HAL Id: jpa-00221956
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Submitted on 1 Jan 1982
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STRESS-INDUCED MARTENSITIC
TRANSFORMATIONS IN Cu-Zn-Al AND Cu-Zn-Ga ALLOYS
T. Saburi, Y. Inada, S. Nenno, N. Hori
To cite this version:
T. Saburi, Y. Inada, S. Nenno, N. Hori. STRESS-INDUCED MARTENSITIC TRANSFORMATIONS
IN Cu-Zn-Al AND Cu-Zn-Ga ALLOYS. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-633-
C4-638. �10.1051/jphyscol:19824101�. �jpa-00221956�
JOURNAL DE PHYSIQUE
CoZZoque C4, suppZ6ment au n o 12, Tome 43, de'cembre 1982 page C4-633
STRESS-INDUCED MARTENSITIC TRANSFORMATIONS IN Cu-Zn-A1 AND Cu-Zn-Ga ALLOYS
T. S a b u r i , Y . I n a d a , S. Nenno and N. Hori
Department of Materials Science and Engineering, Osaka University, Suita, Osaka, Japan
(Accepted 9 August 1982)
A b s t r a c t . - Two-stage p s e u d o e l a s t i c i t y i n Cu-(32-16at%)Zn-(4-16at%)Al a l l o y s and a Cu-2lat%Zn-12at%Ga a l l o y have been i n v e s t i g a t e d by t e n s i l e t e s t i n g . Main i n t e r e s t was t h e i n f l u e n c e o f a l l o y c o m p o s i t i o n and t e s t t e m p e r a t u r e on t h e t w o - s t a g e p s e u d o e l a s t i c i t y b e h a v i o r . I t h a s been found t h a t t h e s h a p e o f t h e p s e u d o e l a s t i c i t y loop changes markedly depending on t h e s e f a c t o r s . By r e d u c i n g e / a - v a l u e below 1.42, t h e s t r e s s - i n d u c e d ai p h a s e becomes s t a b l e . I n t h e Cu-Zn-Ga a l l o y s l i p d e f o r m a t i o n t a k e s p l a c e b e f o r e a; m a r t e n s i t e i s
formed from
~ i .
I n t r o d u c t i o n . - Many B-phase a l l o y s behave p s e u d o e l a s t i c a l l y above t h e i r Ms tempera- t u r e . T h i s p s e u d o e l a s t i c i t y , i n g e n e r a l , i s a s s o c i a t e d w i t h s t r e s s - i n d u c e d marten- s i t i c t r a n s f o r m a t i o n s and i n some o f t h e a l l o y s (Cu-Al-Ni ( 1 , 2 ) , Cu-Zn ( 3 , 4 ) , Cu-Zn- A1 ( 5 - 7 ) , Au-Ag-Cd ( 8 ) ) , t h i s b e h a v i o r o c c u r s i n two o r more s t a g e s , e a c h b e i n g a s s o c i a t e d w i t h a d i f f e r e n t m a r t e n s i t i c t r a n s f o r m a t i o n . I n Cu-Zn-A1 a l l o y s two s u c c e s s i v e t r a n s f o r m a t i o n s o c c u r on s t r e s s i n g ; t h e f i r s t one i s from t h e p a r e n t
61
t o a 9R m a r t e n s i t e (B;) and t h e second i s from t h e B; t o a new m a r t e n s i t e (a1).
I t h a s been known t h a t i n Cu-Zn-A1 a l l o y s of h i g h aluminum c o n t e n t , t h e s t r e s s - induced ai d i s a p p e a r s on u n l o a d i n g ( 5 ) , w h i l e t h e a; i n low aluminum c o n t e n t a l l o y s i s o f t e n r e t a i n e d on u n l o a d i n g ( 6 , 9 ) . The p r e s e n t work was u n d e r t a k e n t o s t u d y t h e i n f l u e n c e o f a l l o y c o m p o s i t i o n on t h e p s e u d o e l a s t i c b e h a v i o r o f Cu-Zn-A1 a l l o y s i n more d e t a i l and a l s o t o examine t h e s t a b i l i t y o f t h e s t r e s s - i n d u c e d a i m a r t e n s i t e .
Behavior o f a Cu-Zn-Ga a l l o y was a l s o s t u d i e d and compared w i t h t h a t o f t h e Cu-Zn- A 1 a l l o y s .
