Precipitation Hardening in Cu-Zn-Be Alloys R. THOMSON AND A. F . CRAWLEY B r a s s e s containing 20 and 30 p c t Zn and up to 1.15 p c t Be have b e e n e x a m i n e d to p r o v i d e t e n s i l e t e s t d a t a on the a g e - h a r d e n i n g r e s p o n s e of t h e s e t e r n a r y a l l o y s . It was found that y i e l d s t r e n g t h s of 1100 M p a w e r e a t t a i n a b l e with cold w o r k i n g p r i o r to aging at 300~ T h e m o d e of p r e c i p i t a t i o n , a s d e t e r m i n e d by e l e c t r o n m i c r o s c o p y and e l e c t r o n d i f f r a c t i o n , a g r e e s s u b s t a n t i a l l y with r e c e n t w o r k on the b i n a r y C u - B e s y s t e m . P r e c i p i t a t i o n c o m m e n c e s a s GP z o n e s on the {001}c~ p l a n e s . The o b s e r v e d p r e c i p i t a t e p h a s e , a f t e r a g i n g t i m e s of up to s e v e n d a y s at 400~ i s CuBe with an o r i e n t a t i o n r e l a t i o n s h i p of the t y p e (301)pp t H (113)~ [010]pp t I, [ i l 0 ] ~ .

THE

p r e c i p i t a t i o n h a r d e n i n g e f f e c t s e x h i b i t e d by b e r y l l i u m - b e a r i n g c o p p e r , t i n b r o n z e , n i c k e l and cup r o - n i c k e l have a l s o b e e n o b s e r v e d *-4 in C u - Z n - N i - B e and t e r n a r y C u - Z n - B e a l l o y s . The b r i e f p u b l i s h e d d e s c r i p t i o n 3 of the l a t t e r s y s t e m i s e x p a n d e d h e r e to e x a m i n e the p o s s i b i l i t y that b e r y l l i u m b r a s s e s m a y aff o r d a u s e f u l r a n g e of t e n s i l e p r o p e r t i e s b e t w e e n t h o s e of the t i n b r o n z e s on the one hand, and c o m m e r c i a l b e r y l l i u m - c o p p e r s on the o t h e r . In addition, an a t t e m p t has b e e n m a d e to identify the c h a r a c t e r i s t i c s of the p r e c i p i t a t i o n r e a c t i o n in the C u - Z n - B e s y s t e m . E X P E R I M E N T A L PROCEDURE A s e r i e s of t e r n a r y a l l o y s w e r e c a s t and f a b r i c a t e d to a p p r o x i m a t e l y 4 m m (3/16 in.) s h e e t , then p r o c e s s e d t h r o u g h a heat t r e a t m e n t and cold r o l l i n g p r o g r a m d e s i g n e d to y i e l d m e c h a n i c a l t e s t d a t a on the e f f e c t s of t h e following f a c t o r s : (a) (b) (c) (d) {e)

Zinc content Beryllium content Aging temperature Aging time Cold work

two levels six levels five levels six levels five levels

20 and 30 wt pct 0 to 1 wt pet 200 to 400~ 0 to 720 rain 0 to 50 pct reduction.

