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Submitted on 1 Jan 1985
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THE INTERNAL FRICTION STUDY OF
INTERFACE DYNAMICS OF NiTi ALLOY IN THE
PROCESSES OF MARTENSITIC AND I/C PHASE
TRANSFORMATION
Luo Laizhong, Zhang Jinxiu
To cite this version:
THE INTERNAL FRICTION STUDY OF INTERFACE DYNAMICS OF NiTi ALLOY IN THE PROCESSES OF MARTENSITIC AND I/C PHASE TRANSFORMATION
LUO LAIZHONG AND ZHANG JINXIU
D e p a r t m e n t
of
P h y s i c s , Z h o n g s h a n U n i v e r s i t y , Guangzhou, C h i n aA b s t r a c t - T w o i n t e r n a l f r i c t i o n p e a k s a s s o c i a t e d w i t h m r t e n s i t i c a n d I / C ( R ) p h a s e t r a n s f o r m t i o n s w e r e o b s e r v e d i n t h e f i r s t
t h e r m a l c y c l e f o r NITi a;loy.By u t i l y z i n g t h e e x p e r i m e n t a l data o f I F ( a s a f u n c t i o n o f T/w,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 o f i n t e r f a c e d y n a m i c s was o b t a i n e d a s v = v * ~ x ~ ( - ~ & / A G - & G ~ ) , a n d t h e e x p r e s s i o n o f I F d u r i n g t h e p r o c e s s o f t r a n s f o r m a t i o n a s Q - ' = C - ~ G * ( ~ F / ~ T ) ~ C ( ~ / ~ ( ~ G - ~ G ~ ) ~ , w h e r e V i s t h e a v e r a g e v e l o c i t y o f p h a s e i n t e r f a c e , A G i s t h e p h a s e t r a n s f o r m a t i o n d r i v i n g f o r c e ; a n d 4Ga i s t h e t r a n s f o r m t i o n r e s i s t a n t f o r c e , w h i c h has t h e o r d e r o f 5 c a l / m o l , 8 c a l / m o l a n d 1 0 c a l / m o l f o r I/R,R/M a n d M/p t r a n s f o r m a t i o n s r e s p e c t i v e l y . The " S o f t Mode E f f e c t " d u r i n g t h e t r a n s f o r m a t i o n p r o c e s s e s h a s b e e n d i s c u s s e d . I- INTRODUCTION The i n t e r n a l f r i c t i o n p e a k a t low f r e q u e n c y i n t h e p r o c e s s o f m r t e n - s i t i c t r a n s f o r m t i o n h a v e b e e n o b s e r v e d i n m n y a l l o y s s u c h a s FeMn ( l ) , N i T i ( 2 ) a n d AuCd ( 3 ) e t a l . . T h e s e - I F p e a k s h a v e c h a r a t e r s o f : 1 ) when t h e f e m p e r a t u r e v a r i a t i o n r a t e T = O , t h e p e a k h e i g h t
i s
p r o p o r t i o n a l t o T/w ( w i s a n g u l a r f r e q u e n c y o f m e a s u r i n g ) ; 2 ) t h e I F i s i n d e p e n d e n t o n t h e a m p l i t u d e o f m e a s u r e m e n t ; 3 ) when ' f = ~ , t h e c h a r a c - t e r i z i n g I F a s s o c i a t e d w i t h t h e t r a n s f o r m a t i o n p r o c e s s d i s a p p e a r s . T h e r e are s o = m o d e l s a t t e m p t e d t o i n t e r p r e t e t h e damping mechanism o f m r t e n s i t i c t r a n s f o r m t i o n ( 4 , 5 , 6 , 3 ) . R e c e n t l y , a n i n t e r f a c e dynamic model h a s b e e n p r o p o s e d by o n e o f t h e a u t h o r s ( 7 ) , a n d t h e I F was c o n s i d e r e d t o be a Maxwell-type v i s c o u s damping r e s u l t e d f r o m t h e m o t i o n o f i n t e r f a c e s i n t h e p r o c e s s o f t r a n s f o r m a t i o n . I n t h i s p a p e r , w e r e p o r t a I F s t u d y o f i n t e r f a c e d y n a m i c s o f N i T i a l l o y i n t h e p r o c e s s o f m r t e n s i t i c a n d I / C ( R ) p h a s e t r a n s f o r m a t i o n .JOURNAL
DE
PHYSIQUE11-EXPERIMENT
The I F , e l a s t i c modulus ( f 2 ) a n d e l e c t r i c r e s i s t a n c e (AR) were measured d u r i n g l i n e a r h e a t i n g a n d c o o l i n g p r o c e s s e s on a n improved
~ 8 ' s
t o r s i o n - a l pendulum.Al1 t h r e e p a r a m e t e r s were measured s i m u l t a n e o u s l y on t h esame specimen , w i t h t e m p e r a t u r e v a r i a t i o n r a t e $=0.25-5K/min a n d
f r e q u e n c y of m e a s u r i n g f-1Hz.The NiTi a l l o y u s e d h a s a nominal composi- t i o n o f Ni-49.7 a t % T i , a n d c o l d r o l l e d t o a t h i n p l a t e . S p e c i m e n s w e r e t a k e n t o t h e d i m e n s i o n of 35x2.5x0.25(mms) a n d w e r e a n n e a l e d f o r 1 h o u r a t 500 OC b e f o r measurement.Al1 t h e measurements of ~ ~ , f ' a n d P R were
c a r r i e d o u t i n t h e f i r s t t h e r m a l c y c l e f o r t h e I F i s d e p e n d e n t s e n s i - t i v e l y on t h e r m l c y c l e s ( 8 ) .
