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REORDERING AND A NEW ORDERED PHASE IN Ni-Al MARTENSITE AFTER AGEING
K. Enami
To cite this version:
K. Enami. REORDERING AND A NEW ORDERED PHASE IN Ni-Al MARTEN- SITE AFTER AGEING. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-727-C4-732.
�10.1051/jphyscol:19824118�. �jpa-00221968�
.JOURNAL DE PHYSIQUE
CoZZoque C.l, supnle'ment ax n o 1 2 , Tome 42, d6cembrw 198%
R E O R D E R I N G A N D A NEW O R D E R E D P H A S E IN Ni-A1 M A R T E N S I T E A F T E R A G E I N G
Gepartvent o f !,lateriuZs Science and Enginee~Lng, Osakc. U n i v e r ~ s i t y , .7uita, Osaku, Japun
( R e v i s e d t e x t a c c e p t e d 28 S e p t e m b e r 1982)
A b s t r a c t . - 'Phe t e m p e r i n g o f t h e m a r t e n s i t e o f t h e 63.8Ni-1Co-A1 a l l o y was i n v e s t i g a t e d by e l e c t r o n m i c r o s c o p y . I t was f o u n d t h a t a new o r d e r e d p h a s e Ni2A1 h a v i n g a m o n o c l i n i c C2/m s t r u c t u r e formed whcn t h e m a r t e n s i t e a ; ( ~ l o ) was a g e d a t 673K f o r s e v e r a l k s . 'I'his s t r u c t u r e i s c l o s e l y r e l a t e d t o t h e h e x a g o n a l S i 2 A l (P3ml) p h a s e o b t a i n e d uhcn t e m p e r i n g t h e m o t h c r p h a s e o f n i c k e - r i c h NiAl a l l o y s , and i s f o u n d t o b e a m a r t e n s i t i c a l l y deformed s t r u c t u r e o f t h e h e x a g o n a l p h a s e . 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 e o b s c r v a t i o n showed t h a t t h e ~ n o r p h o l o g y a n d i n t e r n a l d e f e c t s i n t h e a g e d s p e c i m e n a r e e s s e n t i a l l y t h e same a s t h o s e j n t h e a s - q u e n c h e d m a r t c n s i t c .
I n t r o d u c t i o n . - I t i s w e l l known t h a t t h e n i c k e l - r i c h h i A l B-phase a l l o y e x h i b i t s t h e 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 ( 1 ) . B e s i d e s t h e 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 t h a s been
f o u n d t h a t t h e n i c k e l - r i c h NiAl B - p h a s e a l l o y h a s a s t r o n g t e n d e n c y o f " o r d e r i n g " o f e x c e s s n i c k e l a t o m s and new o r d e r c d p h a s e s h a v i n g NizA1 (2 - 4 ) , a n d NisA13 ( 5 ) s t r u c t u r e s form d u r i n g t e m p e r i n g o f t h e m o t h e r p h a s e p r i o r t o t h e n l a r t e n s i t i c t r a n s - f o r m a t i o n , and o f t h e m a r t e n s i t e p h a s e , r e s p e c t i v e l y . A c c o r d i n g t o ( ? ) , t h e NiZAl p h a s e h a s a n o r d e r e d h e x a g o n a l
~ 3 m l
