On the characteristics of amorphous UFe alloys formed by liquid quenching vs. irradiation techniques

Scripta

M~TALLURGICA

Vol.

14, pp.

1061-1065,

1980

P e r g a m o n Press Ltd. All rights r e s e r v e d

Printed in the U.S.A.

ON THE C H A R A C T E R I S T I C S BY LIQUID Q U E N C H I N G

OF A M O R P H O U S U-Fe ALLOYS F O R M E D VS. I R R A D I A T I O N T E C H N I Q U E S *

R. O. Elliott and D. A. Koss** U n i v e r s i t y of C a l i f o r n i a Los Alamos S c i e n t i f i c L a b o r a t o r y Los Alamos, New Mexico 875~4 and

B. C. @ l e s s e n * * * Department of C h e m i s t r y N o r t h e a s t e r n University Boston, M a s s a c h u s e t t s 02115 (Received June 5, 1980) (Revised August 5, 1980)

Introduction M e t a l l i c glasses are g e n e r a l l y formed by p r o c e d u r e s i n v o l v i n g either liquid q u e n c h i n g or atomic deposition. However, it is also known that n e u t r e n irr a d i a t i o n of certain c r y s t a l l i n e alloys will result in a t r a n s f o r m a t i o n tc the a m o r p h o u s state. The First such report by Bloch was based on the i n t e r m e t a l l i c com p o u n d U6Fe w h i c h became a m o r p h o u s a f t e r an i n t e g r a t e d exposure of 2.3 x 1017 f i s s i o n s / c m 3 (I). In a separate study, Elliott and @lessen have shown that U-Fe alloys can also be melt q u e n c h e d to form glasses (2). To our knowledge, there have been only two other o b s e r v a t i o n s of the formation of amorphous metals by n e u t r o n i r r a d i a t i o n t e c h n i q u e s (3,4), and there is no study which relates an a m o r p h o u s metal p r o d u c e d by i r r a d i a t i o n to that formed by liquid quenching. The purpose of this c o m m u n i c a t i o n is to report d i f f e r e n c e s in structural and thermal c h a r a c t e r i s t i c s of a m o r p h o u s metals based on U6Fe but which are p r o d u c e d by either i r r a d i a t i o n or liquid q u e n c h i n g techniques. For reasons d i s c u s s e d below, only l i q u i d - q u e n c h e d a m o r p h o u s metals are referred to ~s glasses in the following. Experimental The U-14.3 at.% Fe m a s t e r alloy was p r e p a r e d by a r c - m e l t i n g components 99.9% pure. The u r a n i u m used in this study was 93% e n r i c h e d U 2~S The liquid quench technique involves a h a m m e r - a n d - a n v i l , a r c - f u r n a c e q u e n c h i n g unit (5) w h i c h is capable of q u e n c h i n g rates in the vicinity of 105 - 106 K/sec. I r r a d i a t i o n was p e r f o r m e d in the thermal column at the Omega West Reactor in Los Alamos at flux rates of 3.7 and 1.0 x i0 ~I n/cm2/sec to an integrated dose of 4.4 x i017 f i s s i o n s / c m 3. In all cases, the specimens c o n s i s t e d of foils •03 mm thick x 3 mm d i a m e t e r with 2-4 Foils being tested at one time. The foils were e x a m i n e d by x-ray d i f f r a c t i o n (XRD) with Cu K~ r a d i a t i o n and by ~i?ferential s c a n n i n g c a l o r i m e t r y (DSC) in a P e r k i n - E l m e r DSC-2 calorimeter.

