MEDIUM TEMPERATURE PEAKS IN HIGH PURITY ALUMINIUM DOPED WITH 10 ppm COPPER OR SILVER

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MEDIUM TEMPERATURE PEAKS IN HIGH PURITY ALUMINIUM DOPED WITH 10 ppm

COPPER OR SILVER

C. Esnouf, A. Kulik, J. Theumann, M. No

To cite this version:

C. Esnouf, A. Kulik, J. Theumann, M. No. MEDIUM TEMPERATURE PEAKS IN HIGH PURITY

ALUMINIUM DOPED WITH 10 ppm COPPER OR SILVER. Journal de Physique Colloques, 1987,

48 (C8), pp.C8-95-C8-100. �10.1051/jphyscol:1987810�. �jpa-00227114�

JOURNAL DE PHYSIQUE

Colloque C8, suppl6ment au n012, Tome

48, decembre 1987

MEDIUM TEMPERATURE PEAKS IN HIGH PURITY ALUMINIUM DOPED WITH

10

ppm COPPER OR SILVER

C. ESNOUF*, A.

KULIK,

J.F. THEUMANN and M.L. NO'*

Institut d e Genie Atomique, Institut Federal Suisse de Technologic, PHB-Ecublens, CH-1015 Lausanne, Switzerland ' G E M P P M , Bdt. 502, I N S A , F-69621 V i l l e u r b a m e Cedex, France

* * ~ p t o de Fisica del Estado Solido, Facultad de Ciencias, Aptdo 644, SP-48009 Bilbao, Spain

sum&

: Les r e 1 a:tations observ6es v e r s 0.5 Tm dans 1 ' a l u m i n i u m de pctret6 o r d i n a i r e o n t des c a r a c t 6 r i s t i q u e s assez d i f f 4 r e n t e s de r e l l e s observ6es dans l ' a l u m i n l u m de t r s s h a u t e p u r e t g . Dans c e t a r t i c l e , l e s d i f f g r e n c e s s o n t analys6es

2

o a r t i r d 2 & c h a n t i l l o n s de o u a t r e o u r e t 6 s d i f f i r e n t e s .

Summary : I n t h e case o f aluminium o f o r d i n a r y p u r i t y , t h e observed relaxations around 0.5 Tm have a behaviour which is different from that of high p u r i t y aluminium. I n t h i s paoer, t h e d i f f e r e n c e s a r e analyzed using

specimens o f f o u r d i f f e r e n t p u r i t i e s .

INTRODUCTION

---

The mechanisms which c o n t r o l p l a s t i c i t y and c r e e n i n m e t a l s around 0.5 Tm ( T m : m e l t i n g a o i n t ) were o f t e n i n t h e c e n t e r o f i n t e r e s t f o r many experimenters. R e c e n t l y numerous i n t e r e s t i n g works have d e s c r i b e d p r e c i s e l y s e v e r a l mechanisms. Ref ore. orooosed mechanisms around 0.5 Tm were c r o s s - s l i o and s e l f d i f f u s i o n f c r t h e two s t a q e s U and U o f t h e creep i n f c c m e t a l s /I/. P i p e - d i f f u s i o n was c o n s i d e r e d i n o r d e r t o e x p l a i n t h e s t a g e U

,

b u t a f t e r w a r d s a c r o s s - s l i o mechanism was

g e n e r a l 1 y accepted t h e r e .

E l e c t r o n microscoay i n - s i t u o f t h e d i s l o c a t i o n s m i c r o s t r u c t u r e done i n Toulouse /2,3.4/ has c o n t r i b u t e d t o e x a l a i n c r o s s - s l i p mechanism c o n t r o l 1 i n q macroscopic c r e e o i n alctmioium around 200C. T h i s p r o c e s s can b e a c t i v a t e d on1 y when t h e l o c a l s t r e s s e s a r e h i g h enough ( a b o u t 0.75 o f t h e Orowan s t r e s s ) . T h i s v a l u e o f t h e s t r e s s was measured i n t h e Al-Zn a l l o y / 5 / . I n f a c t such a p r o c e s s t a k e s o l a c e a f t e r a n o t h e r mechanism, t h e g l i d e i n t h e non-comoact s l i p p l a n e C1001, by t h e k i n k n u c l e a t i o n a t d i s l o c a t i o n nodes

/A/.

