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Submitted on 1 Jan 1982
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DEFORMATION BEHAVIOUR OF SINGLE CRYSTAL OF Cu-Al MARTENSITIC ALLOYS
A. Gyobu, K. Enami, A. Nagasawa, S. Nenno
To cite this version:
A. Gyobu, K. Enami, A. Nagasawa, S. Nenno. DEFORMATION BEHAVIOUR OF SINGLE CRYS-
TAL OF Cu-Al MARTENSITIC ALLOYS. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-641-
C4-645. �10.1051/jphyscol:19824103�. �jpa-00221958�
DEFORMATION BEHAVIOUR OF
SINGLECRYSTAL OF Cu-A1 MARTENSITIC ALLOYS
*Department o f MechanicaZ Engineering, Niihama TeehnieaZ CoZZege, Ehime, Japan
**Department of Materials Science and Engineering, Osaka University, Suita, Osaka, Japan
***
Department of Physics, Nara Women's University, Nara, Japan(Revised t e x t a c c e p t e d 27 September 1982)
A b s t r a c t . - Deformation b e h a v i o u r and s t r e s s - i n d u c e d m a r t e n s i t e - m a r t e n s i t e t r a n s f o r m a t i o n o f b i n a r y Cu-A1 6 - m a r t e n s i t i c a l l o y s were i n v e s t i g a t e d by t e n s i l e and compression t e s t , X-ray a n a l y s i s and e l e c t r o n m i c r o s c o p y . T h r e e k i n d s o f Cu-A1 a l l o y s h a v i n g 18R(Bi), 18R+2H, and ZH(yi) s t r u c t u r e s i n t h e i n i t i a l as-quenched s t a t e , r e s p e c t i v e l y , were examined. I n t h e specimen w i t h
<001>@ te n s i l e a x i s , i t was found t h a t d e f o r m a t i o n p r o c e e d s by LUders d e f o r - mation. T h a t i s , narrow band a p p e a r s a t f i r s t and t h e n t h i s "deformation"
band p r o p a g a t e s a l o n g t h e t e n s i l e a x i s . I t was found t h a t i n t h e d e f o r m a t i o n band r e g i o n , m a r t e n s i t e - m a r t e n s i t e t r a n s f o r m a t i o n ,
Bi
o r y; + ai(D022) o c c u r s , by u s i n g p r e c e s s i o n X-ray method. I t was a l s o found t h a tyi
m a r t e n s i t e t r a n s ; formed d i r e c t l y t oai
m a r t e n s i t e w i t h o u t p a s s i n g t h e s u c c e s s i v e y i t of3i
t o a 1t r a n s f o r m a t i o n l i k e i n t h e Cu-Al-Ni a l l o y s . When t h e m a r t e n s i t e - m a r t e n s i t e t r a n s f o r m a t i o n t o o k q l a c e a l o n g t h e whole l e n g t h o f t h e t e n s i l e specimen, s i n g l e c r y s t a l o f oil m a r t e n s i t e was o b t a i n e d and t h i s
ai
s i n g l e c r y s t a l was s t a b l e upon u n l o a d i n g t h e t e n s i l e s t r e s s . When t h e a; s i n g l e c r y s t a l specimen which was produced by t e n s i l e d e f o r m a t i o n o f t h e specimen with2H+18R m i x t u r e a l o n g [001]@ d i r e c t i o n , was c o m ~ r e s s e d a l o n g [ 0 0 i ] B (=[001]D022) d i r e c t i o n , t h e r e v e r s e t r a n s f o r m a t i o n a1 t o y i was found t o occur w i t h o u t forming@i