s t r u c t u r e b a s e d on t h e R2 l a t t i c e . R e c e n t l y we f o u n d a new o r d e r c d p h a s e Ni2Al h a v i n g a non no clinic C 2 / m s t r u c t u r e when t h e m a r t e n - s i t e a i ( ~ l o ) o f t h e a l l o y 63.8Ni-1Co-A1 was a g e d a t 673K f o r a few k s . I t i s t h e p u r p o s e o f t h c p r e s e n t r e p o r t t o show t h e c r y s t a l s t r u c t u r e and t h e n ~ i c r o s t r u c t u r e o f t h e new Ni2Al p h a s e .E x p e r i m e n t a l P r o c e d u r e s . - D e t a i l e d p r o c e d u r c s o f t h e p r e p a r a t i o n s o f t h e a l l o y 6 3 . 8 N i - 1 C o - h l ( a t . % ) h a v e b e e n d e s c r i b e d i n t h e p r e v i o u s works ( 1 . 5 ) . T h i n p l a t e s p e c i m e n s w i t h 0.3mm t h i c k f o r Eiil o b s e r v a t i o n w e r e c u t f r o m t h e 6 - s i n g l e c r y s t a l . A f t e r b e i n g homogenized a t 1523K f o r 3 . 6 k s f o l l o w e d by cater-quenching, t h o s e s p e c i m e n s w e r e up-quenched t o 673K a n d a g c d a t t h e same t e m p e r a t u r e f o r 3 . 6 t o 7 . 2 k s . O p t i c a l - a n d e l e c t r o n - m i c r o s c o p e o b s e r v a t i o n o f a g c d s p c c i m c n s \ $ e r e c a r r i e d o u t a t r . t . T h e Ms and As ( o r Af) t e m p e r a t u r e s o f t h e a l l o y were f o u n d t o b e a b o u t 453K and 1053K, r e s p e c t i v e l y , by means o f t h e r m a l a r r e s t nlcssclrcmcnt.
R e s u l t s and D i s c u s s i o n . 1 . M i c r o s t r u c t u r e
1 : i g . l shows an o p t i c a l m i c r o g r a p h o f t h e s p e c i m e n a g c d a t 673K f o r 7 . 2 k s and c o o l e d t o r . t . A p p a r e n t l y a n y c h a n g c i s n o t o b s e r v e d i n t h e morphology o f t h e
" m a r t c n s i t c " s t r u c t u r e i n t h i s p h o t o g r a p h . H o t - s t a g e o p t i c a l m j c r o s c o p y showed t h a t any c h a n g e i n t h e m i c r o s t r u c t u r e , e . g . s u r f a c e r e l i e f s - o r boundary-movement c o u l d n o t h e o b s e r v e d even whcn t h e specimen was h e a t e d up t o 773K, a s was a l r e a d y r e p o r t e d ( 6 ) . T h u s , i t i s c o n c l u d e d t h a t d u r i n g a g e i n g n e i t h 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 f r o m t h e m a r t e n s i t e t o t h e m o t h c r p h a s e n o r t h e d e c o m p o s i t i o n p r o c e s s d o c s n o t o c c u r i n t h i s a l l o y . TEM o b s e r v a t i o n a l s o r e v e a l e d t h a t any d i s t i n c t c h a n g e i n t h e m i c r o s t r u c t u r e o f t h e a s - ~ { u c n c l i c d n l a r t c n s i t c d i d n o t o c c u r a f t e r t e t n p e r i n g a t 673K, F i g s . 2 a n d 5 . I n F i g . 2 ( a ) , many s t a c k i n g f a u l t s o r t u i n s which a r c u s u a l l y o h s e r v e d i n t h e a s - q u e n c h e d N i A l m a r t e n s i t e ( 1 ) a r e s e e n . I n F i g . S ( a ) , a l s o c a n h c s e e n f i n e p a r a l l e l l i n e s . T h e s e l i n e s w e r e f o u n d t o h e t w i n s a s shown i n t h e SAD
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19824118
JOURNAL DE PHYSIQUE
p a t t e r n ( b ) , and d a r k - f i e l d images ( d ) and ( e ) . The p a r e n t ( 1 1 1 ) ~ l o . . t w i n n i n p s y s t e m
- .