The l a s t mechanism has been r e c e n t l y a n a l y z r d by C a r r a r d / 7 / , s t u d y i n g c r e e p i n aluminium m o n o c r y s t a l s o r i e n t e d <110>. Such creep i n C l O t : ] > p l a n e can be

r e s o o n s i b l e f o r t h e U stage. S i m i l a r s t u d v was performed i n maanesium and b e r v ~ l i u m / 8 / where t h e o r i s m a t i c a l i d e i s observed a t t h e

analogous t e m o e r a t u r e s as i n t h e case o f C1001 creep i n aluminium.

For many y e a r s a l r e a d y , I n t e r n a l F r i c t i o n techniques have been used f o r stctdvinq m e t a l s i n t h e s i m i l a r t e m o e r a t u r e r a n g e /9,10/. I n f c c m e t a l s o f o r d i n a r y p u r i t y , a s i g n i f i c a n t r e l a x a t i o n i n p o l y c r y s t a l l i n e m a t e r i a l s was observed ("Ke p e a k " ) . The a c t i v a t i o n energy o f t h a t ohenomenon i s c l ( > s e t o HV ( s e l f d i f f u s i o n e n e r g y ) . I n m o n o c r y s t a l s t h i s r e l a x a t i o n i s much l e s s pronounced / 1 1 / . I n a l l cases two a d d i t i o n a l and s m a l l e r ~ e a k 5 were observed /11,12/. The s o c a l l e d P1 peak of l o w e r energy ( . 7 5 Hv) was p r e s e n t around 47CJK a t 1 Hz.

I n h i g h p u r i t y aluminium t h e Ke peak was n o t observed /13/ and o n l y t h e P1 peak e x i s t s i n deformed samoles. The F1 peak d i s a o p e a r s

c o n s e c u t i v e l y a f t e r 10% t e n s i l e creeo a t 200C i n s t a t i o n a r y stage, and i s r e o l a c e d b y another peak s i t u a t e d near the m e l t i n q p o i n t /14.15/.

The P I peak can be re-cjeveloped by means o f p l a s t i c d e f o r m a t i o n .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987810

JOURNAL

D E

_PHYSIQUE

The aim o f t h e present work i s t h e study o f t h e a n e l a s t i c

p r o p e r t i e s between - 3 and - 8 Tm i n aluminium o f d i f f e r e n t p u r i t l e s between zone r e f i n e d 6N A1 and o r d i n a r y 5N A l . We w i l l t r y t o answer t h e f o l l o w i n g question : Which o f t h e r e l a x a t i o n s i n o r d i n a r y p u r i t y m a t e r i a l s a r e r e l a t e d w i t h t h e i s 0 1 ated d i s l o c a t l o n s . subboundaries o r g r a i n boundaries?

I n t h i s paper we w i l l mainly expose t h e experimental r e s u l t s and t h e i r s h o r t d i s c u s s i o n based on t h e a l r e a d y known models discussed i n

d e t a i l elsewhere /15,16/ and a l s o i n t h i s conference i n t h e paper headed " I n t e r n a l F r i c t i o n a t Medium Temperatures i n High P u r i t y Aluminium" /17/.

EXPERIMENTAL

---

Samples have t h e form o f p l a t e s 1 ~ 5 x 5 0 mm, prepared from

p o l y c r y s t a l l i n e aluminium annealed, deformed o r a f t e r creep. The as- r e c e i v e d s t a t e i s t h e r e s u l t o f r o l l i n g an i n g o t ; a subsequent

annealing up t o 800K can produce t h e r e c r y s t a l l i z a t i o n . Four p u r i t i e s were used :

-

A1 6N melted zone r e f i n e d , e l a b o r a t e d by CECM V i t r y / s e i n e (France).

-

A1 6N ( p r e v i o u s ) doped w i t h 9.4 +-1 ppm o f s i l v e r .

-

A1 6N doped w l t h 10,s ppm + - I ppm o f copper.

-

A1 5N w i t h about 10 ppm o f a l l i m ~ u r i t i e s .

Except one o f t h e 5N aluminium samples, t h e g r a i n s i z e was b i g g e r than t h e t h i c k n e s s o f t h e samoles. Table 1 g i v e s t h e g r a i n s i z e and t h e r a t i o o f g r a i n s i z e t o t h i c k n e s s o f t h e samples.