Solution h e a t t r e a t m e n t s on the a p p r o x i m a t e l y 4 m m (3/16 in.) s h e e t s t a r t i n g m a t e r i a l s w e r e c a r r i e d out at 800~ for 1 h in an i n e r t a t m o s p h e r e , followed by w a t e r quenching to a m b i e n t t e m p e r a t u r e . The r e s u l t ant g r a i n s i z e v a r i e d b e t w e e n 0.03 and 0.1 m m e q u i v a lent g r a i n d i a m e t e r . T h e c h a r a c t e r i s t i c s of the p r e c i p i t a t e p h a s e and the p r e c i p i t a t i o n p r o c e s s in the t e r n a r y s y s t e m w e r e d e t e r m i n e d by e l e c t r o n m i c r o s c o p y , s e l e c t e d a r e a e l e c t r o n d i f f r a c t i o n and X - r a y d i f f r a c t i o n a n a l y s i s of p r e c i p i t a t e s i s o l a t e d by e x t r a c t i o n r e p l i c a s . The c o m p o s i tion e x a m i n e d was Cu-20 p c t Z n - 0 . 8 p c t B e . S a m p l e s of t h i s m a t e r i a l w e r e s o l u t i o n t r e a t e d at 800~ in a r g o n f o r 2 h, c o l d - w a t e r quenched, then a g e d f o r v a r i o u s t i m e s at 300, 350 and 400~ D i s c s p r e p a r e d by s p a r k e r o s i o n m a c h i n i n g w e r e c h e m i c a l l y thinned in 10 p c t s u l f u r i c a c i d , then e l e c t r o p o l i s h e d in 15 p c t n i t r i c a c i d in m e t h a n o l a t - 60~ Extraction replicas were p r e p a r e d by c a r b o n d e p o s i t i o n , followed by e l e c t r o p o l i s h i n g in the n i t r i c a c i d in m e t h a n o l s o l u t i o n . E l e c R. THOMSON and A. F. CRAWLEY are Research Scientists. Scientists, Physical Metallurgy-Research Laboratories, Canada Centre for Mineral and Energy Technology, Ottawa, Canada. Manuscript submitted September 3, 1975. METALLURGICAL TRANSACTIONS A

t r o n m i c r o s c o p y and d i f f r a c t i o n w e r e p e r f o r m e d on a P h i l l i p s EM300 ( o p e r a t i n g v o l t a g e 100 kV) equipped with a g o n i o m e t e r s t a g e and d o u b l e - t i l t h o l d e r . P R O P E R T I E S O F ALLOYS The c o m p l e t e s e t of t e s t d a t a 5 a r e only s a m p l e d h e r e to i l l u s t r a t e the e f f e c t s of f a c t o r s (a) to (e) outl i n e d a b o v e . In F i g . 1, k i n e t i c s of p r e c i p i t a t i o n h a r d e n ing a r e shown by the h a r d n e s s v a r i a t i o n with t i m e at a g i n g t e m p e r a t u r e f o r one of the a l l o y s given 0 and 50 p c t cold r e d u c t i o n b e f o r e aging. M a x i m u m h a r d n e s s v a l u e s w e r e a s s o c i a t e d with aging at 300 to 350~ f o r the a s - q u e n c h e d condition, and at 250 to 300~ for the q u e n c h e d and r o l l e d m a t e r i a l . T h e t i m e s to d e v e l o p t h e s e m a x i m a tended to d e c r e a s e at h i g h e r b e r y l l i u m l e v e l s . The e f f e c t s of zinc and b e r y l l i u m content on the p r e c i p i t a t i o n - h a r d e n i n g r e s p o n s e in the t e r n a r y s y s t e m a r e shown in F i g . 2 in which t e n s i l e t e s t d a t a b e f o r e aging and a f t e r aging to m a x i m u m y i e l d s t r e n g t h a r e p l o t t e d a g a i n s t b e r y l l i u m content. T h e v a l u e s i n d i c a t e d a r e t h o s e o b t a i n e d in m a t e r i a l with z e r o cold r e d u c t i o n and aged at 300~ It w i l l be noted

l .....

|

I'

"-

I

........ I

I

QUENCHED,ROLLED 50~

300 ~ .

.

.

.

I

I

I

REDUCTIONAND AGED .

