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SLIP SYSTEMS IN UO2+x
R. Keller, T. Mitchell, A. Heuer
To cite this version:
R. Keller, T. Mitchell, A. Heuer. SLIP SYSTEMS IN UO2+x. Journal de Physique Colloques, 1981,
42 (C3), pp.C3-73-C3-78. �10.1051/jphyscol:1981308�. �jpa-00220699�
JOURNAL DE PHYSIQUE
Colloque C3, supplément au n°6, Tome 42, juin 1981 page C3-73
SLIP SYSTEMS IN U 02 + x
R . J . K e l l e r , T.E. M i t c h e l l and A.H. Heuer
Department of Metallurgy and Materials Saience, Case Institute of Technology, Case Western Reserve University, Cleveland, Ohio 44106, U.S.A.
Résumé.- Des monocristaux de UÛ2+X avec une large gamme des rapports 0/U ont été déformés plastiquement à 600°, 1000° et 1400°C. Le glissement se produit sur les plans {100},{111} ou sur des combinaisons noncristallogra- phiques de plans {100} - {lll} et {lll} - {110}, mais toujours avec des vecteurs de Burgers1/2<110>.Les basses températures et les rapports 0/U élevés favorisent le glissement {lll} <110> par rapport aux deux glisse- ments {100} <110> et {110} <110> ; toutefois, 1'anisotropie plastique est généralement faible.
A b s t r a c t . - Single c r y s t a l s of U02+x with a wide range of 0/U r a t i o s were p l a s t i c a l l y deformed a t 600°, 1000 and 1400°C. Slip occurred on {100} p l a n e s ,
{ i l l } planes, or on non-crystallographic combinations of {100} - { i l l } and { i l l } - {110} p l a n e s , b u t a l l with 1/2<110>Burgers v e c t o r s . Low temperatures and high 0/U r a t i o s favored { i l l } <110> s l i p over both {100} <110> and {110}
<I10> ; however, p l a s t i c anisotropy was generally small.
P r e v i o u s i n v e s t i g a t i o n s / 1 - 4 / o f t h e s l i p s y s t e m s i n UO- s i n g l e c r y s - t a l s h a v e b e e n i n c o n c l u s i v e and i n c l u d e some a p p a r e n t l y c o n f l i c t i n g r e s u l t s ; t h e n a t u r e o f t h e d e f o r m a t i o n o f UO~ i s c l e a r l y n o t w e l l u n d e r s t o o d . The c o m p l e x i t y o f t h e p o i n t d e f e c t s t r u c t u r e a n d a l a c k o f k n o w l e d g e o f t h e e x a c t n a t u r e o f t h e s e d e f e c t s a t v a r i o u s t e m p e r a t u r e s a n d s t o i c h i o m e t r i e s i s i n no s m a l l m e a s u r e r e s p o n s i b l e f o r t h i s l a c k o f u n d e r s t a n d i n g . As w i t h o t h e r c r y s t a l s o f t h e f l u o r i t e s t r u c t u r e , C a F2 / 5 / , B a F2 / 6 / , a n d C a O - s t a b i l i z e d Z r 02 (CSZ) / 7 / , t h e p r e f e r r e d s l i p s y s t e m i n s t o i c h i o m e t r i c UO„ i s {100} < 1 1 0 > . H o w e v e r , i t i s n o t
c l e a r w h e t h e r {110} o r {111} i s t h e s e c o n d d o m i n a n t s y s t e m a n d w h e t h e r t h e p r e f e r r e d s l i p s y s t e m v a r i e s w i t h 0/U r a t i o . I n t h e p r e s e n t w o r k , s p e c i m e n s h a v e b e e n d e f o r m e d o v e r a w i d e r a n g e o f 0/U r a t i o s a n d t e m p e r - a t u r e s , a n d s l i p t r a c e e x a m i n a t i o n s h a v e b e e n made o f t h e s u r f a c e s .
C o m p r e s s i o n s p e c i m e n s w e r e c u t from UO„ s i n g l e c r y s t a l s t1) i n t h e two o r i e n t a t i o n s shown i n f i g u r e 1 . One o r i e n t a t i o n (fv<029>) p r o - v i d e d l a r g e e q u a l r e s o l v e d s h e a r s t r e s s e s on { i l l } a n d {110} p l a n e s w h i l e s u p p r e s s i n g s l i p on { 1 0 0 } , and t h e o t h e r (,v<123>) p l a c e d t h e l a r - g e s t s h e a r s t r e s s on a {100} p l a n e w i t h a l m o s t a s l a r g e s h e a r s t r e s s e s on { i l l } p l a n e s . The s u r f a c e s t o b e e x a m i n e d o p t i c a l l y w e r e p o l i s h e d , u s i n g a f i n a l p o l i s h w i t h 1 pm d i a m o n d p a s t e .