was s t i l l m a i n t a i n e d a f t e r t h e specimen was tempered a t 673K.2 . C r y s t a l s t r u c t u r e
F i g s . 2 (b)
,
3 ( a ),
4 ( a ) and 5 ( b ) a r c t h e SAD p a t t e r n s t a k e n from t h e specimen aged a t 673K f o r 4 . 8 t o 7 . 2 k s and c o o l e d t o r . t . I n t h e s e p h o t o g r a p h s , " s u p e r -l a t t i c e " r e f l e c t i o n s o f t h e t y p e
n/3<0122*Llo and n/3<022>*Llo ( n : i n t e g e r ) a r e c l e a r l y s e e n 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 " i l o m a r t c n s i t c " , which c a n n o t b e
explained
e i t h e r by t h e Llo o r 2H rnartcn-s i t e s o r by Ni5A13 ( 5 ) s t r u c t u r e . T h i s F i g . 1 O p t i c a l micrograph o f t h e a l l o y s i t u a t i o n i s much l i k e t h e c a s e o f NizA1 63.8Ni-1Co-A1 aged a t 673K f o r 7.2 k s p h a s e found i n t h e n i c k e l - r i c h NiAl mother and c o o l e d t o r . t .
p h a s e ( 2 ) . In t h a t c a s e ( 2 ) , "n/3" t y p e
r e f l e c t i o n s a l o n g <112>*82 and <111>*82 d i r e c t i o n s a p p e a r e d b c s i d c s t h e d i f f r a c t i o n s p o t s o f t h e p a r e n t 6 2 - p h a s e , and t h e fund;lmental c r y s t a l l a t t i c e o f t h c p a r e n t I32 l a t t i c c i s maintained a f t e r ; ~ g c j n g .
F i g . 2 TEM image ( a ) and SAD p a t t e r n ( h ) o f t h e a l l o y 63.8Xi-ICo-A1 aged a t 673K f o r 7 . 2 k s and c o o l e d t o r . t . New " s u p e r l a t t i c e " r e f l e c t i o n s a r e observed b e s i d e s r e f l e c t i o n s o f t h e ~ l o ( a ; ) m a r t e n s i t e , i n (b) t a k e n from t h e [ 1 0 0 ] L l o d i r e c t i o n . T h e s e new " s u p e r l a t t i c e " s p o t s can b c e x p l a i n e d by v a r i a n t s 1 and 2 o f t h e m o n o c l i n i c Ni2AI s t r u c t u r e , ( s e e t e x t ) .
Comparing t h e p r e s e n t r e s u l t s t o t h e h e x a g o n a l Ki2Al p h a s e b a s e d on t h e p a r e n t 82 l a t t i c e , and c o n s i d e r i n g t h e "Bain c o r r e s p o n d e n c e " between t h e 52 and Llo l a t t i c e s we can c o n s t r u c t a model o f t h e c r y s t a l l a t t i c e o f the'new' Ni2A1 p h a s e b a s c d on t h e L l o l a t t i c e , a s shown i n F i g s . 6 and 7 . T h i s s t r u c t u r e h a s a m o n o c l i n i c symmetry and b e l o n g s t o t h e s p a c e g r o u p C2/m. A l l " s u p e r l a t t i c e " s p o t s found i n t h e p r e s e n t a g e d - m a r t e n s i t e a r e w e l l e x p l a i n e d by t h i s m o n o c l i n i c C2/m s t r u c t u r e . I n t h e SAD p a t t e r n s i n d i c e s b a s e d on t h i s s t r u c t u r e a r e shown ( d i f f r a c t i o n s p o t s w i t h s u b s c r i p t s 1 t o 4 ) , b e s i d e s t h o s e of t h e " p a r e n t " Llo l a t t i c e . T h i s s t r u c t u r e i s c l o s e l y r e l a t e d t o t h e h e x a g o n a l Ni$l s t r u c t u r e and i s o b t a i n e d when t h e z - a x i s o f t h e h e x a g o n a l l a t t i c e i s i n c l i n e d a b o u t 20' t o < l l O > h e x . d i r e c t i o n .
