HYDROGEN EMBRITTLEMENT IN Al-Li-Cu-Mg ALLOYS (8090-T651)

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HYDROGEN EMBRITTLEMENT IN Al-Li-Cu-Mg ALLOYS (8090-T651)

F. Binsfeld, M. Habashi, J. Galland, J. Fidelle, D. Miannay, P. Rofidal

To cite this version:

F. Binsfeld, M. Habashi, J. Galland, J. Fidelle, D. Miannay, et al.. HYDROGEN EMBRITTLEMENT

IN Al-Li-Cu-Mg ALLOYS (8090-T651). Journal de Physique Colloques, 1987, 48 (C3), pp.C3-587-

C3-596. �10.1051/jphyscol:1987368�. �jpa-00226599�

JOURNAL DE PHYSIQUE

Colloque C3, suppl6ment au n09, Tome 48, septembre 1987

HYDROGEN EMBRITTLEMENT IN Al-Li-Cu-Mg ALLOYS (8090-T651)

F. BINSFELD, M. HABASHI, J. GALLAND, J.P. FIDELLE*, D. MIANNAY*

and P. ROFIDAL*

Ecole Centrale des Arts et Manufactures, F-92295 Ch.Eitenay-Malabry Cedex, France

* C E A , B.P. 511, F-75752 Paris Cedex 15, France

ABSTRACT

This paper describes the hydrogen embrittlement (HE) o f an A1-Li a l l o y aged a t 190°C and with d i f f e r e n t durations o f ageing (10, 15, 20 and 30 hr).

Two techniques were employed t o measure HE : a) cathodic p o l a r i z a t i o n i n a molten s a l t s bath with -3 VIAg on t e n s i l e specimens ; b ) gaseous hydrogenation on disks. Hydrogen charging was achieved a t 190°C. The r e s u l t s show t h a t HE i s important when the a1 1 oy i s i n the over-aged condition.

INTRODUCTION

A1-Li a l l o y s have gathered strong i n t e r e s t especially i n t h e a i r c r a f t industry. Compared t o conventional high-strengh a1 umini um a1 loys o f the 2000 or 7000 series, i t i s known t h a t A1-Li a l l o y s o f f e r a 10% increase i n Young's modulus along w i t h a 10% decrease i n s p e c i f i c weight, thus making them rather competitive t o new non-metal 1 i c materi a1 s 1 i ke carbon f i b r e reinforced '

composi tes. Moreover, t h e i r mechanical properties are equivalent t o those o f conventional high-strength A1

.

^{a1 loys.}

I n t h e binary Al-Li a l l o y system, t h e 6

'

(A13Li) p a r t i c l e s which p r e c i p i t a t e throughout t h e matrix are responsible f o r strengthening. I n the A1-Li-Cu-Mg a l l o y s apart from the

6

I , semi coherent, S t (AlzCuMg) and TI

(A12CuLi) phases p r e c i p i t a t e during a r t i f i c i a l ageing treatment. 6

'

i s a metastable phase' which forms as spherical p a r t i c l e s which remain coherent w i t h the matrix ( 1 ). During p l a s t i c deformation, these p a r t i c l e s may be cut by moving dislocations such t h a t f u r t h e r deformation along the same s l i p plane i s favoured ; s l i p becomes coplanar (2, 3) and leads t o poor toughness and ducti 1 i ty. The s l i p cop1 anari t y gives ri se t o stress concentrations a t g r a i n boundaries i nduci ng intergranul ar f a i 1 ures (4). The growth r a t e o f

6

depends

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987368

JOURNAL DE PHYSIQUE

o n vacancy c o n c e n t r a t i o n which i n t u r n i s a f f e c t e d by high s o l u t i o n t r e a t m e n t t e m p e r a t u r e f o l 1 owed by c o l d

water

quenched (5

1.

The s t r e n g t h enhancement d u r i n g room t e m p e r a t u r e a g e i n g a p p e a r s

t o

be due

t o

t h e p r e c i p i t a t i o n o f

6 '

phase. Subsequent a r t i f i c i a l a g e i n g g i v e s r i s e

t o a

g r a i n boundary REZ, ( P r e c i p i t a t i o n F r e e Zone) i n d i c a t i n g t h a t $ p r e c i p i t a t i o n i s dependent upon t h e p r e s e n c e o f e x c e s s v a c a n c i e s (5). The P.F.Z. grows according

t o

t 1 / 3 1 aw, where t i s t h e ageing time a t a given ageing t e m p e r a t u r e ( 6 ) . Attempts t o improve t o u g h n e s s o f A1-Li a 1 l o y s have been -based on t h e change i n g r a i n s t r u c t u r e t o i n f l u e n c e t h e f r a c t u r e process. A d d i t i o n o f manganese i s known a s a g r a i n - r e f i n e r b u t a s an improvement

t o

g r o s s i n t e r g r a n u l a r f a i l u r e (7).