Measurements were made a t Genie Atomique Laboratory i n t h e f o r c e d pendulum working under 1 t o r r o f h e l i u m pressure. The measuring system c o n s i s t e d mainly o f t h e 1250A Schlumberger Frequency Hesoonse Analyzer equiped w i t h a p p r o ~ r i a t e e x c i t a t i o n and d e t e c t i o n transducers and a m p l i f i e r s . The temperature r e g u l a t o r c o n t r o l l e d by a HP71 pocket computer w i l l be described elsewhere /18/. Data a r e t r a n s m i t t e d t o a HP9520 computer f o r f u r t h e r processing and a r c h i v i n g .

EXPERIMENTAL RESULTS

We have s t u d i e d t h e i n t e r n a l f r i c t i o n behaviour as a f u n c t i o n o f parameters such as frequency o f o s c i l l a t i o n , o s c i l l a t i n g s t r e s s amplitude, b i a s s t r e s s amp1 i tude, m i c r o s t r u c t u r e ( a f t e r coldwork o r a f t e r creep i n s t a t i o n a r y s t a t e ) on f o u r samDles of alctminium which possess d i f f e r e n t l e v e l s of p u r i t y and i m p u r i t y content. I n t h e case of 6N aluminium, t h e experimental r e s u l t s and t h e i r i n t e r p r e t a t i o n have been p u b l i s h e d a l r e a d y /IS, 16,19/ and w i l l be developed i n t h i s conference i n t h e companion paper p r e v i o u s l y mentioned. I n t h i s work we present t h e r e s u l t s concerning t h e aluminium w i t h o t h e r p u r i t i e s . S i l v e r doeed aluminium :

F i g . 1 p r e s e n t s t h e f r i c t i o n s p e c t r a of 6N aluminium doped w i t h l0ppm s i l v e r f o r d i f f e r e n t f r e q u e n c i e s o f o s c i l l a t i o n ( i n t h r e e decades) i n t h e temoerature range 0.3-0.8 Tm. Using a polynomial law, t h e i n t e r n a l f r l c t i o n background has been s u b t r a c t e d and r e s u l t s a r e presented i n f i g . 2. The a c t i v a t i o n energy o f t h e observed peak has been obtained u s i n g t h e Arrhenius p l o t presented i n f i g . 7 .The i n f l u e n c e of t h e o s c i l l a t i n g s t r e s s amplitude has been t e s t e d and a smooth decrease o f t h e r e l a x a t i o n i n t e n s i t y i s observed ( f a c t o r of - 9 i n 3.5 E-6 - 3.5 E-5 ranee) /20/. The e f f e c t o f a b i a s s t r e s s was a l s o studied, a superimposed t o r s i o n a l s t r e s s was incremented a t t h e

maximum peak temperature o f 545K. Absolute1 y no e f f e c t was detected /20/. The i n f l u e n c e of t h e m i c r o s t r u c t u r a l changes on t h e r e l a x a t i o n peak i s shown i n f i g . 3 . The curve-a concerns aluminium i n t h e as-

r e c e i v e d s t a t e . t h e curve-b i s o b t a i n e d a f t e r a c r e e o o f t h e p r e v i o u s s a m ~ l e

(8.3% t e n s i l e a t 473K w i t h a secondary s t a g e c r e e o r a t e o f 5 10-6 5-1)

,

^{t h e}

curve-c concerns t h e c o l d - worked sample a f t e r t h e p r e v i o u s c r e e p (19% r o l l i n g a t RT)

.

As observed i n 6N aluminium /14/, t h e creep 1 eads t o a disappearance o f t h e r e l a x a t i o n peak and t h e c o l d w o r k provokes i t s reapoearance w i t h a

s i g n i f i c a n t decrease oC i n t e r n a l f r i c t i o n i n t h e

h i g h t e m ~ e r a t u r e range.

