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INTERNAL FRICTION STUDY OF INTERFACE
DYNAMICS FOR STRESS-INDUCED I/C
TRANSITION IN NiTi ALLOY
Li Jianghong, Zhang Jinxiu
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C10, supplement au n012, Tome 46, decembre 1985 page C10-637
INTERNAL FRICTION STUDY OF INTERFACE DYNAMICS FOR STRESS-INDUCED I/C TRANSITION IN NiTi ALLOY
LI JIANGHONG AND ZHANG JINXIU
Department
o f
P h y s i c s , Z h o n g s h a n , G u a n g z h o u , C h i n aA b s t r a c t
-
An i n t e r n a l f r i c t i o n peak and a minimum o f modulus have been found i n t h e process o f s t r e s s - i nduced r e v e r s i b l e incommensurate (I)/commensurate ( c ) t r n s i t i o n i n Ni-49 a t % T i a l l o y . The i n t e r n a lB
f r i c t i o n peak h e i g h t
Q-
and modulus d e f e c t AM/M wer? a s s o c i a t e d w i t h t h e I / c t r a n s i t i o n i n c r e a s e w i t h i n c r e a s i n g s t r a i n r a t e r . An e x p l i c i t f u n c t i o n a l r e l a t i o n s h i p between average v e l o c i t y o f I / c phase i n t e r f a c e Vand e f f e c t i v e phase t r a n s i t i o n d r i v i n g f o r c e AG/=AG-hGR was d e r i v e d , w i t h r e s u l t V=V ( A G - A G ~ ) .
INTRODUCTION I---
The measurement o f i n t e r n a l f r i c t i o n can p r o v i d e a l o t o f i n f o r m a t i o n about t h e process o f phase t r a n s i t i o n s i n c r y s t a l l i n e s o l i d s . But t h e measurements were c a r r i e d o u t , f o r t h e most p a r t , i n t h e process o f c o o l i n g and heating. I n t h e p r e s e n t work, t h e i n t e r n a l f r i c t i o n was i n v e s t i g a t e d i n t h e process of s t r e s s - induced I / c t r a n s i t i o n o f N i T i a l l o y as a f u n c t i o n o f s t r a i n . A f t e r about twenty- f i v e s t r a i n c y c l e s a s t a b l e a l p r e v e r s i p l e stress-induced I / c t r a n s i t i o n can be obtained, and t h e o - r
,
R-E, Q -E and f -E curves were i n v a r i a n t w i t h s t i l l mores t r a i n c y c l e s .
Several models had been proposed t o e x p l a i n t h e i n t e r n a l f r i c t i o n a s s o c i a t e d w i t h m a r t e n s i t e t r a n s i t i o n i n t h e l i t e r a t u r e /1-4/. One of t h e a u t h o r s has p u t f o r w a r d a new phase i n t e r f a c e dynamics model /5/ and t h e expermental r e s u l t s were compared w i t h t h i s new model.
I 1
-
EXPERIMENTThe w i r e sample (+0.8x15Onm) o f Ni-49 a t % T i was annealed a t 500°C f o r one hour and a i r - c o o l e d t o room temperature. I n t e r n a l f r i c t i o n was measured by a m i d d l e t o r s i o n pendulum on a t e n s ' l e t e g t i n g machine m o d i f i e d w i t h a f o u r - t e r m i n a l p o t e n t i a l equipment. The Q - l - r , f - - F , IJ-E and R ( e l e c t r i c a l r e s i s t a n c e ) - r curves were measured s i m u l t a n e o u s l y f o r t h e same specimen i n t h e process o f s t r e s s - i n d u c i n g s t r a i n cycles. The frequency o f measurement was about 1
Hz.
The experimental temperature o f 20-30°C was about 5OC h i g h e r t h a n t h e I / c t r a n s i t i o n temperature o f t h i s N i T i specimen.
C1O-638 JOURNAL
DE
PHYSIQUEI 1 1
-
RESULTS AND DISCUSSIONBecause t h e t e s t i n g temperature i s about 5 O C h i g h e r t h a n t h e t e m p e r a t u r e of I / c t r a n s i t i o n . i t i s p o s s i b l e t o t r a n s f o r m phase I i n t o phase c by s t r e s s - i n d u c i n g and t o observe s u p e r e l a s t i c i t y . The s t r a i n was s u p p l i e d by t h e I-C t r a n s i t i o n f o r t h e process o f l o a d i n g and by t h e C-I t r a n s i t i o n f o r t h e unloading. The s t r a i n i s z e r o when unloaded t o a = 0.
