INVESTIGATION OF THE DISTRIBUTION OF RARE EARTH ELEMENTS IN PURE Al BY THE METHOD OF INTERNAL FRICTION (PART 1)

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INVESTIGATION OF THE DISTRIBUTION OF RARE EARTH ELEMENTS IN PURE Al BY THE

METHOD OF INTERNAL FRICTION (PART 1)

Jiang Zi-Ying, Cai Wei-Ping

To cite this version:

Jiang Zi-Ying, Cai Wei-Ping. INVESTIGATION OF THE DISTRIBUTION OF RARE EARTH ELEMENTS IN PURE Al BY THE METHOD OF INTERNAL FRICTION (PART 1). Journal de Physique Colloques, 1985, 46 (C10), pp.C10-383-C10-386. �10.1051/jphyscol:19851086�. �jpa- 00225471�

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JOURNAL DE PHYSIQUE

C o l l o q u e C10, s u p p l e m e n t au n 0 1 2 , Tome 4 6 , d e c e m b r e 1 9 8 5 page Cl0-383

INVESTIGATION OF THE DISTRIBUTION OF RARE EARTH ELEMENTS IN PURE A 1 BY THE METHOD OF INTERNAL FRICTION (PART 1)

JIANG 21-YING and CAI WEI-PING'

P r t h e a s t U n i v e r s i t y o f T e c h n o l o g y , S h e n y a n g , L i a o n i n g , C h i n a Wuhan I r o n and S t e e l U n i v e r s i t y Wuhan, Hubei, C h i n a

A b s t r a c t

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I n t h i s paper, t h e d i s t r i b u t i o n o f r a r e - e a r t h elements i n p u r e A1 was i n v e s t i g a t e d by t h e method o f i n t e r n a l f r i c t i o n w i t h a h i g h vacuum K e ' s pendulum. The samples a r e p u r e A1 (99.99%) w i t h v a r i o u s c o n t e n t s o f RE (0-3%, n i n e i n number). The e f f e c t o f r a r e - e a r t h a d d i t i o n on g r a i n - boundary r e l a x a t i o n o f A l , and t h e u n p i n n i n g o f d i s l o c a t i o n s a t room t e m p e r a t u r e was measured. It has been found t h a t t h e peak h e i g h t and background decrease w i t h i n c r e a s i n g RE c o n t e n t up t o 0.5%, and t h a t when RE

> 0.5%, t h e peak h e i g h t changes l i t t l e b u t t h e background r a p i d l y i n c r e a s e s w i t h RE c o n t e n t i n c r e a s e . I n view o f t h e s e f a c t s , t h e d i s t r i b u t i o n o f RE i n A1 was i n f e r r e d . The b i n d i n g energy between RE i m p u r i t y and

d i s l o c a t i o n s was e s t i m a t e d t o be about 0.19 eV.

I

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INTRODUCTION

I n r e c e n t years, t h e use o f r a r e e a r t h s (RE) and t h e i r a l l o y s have been growing f a s t , e s p e c i a l l y i n t h e c a b l e i n d u s t r y . But l i t t l e i s known about t h e

d i s t r i b u t i o n o f RE i n Al. It i s known t h a t t h e d i f f e r e n c e between t h e r a r e e a r t h atom and t h e A1 atom i n d i a m e t e r and e l e c t r o n e g a t i v i t y a r e c o n s i d e r a b l e .

Therefore, t h e s o l u b i l i t y o f RE i n A1 i s v e r y s m a l l /I/. However, r e l i a b l e v a l u e s o f s o l u b i l i t y have n o t been obtained. It can be shown t h a t t h e RE atoms i n t h e s t a t e o f s o l i d s o l u t i o n , i f any, s h o u l d have a p r e f e r e n c e f o r s e g r e g a t i n g i n g r a i n boundaries and d i s l o c a t i o n s when t h e RE c o n t e n t i s h i g h ; t h e e u t e c t i c compound o r i n t e r m e t a l l i c compound o f A1-RE may b e formed i n g r a i n boundaries./2/ S i n c e i n t e r n a l f r i c t i o n i s e s p e c i a l l y s e n s i t i v e t o i m p u r i t i e s , we use t h i s method t o study, i n p a r t i c u l a r , t h e e f f e c t o f RE on g r a i n boundary i n t e r n a l f r i c t i o n of A1 and d i s c u s s t h e b e h a v i o r o f RE i n Al.

I 1 - EXPERIMENTAL PROCEDURE AND RESULTS

N i n e samples w i t h d i f f e r e n t RE c o n t e n t s (see T a b l e 1, RE ⁼mischmetal, A1 = 99.99%) were k i n d l y s u p p l i e d by Guangzhou I n s t i t u t e o f Non-ferrous Metal Research. These samples a r e a l l i n cold-drawn s t a t e s w i t h d i a m e t e r s o f 1.2 mm.