E x p e r i m e n t a l P r o c e d u r e . - F i v e Cu-Zn-A1 a l l o y s (nominal aluminum c o n t e n t ; 4 , , 6 , 8 , 1 2 , 1 6 a t % ) and one Cu-Zn-Ga a l l o y (12at%Ga) were p r e p a r e d by m e l t i n g raw m a t e r i a l s (99.99%-Cu, -Zn, - A 1 and 99.999%-Ga) i n e v a c u a t e d q u a r t z c a p s u l e s . S i n g l e c r y s t a l s o f t h e a l l o y s were grown by t h e Bridgman method. The a l l o y s were homogenized f o r 8.64x104 s e c a t 1073K andquenched i n t o i c e d w a t e r . A l l o y c o m p o s i t i o n s were chosen u s i n g t h e d a t a o f Delaey (10) s o t h a t t h e y l i n e up a l o n g t h e Ms=273K l i n e i n t h e t e r n a r y diagram ( F i g . 1 ) . The Ms t e m p e r a t u r e s were d e t e r m i n e d b y e l e c t r i c a l r e s i s t i v i t y measurement and a r e shown i n T a b l e 1, t o g e t h e r w i t h t h e v a l u e s o f e l e c t r o n - a t o m r a t i o ( e / a ) . As a l l o y c o m p o s i t i o n changes a l o n g t h e Ms=273K l i n e , e / a changes a s shown i n F i g . 1.
T a b l e 1 Composition o f a l l o y s , t h e i r t r a n s f o r m a t i o n t e m p e r a t u r e s and e l e c t r o n - a t o m r a t i o .
A l l o y c o m p o s i t i o n ( a t % ) Ms(K) Mf(K) As(K) Af(K) e / a
Cu-31.6Zn-4.4A1 254 236 250 256 1.40
Cu-29.3Zn-6.2A1 248 230 244 251 1 . 4 2
Cu-26.6Zn-8.1A1 253 233 243 255 1 . 4 3
Cu-21.6Zn-11.9A1 223 205 213 226 1.45
Cu-16.1Zn-16.OA1 242 228 238 246 1 . 4 8
Cu-21.4Zn-12.OGa 283 - 1 . 4 5
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19824101
JOURNAL DE PHYSIQUE
F i g . 2 O r i e n t a t i o n o f t h e t e n s i l e a x e s .
F i g . 1 Composition and e l e c t r o n - a t o m r a t i o o f t h e a l l o y s .
C r y s t a l o r i e n t a t i o n s were d e t e r m i n e d by t h e b a c k - r e f l e c t i o n Laue method and t e n s i l e t e s t specimens (3mmxlmmx40mm, gage l e n g t h 25mm) were c u t from t h e s i n g l e c r y s t a l s . The specimens were a l i g n e d i n s u c h a way t h a t t h e y have a t e n s i l e a x i s c l o s e t o [ 0 0 1 ] ~ ~ a s shown i n F i g . 2 . For t h e 4 . 4 a t % A l a l l o y , specimens a t t h e B o r i e n t a t i o n i n F i g . 2 were a l s o p r e p a r e d . T e n s i l e t e s t s were made w i t h a s t r a i n r a t e of 3 x 1 0 - ~ a t v a r i o u s t e m p e r a t u r e s between 77K and 363K. I n s i t u o b s e r v a t i o n s on t h e s t r e s s - i n d u c e d t r a n s f o r m a t i o n s were made by an o p t i c a l microscope f o r t e n s i l e t e s t s a t room t e m p e r a t u r e . T r a n s m i s s i o n e l e c t r o n microscope o b s e r v a t i o n s were made on t h e s t r e s s - i n d u c e d a j m a r t e n s i t e i n 4 . 4 and 6 . l a t % A l a l l o y s s i n c e t h e m a r t e n s i t e was s t a b l e a t room t e m p e r a t u r e i n t h e s e a l l o y s .