~ 250

;. 2 o o -

-1

"--.(oo ~

QUENCMED AND AGED

-I I -

3

I00

----------"'~200 2

I 5

l IO

J ~ J _ _ . _ 20 50

I IOO

l 200

500

TIME, MINUTES

Fig. 1 - - H a r d n e s s vs t i m e at 200, 250, 300, 350, and 400~

for

the Cu-Zn-Be alloy containing 30 pct Zn and 0.5 pct Be. VOLUME 7A, JUNE 1976-865

0.2

04

I

I Cu-20%

9

BERYLLIUM % 0.6 08 I

Zn-

that there appears to be no i n t e r a c t i v e effect of zinc l e v e l , and that the strengthening effect due to p r e c i p i t a tion hardening i n c r e a s e s with b e r y l l i u m content up to the highest b e r y l l i u m l e v e l i n v e s t i g a t e d . As would be expected, i n c r e a s i n g the amount of prior cold w o r k i m p r o v e s the t e n s i l e p r o p e r t i e s of aged m a t e r i a l . To i l l u s t r a t e this, and at the s a m e t i m e r e l a t e the p r o p e r t i e s of t h e s e e x p e r i m e n t a l a l l o y s to other m a t e r i a l s , Fig. 3 s h o w s the v a r i a t i o n in yield strength with prior cold w o r k for 20 pct Zn a l l o y s containing 0, 0.36, 0.48 and 1.15 pct Be. The e x p e r i m e n t a l points show the m a x i m u m yield strength obtained after aging at 300~ w h e r e a s the r e f e r e n c e c u r v e s for tin b r o n z e and b e r y l l i u m - c o p p e r w e r e drawn f r o m published data. 6 A s e l e c t i o n of t e n s i l e t e s t data is given in Table I to indicate the range of p r o p e r t i e s obtainable. The t e s t coupons w h o s e configuration c o n f o r m e d with ASTM Specification E8 for s u b s i z e t e n s i l e s p e c i m e n s (gage length 25.4 m m , gage width 6.25 mm} w e r e pulled in uniaxial tension in an I n s t r o m U n i v e r s a l T e s t Machine at a c r o s s h e a d speed of 1.3 m m / m i n . Metallographic e x a m i n a t i o n of the a l l o y s in the solution treated and quenched condition r e v e a l e d that as the b e r y l l i u m content i n c r e a s e d , the s t r u c t u r e changed

I0

I

I

Be

o C u - 3 0 % Z n - Be

o

UTS -120

800

AGED

,/./,o.

400

~-~ P

~-

s ao~


"/'~

SO cn

-.YS

o.--'-

o

Z O O F ,~/

o b/

t

20

I

60 i ~ 0

I

\'k

"%

l

o..

o

I

l

QUENCHED

~Ox

9

+

4o,,,

~

.o-9 0

N '

. ~-o--

Table I. Typical Properties of Experimental

0.4 06 0.8 BERYLLIUM %

0.2

I0

Fig. 2--As-quenched and quenched and aged tensile properties of ternary alloys as a function of beryllium content.

I

1200

I

I

I

I

~

Cu - 2 Be " / ~ / ' ~ U

- 20Zn I 15B~

160

Zn, Pct

Be, Pct

20 20 20 20 20 30 30 30 30 30

0 0 36 0.36 0 36 1.15 0 0 52 0 52 0 52 0 91

Cold Work, Pct 0 0 50 50 0 0 0 50 50

300 300 300 -

:1=

/i/

/ ozo

I-(D Z LI2 or. F30 O~ a J >-

40

200

300 300 300

120 60 90 360 120 15

I

I

~" I000 --~"" ~\~.~\

120

'

Aging Mln

~

\

#_ soo

UTS,

Mpa

83 124 407 793 1117 83 179 455 827 986

262 338 552 848 1124 283 421 614 917 1138

I

ElongaUon, Pct 70 80 40 4 1 80 61 30 4 3

I

A ALPHA O ALPHA+BETA 9 BETA

9 9

,

\\

W

\\

/ / -

I I0

I 20

1 I 30 40 REDUCTION %

I 50

F i g . 3 - - M a x i m u m yield s t r e n g t h (0.2 pct o f f s e t ) d u r i n g aging at 3 0 0 ~ o f C u - Z n - B e a l l o y s as a f u n c t i o n of p r i o r c o l d w o r k .

D a t a f o r b e r y l l i u m - c o p p e r , 6 tin b r o n z e 6 and c o p p e r - z i n c + a r e included for comparison. 866

YS.