m a r t e n s i t e .I n t r o d u c t i o n . - The s t r e s s - i n d u c e d m a r t e n s i t e t o m a r t e n s i t e t r a n s f o r m a t i o n h a s now been o b s e r v e d i n v a r i o u s @ - b r a s s t y p e m a r t e n s i t i c a l l o y s ( 1 ) . However d e t a i l s o f i t s f e a t u r e , e . g . t r a n s f o r m a t i o n p a t h , t h e s t r u c t u r e o f t h e p r o d u c t p h a s e , t e n s i l e o r compression b e h a v i o u r , a r e d i f f e r e n t i n e a c h a l l o y s y s t e m . On t h e b i n a r y Cu-A1 6- p h a s e a l l o y s y s t e m , s e v e r a l works have been r e p o r t e d on t h e d e f o r m a t i o n o f m a r t e n s i t e p h a s e s (2- 6 ) . T a s e t a l . (6) f i r s t showed t h e s y s t e m a t i c i n v e s t i g a t i o n o f t h e d e f o r m a t i o n i n d u c e d m a r t e n s i t e t o m a r t e n s i t e t r a n s f o r m a t i o n o f 6 s i n g l e c r y s t a l s o f t h e b i n a r y Cu-A1 m a r t e n s i t i c a l l o y h a v i n g 18R s t r u c t u r e , by a combination o f mecha- n i c a l t e s t i n g , an X-ray p o l e f i g u r e method and microscopy. According t o them, t h e as-quenched m a r t e n s i t e Bi(18R) t r a n s f o r m s t o a i ( ~ 0 ~ 2 ) p h a s e when t h e t e n s i l e a x i s i s n e a r <001>f3 d i r e c t i o n and t o ZH(DO19) i n t h e c a s e <011>B t o <111>B d i r e c t i o n s . A s i s w e l l known i n t h e Cu-A1 b i n a r y s y s t e m , t h e r e a r e t h r e e m a r t e n s i t e p h a s e s ,
B ' , @i
andy; ( 7 ) . However, t h e r e i s s t i l l n o s y s t e m a t i c i n v e s t i g a t i o n on t h e d e f o r m a t i o n b e h a v i o u r o f t h e m a r t e n s i t e s o t h e r t h a n ~ i ( l 8 ~ ) m a r t e n s i t e . R e c e n t l y we i n v e s t i g a t e d t h e d e f o r m a t i o n b e h a v i o u r of t h e B s i n g l e c r y s t a l s o f t h e Cu-A1 m a r t e n s i t i c a l l o y s , h a v i n g f3i ( l 8 ~ ) ,
@ i + Y i
and y i ( 2 ~ ) s t r u c t u r e s , r e s p e c t i v e l y , by u s i n g mechanical t e s t - i n g , X-ray a n a l y s i s , o p t i c a l - and e l e c t r o n m i c r o s c o p y . I t i s t h e p u r p o s e of t h e p r e s e n t r e p o r t t o show t h e f e a t u r e o f m a r t e n s i t e t o m a r t e n s i t e t r a n s f o r m a t i o n by t e n s i o n o f t h e s e t h r e e m a r t e n s i t i c a l l o y s and " r e v e r s e " t r a n s f o r m a t i o n o fCii
marten-s i t e by compression.
E x p e r i m e n t a l P r o c e d u r e s . - T h r e e k i n d s o f Cu-A1 f3-phase a l l o y s were m e l t e d by u s i n g p u r e c o p p e r and aluminium ( b o t h 99.99%) by h i g h - f r e q u e n c y vaccuum i n d u c t i o n f u r n a c e , i n t h e g r a p h i t e c r u i c i b l e , and c o o l e d i n t h e c r u i c i b l e s l o w l y t o o b t a i n i n g o t s h a v i n g l a r g e B - g r a i n s . The i n g o t s were homogenized a t 1223K f o r 2 days f o l l o w e d by i c e - w a t e r quenching. The chemical c o m p o s i t i o n of t h e s e t h r e e a l l o y s and t h e s t r u c t u r e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19824103
C4-642 JOURNAL DE PHYSIQUE
of t h e as-quenchedmartensitedetermined by X-raydiffractometer a r e shown i n Table 1.
Table 1. Chemical composition(mass%) o f Cu-A1 f3 a l l o y s and t h e s t r u c t u r e of t h e as-quenched m a r t e n s i t e s .