R e s u l t s . - F i g u r e 3 shows a s t r e s s - s t r a i n c u r v e o f t h e 1 6 . 0 a t % A l a l l o y i n t h e n e a r [ 0 0 1 ] ~ ~ o r i e n t a t i o n a t 292K (50K above Ms). The c u r v e i s c h a r a c t e r i z e d by two s t a g e s b o t h i n l o a d i n g and u n l o a d i n g . By i n s i t u microscope o b s e r v a t i o n it was confirmed t h a t t h e , f i r s t s t a g e c o r r e s p o n d s t o a s t r e s s - i n d u c e d m a r t e n s i t i c t r a n s f o r m a t i o n
(61-to-$1) and t h e second t o a n o t h e r s t r e s s - i n d u c e d t r a n s f o r m a t i o n . S i m i l a r
o b s e r v a t i o n s o f t h e two s t a g e b e h a v i o r i n Cu-Zn-A1 a l l o y s have been made by ~ a r c e l 6 e t a l . ( S ) , by S a t o e t a l . (6) and by Delaey e t a l . ( 7 , 1 1 ) . As w i l l b e shown l a t e r f o r t h e 4 . 4 a t % A l a l l o y t h e second s t a g e c o r r e s p o n d s t o t h e B i - t o - a i t r a n s f o r m a t i o n . The f i r s t s t a g e d u r i n g u n l o a d i n g c o r r e s p o n d s t o t h e a i - t o - B j t r a n s f o r m a t i o n and t h e second t o t h e 6 i - t o - B 1
.
With t h i s 16at%Al a l l o y , t h e f o u r s t a g e s i n t h e above sequence a r e o b s e r v e d up t o 313K (70K above Ms). I t i s t o b e n o t e d t h a t t h e d i f f e r e n c e between G ( B ; % ~ ) ( t h e c r i t i c a l s t r e s s t o i n d u c e t h e B;-to-a; t r a n s f o r m - a t i o n ) and o ( a i + ~ i ) i s e x t r e m e l y l a r g e e130MPa) compared t o t h a t between o(B1+B?) and a (B>+B1) (-30MPa).
m 0-
F i g . 3 S t r e s s - s t r a i n c u r v e o f
, 2 9 2 K t h e Cu-16.1Zn-16.9A1 a l l o y .
The c u r v e shown i s t h e second c y c l e ; a l t h o u g h a b o u t 2% o f permanent s t r a i n remained a f t e r t h e f i r s t c y c l e , t h e r e was no a p p r e c i a b l e permanent
I I s t r a i n a f t e r t h e second
15 2 0 2 5
c y c l e . Elongat Ion (%I
Elongation 1 %
F i g . 4 S t r e s s - s t r a i n c u r v e s o f t h e Cu-21.6Zn-11.9A1 a l l o y .
F i g . 5 S t r e s s - s t r a i n c u r v e s of t h e Cu-29.3Zn-6.2A1 a l l o y a t 297K (a), and a photo-micrograph o f t h e specimen u n d e r s t r e s s ( b ) . As c o m p o s i t i o n changes from Cu-16.1Zn-16.OA1 towards Cu-31.6Zn-4.4A1 ( a s e / a d e c r e a s e s ) , t h e c r i t i c a l s t r e s s o ( B l + a l ) d e c r e a s e s markedly. F i g . 4 shows a s e r i e s o f s t r e s s - s t r a i n c u r v e s o f t h e I l . g a t % A l a l l o y i n t h e n e a r [ 0 0 1 ] ~ ~ o r i e n t a t i o n . I n t h e t e m p e r a t u r e r a n g e between 223K and 263K (40K above Ms), f o u r s t a g e s a p p e a r i n t h e normal o r d e r a s shown i n F i g . 4 ( a ) f o r 243K (20K above M s ) . a(Bl+Bi) and, o ( ~ i + f 3 ~ ) i n c r e a s e r a p i d l y w i t h i n c r e a s i n g t e m p e r a t u r e , w h i l e o (Bj-rcli) and o (al+Bi) show a s l i g h t n e g a t i v e t e m p e r a t u r e dependence. Consequently a ( P i + @ l ) r e a c h e s t h e l e v e l of o(uj+B>) a t 272K. Thus t h e two t r a n s f o r m a t i o n s o c c u r a t t h e same s t r e s s l e v e l on u n l o a d i n g and o n l y one s t a g e a p p e a r s a t t h i s t e m p e r a t u r e . With f u r t h e r i n c r e a s e i n t e s t t e m p e r a t u r e , o(B)+B1) exceeds o(ui+B;) and, t h e r e f o r e , t h e B>-to-B1 t r a n s f o r m a t i o n o c c u r s b e f o r e t h e a i ; t o - B i t r a n s f o r m a t i o n a s shown i n F i g . 4 ( c ) ( a t 2931;). A t 323K ( F i g . 4 ( d ) ) , o(Bl+Bl) r e a c h e s o(B;-..i) and o n l y one s t a g e a p p e a r s on l o a d i n g , s i n c e t h e two t r a n s f o r m a t i o n s o c c u r a t t h e same s t r e s s l e v e l . The s t r e s s d i f f e r e n c e between t h e two s t a g e s o f u n l o a d i n g becomes l a r g e r w i t h i n c r e a s i n g t e m p e r a t u r e , s i n c e o (Bl-tBi) i n c r e a s e s more r a p i d l y .