Mpa

".

o

~Boo

Cu-Zn-Be Alloys

V O L U M E 7A, J U N E 1976

400 25

1 I 30

I Jl 35 40 ZINC %

\ I1 45

F i g . 4 - - I l l u s t r a t e s the s h i f t of the alpha + b e t a p h a s e field in b r a s s e s c o n t a i n i n g 0.2 p e t Be. T h e d a s h e d l i n e s indicate p h a s e b o u n d a r i e s in the b i n a r y s y s t e m , z w h i l e the s o l i d l i n e s d e r i v e f r o m m e t a l l o g r a p h i c e x a m i n a t i o n of t e r n a r y a l l o y s . METALLURGICAL TRANSACTIONS A

IIIII II ii iiiii I

(a) Fig. 6--Bmght field image of Cu-20 pct Zn-0.8 pct Be after aging for 8 days at 300~ Platelets are vmihle on {001}v~ planes.

200 0

PRECIPITATION

O

020

9

O

O (b)

Fig. 5--Electron diffraction patterns of a Cu-20 pct Zn-0.8 pct Be alloy at different stages of the precipitation sequence: (a) after aging for 2 h at 300~C. Relrods along the (001) directions indicate GP zone formation. Zone axis [001]~, (b~ after 8 days at 300~ Intensity maxima have developed on the (001) reirods at about two-thirds of the {002} reciprocal lattice vectors. Zone axis [t001a. f r o m s i n g l e - p h a s e alpha to duplex alpha plus q u e n c h e d beta, i n d i c a t i n g that b e r y l l i u m r e d u c e d the s o l i d s o l u b i l i t y of zinc in copper. The extent of the shift of the s o l v u s l i n e s was roughly d e t e r m i n e d by m e t a l l o g r a p h i c e x a m i n a t i o n of quenched s p e c i m e n s of a s e r i e s of a l loys of fixed b e r y l l i u m content (0.2 pct) and i n c r e a s i n g zinc content. F r o m the o b s e r v a t i o n s noted in Fig. 4, the p o s i t i o n of the t e r n a r y alpha plus beta p h a s e field s u g g e s t s a z i n c e q u i v a l e n t for b e r y l l i u m of 18 to 20 wt pct. METALLURGICALTRANSACTIONSA

CHARACTERISTICS

The steps in the precipitation process can be followed from the electron diffraction patterns in Figs. 5 and 7. Precipitation commences as platelet GP zones on the (001}c e planes. Fig. 5(a) shows the reciprocal lattice section resulting from 2 h aging at 300~ Relrods indicating such GP zone formation 8 are present as continuous streaks along the (001)a directions passing through all of the diffraction spots. These streaks persist after aging for 8 days at 300~ but, as shown in Fig. 5(b), intensity maxima have developed at about two thirds of the (002}a reciprocal lattice vectors. The intensity maxima at about one third of this vector are considered to arise from double diffraction. Fig. 6 shows the alloy structure at this point. Close examination reveals small platelet precipitates lying on the ~001)~ planes against a background of diffuse striations in (ii0) directions. These striations form a "tweed"like structure which has been widely reported in binary Cu-Be alloys and attributed by Tanner 8 to a strain contrast effect. Broader, more intense maxima evident in Fig. 7(a) are produced after aging for 5 h at 350~ whereas after 24 h at this temperature these maxima have broken down and small relrods are evident about the (001)c e directions, Fig. 7(b), at positions corresponding to a d-spacing of 0.270 nm. Thus, transformation to a distinct lattice has been achieved, the relrods indicating a very fine precipitate. The presence of several sets of relrods at this same d-spacing but lying in different directions in the reciprocal lattice suggests several sets of precipitates at different stages of change of habit plane away from ~001)~. The The form of the precipitates after 24 h at 350~ is shown in bright- and dark-field images in Fig. 8(a) and (b). L a r g e r p r e c i p i t a t e s p r o d u c e d by aging for 7 days at 400~ a r e i l l u s t r a t e d in Fig. 9(a). Data f r o m s e v e r a l VOLUME 7A, JUNE 1976--867

@ L

%

ID Ca)

r m t$

10

(bJ

Fig. 7--Same alloy as in Fig, 5 after aging for (a} 5 h at350~ Zone axis [110}ce t3~e , (b) 24 h at 350~ Intensity maxima have divided into discrete spots, corresponding to a d-spacing of the precipitate of 0.270 arr~, Zone axis [110]~ type.

