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ON THE BAMBOO BOUNDARY INTERNAL FRICTION PEAK IN 99.9999 ALUMINIUM
B. Cheng, T. Kê
To cite this version:
B. Cheng, T. Kê. ON THE BAMBOO BOUNDARY INTERNAL FRICTION PEAK IN 99.9999 ALUMINIUM. Journal de Physique Colloques, 1987, 48 (C8), pp.C8-413-C8-416.
�10.1051/jphyscol:1987862�. �jpa-00227166�
JOURNAL DE PHYSIQUE
C o l l o q u e C8, s u p p l b m e n t au n 0 1 2 , Tome 48, d h c e m b r e 1 9 8 7
ON THE BAMBOO BOUNDARY INTERNAL FRICTION PEAK IN 99.9999 ALUMINIUM
B. CHENG and T . S . K;
Institute of Solid State Physics, Academia Sinica, Hefei, China
An i n t e r n a l f r i c t i o n peak h a s been observed i n bamboo c r y s t a l s of 99.9999wt%(6N) A1. The h e i g h t o f t h e peak was found t o be p r o p o r t i o n a l t o t h e number of bamboo boundaries contained i n t h e specimen. Analysis of t h e r e l a x a t i o n parameters of t h i s peak shows t h a t t h i s is a new peak associated w i t h t h e presence of bamboo boundaries.
It was shown r e c e n t l y t h a t t h e h e i g h t of t h e m a c r o c r y s t a l l i n e i n t e r n a l f r i c t i o n peak (bamboo boundary peak) i n 99.999wt%(5N) A 1 i s d i r e c t l y p r o p o r t i o n a l t o the number o f bamboo boundaries i n t h e specimen ( 1 ) . The e x i s t e n c e o f bamboo boundary (when t h e g r a i n s i z e exceeds t h e s m a l l e s t dimension of t h e specimen) is t h u s a n e c e s s a r y c o n d i t i o n f o r t h e appearance of t h i s peak. The e x i s t e n c e of an i n t e r n a l f r i c t i o n peak a s s o c i a t e d w i t h bamboo boundaries cannot b e e x p l a i n e d acdording t o t h e v i s c o u s s l i d i n g model suggested f o r t h e r e l a x a t i o n p r o c e s s a c r o s s t h e g r a i n boundaries i n a f i n e - g r a i n e d specimen i n which t h e r e l a x a t i o n i s l i m i t e d owing t o t h e p r e s e n c e o f g r a i n c o r n e r s ( 2 ) . Consequently, t h i s bamboo boundary peak is not t h e KB peak a p p e a r i n g i n f i n e - g r a i n e d specimens.
I n o r d e r t o confirm t h e i n t e r e s t i n g r e s u l t s concerning t h e c o n t r i b u t i o n of bamboo b o u n d a r i e s t o t h e i n t e r n a l f r i c t i o n peak observed i n m a c r o c r y s t a l l i n e 5N Al, a s y s t e m a t i c s t u d y is s a d e with 6N A 1 and t h e i n t e r n a l f r i c t i o n w a s measured.
The 6N zone-melted A 1 w a s s u p p l i e d by CECM. Vitry-sur-Seine o f CNRS i n t h e form of a t h i n wire o f l m m diameter h o t extruded a t a temperature between 570 t o 6 4 0 ~ , and was wound i n t o l o o p s having a d i a m e t e r o f about lgcmcl
.