Cu A 1 m a r t e n s i t e s t r u c t u r e
a l l o y #
H- 8 87.2 b a l . 18R
H- 7 86.5 b a l . 2H + 18R (mainly 2H)
H- 10 86.2 b a l . 2H
Specimens of 6 s i n g l e c r y s t a l f o r t h e t e n s i l e t e s t i n g with t h e s i z e l m m x 3.5mm x 40mm and f o r t h e X-ray a n a l y s i s with 40.6 and 0.9mm x 13mm were c u t out from t h e l a r g e 6 - g r a i n . The o r i e n t a t i o n of t h e t e n s i l e axes of specimens was determined by t r a c e s of I l l o } ~ t y p e v a r i a n t - v a r i a n t i n t e r f a c e s of m a r t e n s i t e c r y s t a l s . F i r s t we cut out t h e (1101f3 p l a n e c a r e f u l l y by u s i n g t h e two-surface t r a c e a n a l y s i s of a d i s t i n c t (11016 t r a c e . Then we determined t h e o r i e n t a t i o n of t h e t e n s i l e a x i s of t h e specimen, by u s i n g a g a i n t h e t r a c e s of {llO}B t y p e i n t e r f a c e s on t h e {110}6 p l a n e . A l l specimens were t h e n annealed a t 1223K f o r 3.6 ks i n q u a r t z c a p s u l e s under argon atmosphere and quenched i n t o i c e - w a t e ~ . Speciemens f o r compression t e s t - i n g were c u t o u t from t h e s i n g l e c r y s t a l of t h e al m a r t e n s i t e obtained previously by t e n s i l e deformation and m e c h a n i c a l l y p o l i s h e d c a r e f u l l y , f i n i s h e d by e l e c t r o p o l i s h i n g t o t h e s i z e 3mm x 1.7mm x Smm. C r y s t a l s t r u c t u r e of t h e "deformed" specimen both by t e n s i o n and compression, were determined by t h e p r e c e s s i o n X-ray method.
R e s u l t s and Discussion
1. M a r t e n s i t e t o m a r t e n s i t e t r a n s f o r m a t i o n by t e n s i l e t e s t .
F i g . 1 shows t h e s t r e s s - s t r a i n curves o f a l l o y s H-8, H-7 and H-10 by t e n s i o n . T e n s i l e a x i s o f each specimen with
r e s p e c t t o Bl(DO3) i s shown i n t h e
s t a n d a r d s t e r e o g r a p h i c t r i a n g l e s I *l-quenchcd mi.IFnritr l a )
i n s e r t e d . As shown i n F i g . 1 , I lir-"umched m a r t m s > t e Ih,
s t r e s s - s t r a i n curves of a l l o y s H-7
5 " " . I / ..-q"e"ched mareen..ee <=,
(ZH+18R) and H-10 (2H) show a small y i e l d drop followed by long
"easy p l a s t i c flow" r e g i o n up t o 25-30% s t r a i n , while t h a t of a l l o y H - 8 does n o t show a y i e l d - d r o p a p p a r e n t l y . The above d i f f e r e n c e seems due t o d i f f e r e n c e i n t e n s i l e axes between them. I n F i g . 1 , t h e schematic r e p r e s e n t a t i o n o f change i n t h e s u r f a c e s t r u c t u r e d u r i n g e l o n g a t i o n i s shown, a t p o i n t s a , b , c and d on each s t r e s s - s t r a i n curve.
