DEPENDENCE OF ELASTIC MODULUS ON MICROSTRUCTURE IN 2090-TYPE ALLOYS

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DEPENDENCE OF ELASTIC MODULUS ON MICROSTRUCTURE IN 2090-TYPE ALLOYS

M. O’ Dowd, W. Ruch, E. Starke, Jr.

To cite this version:

M. O’ Dowd, W. Ruch, E. Starke, Jr.. DEPENDENCE OF ELASTIC MODULUS ON MI-

CROSTRUCTURE IN 2090-TYPE ALLOYS. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-

565-C3-576. �10.1051/jphyscol:1987366�. �jpa-00226597�

JOURNAL DE PHYSIQUE

Colloque C3, supplBment au n 0 9 , Tome 48, septembre 1987

DEPENDENCE OF ELASTIC MODULUS ON MICROSTRUCTURE IN 2090-TYPE ALLOYS

M.E. O r D O W D ( l ) , W. RUCH, and E . A . STAXKE, Jr.

Department of Materials Science, University of Virginia, Charlottesville, V A 22901, U.S.A.

ABSTRACT

The Young's m o d u l u s , s h e a r m o d u l u s and P o i s s o n ' s r a t i o w e r e d e t e r m i n e d u s i n g a n u l t r a s o n i c p u l s e e c h o t e c h n i q u e . T h r e e c o m m e r c i a l l y f a b r i c a t e d a l u m i n u m - c o p p e r - l i t h i u m a l l o y s a n d an aluminum-lithium b i n a r y a l l o y were examined. The e l a s t i c p r o p e r t i e s w e r e measured a s a f u n c t i o n of a g i n g t i m e , a g i n g t e m p e r a t u r e , amount of s t r e t c h i n g and t e s t i n g d i r e c t i o n . An i n c r e a s e i n Young's modulus due t o d e l t a prime and T1 p r e c i p i t a t i o n h a s been measured and t r e a t e d q u a n t i t a t i v e l y i n c l u d i n g p r e c i p i t a t i o n k i n e t i c s . A s i g n i f i c a n t d e c r e a s e of a b o u t 5 % i n t h e m o d u l u s of e l a s t i c i t y w a s f o u n d i n t h e peak age c o n d i t i o n . T h i s d e c r e a s e can be a t t r i b u t e d t o p r e c i p i t a t i o n of t h e T2 phase. The s h e a r modulus behaves s i m i l a r t o Young's modulus w h i l e t h e P o i s s o n ' s r a t i o remains unchanged. There i s no s i g n i f i c a n t o r i e n t a t i o n dependence of t h e e l a s t i c p r o p e r t i e s on t e s t i n g d i r e c t i o n d e s p i t e t h e f a c t t h a t a t y p i c a l . r o l l i n g t e x t u r e was p r e s e n t .

INTRODUCTION

I t i s w e l l e s t a b l i s h e d t h a t t h e a d d i t i o n of l i t h i u m d e c r e a s e s t h e d e n s i t y and i n c r e a s e s t h e e l a s t i c modulus (1-4). T h i s paper examines t h e i m p o r t a n t p a r a m e t e r s w h i c h i n f l u e n c e t h e e l a s t i c m o d u l u s i n c o m m e r c i a l l y i m p o r t a n t a l u m i n u m - l i t h i u m a l l a y s . T h e s e p a r a m e t e r s i n c l u d e s o l i d s o l u t i o n c o n c e n t r a t i o n s , t h e i r v o l u m e f r a c t i o n s , a n d o r i e n t a t i o n e f f e c t s . I n d u s t r y can implement t h e s e r e s u l t s t o produce aluminum-lithium a l l o y s which p o s s e s s an optinium e l a s t i c modulus.

EXPERIMENTAL PROCEDURE

?'he a l l o y s s t u d i e d i n t h i s i n v e s t i g a t i o n w e r e d a n a t e d by t h e R e y n o l d s M e t a l s Company, Richmond, V i r g i n i a. The m a t e r i a l was r e c e i v e d a s h o t c r o s s - r o l l e d p l a t e w i t h a t h i c k n e s s r f 12 mm. The c o m p o s i t i o n s of t h e a l l o y s a r e g i v e n i n T a b l e I. A l l o y 7 3 i s s i m i l a r i n c o m p o s i t i o n t o ALCOA's 2090.