Zirconium a d d i t i o n of l e s s t h a n 0.2% forms

p '

(A13Zr) p r e c i p i t a t i o n which g i v e s r i s e

to

g r a i n--ref i nement, i n h i b i t i o n o f r e c r y s t a l 1 i s a t i o n and d e c r e a s i n g s h e a r e d

6 '

p a r t i c l e s by t h e moving d i s l o c a t i o n s (8). However, zirconium g i v e s h i g h l y t e x t u r e d s t r u c t u r e s ( 5 ) i n A1-Li a l l o y s .

The Cu and Mg p r e c i p i t a t e heterogeneous1 y d u r i n g a r t i f i c i a l ageing

as

S ' (A1 2CuMg) and TI (A1 2CuLi )

.

The n u c l e a t i o n

sites

o f t h e s e p r e c i p i t a t e s a r e d i s l o c a t i o n s formed d u r i n g quenching, d i s l o c a t i o n s i n t r o d u c e d d u r i n g s t r e t c h i n g and low-angle s u b g r a i n boundaries. Grain boundary p r e c i p i t a t i o n o f

6

(AlLi ) and complex A1-CU-Mg phases occur d u r i n g a r t i f i c i a l ageing ( 9 ) . a s t r e t c h b e f o r e a r t i f i c i a l a g e i n g i n c r e a s e s t h e r a t e of ageing and t h e n i n c r e a s e s t h e y i e l d s t r e n g t h and t h e u l t i m a t e t e n s i l e s t r e n g t h b u t r e d u c e s t h e e l o n g a t i o n

t o

f r a c t u r e . For each chemical composition of A1-Li a l l o y , t h e r e i s

a

s p e c i f i c ageing h e a t t r e a t m e n t c o n d i t i o n (peak aged c o n d i t i o n ) a t which t h e mechanical p r o p e r t i e s a r e optimum. In t h e under-aged c o n d i t i o n , t h e deformation i s l o c a l i z e d w i t h i n s l i p bands w h i l e a t t h e peak c o n d i t i o n t h e deformation i s homogeneous and due

t o

t h e i n c r e a s e d volume f r a c t i o n o f S 1 t h r o u g h o u t t h e matrix. In t h e overaged c o n d i t i o n , t h e p r e c i p i t a t i o n o f 'S'

i s

a t once w i t h i n t h e m a t r i x and i n t h e sub-grain boundaries ( 9 ) .

On t h e o t h e r hand, conventional h i g h - s t r e n g t h aluminium a l l o y s such

as

A1-Zn-Mg, Al-Zn-Mg-Cu and A1-Mg s u f f e r a r e v e r s i b l e hydrogen e m b r i t t l e m e n t whereas A1-Cu and al-Cu-Mg a p p e a r

t o

be r e s i s t a n t

t o

hydrogen i n t r o d u c e d e i t h e r by c a t h o d i c c h a r g i n g o r by exposure

to

water c o n t a i n i n g environments (10).

To t h e b e s t o f

our

knowledge, A1 -Li-Mg-Cu-Zr (8090 a l l o y ) has not been s t u d i e d

so

f a r . In t h i s paper, hydrogen e m b r i t t l e m e n t of 8090

-

T651 was t h e n i n v e s t i g a t e d .

EXPERIMENTAL

The chemical composition and t h e t h i c k n e s s t of t h e 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 a r e given i n t a b l e I .

T a b l e I : Chemical composition and t h i c k n e s s of t h e a l l o y s s t u d i e d ( w t % ) .

...

I

^Li

I

Mg

I

Cu

I

Zr

I

S i

I

Ti

I

Fe I N a , p p m l t , m m l

1

^2.7

1

^1.1

1

^{1 . 3}

1

^0.09

1

^0.02

1

^0.02

1

^0.02

1

³

1

^{0 . 8}

1 1

^2.9

1

^1.1

1

^{1 . 3}

1

^0.09

1

^0.02

1

^0.02

1

^0.02

1

3

1

^{1 . 6}

1

The experimental m a t e r i a l was suppl i e d by CEGEDUR PECHINEY i n t h e form of 0.8 and 1.6

nun

r o l l e d p l a t e i n t h e s o l u t i o n t r e a t e d (535OC d u r i n g I h r and t h e n c o l d w a t e r quenched) and 3% s t r e t c h e d , c o n d i t i o n T-351. Hydrogen charging was achieved by two methods :

1 ) C a t h o d i c a l l y on t e n s i l e specimens having 1.6 m m t h i c k n e s s i n a molten s a l t s bath ( 1 1 ) a t 190°C d u r i n g 10, 15, 20 and 30 h r and a t d i f f e r e n t c a t h o d i c p o t e n t i a l s : -1 .5, -2.0, -2.5 and -3.0 V/Ag. A f t e r hydrogenation, o u t g a s i n g was a c h i e v e d , and QH was measured a t 520°C and 1000°C. Uncharged and hydrogen c a t h o d i c a l l y charged specimens

were

t e n s i l e t e s t e d a t room t e m p e r a t u r e , u s i n g a s t r a i n r a t e o f 2 . 7 . 1 0 - ~ s - ~ t o s t u d y t h e e f f e c t o f hydrogen c h a r g i n g on t e n s i l e p r o p e r t i e s . Reference specimens

were

t h o s e aged a t 1 90°C i n f u r n a c e d u r i n g 10, 15, 20 and 30 h r .