The t e m p e r a t u r e r a n g e i n which t h e t y p i c a l t w o - s t a g e b e h a v i o r a p p e a r s , becomes n a r r o w e r a s e / a d e c r e a s e s and t h e 6 . 2 a t % A l a l l o y ( e / a 1 . 4 2 ) d o e s n o t show t h e two s t a g e s c l e a r l y d u r i n g u n l o a d i n g a t any t e m p e r a t u r e . I n t h e 6 . 2 a t % A l a l l o y , o n l y one s t a g e a p p e a r s b o t h on l o a d i n g and u n l o a d i n g a t 297K, and h y s t e r e s i s o f t h e pseudo- e l a s t i c i t y loop ( s t r e s s d i f f e r e n c e H i n F i g . 5 ( a ) ) becomes l a r g e f o r t h e e n t i r e u n l o a d i n g p r o c e s s . About 22% e l o n g a t i o n i s o b t a i n e d by t h e s t r e s s - i n d u c e d
C4-636 JOURNAL DE PHYSIQUE
t r a n s f o r m a t i o n . F i g . 5(b) shows an o p t i c a l microscope o b s e r v a t i o n made o f t h e d e f o r m a t i o n p r o c e s s i n t h e f l a t s t a g e o f F i g . 5 ( a ) . On s t r e s s i n g , p l a t e s o f t h e most f a v o r a b l e v a r i a n t (A) o f
B i
a r e induced f i r s t . Then p l a t e s o f t h e second v a r i a n t (B) o f 6 1 a r e induced t o c r o s s p l a t e s o f A v a r i a n t , and a t t h e c r o s s i n g o f t h e s e , a\ m a r t e n s i t e i s formed. I n t h i s manner, t r a n s f o r m a t i o n s from Bl t o 61 and 6: t o a? proceed a t t h e same s t r e s s l e v e l f i n a l l y p r o d u c i n g a s i n g l e c r y s t a l o f a ; . I f l o a d i n g i s s t o p p e d a t t h i s p o i n t (P) a l m o s t t h e e n t i r e e l o n g a t i o n d i s a p p e a r s on u n l o a d i n g . However, i f l o a d i n g i s c o n t i n u e d , an a b r u p t i n c r e a s e i n s t r e s s o c c u r s . T h i s i n d i c a t e s t h e end o f t h e s t r e s s - i n d u c e d t r a n s f o r m a t i o n s . When l o a d e d t o Q i n F i g . 5 , a l m o s t t h e e n t i r e e l o n g a t i o n remains even a f t e r complete u n l o a d i n g . T h i s seems t o i n d i c a t e t h a t s t r e s s - i n d u c e d l a t t i c e d e f e c t s h i n d e r t h e r e v e r s e t r a n s f o r m - a t i o n .With t h e 4 . 4 a t % A l a l l o y , t h e two s t a g e s do n o t a p p e a r f o r t h e o r i e n t a t i o n c l o s e t o [ 0 0 l I a 1 c l e a r l y a t any t e m p e r a t u r e , a s shown i n F i g . 6 ( a ) (b) ( c ) . I f t h e specimen i s s t r a i n e d more t h a n
l o % ,
a l a r g e permanent s t r a i n r e m a i n s a f t e r u n l o a d i n g . For t h e o r i e n t a t i o n B , h o w e v e r , t w o s t a g e s a p p e a r s e p a r a t e l y even a t 2 8 3 K ( 3 0 K above fils) a s shown i n F i g . 6 ( d ) . T h l s i s due t o t h e f a c t t h a t t h e Schmid f a c t o r f o r t h e B1-t o - a ; s h e a r i s much s m a l l e r t h a n t h a t f o r t h e ~ ~ - t o - 6 ' ~ s h e a r . As f o r t h e h y s t e r e s i s and t h e r e s i d u a l s t r a i n a f t e r u n l o a d i n g , b o t h of them a r e v e r y l a r g e when t h e specimen is s t r a i n e d i n t o t h e second s t a g e and unloaded; c o n t r a r y t o t h i s , h y s t e r e -
s i s i s much s m a l l e r and t h e e n t i r e s t r a i n i s r e c o v e r e d i f t h e s p e c i - men i s unloaded b e f o r e t h e second s t a g e s t a r t s . T h e r e f o r e , t h e r e s i d u a l s t r a i n and t h e l a r g e h y s t e r o s i s o f t h e
5 10 former c a s e can b e
a t t r i b u t e d t o t h e
F i g . 6 S t r e s s - s t r a i n c u r v e s o f t h e Cu-31.6Zn -4.4A1 a l l o y .