The l a t t i c e c o r r e s p o n d e n c e between t h c " p a r e n t " Llo and t h e new Ni2A1 (C2/m) l a t t i c e i s i l l u s t r a t e d i n F i g . 7 and can be e x p r e s s e d as f o l l o w s :
(100)Ni2Al // (Oil)1210
,
and [100]Ni2Al // [ O i 2 1 ~ 1 0(OIO)Ni2AI // ( 1 0 0 ) L l o [OIO]Ni2AI // [100]Ll0
( 0 0 1 ) N i ~ A l // (021) Ll0 [001]NiZAl // [ O l l j L l o
Thc a p p r o x i m a t e l a t t i c e p a r a m e t e r s o f t h e new Ki2Al p h a s e a r e o b t a i n e d by t h e f o l l o w i n g e q u a t i o n ,
2 2 2 2
a N i 2 A l = J(al.10 + 4cLlo )
.
b Ni2Al = a L l o ,'
Ni2A1 = J ( a ~ i 0 + CLlo1 ,
and B=-79".
I t i s e a s i l y u n d e r s t o o d t h a t f o u r v a r i a n t s o f Ni2A1 (C2/n1) can be formed i n an Llo l n t t i c c . Corresporidencc rriatriccs f o r p l a n e s and d i r e c t i o n s between t h e s e two l a t t i c e s a r e ,
( h k L)Ni2AI = (h k 1 ) L l o 0 1 0
a n d , X
I - : I
0 - 1 1 1 / 3 3 0 0
1
i 1 0 2 1 1 1 ;lI.lo,
f o r t h e v a r i a n t 1 , r e s p e c t i v e l y . Those f o r t h e p l a n e s o f o t h e r t h r e e v a r i a n t s a r e , 0 - 1 0 - 1 0 1 1 0 - 1 ( s u b s c r i p t s 2 t o 4 d e n o t e
By u s i n g t h e s e r e l a t i o n s , we can i n d e x a l l t h e " s u p e r l a t t i c e " r e f l e c t i o n s i n t h e SAL) p a t t e r n , F i g s . 2 t o 5 , a s shown i n t h o s e p h o t o g r a p h s . S u b s c r i p t s 1 t o 4 i n t h o s e SAD p a t t e r n s d e n o t e t h e d i f f r a c t i o n s p o t s from e a c h v a r i a n t c r y s t a l o f Ni2A1.
F i g . 3 SAD p a t t e r n t a k e n from t h e specimen aged a t 673K f o r 7 . 2 k s . " S u p e r l a t t i c e "
r e f l e c t i o n s can b e i n d e x e d a s t h e v a r i a n t 4 c r y s t a l o f t h e m o n o c l i n i c Ni2A1.
3. C a l c u l a t i o n o f t h e s t r u c t u r e f a c t o r f o r Ni2A1 (C2/m).
The a t o m i c p o s i t i o n s of t h e Ni and A l atoms i n t h e new N q A l l a t t i c e , F i g . 6 , a r e as f o l l o w s : N i ; 1 : 0 0 0 , 2:O 0 1 / 2 , 3:1/2 1 / 2 0 , 4:1/2 l / 2 1 / 2 , 5 : 1 / 3 0 113, 6 : 2 / 3 0 2 / 3 , 7 : 1 / 6 1 / 2 2 / 3 , 8 : 5 / 6 1 / 2 1 / 3 , and A l ; I : 2 / 3 0 1 / 6 , I I : 1 / 3 0 5 / 6 , m : 5 / 6 112 5 / 6 , i V : 1 / 6 1 / 2 1 / 6 . A c c o r d i n g l y t h e s t r u c t u r e f a c t o r f o r t h i s l a t t i c e i s ,
F= f N i { l + e x p ~ r i l l + e x p n i ( h + k ) +cxpni (h+k+R) + c x p 2 n i ( h + ! L ) / 3 + e x p 4 n i ( h + R ) / 3 + e x p n i ( h + 3 k + 4 L ) / 3 + e x p n i (5h+3k+2!L) / 3 } +
f A l { C x p ~ i (4h+!L)/3 + e x p n i ( 2 h + 5 R ) / 3 +cxpni(Sh+3k+S!L)/3 + e x p n i ( h + 3 k + L ) / 3 }
C 4 - 7 3 0 .JOURNAL D E P H Y S I Q U E
( b )
iji:.sn;; ~ . . 3 , > , . , I < ,,>;:
.2:;\,
3,": . . I,.; ""0
. ~
< , < I 2 1 1 2 ;
F i g . 4 SAI) p a t t e r n t a k e n from t h e s p e c i m e n a g e d a t 673K f o r 7 . 2 k s . [ ) i f f r a c t i o n s p o t s c o n s i s t o f t h o s e o f t h e v a r i a n t s 2 and 3 o f t h e n l o n o c l i n i c Ni2Al p h a s c .