I

T e m p e r a t u r e C K I -

I

Coeeer doeed a l u m i n i u m :

1

: 0-1 i n t e r n a l f r i c t i o n s p e c t r a o f Ag doped A1 f o r t h e The i n t e r n a l f r i c t i o n s p e c t r a f r e q u e n c i e s : 1 ) . 01

-

2 ) .05 - 3 ) o f t h i s sample a r e shown i n - 1

-

4 ) 1 - 5 ) 10 Hz ( O s c i l l a t i n g f i g . 4 f o r d i f f e r e n t f r e o u e n - amp1

.

7E-6 d u r i n g c o o l i n g )

.

c i e s o f o s c i l l a t i o n . We observe a s l i g h t l y h i g h e r maximum peak.

t e m p e r a t u r e a s comoared w i t h t h e p r e v i o u s sample. S i m i l a r r e s u l t s a s i n t h e case o f s i l v e r doped aluminium a r e o b t a i n e d a s a f u n c t i o n o f b i a s s t r e s s l e v e l a t 560K, a s a f u n c t i o n o f c r e e p ( t h e r e l a x a t i o n peak does n o t e x i s t a f t e r 9% creep and a h i g h i n t e r n a l f r i c t i o n i n c r e a s e t a k e s p l a c e ) and a t 1 a s t a wei 1 - d e f i n e d r e l a x a t i o n i s a l s o d e t e c t e d as a f u n c t i o n o f coldwork a f t e r c r e e p /20/.

The o s c i l l a t i n g s t r a i n a m p l i t u d e e f f e c t is s l i p h t l y d i f f e r e n t , t h e peak h e i g h t seems t o keep a c o n s t a n t

v a l u e i n t h e 1E-6 - 5E-5 range. ELq,

2

: Same r e s u l t s a s F i g . 1 w i t h a s u b s t r a c t i o n o f i n t e r n a l

5d a l u m i n i u m : f r i c t i o n background.

I n t h i s case two samples have been used. The f i r s t ( 1 ) ( a s - r e c e i v e d and annealed) has a l a r g e g r a i n s i z e comoared t o i t s t h i c k n e s s . I t p r e s e n t s a r e l a x a t i o n a t S40K ( 1 Hz) (see f i g . 5 , c u r v e a ) which was analyzed i n t h r e e decades ( f i g . 7 ) . T h i s r e i a x a t i o n s l i g h t l y decreases w i t h t h e o s c i l l a t i n g s t r a i n a m ~ l i t u d e ( f a c t o r o f - 9 i n t h e 3.5 E-6

-

3.5 E-5 r a n g e ) . I t i s a l s o independent o f b i a s s t r e s s l e v e l a t 540K /20/. The second sample ( 2 ) was cre.pt 13% a t 575K and had r e t a i n e d a s m a l l g r a i n s i z e ( - 3 mm comoared w i t h t h e t h i c k n e s s - 8 mm). The r e s u l t s a r e shown i n f i g . 5

,

c u r v e s b and c. Curve b g i v e s t h e i n t e r n a l f r i c t i o n d u r i n g f i r s t h e a t i n g : no r e l a x a t i o n seems t o be p r e s e n t a t 540K b u t one i s seen around 6OOK. I t i s f o l l o w e d by an i m p o r t a n t decrease a t 700K which i s c o r r e l a t e d w i t h an i n c r e a s e o f modulus d e f e c t . Here a r e c r y s t a l l i s a t i o n t a k e s p l a c e l e a d i n g t o a g r a i n s i z e i n c r e a s e t o 1.5 mm ( h e r e a f t e r c a l l e d 5N aluminium ( 3 ) ) .

J O U R N A L

DE PHYSIQUE

ELg,

3

: Ag doped A1 s p e c t r a (Osc. ampl. 3.5 E-6 - 1 Hz) a) as-recei ved and annealed

800K.

b ) as a + t e n s i l e creep o f 8.3% a t 473K.

C ) as b

+

coldwork by r o l l i n g o f 19% a t RT.

148 I28 108 8 8 - m

..-

*. s e -

L

4 0 - 20

0

Efg-

4

:

Cu

doped A1 s p e c t r a ( O s c . ampl. 7 E-6 d u r i n g cool i ng ) without t h e

i n t e r n a l f r i c t i o n background ( f r o m l e f t t o r i g h t : 10

-

^1-

- 1

-

- 0 5

-

- 0 1 Hz).

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-

^'..--. ._<,-.-< ---.