V) ( a ) (b) ( c ) O r i e n t a t i o n
C
5
A . (d) ( e ) O r i e n t a t i o n
1 0 15 R
E l o n g a t i o n ( x )
F i g . 7 S t r e s s - s t r a i n c u r v e s o f Cu-21.4Zn-12.OGa ( a and b J and a photomicrograph o f a h e a v i l y - d e f o r m e d p a r t of t h e specimen ( c )
s t a b i l i t y of
ai.
T h i s i s f u r t h e r confirmed i n F i g . 6 ( e ) , where t h e specimen was s t r a i n e d t i l l t h e end o f t h e f i r s t s t a g e (B1+Bi) a t 294K (above Ms),
c o o l e d t o 247K (below Mf) and loaded a g a i n a t t h i s t e m p e r a t u r e t o i n d u c e t h e Bi-to-cli t r a n s f o r m a - t i o n . I t i s seen t h a t t h e e n t i r e e l o n g a t i o n due t o t h e 6;-to-aj t r a n s f o r m a t i o n r e m a i n s a f t e r u n l o a d i n g .Cu-Zn-Ga a l l o y s behave l i k e Cu-Zn-A1 a l l o y s a s f a r a s t h e B1-to-6; t r a n s f o r m a - t i o n i s concerned ( 1 2 ) . The s t r e s s - s t r a i n curve i n F i g . 7 ( a ) i s t h e one o b t a i n e d f o r t h e 12.0at%Ga a l l o y ( t h e o r i e n t a t i o n o f n e a r [001]81) a t 300K (20K aboye Ms).
The s t r e s s - i n d u c e d e l o n g a t i o n o f a b o u t 9% which c o r r e s p o n d s t o t h e Bj-to-Bl t r a n s - f o r m a t i o n i s c o m p l e t e l y r e c o v e r e d on u n l o a d i n g . A f t e r 9% o f e l o n g a t i o n , an a b r u p t i n c r e a s e o f s t r e s s o c c u r s f o l l o w e d by a n o t h e r y i e l d i n g and t h e second s t a g e i n a way s i m i l a r t o t h e Cu-Zn-A1 a l l o y s . However, t h e second s t a g e d o e s n o t c o r r e s p o n d t o m a r t e n s i t i c t r a n s f o r m a t i o n . I n s t e a d it o c c u r s b y s l i p d e f o r m a t i o n . F i g . 7(b) shows an example. The specimen was s t r e s s e d t o t h e end o f t h e fil-to-6; t r a n s f o r m a t i o n a t 298K (10K above Ms) and t h e n c o o l e d t o 78K (below Mf). S i n c e t h e 8; m a r t e n s i t e i s s t a b l e a t t h i s t e m p e r a t u r e , s t r e s s - d r o p t a k e s p l a c e on u n l o a d i n g . By a p p l y i n g t e n s i l e s t r e s s a g a i n , t h e specimen y i e l d e d a t A. When t h e s t r e s s was removed a f t e r e l o n g a t i o n t o B , t h e e n t i r e p l a s t i c d e f o r m a t i o n remained. On s t r e s s i n g a g a i n t h e specimen e l o n g a t e d more t h a n 30% a t about t h e same s t r e s s l e v e l and f r a c t u r e d . An o p t i c a l microscope o b s e r v a t i o n r e v e a l e d t h a t t h e l a r g e p l a s t i c s t r a i n was due t o l o c a l i z e d s l i p d e f o r m a t i o n and t h a t n e c k i n g o f t h e specimen o c c u r e d a s s e e n i n F i g . 7 ( c ) . I t was found i n t h i s way t h a t s l i p d e f o r m a t i o n t a k e s p l a c e a t a s t r e s s l e v e l lower t h a n i s needed f o r t h e ~ i - t o - a j t r a n s f o r m a t i o n i n t h i s a l l o y .