The a l l o y s were s o l u t i o n h e a t t r e a t e d a t 5500C f o r 3 0 m i n u t e s i n a s a l t b a t h a n d c o l d w a t e r q u e n c h e d ( C W Q ) . A l l t h e s a > x p l e s , a l l o y s 7 3 , 81, 82 a n d t h e b i n a r y a l l o y w e r e a g e d a t l900C f o r t i m e s f r o m 1 0 m i n u t e s up t o 300 h o u r s . They w e r e a l l e x a m i n e d i n t h e u n s t r e t c h e d c o n d i t i o n . Alloy 7 3 was a l s o examined i n a 6 % s t r e t c h e d c o n d i t i o n .

(1)

Naval Air Development Center, Warminster. Pennsylvania. U.S.A.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987366

JOURNAL DE PHYSIQUE

Samples were machined f o r u l t r a s o n i c measurement from t h e c e n t e r of t h e p l a t e . The s a m p l e s were r e c t a n g u l a r , a b o u t 1 2 x 7 x 5 mm3 i n dimensions. Longitudinal and t r a n s v e r s e wave v e l o c i t i e s were measured w i t h a 1 0 MHz u l t r a s o n i c p u l s e echo equipment.

The e l a s t i c modulus, s h e a r modulus, and P o i s s o n ' s r a t i o w e r e c a l c u l a t e d using t h e f o l l o w i n g e q u a t i o n s ( 5 ) :

. . .

R = ( V t / V L ) 2 eq. 1

P = (2*R-1)/(2*R-2)

. . .

^{eq. 2}

G = v ~ ~ * D

. . .

^{eq. 3}

E = D * v ~ ~ * ( ( ~ + P ) * ( ~ - 2 * ~ ) / ( l - P )

. . .

^{eq. 4}

R - R a t i o of v e l o c i t i e s squared P

-

Poisson's r a t i o

G

-

Shear Modulus (GPa) E

-

E l a s t i c Modulus (GPa) D - Density ( g / c c )

V t

-

Transverse v e l o c i t y (m/sec) V

-

Longitudinal v e l o c i t y (m/sec)

Q

The d e n s i t y of e a c h s a m p l e was measured u s i n g Archimedes p r i n c i p l e . The d e n s i t y d i d not change upon aging w i t h i n 0.02%.

T e x t u r e a n a l y s i s of t h e a l l o y s was p e r f o r m e d u s i n g a Siemens t e x t u r e goniometer, s e t up f o r t h e Schulz r e f l e c t i o n technique. Pole f i g u r e s were obtained from each sample.

Transmission e l e c t r o n microscopy was performed using a P h i l l i p s 400 i l 2 0 ~ e v ) i n s t r u m e n t . S m a l l a n g l e x - r a y s c a t t e r i n g (SAXS) was performed a t t h e National Laboratory i n Oak Ridge, Tennessee w i t h CuKa r a d i a t i o n . A Huber G u i n i e r Camera w i t h a q u a r t z monochromator using Cu K a r a d i a t i o n was u s e d i n c o n n e c t i o n w i t h t h e d i r e c t c o m p a r i s o n methoa t o determine volume f r a c t i o n s of second phases.

RESULTS AND DISCUSSION

The m i c r o s t r u c t u r e of a l l o y s 73, 81 and 82 d i s p l a y a n e l o n g a t e d f l a t g r a i n s t r u c t u r e due t o r o l l i n g . T y p i c a l d i m e n s i o n s a r e 220 x 100 x 30 pm3. I n a d d i t i o n t h e r e i s a s u b g r a i n s t r u c t u r e i n t h e s i z e r a n g e of 5 t o 30 pm p r e s e n t . The b i n a r y a l l o y e x h i b i t e d a f u l l y r e c r y s t a l l i z e d , equiaxed g r a i n s i z e ranging from 340 t o 360 pm.

F i g u r e 1 d i s p l a y s t h e r e s u l t s of TEM and 3 u i n i e r x - r a y a n a l y s i s w i t h r e s p e c t t o second p h a s e p r e c i p i t a t i o n a t 1 9 0 ° C a s a f u n c t i o n of aging time. I n t h e s o l u t i o n h e a t t r e a t e d c o n d i t i o n t h e m a t r i x , 6 ' and

~ 1 3 z r d i s p e r s o i d s w e r e e v i d e n t i n t h e t e r n a r y a l l o y s . The l a t t e r change n e i t h e r d i s t r i b u t i o n nor volume f r a c t i o n during aging.