111-RESULTS AND DISCUSSIONS
Two I F p e a k s which s e p e r a t e d c l a r i l y were o b s e r v e d i n t h e d e s c e n d i n g p r o c e s s e v e n f o r t h e f i r s t t h e r m l c y c l e ( f i g . 1) .The f i r s t one p e a k accompanied by a s h a r p minimum of modulus ( f a ) a n d a n a b n o r m l change i n e l e c t r i c r e s i s t a n c e (OR) i s r e s u l t e d from t h e incornmesurate t o com- m e n s u r a t e ( I / R ) p h a s e t r a n s i t i o n . T h e s e c o n d peak accompanied by t h e d e c r e a s e of e l e c t r i c r e s i s t a n c e i s c a u s e d by t h e m r t e n s i t i c t r a n s f o r - mation (R/M).While i n t h e p r o c e s s o f a s c e n d i n g , o n l y one I F p e a k a s s o - c i a t e d w i t h t h e r e v e r s e m r t e n s i t i c t r a n s f o r m t i o n (M/P) was o b s e r v e d . TGe p e a k h e i g h t s of I / R , R / M a n d M/P t r a n s f o r m t i o n a r e p r o p o r t i o n a l t o (T/w) ( f i g . 2 ) , b u t t h e y a r e n o t
a
good l i n e a r r e l a t i o n s h i p a s r e p o r t e d ( 1). C o n s i d e r i n g t h e motion o f p h a s e i n t e r f a c e s i n t h e p r o c e s s o f t r a n s f o r - m t i o n u n d e r a c t i o n of t r a n s f o r m t i o n d r i v i n g f o r c e AG,and a l s o t h e e x i s t a n c e of r e s i s t a n t f o r c e 4 G R , t h e r e e x i s t s a r e l a t i o n s h i p between t h e a v e r a g e moving r e l o c i t y of t h e i n t e r f a c e s V a n d t h e e f f e c t i v e d r i v i n g f o r c e AG' =6G-AGa a s V=q(AG-AGR ).
From t h i s c o n s i d e r a t i o n , a i n t e r f a c e dynamic model r e l a t e d t o I F a n d AM/M ( t h e modulus minimum o f m e a s u r i n g ) i n t h e p r o c e s s o f p h a s e t r a n s f o r m t i o n has been e s t a b l i s h e d a s where n i s t h e c o u p l i n g f a c t o r , J l i s t h e s h e a r modulus,dF/dT i s t h e t r a n s f o r m a t i o n r a t e of new p h a s e a n d E. i s t h e t r a n s f o r m a t i o n s t r a i n . T h i s e x p r e s s i o n c a n e x p l a i n r e a s o n a b l y a l l t h e t h r e e c h a r a c t e r i s t i c s of I F d u r i n g I / R a n d M/P t r a n s f o r m a t i o n mentioned a b o v e . Equ. ( 1) c o u l d be r e a r r a n g e d a s-p
(AG' ) = C * ~ L O ~ ? ( ~ G ' ) / d ~ ~ ' = d ' w / @ o d ~ / d ~ ) ( 3 )A l l t h e p a r a m e t e r s i n t h e r i g h t hand s i d e of e q u . ( 3 ) can be measured by e x p e r i m e n t s . S o , b y u t i l y z i n g e q u . ( 3 ) a n d e x p e r i m e n t a l d a t a , a n e x p l i c i t f u n c t i o n a 1 r e l a t i o n of V = p ( A G 1 ) c a n be o b t a i n e d . For t h e f i r s t o r d e r p h a s e t r a n s f o r m t i o n , t h e v a r i a t i o n of e n t h a l p y A H w i t h t e m p e r a t u r e c a n be i g n o r e d , t h e n t h e c h e m i c a l d r i v i n g f o r c e can be w r i t t e n a s AG=aH*(T-T,)/T, ( 4 )
where
To
i s t h e b a l a n c e t e m p e r a t u r e between two p h a s e , a n d A H was measured by DSC-IIC (PERKIN-ELMER).
T a k i n g AGA a s a p a r a m e t e r t o be d e t e r m i n e d n a n d u s i n g t h e l i n e a r a n a l y s e methodewe g e t ( f i g . 3 )
8 c a l / m o l a n d 1 0 c a l / m o l f o r I / R ,R/M a n d M/P t r a n s f o r m t i o n s , r e s p e c - t i v e l y .
p u t e q u . ( 5 ) i n t o e q u . ( l ) , w e o b t a i n e d t h e e x p r e s s i o n o f I F d u r i n g p h a s e t r a n s f o r m a t i o n a s
JOURNAL
DE PHYSIQUE
F i g . 2-The Q" -?/w c u r v e s f o r I / R , R / M a n d M/P t r a n s f o r m t i o n s F i g . 1 - P l o t s o f i n t e r n a l f r i c t i o n modulus a n d r e s i s t a n c e v s t e m p e r a t u r e tn. i r - 3 UIO *C-AGR>F i g . 4-The AM/M-?/w c u r v e o f F i g . 3-Logp(A G-AGa) -Log(AG-AGR)