*Work p e r f o r m e d

under

auspices

of the

U. S. Department

of Enersy

**On sabbatical leave from M i c h i g a n T e c h n o l o g i c a l University; present address is: Dept. of M e t a l l u r g i c a l E n g i n e e r i n g , M i c h i g a n T e c h n o l o g i c a l University, Houghton, MI 49931 ***Research Office

supported

by the

Office

of Naval

Research

1061 0036-9748/80/101061-0552.00/0

and the Army

Research

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A M O R P H O U S U-Fe ALLOYS

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Results Typical XRD p a t t e r n s for a m o r p h o u s U-Fe alloys in terms of i n t e r f e r e n c e functions I(K) [K = 4w sine/k] are shown in Fig. i. All of the samples exhibit three rather broad, a s y m m e t r i c peaks in the range of K values investigated, and all of the samples e x h i b i t e d peaks at roughly the same value of K, as shown in Table I. However, there are significant d i f f e r e n c e s in the det a i l e d nature of these peaks. The liquid q u e n c h e d glass c o n s i s t e n t l y exhibits a m u c h more intense first peak w h i c h has a s i g n i f i c a n t l y smaller h a l f - w l d t h than that of the a m o r p h o u s alloy p r o d u c e d by i r r a d i a t i o n (see Table I). A q u e n c h e d - a n d - l r r a d i a t e d glass was also i n v e s t i g a t e d ; it yields d i f f r a c t i o n patterns w i t h peaks of i n t e n s i t y and w i d t h w h i c h are i n t e r m e d i a t e b e t w e e n those of the liquid q u e n c h e d glass and the i r r a d i a t e d amorphous alloys. The irradiated a m o r p h o u s alloys show more d i f f r a c t e d intensity b e t w e e n the first and second peaks as well as b e t w e e n the second and third peaks than does the liquid q u e n c h e d glass as can be seen by careful e x a m i n a t i o n of Fig. I. Thus the interference functions in Fig. 1 indicate that while there is a great deal of similarity in the structure of these a m o r p h o u s alloys, there are also significant d i f f e r e n c e s in certain aspects of the structure of the U-Fe glass formed by liquid q u e n c h i n g w h e n c o m p a r e d to an a m o r p h o u s alloy formed by irradiation. That a d i f f e r e n c e in structure b e t w e e n i r r a d i a t e d and liquid q u e n c h e d a m o r p h o u s metals exists is s u b s t a n t i a t e d by the d i f f e r e n t i a l s c a n n i n g calorimetry (DSC) data o b t a i n e d upon h e a t i n g the glasses. Such data is shown in Fig. 2 and indicates several features. C r y s t a l l i z a t i o n of the liquid q u e n c h e d U-Fe glass i n v o l v e d two e x o t h e r m i c effects and thus occurs over a range of temperatures. In contrast, the c r y s t a l l i z a t i o n process of the irradiated and the q u e n c h e d / I r r a d l a t e d a m o r p h o u s glasses is c h a r a c t e r i z e d by a single, sharp exot h e r m o c c u r r i n g at a t e m p e r a t u r e about 15K h i g h e r than the first e x o t h e r m of the n o n - l r r a d l a t e d glasses. The other distinct d i f f e r e n c e a m o n g the glasses involves the total heat of c r y s t a l l i z a t i o n . For most glasses, this is about 40% of the heat of fusion of the alloy, which would c o r r e s p o n d to % 18.8 J / g m for the c o m p o u n d U6Fe.* This value is comparable to 19.7 J/gm observed for the liquid q u e n c h e d glass in Fig. 2 but is d i s t i n c t l y lower than the 31.8 J/gm o b s e r v e d for the a m o r p h o u s alloy formed by irradiation. Many tests have reproduced the e n h a n c e m e n t of the heat of c r y s t a l l i z a t i o n of i r r a d i a t e d U-14.3 at.% Fe a m o r p h o u s alloys. T y p i c a l l y the heat r e l e a s e d is in the range of 31.8 to 32.6 J / g m c o m p a r e d to 17.6 to 20.5 J/gm for that of the liquid q u e n c h e d glass of the same alloys. In all cases the c r y s t a l l i z a t i o n process r e s u l t e d in the same XRD p a t t e r n s w h i c h are c h a r a c t e r i s t i c of the U6Fe compound. Discussion A d e t a i l e d a c c o u n t i n g of the structural d i f f e r e n c e s r e s u l t i n g in the b e h a v i o r in Figs. 1 and 2 is b e y o n d the scope of the i n f o r m a t i o n p r e s e n t l y available. However, certain inferences can be made. In the absence of a study of the radial d i s t r i b u t i o n f u n c t i o n of these a m o r p h o u s metals, the i n t e r f e r e n c e functions in Fig. 1 may be used to give an i n d i c a t i o n of their structural characteristics. U s i n g the p o s i t i o n of the first peak KI, the a p p r o x i m a t e mean i n t e r a t o m l c d i s t a n c e s of the first nearest n e i g h b o r shell of atoms d I can be o b t a i n e d by use of the E h r e n f e s t formula (9,10): d I x K 1 = <, where < = 7.90 ± 0.i0 (i0). The values of d I for the different glasses are listed in Table I a l o n g w i t h the atomic d i a m e t e r of u r a n i u m c o r r e c t e d for a c o o r d i n a t i o n n u m b e r of twelve (ii). Table I shows that the values of d I do not d i f f e r greatly among the amorphous alloys and, w i t h i n the u n c e r t a i n t y of the value of K, d I agrees well with the U - U d i s t a n c e s based on the Goldschmldt diameter. The r e l a t i v e positions *The e s t i m a t e d heat of fusion of the c o m p o u n d U6Fe (46.9 J/gm) is based on a w e i g h t e d average of the heats of fusion of pure U (6) and Fe (7) and the e n t r o p y of m i x i n g due to the f o r m a t i o n of the compound (8).