S e v e r a l p i e c e s o f wire about l l c m l o n g were c u t from t h e w i r e l o o p , and were s t r a i g h t e n e d c a r e f u l l y . M e t a l l o g r a p h i c examination shows t h e m i c r o s t r u c t u r e o f each w i r e p i e c e is heterogeneous and c o n s i s t s of a m i x t u r e o f f i n e g r a i n s and very l a r g e g r a i n s e x t e n d i n g a c r o s s t h e d i a m e t e r o f t h e w i r e .One p i e c e of t h e w i r e w a s t w i s t e d a t room temperature i n - s i t u of t h e i n v e r t e d t o r s i o n pendulum a p p a r a t u s t o +0.7%x2 ( i . e . t h e w i r e w a s t w i s t e d i n one s e n s e of r o t a t i o n t o 0.7%. t h e n t w i s t e d i n t h e o p p o s i t e s e n s e o f r o t a t i o n t o 0.7,%, and t w i s t e d back t o t h e o r i g i n a l p o s i t i o n ) , and then annealed a t 9OOK f o r l h . This g i v e s f o r t h e number o f bamboo boundaries i n a specimen of lOcm l o n g N=18. The bamboo boundary i n t e r n a l f r i c t i o n peaks measured i n descending temperatures with two d i f f e r e n t f r e q u e n c i e s a r e shown by c u r v e s 1 , 2 o f Fig.1. The curve with d a t a p o i n t s i s t h e experimental curve and t h e s o l i d curve is t h e curve with the high-temperature i n t e r n a l f r i c t i o n background s u b t r a c t e d by assuming t h a t t h e background obeys an e x p o n t i a l r e l a t i o n s h i p . With t h e i n t e r n a l f r i c t i o n background s u b t r a c t e d . we g e t f o r t h e peak temperature o f t h e i n t e r n a l f r i c t i o n peak Tp, the
his
was prepared by Mr. Q . C . Uu in CECM with t h e h e l p of M r . J . E . P a a t o lArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987862
C8-414 JOURNAL DE PHYSIQUE
h e i g h t o f t h e peak
%Ax
and t h e number o f times t h a t t h e halfwidth o f t h e peak i s b r o a d e r than t h a t o f t h e normal Debye peak m : 4 6 0 ~ . 0.0398 and 2.59 r e s p e c t i v e l y f o r f=1.25Hz and 444K. 0.0398 and 2.63 f o r f=0.36Hz. The a c t i v a t i o n energy determined from t h e temperature s h i f t o f t h e peak w i t h frequency o f v i b r a t i o n i s 1.44eV. which is s i m i l a r t o t h a t f o r 5 N A 1 ( 1 ) .F i g . 1 The bamboo boundary peak w i t h N = 1 8 i n a specimen o f lOcm long. Curve 1 , f = l . 25Hz. Curve 2 , f =O. 36Hz. The average s t r a i n amplitude A, ~ 1 x 1 0 -
I n o r d e r t o g e t l a r g e bamboo g r a i n s , a n o t h e r p i e c e o f wire w a s s t r e t c h e d a t room temperature t o 2% and d i s p l a c e d i n s i d e a f u r n a c e with predetermined temperature g r a d i e n t having a h i g h e s t temperature o f about 890K ( 3 ) . It w a s then annealed f u r t h e r a t 873K f o r 2h. Then t h e number o f bamboo boundaries contained i n t h e specimen i s 8*1 and we g e t Tp=444K, x : x = ~ . 0 1 8 0 and m=2.83 w i t h f=1.15Hz a t T,.
One p i e c e o f w i r e w a s annealed i n vacuum ( 1 0 - ' t o r r ) a t 673K f o r l h . T h i s g i v e s N=16, Tp=442K. C&A,=0.0346, and m=2.80 w i t h f = l . I 8 H z at Tp.
Another p i e c e o f w i r e w a s annealed i n vacuum ( 1 0 - ' t o r r ) a t 800K f o r 4h. This g i v e s N=20 and w e g e t Tp=428K, qi,=0.0468. and m=2.86 with f=1.59Hz a t Tp
.
The r e l a t i o n s h i p between
Xix
and N i s shown by Fig.2. It i s seen t h a tx:,
i sd i r e c t l y p r o p o r t i o n a l t o N, and p a s s e s through t h e o r i g i n . T h i s r e s u l t is i d e n t i c a l with t h a t observed i n 5 N A 1 (1). The l i n e a r r e l a t i o n s h i p between
%A,
and Ns i g n i f i e s t h a t t h e r e l a x a t i o n s t r e n g t h d e c r e a s e s w i t h t h e i n c r e a s e o f t h e l e n g t h of bamboo g r a i n s . T h i s i s t r u e i n both f o r 5 ~ ' and 6N A l . I n t h e c a s e o f f i n e - g r a i n e d specimens, i t w a s shown t h a t t h e r e l a x a t i o n s t r e n g t h ( o r twice t h e h e i g h t of t h e Kg peak) is independent o f t h e g r a i n s i z e . An i n c r e a s e o f g r a i n s i z e o n l y s h i f t s t h e peak t o a h i g h e r temperature. A s such, t h e bamboo boundary peak behaves q u i t e d i f f e r e n t l y i n comparison w i t h t h e Kl peak, and i t is a new peak o f d i f f e r e n t o r i g i n .