d i f f r a c t i o n p a t t e r n s of p r e c i p i t a t e and m a t r i x w e r e a n a l y z e d in the c o m p u t e r p r o g r a m d e s c r i b e d i n a n e a r l i e r p a p e r 9 to d e t e r m i n e l a t t i c e s y m m e t r i e s and o r i e n t a t i o n r e l a t i o n s h i p s , The p r e c i p i t a t e l a t t i c e was shown to be s i m p l e cubic with the cell edge a = 0,270 0.002 nm having an o r i e n t a t i o n r e l a t i o n s h i p with the fcc m a t r i x of the type, (301)pp t II (l13)a

[oiO)ppt ~, [ho]~. The d i f f r a c t i o n p a t t e r n i l l u s t r a t e d i n F i g . 9(b) and i n dexed in Fig. 9(c) d e m o n s t r a t e the p a r a l l e l i s m of the 86g-VOLUME 7A, JUNE 1976

.

(bJ

Fig, S--Ca) Bright-field image of precipitates in Cu-20 pet Zn-0,8 pct Be after aging 24 h at 350~ (b) Dark field of same area as (a) taken at a precipitate reflection corresponding to d = 0.270 nm. ~OiO}ppt and [110 ]a zone a x e s . C o n s i d e r a t i o n of l a t t i c e s y m m e t r y d e m o n s t r a t e s that this type of o r i e n t a t i o n r e l a t i o n s h i p can have twelve v a r i a n t s , s e v e r a l of which w e r e o b s e r v e d i n this i n v e s t i g a t i o n . One of t h e s e v a r i a n t s would be

(301)ppt II (11~)~ [0i0]ppt il [ilO]a d e m o n s t r a t i n ~ that each d i r e c t i o n a l p a r a l l e l i s m can have one of two p l a n a r p a r a l l e l i s m s . F i g , 7(b) c a n be u n d e r s t o o d as d e m o n s t r a t i n g a t r a n s f o r m a t i o n which will r e s u l t in two f a m i l i e s of p r e c i p i t a t e s whose o r i e n METAL[,URGICAL TRANSACTIONSA

I

Z,

(a)

(b)

002 0

101 0

IO0

0

o

101" o

111

111 001

0

0

Fig. 9--(a) P r e c i p i t a t e s of CuBe in the t e r n a r y Cu-20 pet Z n 0.8 pct Be alloy a f t e r aging at 400~ for 7 days. (b) D i f f r a c tion p a t t e r n showing the p a r a l l e l i s m of the [0[0]pp t and the [[10] a zone axes. (c) Indexed s c h e m a t i c of diffraction p a t t e r n in (b), e - - M a t r i x , (3--precipitate.

ooT o

111

0

111 Q _O

Too 0

101

0

__0~

t01 o

002

ration r e l a t i o n s h i p s with the m a t r i x will be of the above type with a common d i r e c t i o n a l p a r a l l e l i s m . Though the computer p r o g r a m is concerned with l a t t i c e s and not s t r u c t u r e s , nonetheless the d e r i v e d l a t t i c e s y m m e t r y and dimensions a r e consistent with the phase CuBe which has a B2-type s u p e r l a t t i c e and o c c u r s in the b i n a r y Cu-Be s y s t e m ~0-13 This was conf i r m e d by the examination of p r e c i p i t a t e s in a b i n a r y Cu-1.27 pct Be alloy. F i n a l l y , the p r e c i p i t a t e c o m p o s i tion was f u r t h e r confirmed by X - r a y energy d i s p e r s i v e a n a l y s i s on e x t r a c t e d l a r g e p r e c i p i t a t e s produced by slow cooling from 800~ It is i n t e r e s t i n g to note that e l e c t r o n diffraction studies on individual p r e c i p i t a t e s METALLURGICAL TRANSACTIONS A