(^Obtained from OMCCorp., Atlanta, GA.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981308
JOURNAL DE PHYSIQUE
COMPRESSION ORIENTATIONS A N D SCHMIDT FACTORS
F i g . 1.- S t e r e o g r a p h i c t r i a n g l e showing compression o r i e n t a t i o n s and t h e Schmidt f a c t o r s of major s l i p systems.
The O/U r a t i o s were e s t a b l i s h e d by f l o w i n g CO/C02 m i x t u r e s o v e r
-
t h e specimens a t 1300°C f o r 48 h o u r s ; a Y 2 0 3 - s t a b i l i z e d Zr02 s o l i d e l e c t r o l y t e O2 s e n s o r ( was used t o m o n i t o r oxygen p a r t i a l p r e s s u r e s . For O/U r a t i o s 2 2.001, t h e d a t a o f Hagamark and B r o l i /8/ were used t o d e t e r m i n e t h e CO/C02 m i x t u r e s , w h i l e more s t o i c h i o m e t r i c specimens were p r e p a r e d u s i n g CO/C02 m i x t u r e s a p p r o p r i a t e t o oxygen p o t e n t i a l s
nGO2
( x , T ) i n U02+x c a l c u l a t e d f o r a t h e o r e t i c a l model /9,10/. T e s t s were conducted i n a p p r o p r i a t e CO/C02 m i x t u r e s a t 600°, 1000' and 1400°C i n an I n s t r o n t e s t i n g machine equipped w i t h an i n - s i t u Y 2 0 3 - s t a b i l i z e d Zr02 s e n s o r t o measure p I n i t i a l s t r a i n r a t e s were a p p r o x i m a t e l y5 1 0 - ~ / ~ . 0 2 '
Specimens deformed a l o n g t h e two o r i e n t a t i o n s showed a marked v a r i a t i o n i n s l i p s y s t e m w i t h b o t h t e m p e r a t u r e and O/U r a t i o ( F i g s . 2 and 3 ) . The prim- y s l i p s y s t e m on specimens deformed a l o n g < i 2 3 > a t 600°C was t h e m t h i g h l y s t r e s s e d (111) <110> system. A t 600°C, s p e c i - mens e x h i b i t e d r a p i d h a r d e n i n g a f t e r i n i t i a l y i e l d t o an upper y i e l d p o i n t w i t h a s u b s e q u e n t d r o p i n s t r e s s . Those s a m ~ l e s which were exami- ned a f t e r t e s t s s t o p p e d d u r i n g o r s h o r t l y a f t e r t h i s s t r e s s t r a n s i e n t had secondary t r a c e s on { l o o ) and o t h e r { l l l l p l a n e s due t o s e c o n d a r y systems b e i n g a c t i v a t e d a t h i g h e r a p p l i e d s t r e s s e s .
Specimens of t h i s o r i e n t a t i o n deformed a t 1000°C showed changes i n s l i p s y s t e m s w i t h v a r y i n g O/U r a t i o s : a s shown i n f i g u r e 2. The
( 2 ) ~ b t a i n e d from Zircoa D i v i s i o n , Corning Glass Works, Solon, Ohio
most s t o i c h i o m e t r i c specimens were o b s e r v e d t o g l i d e on a ( 1 0 0 ) p l a n e ; however, t h o s e w i t h h i g h e r O/U r a t i o s e x h i b i t e d n o n - c r y s t a l l o g r a p h i c s l i p , which was a combination o f s l i p on t h e most h i g h l y s t r e s s e d { l o o } and ( 1 1 1 ) p l a n e s w i t h t h e same primary B u r g e r s v e c t o r . The most h i g h l y s t r e s s e d { 1 1 1 ) < 1 1 0 > system had a d i f f e r e n t B u r g e r s v e c t o r , b u t f a i n t t r a c e s c o r r e s p o n d i n g t o t h i s s y s t e m were s e e n on specimens w i t h O/U r a t i o s 2 2 . 0 1 . A t 1 4 0 0 ° C , s i n g l e s l i p on ( 1 0 0 ) p l a n e s was o b s e r v e d , r e g a r d l e s s o f O/U r a t i o .
S L I P PLANES I N U 0 2 + FOR < U > - [ 7 2 3 ]
Fig. 2.- S l i p p l a n e s i n U02+x deformed a l o n g [ i 2 3 ] .