They were redrawn t o a d i a m e t e r o f 0.9 m f o r i n t e r n a l f r i c t i o n measurement b y Ke's t o r s i o n a l pendulum i n a vacuum o f about 5 x 1 0 " ~ T o r r . These samples a r e about 300 m l o n g , and annealed a t 720 K f o r two h o u r s i n t h e i n t e r n a l f r i c t i o n

apparatus. Measurements were c a r r i e d o u t w i t h t h e t e m p e r a t u r e d e c r e a s i n g about 1°C/min. The e x p e r i m e n t a l grain-boundary i n t e r n a l f r i c t i o n c u r v e s were o b t a i n e d as shown i n Fig. 1 and Fig. 2. The background o f e x p e r i m e n t a l c u r v e s i s

s u b t r a c t e d a c c o r d i n g t o t h e method p r o v i d e d i n another paper, and t h e t r u e g r a i n boundary i n t e r n a l f r i c t i o n was o b t a i n e d as shown i n Fig. 3. These c u r v e s a r e f i t by f o l 1 owing e q u a t i o n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851086

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JOURNAL DE PHYSIQUE

2

A/2 J i

I>

e-w sech C H ~ / R ( ~ / T

-

l / T m ) + BW] dW t g O =

1 + A / J ~

1 1

e -w2 { l + exp 2[Rm/~ (1/T

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^ITm)+ B W J - ~ ~ W

where A i s t h e r e l a x a t i o n s t r e n g t h , W = z/6, Z=l n ( T / T ), T i s t h e r e l a x a t i o n time, r t h e most probable value o f T, 6 = ( B ~ + B ~ / T ] , wEere 8 , 6, and BH, are t h e d i s t r i b t t i o n widths o f I n ^T, I n r0 and t h e a c t i v a t i o n energy H r e s p e c t i v e l y , and Hm i s t h e most probable value o f H. Tm i s t h e temperature when o ~,=1. Thus t h e s e r i e s parameters are obtained and l i s t e d i n Table 1.

I 1 1

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DISCUSSION

It i s thought t h a t t h e r e e x i s t s a d i s l o c a t i o n network i n t h e g r a i n boundaries.

Under t h e a p p l i c a t i o n o f stress, t h e d i s l o c a t i o n moves by g l i d e and c l i m b /3/. I n t h e case o f A1-RE a l l o y s , s i n c e RE'S atom s i z e i s l a r g e compared w i t h Al, t h e r e i s a s t r o n g tendency o f RE atoms t o segregate t o t h e g r a i n boundaries, and t h e

movements o f g r a i n boundary d i s l o c a t i o n s i s r e s t r i c t e d by t h e RE atoms, so t h a t t h e peak h e i g h t o r t h e r e l a x a t i o n strength, A, r a p i d l y decreases w i t h RE content, as i n d i c a t e d i n Table 1, No. 1 t o No. 5-1 ( f r o m 0.01% t o 0.50% RE). When RE = 0.50%, t h e s o l i d s o l u t i o n s t a t e RE i n g r a i n boundaries i s saturated, and A changes l i t t l e o r increases s l i g h t l y , which may have a c o n t r i b u t i o n by phase boundaries, s i n c e an amount o f A1-RE e u t e c t i c compound has been observed i n specimens by m e t a l l o g r a p h i c microscope. So f o r t h e r e l a x a t i o n s t r e n g t h , A, o f specimen 1 t o be g r e a t e r than specimen 0, i t may be caused by t h e c l e a r i n g action. When t h e RE content i s small, i.e. RE < 0.01%, some non-RE i m p u r i t y atoms form a compound o u t o f RE, so t h a t t h e g r a i n boundaries o f 1 become more clean than pure A1

(99.99%). Consequently, t h e g r a i n boundary r e l a x a t i o n h e i g h t o f specimen No. 1 i s g r e a t e r than t h a t f o r u l t r a - p u r e Al, l i k e our specimen No. 0. There i s evidence t h a t i f No. 1 and No. 0 specimens a r e annealed a t t h e same c o n d i t i o n (720K), t h e g r a i n s i z e o f t h e former i s about 0.32 mm, and t h e l a t t e r 0.20 mm. T h e r e a f t e r t h e g r a i n s i z e decreases w i t h RE c o n t e n t increase (see Table 2), except f o r specimen No. 3.

From Table 1, i t can be seen t h a t b o t h Hm and 6 change w i t h RE content.