in s l o w - c o o l e d s p e c i m e n s did not y i e l d c o n s i s t e n t o r i entation r e l a t i o n s h i p s although the p r e c i p i t a t e phase was the s a m e as in quenched mud aged a l l o y s . This was i n t e r p r e t e d as indicating c o a r s e , noncoherent p r e c i p i tates or that in the equilibrium state with the m a t r i x the p r e c i p i t a t e s have an orientation r e l a t i o n s h i p ~ diff e r e n t to that given above. The r e s u l t s p r e s e n t e d h e r e d e m o n s t r a t e that both the b i n a r y Cu-Be and t e r n a r y Cu-Zn-13e s y s t e m s p r o duce the s a m e p r e c i p i t a t e , with the s a m e growth habit. The decomposition sequence o b s e r v e d a g r e e s substant i a l l y with that d e s c r i b e d for the b i n a r y alloy by Bonfield and Edwards, 12 viz VOLUME 7A, JUNE 1976 ~176

supersaturated

solid solution ~

GP zones ~

y'~

T

where both T' and ~ are the CuBe phase, differing only in their orientation relationship with the matrix. With the precipitation heat treatments employed in the present study, no evidence was found to support the existence of an intermediate phase with a body-centered tetragonal lattice as reported in several investigat i o n s 11'13'15 o f t h e b i n a r y a l l o y o r o f d i s t i n c t f i r s t - o r d e r precipitate reflections corresponding to a d-spacing of other than 0.270 nm, which is the cell edge length of CuBe.

CONCLUSIONS I) Tensile test data on quenched and aged Cu-Zn-Be alloys have shown that these alloys afford a range of tensile properties intermediate between tin bronzes on the one hand and commercial Cu-Be alloys on the other. 2) Beryllium reduces the solid solubility of zinc in copper. The observed shift of the solvus line in a range of Cu-Zn alloys with a fixed 0.2 pct Be content indicated a zinc equivalent of beryllium of 18 to 20 pct. 3) The decomposition sequence in ternary Cu-Zn-Be alloys is the same as that recently reported for binary Cu-Be alloys, viz supersaturated

solid solution ~

870 VOLUME 7A, JUNE 1976

GP zones ~

y'~

where T' and T are the phase CuBe which has a B2type superlattice and a cell edge a = 0.270 nm.

ACKNOWLEDGMENT The authors thank D. R. Kiff and R. V. Carmody their technical assistance in this investigation.

for

REFERENCES 1. W. D. Robertson and R S. Bray Preeipitattonfrom SolidSolutlon, p. 328, ASM Pubhcauons, 1958 2 P J Scherbner U.S Patent No 3,287,110, 1966 3 Brit. Pat. 1,032,000, 1966 4. P. S. Hanson- U S. Patent No 3,166,410. 5 R. Thomson Report MRP/PMRL-75-1 I(R) Physical Metallurgy Research Laboratories. CANMET, Department of Energy, Mines and Resources, Ottawa, Canada, 1975 6 Metals Handbook, ASM, 1961,'~ol !, pp. 1018, 1027. and 1038. 7 lbtd, 1973, vol 8, p. 271. 8. L E Tanner Phil Mag., 1966, vol. 16, pp 111-30 9. A. F. Crawley and K S. Mdhken. Acta Met, 1974, vol 22, pp. 557-62. 10 W B. Pearson A Handbook of Latttce Spactngs and Stntctures of Metals and Alloys, p 453, Permagon Press, 1958 1l K Shlrmzu, Y Mlkaml, H. Mstam, and K. Otsuka Trans Jap. Inst. Metals, 1971,vol 12. pp 206-13. 12 W Bonfield and B C Edwards J Mater. Sct, 1974, vol 9, pp. 309-408. 13. S Yamamoto, M Matsul, and Y. Munkaml Trans, Jap hist. Metals, 1971, voI. 21, pp. 159-65. 14 W Bonfleld and B C Edwards J Mater. Set, 1974, vol 9, pp 409-14 15. A H Gelsler, J H. Mallery, and F. E. Ste~gert Trans. AIME, 1952, wl 194, pp. 307-16.

METALLURGICAL TRANSACTIONS A