I t was found by u s i n g o p t i c a l -
microscopy t h a t r e o r i e n t a t i o n of t h e <Era," (-,
as-quenched m a r t e n s i t e
yi
o r 6 ioccurred with i n c r e a s i n g s t r e s s F i g . 1 S t r e s s - s t r a i n curves o f Cu-A1 around t h e p o i n t b. When t h e m a r t e n s i t i c a l l o y s by t e n s i o n . s t r a i n reached about
l o % ,
b e f o r e,
completing t h e r e o r i e n t a t i o n of y l
o r 6 i , suddenly narrow band of "pink-phase"
ai
c r y s t a l appeared and d u r i n g f u r t h e r e l o n g a t i o n , i t grew continuously along t h e whole l e n g t h of t h e specimen by " ~ u d e r s "deformation, d. This "pink" a i phase was s t a b l e upon unloading t h e t e n s i l e s t r e s s and it was found by X-ray Laue photographs taken along t h e whole l e n g t h of t h e "pink"
region of t h e specimen t h a t t h e s i n g l e c r y s t a l of ai phase was formed by t e n s i l e deformation. The above a l l f e a t u r e s were commonly observed i n a l l t h r e e a l l o y s used h e r e , and e s s e n t i a l l y t h e same a s t h e s t r e s s - s t r a i n behaviour i n t h e case of
Bi
t o a it r a n s f o r m a t i o n by Tas e t a1 ( 6 ) . The macroscopic s t r a i n up t o 30% by t e n s i l e defor- mation of t h e specimen whose t e n s i l e a x i s i s n e a r [001]f31 d i r e c t i o n i s q u i t e
reasonable when c o n s i d e r i n g t h e Bain correspondence between t h e mother B1(D03) phase and t h e f i n a l product a i ( ~ 0 2 2 ) phase, ( 6 , s ) .
completely deformed r e g i o n of t h e specimen of a l l o y H-7 and shows t h a t t h e specimen i s transformed t o t h e
ai
(D022) s i n g l e c r y s t a l completely.The l a t t i c e parameters of t h e
ai
(D022) phase determined by t h e above X-ray photograph a r e , a=0.359, c=0.755 nm and c/a=2.10. I t was a l s o found t h a t t h e i n i t i a l t e n s i l e a x i s n e a r [OO1]B1 became [001]D022.
I n t h e p r e s e n t a l l o y s H-7 and H-10, it was found t h a t yi(2H) y a r t e n s i t e transformed d i r e c t l y t o a 1 marten- s i t e without p a s s i n g t h e s u c c e s i v e y i t o
Bi
t o aj t r a n s f o r m a t i o n l i k e t h e Cu-Al-Ni a l l o y s ( I ) , by i n s i t u o b s e r v a t i o n d u r i n g e l o n g a t i o n of t h e specimen i n a small t e n s i l e j i g mounted on t h e goniometer head of t h e p r e c e s s i o n X-ray camera, Fig.3.F i g . 3 i s t h e X-ray p r e c e s s i o n photographs t a k e n from t h e s l i g h t l y deformed r e g i o n , ( a ) , from t h e boundary r e g i o n of t h e i n i t i a l m a r t e n s i t e and "pink-phase" band (b) and from t h e completely transformed region t o "pink-phase", (c) o f a f l o y H-7. Any d i r e c t evidence on y1 t o
Bi
t r a n s f o r m a t i o n has n o t been found i n t h i s experiment.F i g . 2 P r e c e s s i o n X-ray photograph of
ai
(D022) m a r t e n s i t e s i n g l e c r y s t a l o b t a i n e d by t e n s i l e deformation. Alloy H-7.
Mo, no f i l t e r , 40kV, 15111.4 x 24 h r .
F i g . 3 P r e c e s s i o n X-ray photographs t a k e n from t h e specimen under t e n s i o n . Alloy H-7. (a) D i f f r a c t i o n p a t t e r n taken from s l i g h t l y r e o r i e n t e d y i ( 2 ~ ) m a r t e n s i t e .
(b) D i f f r a c t i o n p a t t e r n taken from t h e boundary r e g i o n between y i and "pink-phase"
showing r e f l e c t i o n s from 2H and DO22 s t r u c t u r e s . ( c ) D i f f r a c t i o n p a t t e r n taken from t h e completely transformed region showing r e f l e c t i o n s only from DO22 s t r u c t u r e , beax// 110*D022. Mo, no f i l t e r , 40kV, 15mA x 24hr.
