e t a l l u r g i c a l and m e c h a n i c a l p r o p e r t y e v a l u a t i o n o f t h e f a b r i c a t e d a l l o y s .

P r e v i o u s r e p o r t s have d e s c r i b e d t h e s e p a r a t i o n and p u r i f i -

c a t i o n o f 8 0 0 g o f t e c h n e t i u m metal powder , m e l t i n g o f t e c h n e - t i u m a n d W-Tc a l l o y s , a n d some p r o p e r t i e s o f t h e a r c c a s t a l l o y s .

CURRENT PROGRESS

D u r i n g t h e p a s t qi iar tcr t h e remelting o f t h e a l l o y s by

e l e c t r o n beam m e l t i n g was c o m p l e t e d , r a d i o g r a p h y and d e n s i t y

m e a s u r e m e n t s made, and b u t t o n s were s e a l e d i n molybdenum c a n s by e l e c t r o n beam w e l d i n g i n p r e p a r a t i o n f o r f a b r i c a t i o n .

I t was n e c e s s a r y t o b r e a k up t h e a r c c a s t b u t t o n s p r i o r t o

e l e c t r o n beam m e l t i n g . A l l o y s up t o 3 0 a t . % Tc and t h e 6 0 a t . %

Tc a l l o y were b r o k e n w i t h hammer b l o w s . The f r a c t u r e s u r f a c e s

shown i n F i g u r e 1 i n d i c a t e t h e marked e f f e c t o f t e c h n e t i u m

a d d i t i o n s on t h e c a s t g r a i n s t r u c t u r e . A l l o y s o f h i g h e r t e c h n e -

t i u m c o n t e n t c o u l d n o t be b r o k e n i n t h i s manner and r e q u i r e d

r e p e a t e d b lows of a 6000 l b p n e u m a t i c hammer t o f r a c t u r e . The

2 BNWL-196

50 at.% Tc alloy was particularly difficult to break and was cold forged as indicated in Figure 2. This alloy is approximately the limit of solid solubility in the as-cast condition.

The melting was performed in a 10 kW electron beam evaporator unit in a four-compartment water-cooled copper crucible at a pres- sure of approximately 5 x lom7 ‘Torr. Alloys up to 30 at.% TC were difficult to melt and solidify into a well formed button. Alloys of higher technetium content melted much more smoothly, probably due to the lowered melting point. Losses ranging from zero to approximately 8 g out of about 30 g occurred during melting due to evaporation and spatter. Radiographs of the remelted buttons indicated that essentially all of the porosity observed in the arc melted material was eliminated.

The alloys were all given a homogenization anneal prior to canning for fabrication to help relieve the coring observed in the structure of the arc cast material. This treatment consisted of the following cycle in hydrogen atmosphere:

Heating 5 hr to 1200 OC 16 hr at 1200 O C

2 hr to 1700 O C

70 hr at 1 7 0 0 OC Cooling 3 hr to 800 OC

%5 hr to room temperature The material was in contact with tungsten throughout this cycle. No contamination of the furnace interior or exit gas was observed and the alloys were removed with clean, lustrous surfaces.

The densities were determined by weighing in air and CC14. These values are shown in Table I and Figure 3 .

I . I '

i ?' 3 BNWL - 19 6

TABLE I

Alloy No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 18

DENSITY OF W-TC ALLOYS

Intended Composition Density at.% Tc g/cm3

2.5 3.5 5.0 5.0 10.0 10.0 20.0 20.0 30.0 30.0 40.0 40.0 50.0 5 0 . 0

6 0 . 0

0

19.306 19.301 19.215 19.327 18.976 19.316 18.627 19.217 18.171 18.511 16.518 16.256 15.496 15.479 14.628 19.330

The only explanation for deviation from theoretical density is the selective evaporarion u f t e c h n e t i u m d u r i n g m e l t i n g . The losses were not as significant at the higher technetium levels. This is felt to be due to the lowered melting points and accom- panying lower vapor pressure of technetium. A preferred sequence of alloy preparation would be initial electron beam melting of the individual components for gas removal, followed by inert gas arc melting to form the alloys. A further check on composition will be made after fabrication by measuring Tc activity and lattice parameters of the alloys.

99

4 B NW I, - 1 9 6 I

The a l l o y b u t t o n s were s e a l e d i n molybdenum c a n s 1 1 / 2 i n .

O D x 3 / 1 6 i n . wal l t h i c k n e s s and 3 / 4 i n . h e i g h t by e l e c t r o n beam w e l d i n g e n d c a p s i n p l a c e . The c a n s t o c k w i l l s e r v e as p r o t e c t i v e

c l a d d i n g d u r i n g h e a t i n g and f a b r i c a t i o n .

A s e c t i o n o f e l e c t r o n beam m e l t e d p u r e t e c h n e t i u m , p r e v i o u s l y

h o t f o r g e d t o 0 , 0 4 7 i n . t h i c k n e s s , was h o t r o l l e d t o 0 . 0 1 5 i n . t h i c k n e s s a t a p p r o x i m a t e l y 1 5 0 0 O C i n e l e v e n r o l l p a s s e s . The metal was c l a d w i t h 0 . 0 3 0 i n . t h i c k s h e e t s o f molybdenum, h e a t e d i n a h y d r o g e n f u r n a c e a d j a c e n t t o t h e r o l l s o f t h e m i l l , a n d c o o l e d i n a h y d r o g e n a t m o s p h e r e chamber on t h e e x i t s i d e o f t h e r o l l s .

The molybdenum was c h e m i c a l l y s t r i p p e d , r e v e a l i n g a r o u g h i r r e g u - l a r s u r f a c e on t h e t e c h n e t i u m ( F i g u r e 5 ) . A s e c t i o n was s h e a r e d

w i t h o u t p r o d u c i n g c r a c k s . E x a m i n a t i o n o f t h e m i c r o s t r u c t u r e

( F i g u r e 5 ) r e v e a l e d c o m p l e t e r e c r y s t a l l i z a t i o n w i t h a g r a i n s i z e o f a b o u t 0 . 1 5 0 mm a v e r a g e g r a i n d i a m e t e r .

5

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Theoretical -

-

-

I I I I I 1 0 1 0 20 30 40 50 60

at.% Technetium

FIGURE 3 D e n s i t y o f E l e c t r o n Beam M e l t e d W-Tc A l l o y s

8 BNWL - 1 9 6

FIGURE 4 Assembly of Alloy Buttons in Molybdenum Containers

by Electron Beam Welding

9 BNWL-196

a a, 4 u 4 0 a0

W O 4 W W

1 0

. BNWL - 1 9 6

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