By p l o t t i n g c r i t i c a l s t r e s s e s f o r t h e f i r s t and t h e second y i e l d i n g i n Cu-Zn-A1 and Cu-Zn-Ga a l l o y s a g a i n s t t h e n o r m a l i z e d t e s t t e m p e r a t u r e ( t e s t t e m p e r a t u r e minus t h e t e m p e r a t u r e where t h e e x t r a p o l a t e d s t r e s s becomes z e r o (Ms)), one o b t a i n s l i n e a r r e l a t i o n s shown i n F i g . 8 . The c r i t i c a l s t r e s s e s f o r r e v e r s e t r a n s f o r m a t i o n s were n o t p l o t t e d i n t h i s f i g u r e t o a v o i d c o m p l i c a t i o n . S i m i l a r p l o t s have been o b t a i n e d by S a t o e t a1. (13) r e c e n t l y . One f i n d s i n F i g . 8 t h e f o l l o w i n g s . ( i ) The O ( B ~ + B ; ) v e r s u s t e m p e r a t u r e r e l a t i o n s have a l a r g e p o s i t i v e s l o p e . (ii) The s l o p e
( d ~ / d T ) ~ ~ , ~ j i n c r e a s e s w i t h i n c r e a s i n g aluminum c o n t e n t ; it i s 1 . 7 6 ( M ~ a / ~ ) f o r 4 . 4 a t % A l , 2.00 f o r 8 . l a t % A l and 2 . 1 0 f o r l b . O a t % A l . Using t h e C l a u s i u s - C l a p e y r o n e q u a t i o n , t h e c o r r e s p o n d i n g e n t r o p y change (AS) f o r t h e 1 6 . 0 a t % ~ l a l l o y was c a l c u l a t - ed t o be 1.45 (J/mol. K ) ( t h e l a t t i c e p a r a m e t e r , a=0.5996nm f o r a Cu-lSat%Zn-l7at%Al
Temperature
F i g . 8 C r i t i c a l s t r e s s e s p l o t t e d a g a i n s t t h e n o r m a l i z e d t e s t t e m p e r a t u r e ( t e s t t e m p e r a t u r e minus Bls). O r i e n t a t i o n d i f f e r e n c e was t a k e n i n t o a c c o u n t by n o r m a l i z i n g t o t h e o r i e n t a t i o n o f t h e 8 . l a t % A l a l l o y .
JOURNAL DE PHYSIQUE
(14) was u s e d t o c a l c u l a t e t h e d e n s i t y ) . (iii) The a(@i+$l) v e r s u s
300
-
t e m p e r a t u r e p l o t s have a s m a l ln e g a t i v e s l o p e . (iv) 0 @?+a?) i n c r e a s e s w i t h i n c r e a s i n g e / a .
o(&+a;) and o ( a i + ~ ; ) a t 253K
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a r e p l o t t e d a g a i n s t e / a a s shown i n0
I r ( ~ J F i g . 9 . I t can b e s e e n t h a t
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~ ( ~ i - i ) and a (a)+B\) have a l i n e a r"3
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'0 E r e l a t i o n w i t h r e s p e c t t o e / a . The
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ua T(ajB:, c r i t i c a l r e s o l v e d s h e a r s t r e s s T
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f o r i n d u c i n g a) from
B i
can b e o b t a i n e d by m u l t i p l y i n g t h e Schmid f a c t o r (known from t h e , o r i e n t a t i o n r e l a t i o n between t h e 61 and a ) ) . T v a l u e s a r e a l s o p l o t t e d i n F i g . 9 .Oo 5 10 15
a t % A l 20 By e x t r a p o l a t i n g t h e T ( a i + b i )
L I I I I I I v e r s u s e / a r e l a t i o n , one f i n d s t h a t
1.31 1 4 1 1.42 1.44 1.46 1 1.50 r ( a i + B i ) becomes z e r o f o r a l l o y s
va
w i t h an e / a v a l u e s m a l l e r t h a a 1.41.F i g . 9 . C r i t i c a l s t r e s s e s t o form a1 a s a T h i s c o i n c i d e s w i t h t h e f a c t t h a t f u n c t i o n o f e / a ( o r c o m p o s i t i o n )
.