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AMORPHOUS U - F e ALLOYS

i063

of the first and second maxima (K] and K 2) of the interference function are similar to numbers for amorphous ~lloys prepared by several different techniques; K2/K 1 = 1.68 In this study vs. (K2/K])Av ~ = 1.75 for ten different amorphous alloys (see Table 1 of Ref. Ii). These'calculations confirm the conclusion based qualitatively on Fig. 1 that there is much similarity in the structure of these amorphous alloys as well as others based on significantly different alloys and preparation techniques. The differences in the amorphous metal structure brought about by fission fragment bombardment are strongly reflected in the resulting loss of intensity and broadening in the first XRD peak in Fig. 1 (see Table I). Such behavior indicates an increase in structural disorder in the irradiated alloys, which is consistent with the increased energy released on crystallization of the irradiated alloys (Fig. 2). Previous studies have suggested that many amorphous alloys may have very similar structures regardless of preparation (10,1214). In the present study, the very large differences between the amorphisation processes of liquid quenching versus irradiation results in less short range order in the irradlation-produced glasses. Irradiation can cause amorphlsatlon of an alloy by the rapid cooling of the thermal spike induced by atomic collisions with fission fragments and the resulting displacement cascades (4,15). We, therefore, conclude that such a combined thermal/atomlc displacement proce§s results in an amorphous solid with a structure characterized by a reduced degree of short range order in the irradiation produced amorphous alloy. The resulting "loss of local structure" would account for the decrease in intensity and broadening of the diffraction peaks. It would also be consistent wlth the increased and well-deflned exothermic peak in the DSC data if, as appears quite possible, the resulting structure of the irradiated amorphous alloy requires a greater amount of atomic rearrangement upon crystallization to U6Fe, where thls rearrangement proceeds only at a higher temperature than In the irradiated glass, but In a one-step, coordinated manner. It should be noted that this does not imply that the irradiated amorphous alloy is more llke a liquid than the liquid-quenched glass. On the contrary, the irradiated amorphous alloy is quite probably not a glass in the sense of the definition that the internal structure of a glass is closely related to that of a corresponding supercooled liquid which precedes it in its formation; instead, it is a different amorphous solid requiring further structural characterization for a description. Modeling the atomic displacement cascade caused by the neutron irradiation as a thermal spike, Kramer, Johnson, and Cline calculate the "effective quench rate" of the cascade region in a metallic glass irradiated by fast neutrons to be ~ i0 I~ - i0 Is K/sec (15). Although the present experimental conditions differ somewhat, it Is certain that the "effective quench rate" induced by neutron irradiation was much greater than l0 s - 106 K/sec which was used to produce the liquid quenched glass. The differences In short range order which are observed between the irradiated amorphous solid and the llquid quenched glass thus are not surprising; the "structural relaxation" or "atomic regrouping" which takes place In liquid quenched metallic glasses upon aging short times at temperatures somewhat lower than the crystallization or glass transition temperature (16,17) could not occur at the rapid quench rates. The work by Bloch (i), Bethune (3), Lesuer (4) and this study raise the question as to which particular crystalline alloys, especially intermetallics, are susceptible to amorphisatlon by fission fragment irradiation. At this time the evidence is insufficient to classify the intermetallics accordingly; however, it is likely that the Intermetallics which form glasses readily by liquid quenching (18) are also prone to forming amorphous solids by fission fragment bombardment. The present compound U6Fe belongs to a group of actlnlde phases which readily form glasses upon liquid quenching (18); f-electron bonding may be responsible for its ready amorphisation (19). This study also raises the question of irradiation