A f t e r 1 0 m i n u t e s a g i n g a t 1 9 8 C t h e r e i s e v i d e n c e of t h e T I p h a s e i n a l l o y 73, b u t n o t i n a l l o y s 81 o r 82. This can be explained by t h e h i g h e r Cu c o n t e n t of 73 r e s u l t i n g i n a s t r o n g e r d r i v i n g f o r c e f o r T1 p r e c i p i t a t i o n . The T 1 p h a s e n u c l e a t e s h e t e r o g e n e o u s l y a t g r a i n and subgrain boundaries. The p l a t e l e t s , a f t e r 1 0 minutes aging a t 190°C, a r e a p p r o x i m a t e l y 72 nm l o n g and 8 nm wide.

A f t e r a p p r o x i m a t e l y 90 m i n u t e s a g i n g t i m e t h e T1 p h a s e i s a p p a r e n t i n a l l t h r e e a l l o y s . A f t e r 8 h o u r s a g i n g a t 1900C, t h e r e i s p r e s e n t i n a l l t h r e e a l l o y s some T2 p h a s e w h i c h n u c l e a t e s p r e f e r e n t i a l l y along t h e g r a i n boundaries.

The volume f r a c t i o n of 6' a s a f u n c t i o n of a g i n g t i m e was examined f o r a l l o y 81.

T a b l e I 1 shows t h a t t h e d i r e c t c o m p a r i s o n method y i e l d e d more c o n s i s t e n t r e s u l t s t h a n t h e TEM method. I n t h e f o r m e r method t h e i n t e g r a t e d i n t e n s i t y r a t i o of t h e (200) and (100) d i f f r a c t i o n l i n e was measured from a G u i n i e r camera e x p o s u r e compared t o t h e c a l c u l a t e d v a l u e and s o l v e d f o r t h e volume f r a c t i o n . At s h o r t a g i n g t i m e s t h e s u p e r l a t t i c e l i n e was t o o weak t o be m e a s u r e d q u a n t i t a t i v e l y and t h e r e f o r e a SAXS Kratky p l o t was used.

F i g u r e 2 shows t h e g' volume f r a c t i o n i n a l l o y 81 a s a f u n c t i o n of aging time. he SAXS d a t a p o i n t s ( a s t e r i s k s ) have been c a l i b r a t e d w i t h t h e d i r e c t comparison r e s u l t s ( c i r c l e s ) a t 4 0 min. aging time.

It i s evident from Guinier camera and TEM r e s u l t s t h a t t h e d e l t a p r i m e volume f r a c t i o n r e m a i n s e s s e n t i a l l y c o n s t a n t a t l o n g e r a g i n g times. SAXS d a t a i n Figure 2 shows an i n c r e a s e i n volume f r a c t i o n of second phases beyond 1 0 0 min., caused by T 1 and T2 p r e c i p i t a t i o n . The i n t e r p r e t a t i o n of t h e SAXS d a t a i n a more q u a n t i t a t i v e way i s r e s t r i c t e d due t o t h e c o m p l i c a t e d s h a p e and s t r u c t u r e of T 1 and T2.

A l l t e r n a r y a l l o y s e x h i b i t t h e same (110) [ 1 i 2 ] t y p e t e x t u r e ( F i g u r e 3 ) . The maximum t i m e s random number of t h e (200) p o l e was 11, 7 and 10 f o r a l l o y s 73, 81 and 82, r e s p e c t i v e l y .

F i g u r e 4 shows t h e Young's Modulus of t h e b i n a r y a l l o y a s a f u n c t i o n of a g i n g t i m e a t 1900C. I t e x h i b i t s an i n c r e a s e i n t h e e l a s t i c modulus up t o a p p r o x i m a t e l y 80 m i n u t e s a g i n g time. The maximum modulus i s approximately 80 GPa. 1 GPa i s t h e l a r g e s t o v e r a l l change i n modulus measured f o r t h e b i n a r y a l l o y where 6' and s o l i d s o l u t i o n a r e t h e only phases present.

The e l a s t i c modulus v e r s u s a g i n g t i m e a t 190°C f o r t h e t e r n a r y a1 l o y s i n t h e u n s t r e t c h e d c o n d i t i o n , l o n g i t u d i n a l d i r e c t i o n i s given i n Figure 5. They reach a maximum e l a s t i c modulus a t approximately 1 0 h o u r s a g i n g a t 1 9 0 0 C . The maximum modulus of a l l o y 73 i s 82 GPa.

Alloys 81 and 82 reach a maximum modulus of approximately 80 GPa.