F i g . 4 shows t h e TEM image and SAD p a t t e r n taken from t h e ai phase of a l l o y H-7, obtained by t h e t e n s i l e deformation. As shown i n t h i s photograph, t h e r e a r e dense s t a c k i n g f a u l t s on { 1 1 2 ~ ~ 0 ~ ~ ( = { l l l ) f ~ ~ ) p l a n e . I n t h e SAD p a t t e r n , f i n e s t r e a k s
C4-644 JOURNAL DE PHYSIQUE
p e r p e n d i c u l a r t o t h e t r a c e of t h e f a u l t s a r e seen. This s i t u a t i o n i s q u i t e d i f f e r e n t from t h e case of t h e deformation induced s i n g l e c r y s t a l of ~ l o ( a ; ) phase i n t h e N i A l marte- s i t e ( 9 ) , i n which no s t a c k i n g f a u l t n o r twin was observed 'in t h e
"deformation induced" s i n g l e c r y s t a l . T h i s d i f f e r e n c e can b e a t t r i b u t e d t o t h e deference i n t h e formation p r o c e s s of " s i n g l e c r y s t a l " o f a i o r aJ(L1o) phase between them. I n t h e c a s e of N i A l a l l o y , t h e m a r t e n s i t e a2(Llo) i t s e l f i s " s t a b l e " and t h e s i n g l e c r y s t a l of a; m a r t e n s i t e without f a u l t s formed due t o "detwinnine" o f i n t e r n a l t w i n s , ( 9 ) . While i n t h e
p r e s e n t a l l o y , l i k e i n t h e Cu-Al-Ni Fig.4 TEM image and SAD p a t t e r n of
ai
a l l o y , t h e a i phase would be made by (D022) s i n g l e c r y s t a l o b t a i n e d by i n t r o d u c i n g s t a c k i n g f a u l t s t o y i o r t e n s i l e deformation. Alloy H-7.
$1 and t h u s p a r t i a l d i s l o c a t i o n s o r s t a c k i n g f a u l t s could not be swept
out completely by deformation. Tas and Delaey a l r e a d y showed t h a t dense s t a c k i n g f a u l t s remain i n t h e
ai
m a r t e n s i t e produced fromBi
m a r t e n s i t e (10).
The f a c t t h a t dense s t a c k i n g f a u l t s remain i n t h e " s i n g l e c r y s t a l " of a; phase i n t h e p r e s e n t a l l o y a l s o s u g g e s t s t h a t d u r i n g y i t o a; transformation, g l i d i n g of p a r t i a l d i s l o c a t i o n s a s s o c i a t e s simultaneously and t h o s e p a r t i a l d i s l o c a t i o n s ( s t a c k i n g f a u l t s ) would s t a b i l l i z e t h e a; phase, and consequently t h e a; s i n g l e c r y s t a l remains s t a b l e even a f t e r unloading t h e t e n s i l e s t r e s s .2 . "Reverse"transformation from C L ~ t o y i by compression.
F i g . 5 shows t h e s t r e s s - s t r a i n curve of t h e s i n g l e c r y s t a l of a; phase o f a l l o y H-7 compressed along [ o o ~ ] D o ~ ~ (= [ 0 0 i ] ~ i ) a x i s . The s t r e s s - s t r a i n curve shows t h e two-step y i e l d i n g . Change i n t h e micro- s t r u c t u r e i n each s t a g e of compression, b , c , d i s shown s c h e m a t i c a l l y i n t h e i n -
s e r t e d f i g u r e s . Before deformation, t h e specimen i s a complete s i n g l e c r y s t a l of pink-coloured a: phase. During compres-
s i o n beyond t h e 1 s t y i e l d p o i n t , f i n e s t r e a k s with yellow-colour appeared, b , and t h e i r numbers and t h i c k n e s s i n c r e a s - ed with i n c r e a s i n g s t r a i n , c . In t h e r e g i o n d, t h e specimen was covered almost by yellow-coloured p l a t e s .