Experimental r e s u l t s showed t h a t Tp o f t h e bamboo boundary peak d e c r e a s e s with an i n c r e a s e i n p u r i t y of aluminium. The T, i n 5 N A 1 l i e s w i t h i n 556 t o 523K ( 1 ) while t h a t i n 6N A 1 l i e s w i t h i n 457 t o 423K. Furthermore. T, a l s o v a r i e s with t h e p r e v i o u s thermo-mechanical t r e a t m e n t s a p p l i e d t o t h e specimen b e f o r e t h e e s t a b l i s h m e n t of bamboo g r a i n s although t h e r e l a x a t i o n s t r e n g t h d o e s n o t . This means t h a t t h e r e l a x a t i o n dynamics depends upon t h e h i s t o r y of formation o f bamboo g r a i n s and t h e p u r i t y o f t h e specimen.
F i g . 2 The r e l a t i o n s h i p between
xtx
and N.The l i n e a r r e l a t i o n s h i p between
xi,
and N observed i n 5 N and 6N A 1 shows d e f i n i t e l y t h a t t h e bamboo boundary peak is connected with t h e p r e s e n c e of bamboo boundaries. The appearance o f an i n t e r n a l f r i c t i o n peak s i g n i f i e s t h a t t h e r e l a x a t i o n p r o c e s s a s s o c i a t e d with bamboo boundaries is l i m i t e d . I n t h e c a s e of t h e K6 peak observed i n f i n e - g r a i n e d specimens, t h e r e l a x a t i o n a c r o s s t h e g r a i n boundaries i s l i m i t e d because o f t h e p r e s e n c e o f g r a i n edges. Now t h e q u e s t i o n a r i s e s as t o what i s t h e f a c t o r l i m i t i n g t h e r e l a x a t i o n p r o c e s s i n t h e case of bamboo g r a i n s w i t h o u t g r a i n edges. R e s u l t s o f t r a n s m i s s i o n e l e c t r o n microscopic o b s e r v a t i o n showed t h a t p o l y g o n i z a t i o n boundaries e x i s t e d abundantly n e a r t h e bamboo b o u n d a r i e s and t h e b o r d e r of t h e specimen( 4 ) .
A s is pointed o u t by F u j i t a ( 5 ) . i n t h e c a s e o f "bamboon c r y s t a l s , t h e boundary p l a n e is deformed t o a~complex shape by i n t e r n a l s t r e s s induced by p i l e up d i s l o c a t i o n s and i t c o n s i s t s of zigzag shaped d i s l o c a t i o n s ; t h e d i s t r i b u t i o n o f d i s l o c a t i o n s becomes more homogeneous a s t h e g r a i n s i z e d e c r e a s e s . I t seems t h a t t h e bamboo boundary peak may r e s u l t as a combined e f f e c t of bamboo boundaries and t h e d i s l o c a t i o n c o n f i g u r a t i o n s nearby ( s u c h a s t h e p o l y g o n i z a t i o n boundaries o r p i l e up d i s l o c a t i o n s ) . And such i r r e g u l a r i t i e s nearby t h e bamboo boundaries w i l l i n t e r f e r e and l i m i t t h e s l i d i n g a l o n g t h e boundaries and t h u s p l a y a somewhat s i m i l a r r o l e as t h e g r a i n edges i n f i n e - g r a i n e d specimens. Such an e f f e c t h a s been observed i n c r e e p experiments with b i - c r y s t a l s ( 6 ) .I f t h e i n t e r f e r e n c e o f t h e d i s l o c a t i o n c o n f i g u r a t i o n nearby a bamboo boundary is t h e c o n t r o l l i n g f a c t o r of t h e r a t e of s l i d i n g a l o n g t h e boundary, t h e n t h e r e l a x a t i o n t i m e and t h u s T, w i l l depend on t h e a c t u a l d i s l o c a t i o n c o n f i g u r a t i o n e s t a b l i s h e d nearby t h e boundary d u r i n g t h e formation o f t h e bamboo g r a i n s . T h i s may be t h e r e a s o n why Tp v a r i e s with p r e v i o u s thermo-mechanical t r e a t m e n t s a p p l i e d t o t h e specimen. The p u r i t y o f t h e specimens may a l s o i n f l u e n c e t h e framework of t h e d i s l o c a t i o n c o n f i g u r a t i o n under o t h e r w i s e s i m i l a r c o n d i t i o n s .