"damage" to a glassy

1064

AMORPHOUS U-Fe ALLOYS

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alloy. There is some evidence to suggest that structured changes of a m o r p h o u s alloys can occur upon i r r a d i a t i o n (15,20-22) a l t h o u g h the opposite c o n c l u s i o n has also been drawn (4). The results on the U-Fe alloys show that if a fissionable glassy alloy is exposed to irradiation, then there will be identifiable changes in the r e s u l t i n g atomic structures and thermal properties. W h e t h e r such structural d i f f e r e n c e s result in significant changes of other p r o p e r t i e s remains to be demonstrated. Summary A m o r p h o u s alloys based on a U-14.3 at.% Fe alloy have been p r e p a r e d by a liquid q u e n c h i n g and/or i r r a d i a t i o n technique. The r e s u l t i n g a m o r p h o u s alloys, as c h a r a c t e r i z e d by x-ray d i f f r a c t i o n and d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y data, are similar but not identical. When compared to the l i q u i d - q u e n c h e d glass, the i r r a d i a t e d m a t e r i a l shows a less intense, broader first peak in the i n t e r f e r e n c e f u n c t i o n data and a larger, n a r r o w e r e x o t h e r m i c peak upon crystallization. We conclude that the much h i g h e r "effective quench rates" inherent in fission fragment b o m b a r d m e n t can produce an amorphous metal with a structure c h a r a c t e r i z e d by a reduced degree of short range order when compared to a l i q u i d - q u e n c h e d glass. The i r r a d i a t e d a m o r p h o u s alloy is p r o b a b l y not a glass in the sense that the structure of a glass is closely related to that of the s u p e r c o o l e d liquid which p r e c e d e d it in its formation; it is more like a different a m o r p h o u s solid r e q u i r i n g further structural c h a r a c t e r i z a t i o n for a description. These results also indicate that the structure of liquid q u e n c h e d glasses will be a f f e c t e d by subsequent fission fragment irradiation. Acknowledgements The authors would like to thank R. N. R. Mulford, D. E. Peterson, and M. E. B u n k e r for their technical a s s i s t a n c e and s t i m u l a t i n g discussions. One of the authors, D. A. Koss, would like to a c k n o w l e d g e the support of the N a t i o n a l Science F o u n d a t i o n through a Science Faculty P r o f e s s i o n a l Development Grant in support of his s a b b a t i c a l leave activities at Los Alamos Scientific Laboratory. References i. 2. 3. 4. 5. 6. 7. 8. 9. i0. Ii. 12. 13 14 15 16 17 18 19. 20. 21. 22.