Fig.6 shows t h e X-ray p r e c e s s i o n photograph taken from t h e specimen compressed t o s t a g e d, i n Fig.5. This p a t t e r n i s w e l l explained by t h e d i f f - r a c t i o n p a t t e r n of t h e s i n g l e c r y s t a l of 2H s t r u c t u r e (beam //001*2~zone).
10 20 30 T h e r e f o r e , it i s concluded t h a t yellow-
straln 1%) p l a t e s
faun!
i n t h e s t a g e d , i n F i g . 5 , i s t h e 2H(yl) m a r t e n s i t e by "reverse"Fig.5 S t r e s s - s t r a i n curve of s i n g l e t r a n s f o r m a t i o n from t h e a; phase.
c r y s t a l of a i m a r t e n s i t e , by compression. However, no c l e a r evidence o n l t h e
Alloy H-7. r e v e r s e t r a n s f o r m a t i o n from a1 t o
Bi
was observed i n t h e p r e s e n t experiment.
The l a t t i c e parameters o f t h e 2H m a r t e n s i t e by "reverse" t r a n s -
" r e v e r s e " t r a n s f o r m a t i o n from a;
c r y s t a l b y compression. A l l o y k-7.
Mo, no f i l t e r , 40kV, 15mA x 24hr. F i g . 7 P r e c e s s i o n X-ray photograph t a k e n from t h e svecimen comaressed and unloaded f o r m a t i o n a r e , a=0.454, b=0.516 and t o t h e p o i n t f i n F i g . 5 . A l l o y H-7. Mo, c=0.421 nm, which a r e s l i g h t l y no f i l t e r , 40kV, 15mA.x 24hr.
d i f f e r e n t from t h o s e o f t h e a s -
quenched 2H m a r t e n s i t e , a = 0 . 4 5 5 , b=0.522 and c=0.427 nm. The above d i f f e r e n c e would b e a t t r i b u t e d t o t h e d i f f e r e n c e i n t h e c o n f i g u r a t i o n o f f a u l t s between two
yi
m a r t e n s i t e s . By f u r t h e r compression t h e 2nd y i e l d appeared i n t h e s t r e s s - s t r a i n c u r v e , e , and a t t h i s s t a g e a g a i n "pink-phase1' a p p e a r e d i n t h e y e l l o w 2H m a r t e n s i t e . However, b e f o r e c o m p l e t i o n o f 2H t o a; t r a n s f o r m a t i o n , t h e specimen was f r a c t u r e d .
I n F i g . 7 , an X-ray p r e c e s s i o n p h o t o g r a p h t a k e n from t h e specimen a f t e r u n l o a d i n g t h e compression s t r e s s , i s shown, ( a ) . I n t h i s p h o t o g r a p h s t r e a k s a l o n g
[112]D022(=<lll>fcc) d i r e c t i o n a r e s e e n . Along t h e d i f f u s e s t r e a k s , t h e r e a r e weak i n t e n s i t y maxima, a s i l l u s t r a t e d i n t h e key diagram ( b ) , b e s i d e s t h e d i f f r a c t i o n s p o t s o f DO22 s t r u c t u r e . These weak i n t e n s i t y maxima a r e w e l l e x p l a i n e d b y 2H s t r u c t u r e , however d i s t a n c e between two maxima a l o n g [ 0 0 1 ] 2 ~ d i r e c t i o n , s u c h a s A and B i n (b) i s s l i g h t l y d i f f e r e n t . T h i s s u g g e s t s t h a t t h e p r e s e n t 2H s t r u c t u r e i s n o t e x a c t 2H s t r u c t u r e , b u t f a u l t e d 2H s t r u c t u r e , and a l s o s u g g e s t s t h a t g r a d u a l change from 2H (hexagonal) l a t t i c e t o DO22 ( t e t r a g o n a l ) l a t t i c e o c c u r r e d d u r i n g compression beyond t h e 2nd y i e l d p o i n t e , i n F i g . 5 .
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