A s t o t h e l i n e a r r e l a t i o n s h i p between
x:,
and N, an i n t e r p r e t a t i o n may be suggested below. The energy d i s s i p a t e d d u r i n g t h e s l i d i n g a l o n g t h e boundaries may be measured by t h e p r o d u c t o f t h e r e l a t i v e displacement a c r o s s t h e boundary and t h e s h e a r s t r e s s r e s i s t i n g t h e displacement. I n t h e optimum temperature range, s i n c e t h e s h e a r stress is c o n s t a n t , t h e i n t e r n a l f r i c t i o n is p r o p o r t i o n a l t o t h e grain-boundary a r e a p e r u n i t volume times t h e a v e r a g e r e l a t i v e displacement a c r o s s a g r a i n boundary. F o r f i n e - g r a i n e d specimens w i t h g r a i n edges, t h e r e l a t i v e displacement i s d i r e c t l y p r o p o r t i o n a l t o t h e g r a i n s i z e d and t h e grain-boundaryC8-4 16 JOURNAL DE PHYSIQUE
a r e a p e r u n i t volume i s i n v e r s e l y p r o p o r t i o n a l t o d. s o t h a t t h e energy d i s s i p a t i o n i s independent o f 1 ( t h e average d i s t a n c e between bamboo b o u n d a r i e s ) , b u t t h e grain-boundary a r e a p e r u n i t volume is i n v e r s e l y p r o p o r t i o n a l t o 1, s o t h a t t h e i n t e r n a l f r i c t i o n is i n v e r s e l y p r o p o r t i o n a l t o 1 o r d i r e c t l y p r o p o r t i o n a l t o N.
I n p a s s i n g , i t is worthwhile t o p o i n t o u t t h a t i n t h e r e c e n t work o f Iwasaki ( 7 ) and Gondi e t a l . ( 8 ) concerning t h e high temperature i n t e r n a l f r i c t i o n peak of 5N and 4N A l , t h e specimens used a r e n o t p o l y c r y s t a l l i n e i n t h e u s u a l sense, s i n c e t h e g r a i n s i z e a l r e a d y exceeded t h e specimen diameter. The peak they assigned t o be t h e K6 peak i s a c t u a l l y t h e macro-crystalline boundary peak o r t h e bamboo boundary peak.
REFERENCES
( 1 ) T.S. KB and B.S. Zhang, Phys. S t a t . S o l . , ( a ) 9 6 , (1986). 515 ( 2 ) T.S. KB, Phys. Rev., 71, (1947). 533
(3) T.S. K6, P. Cui and C.M. Su, Phys. S t a t . Sol.. ( a ) 8 4 . (1984), 157
( 4 ) L.D. Zhang and T.S. K6. Proc. Yamada Conference I X D i s l o c a t i o n i n S o l i d s , ed. H. Suzuki e t a l . , University of Tokyo P r e s s , (1985). p. 279
( 5 ) H. F u j i t a . Suppl. t o Trans. Japan I n s t . Metals, 27. (1986). 1959, (Discussion t o T.S. K @ ' s paper on p. 679)
( 6 ) D. McLean. Grain Boundaries i n Metals. Oxford U n i v e r s i t y P r e s s . (1957). p. 286 ( 7 ) K. Iwasaki, Phys. S t a t . Sol., (a)79, (1983). 115 ; 81, (1984). 485
( 8 ) Gondi, A. S i l i and E. B o n e t t i . Phys. S t a t . S o l . , (a)99, (1987). 375