, ,

-

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3 ⁵ 8 2 83

^{m 8}

T e m p e r a t u r e C K I

f h q c d b a

Fig,

Z

: Arrhenius p l o t s according t o samples described i n Fig. 6 . a) 6 N A1.

b) hg doped A l .

C ) CU doped A l . d ) 5N A1.

to-

- - -

108

80

m 68 rn m

- _*

40

H

20

ELg, J- : 5 N s p e c t r a (Osc.

ampl. : 7 E - 6 , 1 Hz) : a) as-recei ved and anneal ed

a t 8 0 0 K ( s a m ~ l e 1).

b ) n o t annealed and c r e p t 13% a t 575K (sample 2 ) , f i r s t heating.

C ) as b + f i r s t c o o l i n g (samole 3 )

d) as c + t e n s i l e creep of 11% a t 477K.

' ' % a

-

. . .

:.._.

. . .

. . .

. _.-..

.

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D

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^{a I}

I H

T e m p e r a t u r e CKI

D u r i n g c o o l i n g (see c u r v e c ) and subseauent h e a t i n g s we observe a d i m i n i s h e d r e l a x a t i o n a t 580K. I n o r d e r t o t e s t t h e b e h a v i o u r o f t h i s l a s t peak, we have oerformed a new creen exoeriment (11% creep a t 477K -crtrve d )

.

^We see an i m o o r t a n t decrease o f t h e r e l a x a t i o n a s observed i n our o r e v i o u s s t u d y on bN doped samples h a v i n g s i m i l a r g r a i n s i z e .

I

G r a i n R a t i o Peak A c t i v . Frequency A f t e r s i z e

d B/e

temp. energy f a c t o r f o c r e e p I n f i g . 6 we can compare

i n t e r n a l f r i c t i o n s ~ e c t r a o f aluminium w i t h d i f f e r e n t l e v e l s o f p c ~ r i t y and a1 so f o r s i m i l a r g r a i n s i z e under t h e c o n d i t i o n o f o r a i n s i z e exceeding t h e sample thici:.ness.

C o n c l u s i o n s on t h e peak h e i g h t d i f f e r e n c e a r e d i f f i c u l t because i t i s c o r r e l a t e d w i t h d i s l o c a t i o n d e n s i t y b e f o r e and d u r i n g f i r s t a n n e a l i n g . The A r r h e n i u s p l o t s a r e shown i n f i g . 7 and t h e b e s t f i t s f o r a c t i v a t i o n energy and f reauency f a c t o r a r e g i v e n i n t a b l e 1.

Except i n t h e case o f 5N

1.5 1.5 470 1.01 1. E+11 No peak.

-

L . 2. 526 1.27 1.7 E+12 No peal.:

1.5 1.5 562 1.56 9 . 7 E + 1 3 N o p e a k

1.2 2. ^c- d.27 1.27 8. E + i 1

---

7

- 4 - 4 610

--

--- _Peak

,

1.5 1.8 570

--

^{--- No peak}

T a b l e

1

: Sample d a t a (0 g r a i n s i z e i n mm, e t h i c k n e s s i n mm, t e m p e r a t u r e i n K e l v i n , energy i n eV and f r e q u e n c y f a c t o r i n 5-1.

aluminium ( 2 ) , t h e b e h a v i o u r

FLq, 6

: Contparaison o f i n t e r n a l o f a1 1 o t h e r samples i s f r i c t i o n s p e c t r a tosc. ampl. 7E-6 e x a c t 1 y t h e same, e s o e c i a1 1 y d u r i n g c o o l i n g , I Hz) + o r as- t h e disappearance o f t h e r e c e i v e d and 800b: annealed s t a t e : r e l a x a t i o n a f t e r adequate a ) 6N A1 - b ) Ag doped A 1

-

c ) creep. A l s o one o b s e r v e r a CLI dooed A l

-

d ) 5N A1 ( s i m i l a r v e r y deep evo:utiorl o f g r a i n s i z e around 1.5 mm).

i n t e r n a i f r i c t i o n i n t h e h i g h

t e m o e r a t u r e r a n y e : h i g h a f t e r creep, l o w a f t e r coldwork and i n t e r m e d i a t e v a l u e s a f t e r anneal i ng o f t h e a s - r e c e i ved m a t e r i a1

.