But d u r i n g t h e f i r s t s e v e r a l s t r a i n c y c l e s , t h e t r a n s i t i o n i s not c o m p l e t e l y r e v e r s i b l p , because t h e r e i s a small i n c r e a s i n g amount of i n t e r n a l f r i c t i o n peak h e i g h t O-p, a small remanent e l e c t r i c r e s i s t a n c e increment and a modulus decrement a f t e r u n l o a d i n g t o o=O and E=O. It means t h a t a small amount o f phase C remains a f t e r each s t r a i n c y c l e , as confirmed by x - r a y d i f f r a c t i o n measurement. The
remanent amount o f phase C tends t o a s a t u r a t e d v a l u e a f t e r about t w e n t y - f i v e s t r a i n c y c l e s , t h n a c o m p l e t e l y r e v e r s i b l e s t r e s s - i n d u c e d I l c t r a n s i t i o n can be o b t a i n e d
f
and t h e 0- -E, R-E and a-E curves a r e reproduced c o m p l e t e l y d u r i n g f u r t h e r s t r a i n
c y c l e s
.
The e f f e c t o f s t r a i n r a t e
;
( f r o m 0 . 7 9 ~ 1 0 - ~ / s t o 1 7 . 7 ~ 1 0 - ~ / ~ ) on a-E, AR/R-E,AM/M-E and Q-'-E curves was exam-ned i n t h e specimen. As shown i n Figs. 1 t o 4, t h e i n t e r n a l f r i c t i o n peak h e j g h t 0 - I , modulus d e f e c t AM/M and t h e area o f U-E l o o p
i n c r e a s e w i t h i n c r e a s i n g E , b u t P t h e AR/R-E c u r v e i s r o u g h l y unchanged. The l a s t r e s u l t means t h a t t h e e f f e c t o f E i s n o t a s s o c i a t e d w i t h t h e p o s s i b l e small change
o f t e m p e r a t u r e i n t h e process o f s t r e s s - i n d u c e d I / c t r a n s i t i o n .
From phase i n t e r f a c e dynamics and t h e o r y o f i n t e r n a l f r i c t i o n . an e x p r e s s i o n had been d e r i v e d by one o f t h e a u t h o r s as f o l l o w s 15-71:
dlnf(AG-AGR)
;
dF=
--
-
~(AG-AGR) MO-l d ~ (1)
where ~ ( A G ' ) = V(AG') i s t h e average v e l o c i t y o f p h a i e i n t e r f a c e V as a f u n c t i o n of AG'
,
AG'=AG-AG i s t h e e f f e c t i v e phase t r a n s i t i o n d r i v i n g f o r c e and A G ~ i s t h eR
r e s i s t a n c e e x e r t e d on t h e moving i n t e r f a c e . bG(o) can he c a l c u l a t e d f r o m thermo- dynamics as AG(u) = ( U - U ~ ) E ~ , a i s t h e s t r e s s a t which t h e two phases a r e i n balance, E i s t h e s t r a i n p r o v i a e d by t h e t r a n s i t i o n . Using equ. (1) and t h e
experiment% r e s u l t s i n Fig. 1, an e x p l i c i t e x p r e s s i o n f o r V(AG1 ) can be d e r i v e d as (Fig. 5)
v
=v*
( A G - A G ~ ) , ( 2 )and AG = l c a l / m o l , where V* and m a r e dynamics parameters. A c c o r d i n g t o equ. ( ? ) , t h e i n a e r f a c e i s movable o n l y when AG>AGR.
From equ. ( 1 ) we have
where A M ' / M i s t h e modulus d e f e c t produced by t h e moving i n t e r f a c e . Assuming t h e e f f e c t o f t h e s o f t mode i s AMu/M, we have
AM
€ 0 AM' n d l n f ( A G 1 ) dF
=z+-FT/b
de~--xii]
/ I / Delorme, J.R., 1971, J. Phys.,
32,
101./2/ Dejonghe, e t al., 1976, S c r i p t a Met.,
g,
1125./3/ M e r c i e r , 0.. Melton, K.N., De P r e v i l l e , Y. 1979, Acta Met.,
27,
1467. /4/ Yang Z h a o j i n , Zou Yifeng, Zhang Z h i f a n g and Wang Yening, 1987, Acta Met., S i n i c a ,18,
21./5/ Zhang J i n x i u and L i Xiejun, Acta o f Zhongshan U n i v e r s i t y , 1985,