I n t h e o t h e r o r i e n t a t i o n ('L < 0 2 9 > ) , a l t h o u g h d u p l e x s l i p was i n - v a r i a b l y o b s e r v e d , a s i m i l a r t r a n s i t i o n o c c u r r e d a s shown i n f i g u r e 3 . A t 6 0 0 ° C , s l i p o c c u r r e d on
(1111
< 1 1 0 > s y s t e m s a t a l l O/U r a t i o s . A t1 0 0 0 ° C , a t r a n s i t i o n a g a i n o c c u r r e d , such t h a t t h o s e specimens w i t h O/U r a t i o s g r e a t e r t h a n 2 . 0 0 1 underwent (111) < 1 1 0 > g l i d e , and t h o s e w i t h r a t i o s l e s s t h a n 2 . 0 0 1 showed n o n - c r y s t a l l o g r a p h i c s l i p . By way of c o n t r a s t , t h i s n o n - c r y s t a l l o g r a p h i c s l i p a p p e a r e d t o b e a combina- t i o n of g l i d e on t h o s e ( 1 1 1 1 and ( 1 1 0 ) p l a n e s w i t h t h e same p r i m a r y
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B u r g e r s v e c t o r . Specimens w i t h a n O/U r a t i o o f 2.001 a p p e a r t o b e n e a r a t r a n s i t i o n c o m p o s i t i o n , a s b o t h t y p e s of s l i p b e h a v i o r have been ob- s e r v e d . A t 1400°C, s l i p was g e n e r a l l y o f t h i s n o n - c r y s t a l l o g r a p h i c t y p e , w i t h t h e s l i p p l a n e n e a r e r (1111 a s O/U r a t i o s i n c r e a s e d .
\
S L I P PLANES IN U O p + FOR < u > - [029]
F i g . 3 . - S l i p planes i n UO 2+x deformed along [029]
.
I t s h o u l d be emphasized t h a t w h i l e s m a l l v a r i a t i o n s i n t h e com- p r e s s i o n a x i s must a f f e c t t h e o r i e n t a t i o n o f n o n - c r y s t a l l o g r a p h i c s l i p p l a n e s , t h e o b s e r v e d s l i p p l a n e d i d n o t u s u a l l y c o r r e s p o n d t o a p l a n e of maximum r e s o l v e d s h e a r s t r e s s . T h i s i s e s p e c i a l l y t r u e f o r t e s t s a t 1000°C f o r <o> a < i 2 3 > , where t h e o b s e r v e d combination of (100) and {ill} p l a n e s had a lower Schmidt f a c t o r t h a n t h e o r i g i n a l {100] <110>
system.
A p a r t i c u l a r l y s t r i k i n g f e a t u r e o f t h e s l i p t r a c e s on a l l s p e c i - mens, whether c r y s t a l l o g r a p h i c o r n o t , i s t h e wavy n a t u r e o f t r a c e s p r o - duced by screw d i s l o c a t i o n s . A t y p i c a l example i s shown i n f i g u r e 4 , where t h e t r a c e s on f a c e B a r e q u i t e wavy. The preponderance o f wavy
s l i p i n d i c a t e s t h a t c r o s s - s l i p i s b o t h v e r y e a s y and i m p o r t a n t t o t h e d e f o r m a t i o n p r o c e s s . I t i s , however, g e n e r a l l y n o t p o s s i b l e t o a n a l y z e a c t u a l c r o s s - s l i p p l a n e s by t r a c e a n a l y s i s , even a t v e r y low s t r a i n s .
F i g . 4.- S l i p t r a c e s on a specimen o f U02+*, w i t h on O/U r a t i o o f 2.000005, d e f o r - med a t 1 0 0 0 ° ~ .
Although p r i o r work h a s n o t d i s c u s s e d t h e s e t r a n s i t i o n s o f s l i p system w i t h b o t h t e m p e r a t u r e and c o m p o s i t i o n , t h e r e a r e r e s u l t s i n t h e l i t e r a t u r e which a r e comparable t o some o f t h e ~ e s u l t s we have found.