108

00

6)

- _*

5

48

C(

The more s u r p r i s i n g r e s u l t i s t h e s h i f t o f t h e r e l a x a t i o n peak and change o f t h e a c t i v a t i o n energy between t h e h i g h p u r i t y sample and t h e o t h e r s l e s s pure. Undoubted1 y, t h e a c t i v a t i o n f o r 6N aluminium cannot be compared w i t h t h e bull; d i f f u s i o n energy (Hv- 1.3-1.5 e V ) and t h e n t h e doubt e x i s t s f o r t h e o t h e r p u r i t i e s . A l s o we observe an i n c r e a s e of f r e q u e n c y f a c t o r i n l o w o u r i t y samples which i s c n m o a t i b l e w i t h a d i m i n u t i o n o f d i s l o c a t i o n l e n g t h L ( f o

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JOURNAL DE PHYSIQUE

v a r i a t i o n ? T h e o r e t i c a l l y such a v a r i a t i o n e x i s t s : H=Ho-vubut t h e v a r i a t i o n o f t h e a c t i v a t i o n volume v w i l l b e v e r y l a r g e (1.E4 b 3 ) . I n f a c t , such a l a r g e a c t i v a t i o n volume change w i l l b e e a s i l y d e t e c t e d b y o s c i 11 a t i n g s t r e s s changes w h i l e n o t so l a r g e t e m p e r a t u r e s h i f t s have been o b t a i n e d (

<

201:: between 3 E-6 and 3 E-5

p).

We c o n c l u d e t h a t t h e observed r e l a x a t i o n s a r e governed b y one o r more mechanisms w i t h p u r e l y d i f f e r e n t c h a r a c t e r i s t i c e n e r g i e s . N e v e r t h e l e s s e x c e o t f o r t h e case o f t h e 5N aluminium ( 2 ) s a m ~ l e , t h e s i m i l a r i t y i n t h e b e h a v i o u r o f t h e r e i a x a t i o n s o f a l l o t h e r samples i n d i c a t e s t h a t a common p r o c e s s o f r e 1 a x a t i o n i s i n v o l v e d . The i n t r i n s i c d i s l o c a t i o n

processes, such a s c r o s s - s l i p o r non-compact C l O O > g l i d e , a r e n o t 50 s e n s i t i v e t o i m p u r i t i e s . For t h e r e a s o n s e x p l a i n e d i n a n o t h e r paper o f t h i s c o n f e r e n c e /17/, t h e chosen p r o c e s s i n 6N aluminium i s t h e j o g m o t i o n on screw d i s l o c a t i o n s governed b y p i p e - d i f f u s i o n mechanism.

Here i t appears t h a t i m p u r i t i e s decrease t h e d i s l o c a t i o n m o b i l i t y which enables a more e f f i c i e n t p r o c e s s o f vacancy n u c l e a t i o n i n t h e b u l k governed b y t h e a c t i v a t i o n energy Hv t o come i n t o e f f e c t .

The r e l a x a t i o n observed i n t h e 5N aluminium ( 2 ) samole on t h e c o n t r a r y does n o t correspond t o t h e p r e v i o u s l y d e s c r i b e d orocesses, s i n c e t h i s r e l a x a t i o n i s p r e s e n t a f t e r creep a t 616K. So t h i s a f f o r d s u s a d i r e c t o b s e r v a t i o n o f g r a i n s i z e e f f e c t . We can comoare t h i s r e s u l t w i t h t h e o b s e r v a t i o n s r e p o r t e d b y t h e c h i n e s e group /21/ which observes d i f f e r e n t r e l a x a t i o n s a t t h e same temperatures. The e x i s t e n c e o f bamboo boundary i n t h e soecimen i s a necessary c o n d i t i o n f o r t h e apDearance o f t h e peal: a t 540K. Such a peal: i s a t t r i b u t e d t o t h e combined e f f e c t o f t h e bamboo b o u n d a r i e s and t h e d e f e c t c o n f i g u r a t i o n as subboundaries. I n f a c t t h e p r o c e s s g i v i n g t h e bamboo boundary peak w i 11 be known f r o m m i c r o s t r u c t u r a l c h a r a c t e r i z a t i o n s b y e l e c t r o n m i c r o s c o p i c o b s e r v a t i o n s .

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