F i g . 5 E l e c t r o n m i c r o g r a p h s s h o w i n g t h e i n t e r n a l t w i n s i n t h e s p e c i m e n a g e d a t 673K f o r 4 . 8 k s . ( a ) TEM image. ( b ) SAI) p a t t e r n t a k e n from [ ~ l l ] l , l o d i r e c t i o n . T h i s p a t t e r n can b e i n d e x e d a s t h e t w i n n i n g p a t t e r n o f ( I l l ) l , l o t w i n , ( c ) . ( d ) D F image u s i n g t h e d i f f r a c t i o n s p o t 1 i n ( b ) . ( c ) Dl: image u s i n g t h e d i f f r a c t i o n s p o t 2 ( t w i n s p o t ) i n ( h ) . S u p e r s c r i p t
'r
i n ( c ) d e n o t e s t w i n r e f l e c t i o n .( 1 0 0 ) ~ i 2 ~ 1 / /
( o i l )
L ~ O ,,,, (010)Ni2A1// ( 1 0 0 ) t l o)NizA1//(021) L l o
/ C
I I i g . 6 C r y s t a l s t r u c t u r e o f m o n o c l i n i c \ I"l"lua
C2/m Xi2Al l a t t i c c .
a n d , F = 8 f h i + 4 f ~ 1 , For t h e fundamental
r e f l e c t i o ; ; ~ o f t h e " p a r e n t " L l o l a t t i c e , F i g . 7 I . a t t i c e c o r r e s p o n d e n c c b e t w e e n t h c S 1 = + 4 ( V ~ i - f ~ l ) , f o r t h e s u r j e r l a t t i c e p a r e n t L l o and t h e monoclinic lii2Al
r e f l e c t i o n s o f t h e " p a r e n t " L l o l a t t i c e ,
l a t t i c e . S2=52 ( f ~ i - f ~ l ) , f o r t h e " s u p e r l a t t i c e "
r c f l e c t i o n s o f t h e Ni2Al(C2/m) l a t t i c e .
*]'he r e f l c c t i o n i n t e n s i t i e s e x p e c t e d from t h e a b o v c s t r u c t u r e f a c t o r a r e i n f a i r l y good a g r e e m e n t w i t h t h o s c o b s e r v c d i n t h e p r c s e n t e x p c r i m c n t , F i y s . 2 t o 5 .