The s h e a r modulus e x h i b i t s t h e same t r e n d s a s t h e Young's modulus ( s e e F i g u r e 6 ) . The v a l u e s r a n g e d from 29 t o 31 GPa. The P o i s s o n ' s r a t i o measurements d i d n o t e x h i b i t any s i g n i f i c a n t v a r i a t i o n a s a f u n c t i o n of aging time. The v a l u e s ranged between 0.30 and 0.33.

The v a r i a t i o n i n t h e e l a s t i c modulus e x h i b i t e d by t h e s e a l l o y s can be explained by changes i n t h e m i c r o s t r u c t u r e . During aging, t h e g r a i n s i z e , g r a i n o r i e n t a t i o n ( t e x t u r e ) and d e n s i t y remain unchanged.

Therefore, t h e p r e c i p i t a t i o n of second phases i s r e s p o n s i b l e f o r t h e changes i n e l a s t i c behavior.

The change i n modulus of 1 GPa e x h i b i t e d by t h e b i n a r y a l l o y i s due t o t h e i n c r e a s i n g volume f r a c t i o n of d e l t a prime. Beyond 100 m i n u t e s a g i n g t h e volume f r a c t i o n of d e l t a p r i m e r e m a i n s c o n s t a n t . Coarsening of t h e d e l t a prime has no measurable e f f e c t on t h e Young's modulus. This has a l s o been r e p o r t e d by Brous:;aud and Thomas (6).

A volume f r a c t i o n of 12.6% d e l t a prime was determined using t h e G u i n i e r camera on a s a m p l e which had b e e n aged 200 hours. T h i s corresponds w e l l w i t h a value of 11.5% c a l c u l a t e d u s i n g t h e l e v e r r u l e w i t h t h e m i s c i b i l i t y gap d a t a r e p o r t e d by Cocco e t al. ( 7 ) .

Using a l i n e a r r u l e of m i x t u r e s t h e modulus of t h e d e l t a p r i m e can be c a l c u l a t e d using t h e f 01 lowing equation:

E = f g , E 6 , + (1

-

f 6 . ) ( E A l +

xcLi)

_{S S}

. . . . ^.

^{eq. 5.}

E

-

measured modulus

f

-

6 ' v o l u m e f r a c t i o n E g :

-

modulus of d e l t a prime E A ~

-

modulus of aluminum

X - c o n s t a n t which d e p i c t s t h e dependence of t h e modulus of t h e m a t r i x p h a s e on t h e a m o u n t of l i t h i u m i n s o l i d s o l u t i o n .

JOURNAL DE PHYSIQUE

c:

;

- L i t h i u m c o n c e n t r a t i o n i n s o l i d s o l u t i o n (6.25 a t % a t m e t a s t a b l e e q u i l i b r i u m )

E A l a n d X h a v e b e e n d e t e r m i n e d by a l i n e a r r e g r e s s i o n of d a t a r e p o r t e d by M u l l e r e t a l . (8). They a r e 70.8 and 1.235, r e s p e c t i v e l y . The modulus of d e l t a prime c a l c u l a t e d u s i n g t h e above e q u a t i o n w i t h E

= 80.7 GPa i s 97 G P ~ . T h i s v a l u e i s r e a s o n a b l y c l o s e t o 1 0 6 a n d 96 GPa r e p o r t e d e l sewhere ( 6 , 8 , 9 ) .

E q u a t i o n 5 w a s a l s o u s e d t o p r e d i c t t h e c h a n g e i n m o d u l u s a s a f u n c t i o n of d e l t a prime volume f r a c t i o n . The l i t h i u m c o n c e n t r a t i o n i n t h e s o l i d s o l u t i o n ( C S S ) c a n b e r e l a t e d t o t h e d e l t a p r i m e v o l u m e f r a c t i o n a c c o r d i n g t o t h e f o l l o w i n g e q u a t i o n :

c&A

^{= (yLi -} c L i f s f ) / ( l - _{s S} f 6 1 )

. . . . . . ^.

^{eq. 6}

yLi - t o t a l a t o m i c f r a c t i o n of l i t h i u m i n t h e a l l o y

c:;

⁼ 0.225 a c c o r d i n g t o Cocco e t a l . ( 7 ) .