Sawbridge and Sykes /1/ deformed s i n g - . c r y s t a l s i n a r g o n a t 1327OC and found (1111
-
(110) composite s l i p f o r specimens o r i e n t e d s i m i l a r l y t o o u r < 0 2 9 > d i r e c t i o n . Yust and McHargue /2/ performed t e s t s on s p e c i - mens w i t h O/U r a t i o s from 2.03 t o 2.1 and found n o n - c r y s t a l l o g r a p h i c s l i p on a v a r i e t y of p l a n e s between {111} and (112) a t 800° and 1000°C, c o r r e s p o n d i n g t o o u r r e s u l t s f o r <o> % <i23>. They had p r e v i o u s l y /3/t e s t e d s i m i l a r c r y s t a l s o f s t o i c h i o m e t r i c composition i n hydrogen be- tween 550°and 1350°C and r e p o r t e d {loo) < 1 1 0 > s l i p . Blank and Ronchi / 4 / r e p o r t e d {111} < 1 1 0 > a s a s l i p s y s t e m i n U02+x s i n g l e c r y s t a l s and s u g g e s t e d t h a t b o t h {loo} < 1 1 0 > and (1111 < 1 1 0 > a r e a b l e t o o p e r a t e i n n o n - s t o i c h i o m e t r i c c r y s t a l s .
The change i n s l i p s y s t e m w i t h t e m p e r a t u r e and c o m p o s i t i o n i s a l m o s t c e r t a i n l y r e l a t e d t o d e f e c t - d i s l o c a t i o n i n t e r a c t i o n s and t h e changes i n d e f e c t s t r u c t u r e s w i t h O/U r a t i o s . Catlow /11/ h a s used M o t t - L i t t l e t o n t y p e c a l c u l a t i o n s t o show t h a t t h e r e i s a s e r i e s o f d e f e c t c l u s t e r s o f v a r y i n g c o m p l e x i t y t h a t o c c u r a t d i f f e r e n t O/U
2
-
r a t i o s i n U02+x. These r a n g e from s i n g l e 0 i n t e r s t i t i a l - h o l e c l u s t e r s t o c o m p l i c a t e d c l u s t e r s c o n t a i n i n g s i x 0 2- i n t e r s t i t i a l s , t h r e e vacan-
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5
+
c i e s on t h e oxygen s u b l a t t i c e , and t h e a s s o c i a t e d U i o n s n e c e s s a r y f o r e l e c t r o s t a t i c n e u t r a l i t y . I t i s a l s o noteworthy t h a t t h e tendency f o r c l u s t e r i n g w i l l be g r e a t e r a t lower t e m p e r a t u r e s f o r a g i v e n com- p o s i t i o n . W e t h e r e f o r e s u g g e s t t h a t , a t lower t e m p e r a t u r e s (600°C) o r f o r t h e l a r g e r O/U r a t i o s a t h i g h e r t e m p e r a t u r e s ( l O O O ° C ) , d e f e c t com- p l e x e s form and i n t e r a c t w i t h moving d i s l o c a t i o n s , changing t h e p l a s t i c a n i s o t r o p y s u c h t h a t {111)<110> s l i p i s f a v o r e d s l i p .
T h i s work i n d i c a t e s t h a t t h e c h o i c e o f dominant s l i p system i n t h e d e f o r m a t i o n o f U02+x s i n g l e c r y s t a l s i s dependent on U/O r a t i o , t e m p e r a t u r e , and o r i e n t a t i o n . (111) <110> s l i p i s f a v o r e d by low tem- p e r a t u r e s and h i g h O/U r a t i o s , w h i l e (100) <110>
i s
f a v o r e d by h i g h t e m p e r a t u r e s and low O/U r a t i o s . (110) <110> i s n e v e r t h e dominant system, b u t a t h i g h t e m p e r a t u r e s t h e r e a p p e a r s t o be l i t t l e p l a s t i c a n i s o t r o p y between i t and {111} <110>. The s m a l l p l a s t i c a n i s o t r o p y of U02+x promotes c r o s s - s l i p , which i s e x t e n s i v e l y o b s e r v e d under a l l c o n d i t i o n s i n v e s t i g a t e d .A c k n o w l e d g e m e . - T h i s i n v e s t i g a t i o n was s u p p o r t e d by t h e Department o f Energy under g r a n t DEAC0277ER04217.
R e f e r e n c e s
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(1971) 33 /2/ Yust, C.S. and McHargue, C . J . ,5.
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31 (1969) 121
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174-80, P r o c e e d i n g s I n t . Conf. on Plutonium and O t h e r A c t i n i d e s , 4 t h S a n t e Fe, New Mexico ( 1 9 7 0 ) ./5/ Evans, A.G. and P r a t t , P.L., P h i l o s . Mag.
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(1964) 3325 /7/ MeCartney, X.L., Donlon, W.T. and Heuer, A.H. J. Mat. S c i .15 (1980) 1063
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(1978) 10/lo/
deFranco, M. and Catesoupe, J . P . , i n : Plutonium and O t h e r A c t i n i d e s , 173, H . Blank and R . L i n d e r , e d s . (North-Holland P u b l . Co., Amsterdam) 1976/11/ Catlow, C . R . A . , ? r o c . R. Soc. London A