does n o t t r a n s f o r m backwards i n a : a x i a l s t r e s s , T : r e s o l v e d s t r e s s . t h e s e a l l o y s . I f one p l o t s t h ev a l u e s o f { ~ ( B i + a i ) +T (ai+Bi) } / 2 , one o b t a i n s t h e broken l i n e shown i n F i g . 9 . T h i s l i n e i s e x t r a p o l a t e d t o z e r o s t r e s s a t e/a=1.39 i n d i c a t i n g t h a t below t h i s e / a v a l u e ,
ai
p h a s e i s s t a b l e c h e m i c a l l y .C o n c l u s i o n . - The i n f l u e n c e o f a l l o y c o m p o s i t i o n on t h e p s e u d o e l a s t i c b e h a v i o r of Cu-Zn-A1 a l l o y s i s s i g n i f i c a n t . ~ ( s i ~ i ) and ~ ( a i - t ~ i ) d e c r e a s e markedly a s e / a d e c r e a s e s and t h e s t r e s s - i n d u c e d a; m a r t e n s i t e is s t a b l e i n Cu-Zn-A1 a l l o y s with an e / a v a l u e s m a l l e r t h a n 1 . 4 1 . As f o r t h e t e m p e r a t u r e dependence, ~(Bi-tcli) and a ( a i + @ i ) a r e a l m o s t c o n s t a n t a l t h o u g h t h e r e i s a s l i g h t , n e g a t i v e t e m p e r a t u r e dependence. a ( ~ ~ + ~ i ) v e r s u s t e m p e r a t u r e p l o t s have a l a r g e p o s i t i v e s l o p e whic? i s a l m o s t independent o f a l l o y c o m p o s i t i o n . I n t h e Cu-Zn-Ga a l l o y , o n l y t h e Bl+Bl t r a n s f o r m a t i o n can b e s t r e s s - i n d u c e d . The
BjWi
t r a n s f o r m a t i o n does n o t o c c u r , s i n c e s l i p d e f o r m a t i o n b e g i n s b e f o r e t h e t r a n s f o r m a t i o n . T h e r e f o r e , p s e u d o e l a s t i c i t y i s one s t a g e i n t h i s a l l o y .R e f e r e n c e s .
(1) Otsuka K , Sakamoto H . and Shimizu K . , Acta Met. (1979) 585.
(2) Brown L. C . , Met. T r a n s . 6A (1975) 1124.
( 3 ) S c h r o e d e r T. A. and wayman?. M. Acta Met. 26 (1978) 1745.
(4) Arneodo W . and A h l e r s M . , S c r i p t a Met.
7
(1973) 1287.(5) ~ a r c e l b G . , A h l e r s M . and R a p a c i o l i R . , Z . M e t a l l k d e
70
(1979) 732.(6) S a t o H . , Takezawa K . and S a t o S . , P r o c . I o i n t US/Japan Seminar, Troy, (1979) 92.
(7) Delaey L . , J a n s e n J . , Van Humbeeck J . , Luyten J . and D e r u y t t e r e A . , P r o c . I n t . Conf. on M a r t e n s i t i c T r a n s f o r m a t i o n s , Cambridge, MA, (1979) 645.
(8) Miura S . , Hori F. and N a k a n i s h i N . , P h i l . Mag.
40
(1979) 611.(9) Takezawa K . and S a t o S . , P r o c . I n t . Conf. on M a r t e n s i t i c T r a n s f o r m a t i o n s , Cambridge, MA, (1979) 661.
(10) Delaey L . , Z. M e t a l l k d e
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(1967) 388.(11) Delaey L . , Van Humbeeck J , Chandrasekaran M . , J a n s e n J . , Andrade M. and Mwamba N . , M e t a l s Forum, 4 (1981) 164.
(12) S a b u r i T . , Nenno
ST,
Hasunuma J . and T a k i i H . , Proc. I n t . Sympo. on M a r t e n s i t i c T r a n s f o r m a t i o n s , Kobe, (1976) 251.(13) S a t o H . , Takezawa K . and S a t o S . , S c i . Rep. PITU A29 S u p p l - 1 (1981) 85.
(14) C h a k r a v o r t y S . and Wayman C. M., A c t a Met.