Up t o a p p r o x i m a t e l y 90 m i n u t e s a g i n g , t h e u n s t r e t c h e d t e r n a r y a l l o y s c a n b e t r e a t e d a s two p h a s e m a t e r i a l s c o m p r i s e d of t h e s o l i d s o l u t i o n and d e l t a p r i m e p h a s e s . The a g i n g k i n e t i c s of d e l t a p r i m e can be d e s c r i b e d u s i n g an e q u a t i o n from T u r n b u l l ( 1 0 ) :

f - e q u i l i b r i u m volume f r a c t i o n f y , - volume f r a c t i o n of 6 ' a t time, t to

-

c o n s t a n t

B - c o n s t a n t .

T h i s e q u a t i o n d e s c r i b e s w e l l t h e m e a s u r e d c h a n g e i n v o l u m e f r a c t i o n of d e l t a p r i m e up t o a b o u t 1 0 0 m i n u t e s a g i n g t i m e . The p a r a m e t e r s u s e d w e r e f = 0.2,

t o

= 2.7705 min. a n d B = 0.3196 m i n - l .

U s i n g e q u a t i o n s 5 , 6, a n d 7 t h e c h a n g e i n m o d u l u s f o r a l l o y 8 1 aged up t o where T1 b e g i n s t o p r e c i p i t a t e was c a l c u l a t e d ( s e e F i g u r e 7 ) . One c a n s e e t h a t 6

'

p r e c i p i t a t i o n h a s o n l y a weak e f f e c t on t h e Young's modulus.

T h e i n c r e a s e i n E b e y o n d 9 0 m i n u t e s i s c a u s e d b y T1 p r e c i p i t a t i o n . A T 1 v o l u m e f r a c t i o n of .7% was d e t e r m i n e d a f t e r 4 h o u r s a g i n g u s i n g t h e d i r e c t c o m p a r i s o n method. Assuming a l i n e a r r u l e of m i x t u r e s t h e m o d u l u s of T1 c a n b e c a l c u l a t e d u s i n g t h e f o l l o w i n g e q u a t i o n :

U s i n g c o n s t a n t s f r o m e q u a t i o n 5 f o r t h e m o d u l u s of t h e s o l i d s o l u t i o n (ESS) t h e T1 modulus c a l c u l a t e s t o a b o u t 350 GPa. T h i s v a l u e i s o v e r two t i m e s h i g h e r t h a n a r o u g h a p p r o x i m a t i o n of t h e l o w e r bound performed e a r l i e r (14).

The d r o p i n E o c c u r s a t a p p r o x i m a t e l y 8 t o 1 0 h o u r s a g i n g t i m e w i t h t h e p r e c i p i t a t i o n of t h e i c o s a h e d r a l T2 phase. The d a t a s u g g e s t s t h a t T2 h d s a n e x t r e m e l y low i n t r i n s i c m o d u l u s b e c a u s e i t s v o l u m e f r a c t i o n a p p e a r s t o be s m a l l . From F i g u r e 2 f o l l o w s t h a t t h e volume f r a c t i o n of d e l t a p r i m e a t t h e l o n g e r a g i n g t i m e s r e m a i n s c o n s t a n t . T h i s i n d i c a t e s t h a t t h e T2 phase may grow somewhat a t t h e expense of t h e T1 p h a s e b u t n o t a t t h e e x p e n s e of d e l t a p r i m e . I t may a l s o t a k e l i t h i u m o u t of s o l i d s o l u t i o n , t h u s d e c r e a s i n g t h e m o d u l u s of t h e m a t r i x phase even f u i i h e r .

The t y p e of p r e c i p i t a t e s a r e t h e same i n a l l t h r e e t e r n a r y a l l o y s . However, t h e k i n e t i c s of p r e c i p i t a t i o n a r e d i f f e r e n t . The

e a r l i e r o n s e t of T1 p r e c i p i t a t i o n i n t h e h i g h copper a l l o y , 73, shows up a s an e a r l i e r i n c r e a s e i n modulus and a l a r g e r d i f f e r e n c e between s t a r t i n g and peak modulus c o n d i t i o n . The l a t t e r may b e e x p l a i n e d by a h i g h e r T1 volume f r a c t i o n .

The m o d u l u s of a l l o y 7 3 , s t r e t c h e d 6 % , i s 2 GPa l o w e r t h a n t h e u n s t r e t c h e d m a t e r i a l ( F i g u r e 8). T h i s i s due t o t h e i n c r e a s e d amount of d i s l o c a t i o n s i n t h e s t r e t c h e d m a t e r i a l w h i c h c a n r e s u l t i n a n e l a s t i c s t r a i n e f f e c t s t h e r e b y r e d u c i n g t h e n e a s u r e d modulus. There i s a more homogeneous p r e c i p i t a t i o n of t h e T1 ghase w i t h i n t h e m a t r i x a t d i s l o c a t i o n j o g s (11). The i n c r e a s e i n m o 3 u l u s i n t h e s t r e t c h e d m a t e r i a l o c c u r s a t a s h o r t e r a g e t i m e d u e t o t h e i n c r e a s e i n t h e k i n e t i c s of p r e c i p i t a t i o n .