4.Ni2A1 and NisA13
I n t h e p r e v i o u s work ( S ) , i t was shown t h a t NisA13 p h a s e fornwd d u r i n g a g e i n g t h e p r e s c n t a l l o y between 573Kand67'K f o r s e v c r s l t e n m i n . l n t h c p r c s e n t e x p e r i m e n t , i t was found t h a t Ni2Al p h a s e d i d n o t form bclow 673K o r e v e n a h o v c 673K, o n c e N i s A 1 3 p h a s e f o r m c d . I t was a l s o found t h a t t h e ?li5A13 phase was s t a b l c upon h c a t i n g up t o 773K. I t i s t h u s c o n c l u d e d t h a t t h c Ni2Al p h a s e forms d i r e c t l y f r o m t h e " p a r e n t " 1.10 p h a s e , and c a n o n l y b c o b t a i n e d when t h e s p c c i m e n i s h c a t c d r a p i d l y above 673K u i t h - o u t f o r m i n g h'igAI3 p h a s c . A r k h a n g e l ' s k a y a e t a 1 . ( 4 ) * s u g g e s t e d t h a t t h c Ni2Al p h a s e f o r n ~ c d d u r i n g s l o w c o o l i n g t h e s p e c i m e n f r o m 3473K t o r . t . (*by t h e i r model f o r t h e c r y s t a l s t r u c t u r e o f Ni2A1, s u p e r l a t t i c e r e f l c c t i o n s found i n t h e p r e s c n t e x p e r i m e n t c o u l t l n o t be e x p l a i n e d ) . T h e r c f o r c , i t is p o s s i h l c t o c o n s i d c r t h a t p r e s c n t mono- c l i n i c Yi2Al f o r m s m a r t c n s i t i c a l l y from t h e h e x a g o n a l Yi2Al which formed p r i o r t o t h c n l a r t e n s i t i c t r a n s f o r m a t i on. Ilowevcr, a s a l r e a d y d e s c r j b c d , a n y " r c v e r s e " t r a n s - f o r m a t i o n o r " d e c o m p o s i t i o n " h a s n o t b e e n o b s e r v c d d u r i n g h e a t i n g up t o 773K i n t h e p r c s e n t e x p e r i m e n t . C o n s e q u e n t l y , i t i s c o n c l u d e d t h a t t h e p r e s c n t Ki2A1 p h a s e would h e t r a n s f o r m c d from t h e L l o n l a r t c n s i t e d u r i n g a g c i n g a t 673K.
By c o m p a r i n g t h e p r e v i o u s r e s u l t on t h e f o r m a t i o n o f Ni2.41 i n t h e p a r e n t 82 p h a s c (2) and t h c p r e s c n t r e s u l t , onc can s e c t h c v e r y common f c a t u r e o f t h e
" r c o r d c r i n g " o f n i c k e l a t o m s . T h a t i s , i n t h c NizAl p h a s e formed i n t h c "1,arcnt" B2 p h a s c , " s u p e r l a t t i c c " r e f l c c t i o n s t ) . p c 1/3<112>*82 and 1 / 3 < l l l > * 1 3 2 a p p e a r c d ( s e e F i g s . 4 t o 6 in ( 2 ) ) . T h e s c d i r e c t i o n s j u s t c o r r e s p o n d t o < O l l > * L l o and <021>*LlO d i r e c t i o n s , r e s p e c t i v e l y , hen c o n s i d e r i n g t h e B a i n correspondence b e t w c e n 82 a n d L l o l a t t i c e s . T h e r e f o r e , i t i s q u i t e n a t u r a l t o c o n s i d c r t h a t s i ~ n i l a r " r e o r d e r i n g "
1 ) r o c e s s o f e x c e s s n i c k e l atoms would o c c u r i n t h e n i c k e l - r i c h Yi.41 a l l o y d u r i n g a g e i n g , i r r e s p e c t i v e o f t h e i n i t i a l s t a t c , i . c . o f t h c p a r c r l t 02 o r t h e ~ l l a r t e n s i t e 1.10.
Acknok1edgement.- The a u t h o r rr.islies t o t h a n k P r o f e s s o r S.l\'cnno f o r h i s c o n t i n u e d i-and e n c o u r a g e m e n t t h r o u g h o u t t h i s experiment.
JOURNAL LIE PHYSIQUE
References.
1. K.Enami, S.Nenno and K.Shimizu: 'Trans.JIM., E(1973), 161.
2. F.Reynaud: J .Appl.Cryst., 2(1976), 263.
3 . A.Lasalmonie: Scripta Met., g(1977), 527.
4. A.A.Arkhangeltskaya, V.S.l.itvinov and V.V.Poleva: Phys.Met.Metallog.,~(1979), 1 1 5 .
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6. K.Enami and S.Nenno: Mct.Trans., 2(1971), 1487.