J. Bloch, J. Nucl. Mat'l. 6, 203 (1962). B. C. Giessen and R. O. Elliott, in "Rapidly Q u e n c h e d Metals III," Vol. I, p. 406, The Institute of Metals, London (1978). B. Bethune, J. Nucl. Mat'l. 30, 197 (1969). D. Lesuer, Fizika 2 Suppl. 2, 13.1 (1970). M. Fischer, D. E. Polk, and B. C. Giessen in Proc. Conf. Rapid Solidification Processing, Claitor's Publ. Div., Baton Rouge, LA, p. 140 (1978). H. P. Stevens, High Temp. Sci. 6, 156 (1974). L. S. Darken and R. P. Smith, Ind. Eng. Chem. 43, 1815 (1951). O. K u b a s c h e w s k i , E. L. Evans, and C. B. Alcoek, "Metallurgical T h e r m o c h e m istry," p. 212, P e r g a m o n Press, New York (1967). A. K. Sinha and P. Duwez, J. Phys. Chem. Solids 32, 267 (1971). B. C. Giessen and C. N. J. Wagner, in Physics and Chemistry of Liquid Metals, p. 666, Marcel Dekker, New York (1972). W. B. Pearson, "The Crystal C h e m i s t r y and Physics of Metals and Alloys," W i l e y - l n t e r s c i e n c e , New York, NY, p. 151 (1972). C. N. J. Wagner, Vac. Sci. Technol. 6, 650 (1969). G. S Cargill, J. Appl. Phys. 41, 12 (1970). D. G Walker, J. Nucl. Mat'l. 37, 48 (1970). E. A Kramer, W. L. Johnson and C. Cline, Appl. Phys. Lett. 35, 817 (1979). H. S Chen and E. Coleman, Appl. Phys. Lett. 28, 245 (1976). R. L Freed and J. B. V a n d e r Sande, J. Non-Cryst. Solids 27, 9 (1978). B. C Giessen and D. E. Polk, in "Theory of Alloy F o r m a t i o n , " L. H. Bennett, Ed., The Met. Soc. - AIME (1980), in print. R. O. Elliott and B. C. Giessen, to be published. B. T. Chang and J. C. M. Li, Scripta Met. ii, 933 (1977). K. Doi, H. Kayano and T. Masumoto, Appl. Phys. Lett. 31, 421 (1977). ' R. Yamamoto, H. Shibuta and M. Doyama, J. Nucl. Mat'l. 85, 603 (1979)

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A M O R P H O U S U-Fe ALLOYS

'

'

'

'

Ii

6b I /

U-14.3 at°/o Fe

!f

. . . .

I

'

U-14.3 at °/o Fe

/

'

1065

'

'

'

I

'

'--

~IRRADIATED ( 31.8 J/g )

4j

-

LIOUIDQUENCHED 1 °~ t

I ~(IR243 RADI J/g)ATED ~ L I Q U I D QUENCHED

2

o

QUENCHEDI I\

I LIQUID

I 500

o 20

30

40

50

K (nm)-i

OO

70

.

80

Fig. 1. D i f f r a c t i o n patterns [in terms of i n t e r f e r e n c e functions I (K)] of an a m o r p h o u s U-14.3 at.% as formed by liquid quench and/or i r r a d i a t i o n techniques.

550 DEGREES K

600

Fig. 2. Rate of energy release as a f u n c t i o n of t e m p e r a t u r e for U-i4.3 at.% Fe metallic glasses formed by liquid quench and/or i r r a d i a t i o n techniques. Heating rate is 80 K/min.

TABLE

I

Data on Peak P o s i t i o n of I(K) and I n t e r a t o m i e D i s t a n c e on the U-14.3 F e - A m o r p h o u s Alloy

Condition

Peak

height t

Positions of K 1 in nm -I of peak m a x i m a of I(K)

Nearest n e i g h b o r d i s t a n c e * d I in nm

-i Width

(nm)

KI

K2

Goldschmidt Diameter nm for U

K2/K I

Liquid Q uen c h e d

48/I.0

25.1

42.5

1.69

0.315

0.310

Irradiated

26/2.5

25.4

42.7

1.68

0.311

C.310

TPeak height is r e l a t i v e at half height. * Cal c u l a t e d

using

unites

the E h r e n f e s t

as m e a s u r e d

formula;

from

I(K)

see text.

= 0 in Fig.

i; peak w i d t h

is