A l t h o u g h we d i d n o t e x p e r i m e n t a l l y o b s e r v e a n i n f l u e n c e of t e s t i n g d i r e c t i o n o n t h e m o d u l u s , we c a l c u l a t e d m o d u l i f o r v a r i o u s t e s t i n g d i r e c t i o n s from e l a s t i c c o n s t a n t d a t a p u b l i s h e d by M u l l e r e t a l . ( 8 ) .

L i n e a r r e g r e s s i o n a n a l y s i s was performed t o d e t e r m i n e t h e e l a s t i c c o n s t a n t s of o u r a l l o y s . U s i n g t h e s e e l a s t i c c o n s t a n t v a l u e s t h e modul; a r e c a l c u l a t e d and l i s t e d a c c o r d i n g t o (12) i n Table 111, a l o n g w i t h p u r e aluminum from r e f e r e n c e (13).

The h i g h e s t modulus, a s expected, i s i n t h e [ I l l ] d i r e c t i o n . The maximum t h e o r e t i c a l d i f f e r e n c e i n m o d u l i d u e t o t e s t i n g d i r e c t i o n (Emax) i s o n l y about h a l f i n aluminum-lithium a l l o y s compared t o p u r e aluminum. From a t h e o r e t i c a l p o i n t of view t h e A 1 - L i s o l i d s o l u t i o n a l l o y s can be e x p e c t e d t o be even more e l a s t i c a l l y i s o t r o p i c t h a n p u r e a l u m i n u m . F i g u r e 9 s h o w s t h a t e v e n d u r i n g a g i n g t h e r e i s n o d i r e c t i o n a l i t y of t h e Young's modulus o b s e r v a b l e w i t h i n e x p e r i m e n t a l e r r o r d e s p i t e t h e f a c t t h a t a w e l l p r o n o u n c e d r o l l i n g t e x t u r e i s p r e s e n t .

CONCLUSIONS

1. T h e Y o u n g ' s m o d u l u s i n c r e a s e s o n l y s l i g h t l y d u e t o t h e p r e c i p i t a t i o n of d e l t a prime , ( a b o u t 0.1 GPa/vol%).

2. The T1 p h a s e c o n t r i b u t e s p o s i t i v e l y t o t h e e l a s t i c modulus.

I t s i n t r i n s i c modulus i s e s t i m a t e d t o be a p p r o x i m a t e l y 350 GPa.

3. A maximum i n c r e a s e i n E w i t h a g i n g t i m e of a p p r o x i m a t e l y 5% can b e a t t r i b u t e d t o t h e p r e c i p i t a t i o n of T 1 , a n d t o a l e s s e r e x t e n t of 6 ' , f o r t h e a l l o y s examined.

4. T h e r e i s a s i g n i f i c a n t d r o p i n t h e m o d u l u s a t t h e peak a g e d c o n d i t i o n (5%). I t i s a s s o c i a t e d w i t h t h e p r e c i p i t a t i o n of t h e T2 p h a s e .

5. Al-Cu-Li a l l o y s w h i c h h a v e b e e n s t r e t c h e d 6 % w i l l show a s m a l l e r , b u t f a s t e r i n c r e a s e i n m o d u l u s upon a g i n g . E a r l i e r o c c u r r e n c e of t h e T1 phase and enhanced p r e c i p i t a t i o n k i n e t i c s a r e r e s p o n s i b l e f o r t h i s phenomenon,

6. T h e r e i s no o r i e n t a t i o n d e p e n d e n c e of t h e e l a s t i c m o d u l u s observed i n t h e s e a1 loys.

ACKNOWLEDGEMENT

The a u t h o r s w o u l d l i k e t o a c k n o w l e d g e t h e s p o n s o r s h i p of t h e O f f i c e of Naval R e s e a r c h , G r a n t #N00014-85-K0526, w i t h D r . B r u c e MacDonal d, program manager.

JOURNAL D E PHYSIQUE

REFERENCES

1. E.A. S t a r k e , J r . , T.H. S a n d e r s , Jr., a n d I. P a l m e r . "New Approaches t o A l l o y Development i n t h e A1-Li System," J o u r n a l of M e t a l s

33

( 1 9 8 1 ) p. 24.