Reference /4/ describes t h a t t h e d i s t r i b u t i o n

OF

i m p u r i t i e s g r a i n boundary behaves as a Gaussian d i s t r i b u t i o n . From t h i s we deduced t h a t 6 = G JZ when c i s very small, where G i s constant, c i s RE content. Taking smaTl RE content specimens No. 1, 2 and 3 i n Table 1, t h e p l o t o f BH versus Jc i s made as shown i n Fig. 4 which appears t o show a good l i n e a r i t y . Therefore, i t i s v e r i f i e d t h a t t h e d i s t r i b u t i o n o f H a r i s e s from c o n c e n t r a t i o n f l u c t u a t i o n s o f s o l u t e atoms o f RE i n t h e g r a i n boundary.

For an e s t i m a t e o f t h e b i n d i n g energy between RE atoms and d i s l o c a t i o n , t h e unpinning s t r a i n o f d i s l o c a t i o n s was measured a t v a r i o u s temperatures near room temperature f o r two samples (RE=O.Ol%wt, RE=O.OG%wt). According t o r e f e r e n c e /5/, the f o l l o w i n g expression can be deduced:

where A* i s t h e amplitude which corresponds t o t h e unpinning strain; E*, 6 a r e constant. The experimental d a t a i s l i s t e d i n Table 3, and t h e p l o t InA* % g a i n s t 1/T i s shown i n Fig. 5. These two curves a r e w e l l f i t by two s t r a i g h t l i n e s w i t h t h e same slope:

I n A* = -4.5 + 2143/T f o r O.Ol%wt RE I n A* = -5.0 + 2143/T f o r 0.06%wt RE

From t h e above e m p i r i c a l expression t h e b i n d i n g energy betwen RE atom and d i s l o c a t i o n i s obtained. The value i s about 0.19 eV.

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From t h e d i s c u s s i o n above, i t may be concluded t h a t :

1. When RE < 0.01%, t h e c l e a r a n c e a c t i o n i s m a i n l y due t o t h e a c t i v i t y o f RE. 2. When RE > 0.01%, t h e RE elements a c t as s o l u t e atoms s e g r e g a t i n g t o t h e g r a i n boundaries up u n t i l about 0.5% and meanwhile p a r t o f RE elements a c t as s o l u t e atoms e x i s t i n g i n t h e i n t e r i o r o f t h e g r a i n s . These RE atoms a r e l o c a t e d m a i n l y i n t h e d e f e c t s o f d i s l o c a t i o n s . I n t h e case o f Al, t h e 0.5% RE c o n t e n t i s a s a t u r a t i n g c o n t e n t f o r g r a i n boundaries. 3. When RE > 0.5%, t h e AT-RE e u t e c t i c compound i s formed.

Table-?' Grainboundary r e l a x a t i o n p a r a m e t e r s

Note: -=Hm/~(l/? I/!Pm)

,

No. 5-2 6 3 . 0 " ~ g h r , No. 7-2 620-12 7 h r a n n e a l e?i:

Note: No. 5-2 and 7-2 i s annealed a t 640 C 3 h r and 620 C 7hr r e s p e c t i v e l y .

Table-2 Grain s i z e w i t h d i f f e r e n t RE c o n t e n t ( 4 5 0 ~ ~ 2hr an- n e a l e d )

Table-7 lnA* v a l u e a t d i f f e r e n t T f o r suecimen. No. 2 and 3.

NO.

~ ~ 1 0 ~

(mm)

0 1 2 3 4 5-1 5-2 6 7-1 7-2

20 32 1 6 6.3 11 2.0 1 8 1.2 0.78 2.4

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C10-386 JOURNAL DE _PHYSIQUE

r No.

" ₃ p E a . 0 6

I

Fig. 1 Q'I v e r s u s T ex- permental curves(varioui.

RE content i n pure ~ 1 ) .

Tig. 3 Q-1 v e r s u s e I / T curves ob- t a i n e d from Fig. 1 and Fig. 2 a f t e r s u b t r a c t l o n of background.

Fig. 2 Q-I v e r s u s T expe- r i m e n t a l curves f o r specimen9 No. 6-8.

Fig. 4 B H a s a f u n c t i o n of RE content.

Fig. 5 Curves of InA* a s a f u n c t i o n of r e c i p r o c a l tempera- t u r e f o r specimens A1-0 01 %RE and A l - 0.06% RE.

Reference

/ I / Gschneidner A.Fr. Rare E a r t h a l l o y s (1 961 ) c o l o n l a l p r e s s . U . S .A.

/2/ Cheng Jia-ning and Yu Qui-3% Rare Earth 4, (1 9 8 d ) 1 ( I n Chinese) /3/ Robert J.T.A. and Barrandape Trans. AINE .242 (1968) 2299 /4/ N0wick.A.S. and Berry.B.S. Acta Met. 10 (1962) 312

/5/ Weinig:S. and Mach1in.F.S _J. Appl. Phys. 27 (1956) 734