2. G.G. Wald, NASA C o n t r a c t o r R e p o r t 1 6 5 7 6 , L o c k h e e d

-

C a l i f o r n i a Company, Burbank, CA (May 1 9 8 1 ) .

3. W. K o s t e r a n d W. Rauscher, Z. M e t a l l k d e

39

(1948) p. 111.

4. K.K. S a n k a r a n a n d N. J. G r a n t : A l u m i n u m - ~ i t h i u m A l l o y s , e d s . T.H.

S a n d e r s , Jr., a n d E.A. S t a r k e , Jr.. TMS-AIME, W a r r e n d a l e , PA (1981) p. 205.

5. J. K r a u t k r a m e r a n d H. K r a u t k r a m e r , U l t r a s o n i c T e s t i n g pf Materials, 2nd e d . , S p r i n g e r - V e r l a g , New York ( 1 9 7 7 ) .

6. F. B r o u s s a u d a n d M. Thomas, " I n f l u e n c e o f D e l t a P r i m e P h a s e C o a l e s c e n c e o n Younu's M o d u l u s i n a n Al-2.5 w t % L i A l l o v . " - . A l u m i n u m - L i t h i u m ~ l i o y s

u,

e d s . C. Balcer, P.J. G r e g s o n , S.J.

----

H a r r i s a n d C.J. P e e l , I n s t i t u t e o f M e t a l s , London, UK ( 1 9 8 6 ) p.

7. G. Cocco, G. F a g h e r a z z i a n d L. S c h i f f i n i , " D e t e r m i n a t i o n of t h e D e l t a P r i m e C o h e r e n t M i s c i b i l i t y Gap i n t h e A1-Li System by S m a l l - Angle X-ray S c a t t e r i n g , " J. Appl. C r y s t .

10

(1977) pp. 325-327.

8. W. M u l l e r , E. B u b e c k a n d V. G e r o l d , " E l a s t i c C o n s t a n t s of A1-Li S o l i d S o l u t i o n s a n d P r e c i p i t a t e s , " Aluminum-Lithium A l l o y s

m,

I n s t i t u t e of M e t a l s , London, UK ( 1 9 8 6 ) , p. 435.

9. B. N o b l e , S.J. H a r r i s , a n d K. D i n s d a l e , "The E l a s t i c M o d u l u s o f Aluminum-Lithium A l l o y s , " J o u r n a l of M a t e r i a l s S c i e n c e

17

(1982) p. 461-468.

10. D. T u r n b u l l , S o l i d S t a t e P h y s i c s

3

(1956) p. 226.

11. W i l l i a m A. Cassada, 111, Ph.D. T h e s i s , u n i v e r s i t y of ~ i r g i n i a . May 1987.

12. E. K r o n e r , S t a t i s t i c a l C o n t i n u u g M e c h a n i c s , S p r i n g e r B e r l i n ( 1 9 7 1 ) .

13. C. K i t t e l , I n t r o d u c t i o n t o S o l i d S t a t e P h y s i c s , 4 t h E d i t i o n , J o h n Wiley a n d Sons, I n c . , New York, NY (1971) p. 149.

14. E. Agyekum, W. Ruch, E.A. S t a r k e , Jr., S.C. J h a a n d T.H. S a n d e r s ,

"The E f f e c t o f P r e c i p i t a t e Type o n t h e E l a s t i c P r o p e r t i e s o f A l -

Li-Cu a n d ~ l - ~ i - C U - ~ g ~l l & ~ " , ~ l u m i n u m - ~ i t h i u i A l l o y s

u,

I n s t i t u t e of M e t a l s , London, UK (1986) p. 448.

TABLE I. ALLOY COMPOSITIONS

ALLOY

-

A 1

-

^Cu

^-

^{L i}

-

^{Z r} C u / L i r a t i o

w t %

-

a t 8

B i n a r y 9 7 . 8 5 2 . 0 0

9 2 . 6 0 7 . 3 6

TABLE 11. VOLUME FRACTION OF DELTA PRIME

A 1 loy A g e t i m e TEM Direct C o m p a r i s o n

a t 1 9 0 C M e t h o d M e t h o d

8 1 4 h r s 1 1 . 2

8 h r s 8 h r s 8 h r s

81 2 0 h r s

8 1 2 0 h r s

8 1 1 0 0 h r s 1 3 . 9

TABLE 111. THEORETICAL MODULI FOR S O L I D SOLUTIONS

A 1 loy C r y s t a l l o g r a p h i c d i r e c t i o n < h k l >

J O U R N A L DE PHYSIQUE

- - - A L L O Y 73

-

^{ALLOY 81, 8 2}

---

T2

-

--- - - - - --- - - - -

^-p

Tl _*

---- --- - - - - - - - - - - - -

^{- - p}

6'

^rn

loa

1 I I

10' 1

o2

10"

12

AGE TIME

9190

C (MINUTES)

F i g u r e 1. p r o f i l e of t h e o c c u r r e n c e of t h e d e l t a p r i m e , T 1 a n d T 2 p h a s e s i n a l l o y s 7 3 , 81, a n d 82.

AGE TIb?E 1 190 C (MINUTES)

F i g u r e 2. The v o l u m e f r a c t i o n of d e l t a p r i m e i n a l l o y 8 1 a f t e r a g i n g a t 1 9 0 C. ( 0 ) G u i n i e r c a m e r a d a t a : ( * ) S A X S d a t a normalized.

F i g u r e 3 . P o l e f i g u r e s a ) A l l o y 7 3 (111). b) A l l o y 7 3 ( 2 0 0 ) . c) A l l o y 8 1 ( I l l ) , d ) A l l o y 8 1 ( 2 0 0 ) , e ) A l l o y 8 2 ( I l l ) , a n d f ) A l l o y 8 2 ( 2 0 0 ) .

JOURNAL DE PHYSIQUE

7 5 . 0 ~ ' " ' " ' " ' " " " " ' ' ' ' ' ' ' ' 1 3 ' " " " ' I

I

oO

10' I

o2

10 10'.

ACE TIME (MINUTES)

F i g u r e 4. E l a s t i c modulus v e r s u s a g i n g t i m e a t 190°C of a l l o y .

--- 1

W 79.0

-

78.0 -

. . . . .. ... .

-

.

^-

. 76. J

1

I

75.0 ^I

. . . .

^{,... 1 ,}

. .

^{! . I}

. . .

¹ , . . m I

.

^I

I

o0 i

^{O' . 10' i 0" 1 0'}

ACE TIME B 190 C .:IINUTC_S)

t h e b i n a r y

F i g u r e 5. Young's modulus v e r s u s a g i n g t i m e a t 190°C f o r a l l o y s 73, 81 and 82 i n t h e l o n g i t u d i n a l t e s t i n g d i r e c t i o n .

Figure 6. S h e a r modulus vs. a g i n g t i m e a t 190°C f o r a l l . o y s 7 3 , 81 and 82.

32.0

--

75.0 ^I , , , I , , I

.

^{, ,,,,.I I}

^.

^{1 I}

1

oO

10' 1 02 1

o3

10'

ACE TIME R 190 C (MINUTES)

31.0

30.0

-C .(

Figure 7. E l a s t i c m o d u l u s v e r s u s a g i n g t i m e f o r a l l o y 81.

E x p e r i m e n t a l d a t a i s c o m p a r e d w i t h a t h e o r e t i c a l p r e d i c t i o n .

-

-

⁷³

29.0

Q

0 28.0

27.0

26.0

25.0

-

⁸¹

82

-

- -

1 0%

I I , , , . , , , , I

.

, , , , . ,

10'

loZ

1

o3 2

AGE TIME B 190 C (MINUTES)

JOURNAL DE PHYSIQUE

F i g u r e 8. Young's m o d u l u s v e r s u s a g i n g t i m e a t 1900C of a l l o y 7 3 s t r e t c h e d 6 % .

75.0

-

ⁱ

I

4

F i g u r e 9. Young's modulus v e r s u s a g i n g t i m e a t 1900C f o r t h e s h o r t t r a n s v e r s e , l o n g t r a n s v e r s e and l o n g i t u d i n a l d i r e c t i o n s of a l l o y 8 2 .

75.0 ^{I I I}

1

on

10' 1

o2

1

o3

l o 4 ^{L l}

TI!4E (MINUTES)

80.0

.;; 79.0

i3

W 78.0

77.0

76.0

75.0

- - -

- - ^{- - - - -}

^,

^{- -}

... .

^{. - . . .}

. .

. . .

. .

. --

I 1 1 1 + , 1 8 1 1 1 1 1 1 1 1 1 1 1 t 1 1 3 1 1 1 1 1

1

o0

10' 1

o2

1

c3

10'

AGE TIME R 193 C (MIIIUTES)