2 ) Gaseous hydrogen on d i s k s having 0 . 8

mm

t h i c k n e s s . The d e t a i l s of t h i s method

were

d e s c r i b e d elsewhere (12). The r e f e r e n c e g a z was helium. The f o l l owing procedures

were

achieved :

a ) i n c r e a s i n g t h e r a t e of hydrogen p r e s s u r e A P/ A t from 0.007 t o 188

-4

M%hi&&ternal hydrogen). The a l l o y was i n T651 c o n d i t i o n ;

b) thermal hydrogen o r helium charging on both s i d e s a t 1 90°C, d u r i n g 20 h r . Gas p r e s s u r e was 400 Pa ( i n t e r n a l hydrogen) ;

c ) c a t h o d i c a l l y hydrogen c h a r g i n g a t 190°C d u r i n g 2 0 h r and w i t h -3V/Ag ( i n t e r n a l hydrogen).

Tn

t h e two l a s t c o n d i t i o n s e i t h e r he1 ium ( b ) or/and hydrogen g a s ( c )

were

usedtochieve f a i l u r e .

All t h e f a i l u r e s

were

c a r r i e d o u t a t 20°C. F r a c t u r e s u r f a c e s

were

examined using a scanning e l e c t r o n microscope.

JOURNAL DE PHYSIQUE

EXPERIMENTAL RESULTS

1 ) C a t h o d i c a l l y hydrogen c h a r g i n g

F i g u r e 1 shows t h a t t h e outgased QH i s an i n c r e a s i n g f u n c t i o n

as

t h e a p p l i e d c a t h o d i c p o t e n t i a l l e v e l and t h e t i m e o f hydrogen c h a r g i n g a r e i n c r e a s e d whatever t h e o u t g a s i n g t e m p e r a t u r e i s 520°C o r i s 1 000°C. However, QH measured

a t

1000°C i s h i g h e r t h a n t h a t o b t a i n e d a t 520°C showing t h a t m o l e c u l a r hydrogen t r a p p i n g

occurs

and i n c r e a s e s with t h e s e v e r i t y o f hydrogen c h a r g i n g c o n d i t i o n . QH p r i o r

t o

hydrogen c h a r g i n g i s measured

a t

520°C t o be a b o u t 5 ppm f o r

t

= 1 . 6

m

and a b o u t 1 0 ppm f o r t = 0.8

nun,

and i s due

t o

quenching t h e a l l o y from 535°C i n c o l d water.

F i g u r e 2 shows t h e v a r i a t i o n of t h e y i e l d s t r e n g t h

Re

a s a f u n c t i o n o f hydrogen c h a r g i n g t i m e i n t h e molten s a l t s bath a t f r e e p o t e n t i a l and a t -3V/Ag, and a s a f u n c t i o n o f a g e i n g time when t h e ageing t r e a t m e n t i s achieved i n t h e f u r n a c e with o r w i t h o u t vacuum. The y i e l d s t r e n g t h

is

independent on t h e a g e i n g t i m e and on t h e c a t h o d i c p o t e n t i a l l e v e l and dxceeds t h o s e due

t o

a g e i n g h e a t t r e a t m e n t i n f u r n a c e d u r i n g v a r i o u s t i m e s ; t h e i r

Re

a c h i e v e s a maximum f o r 15 h r ageing.

Maximum t e n s i l e s t r e n g t h Rm v a r i a t i o n a s a f u n c t i o n of a g e i n g t i m e i s very s e n s i t i v e t o t h e ageing h e a t t r e a t m e n t c o n d i t i o n , f i g u r e 3 . However, Rm v a l u e s measured i n t h e molten s a l t s b a t h a r e higher t h a n t h a t o b t a i n e d when u s i n g t h e f u r n a c e t o a c h i e v e t h e ageing h e a t t r e a t m e n t . Independently o f t h e h e a t t r e a t m e n t c o n d i t i o n , t h e maximum

stress

Rm i s a l s o maximum f o r 1 5 h r ageing.

D u c t i l i t y l o s s

F

% due t o hydrogen c h a r g i n g i s a b o u t 20% f o r a g e i n g t i m e v a r y i n g f r o m l O t o 2 0 h r , f i g u r e 4 . % d r a s t i c a l l y i n c r e a s e s u p t o 75% f o r a 30 h r a g e i n g time.

2 ) Gaseous hydrogen c h a r g i n g

For a1 1

test

c o n d i t i o n s , t h e d i s k s c e n t r a l p a r t (under p r e s s u r e ) b r e a k s i n t o numerous 1 i t t l e p i e c e s , f i g u r e 5 , i n d i c a t i n g t h e m a t e r i a l b r i t t l e c o n d i t i o n .

we

have t o remember t h a t t h e r e t a i n e d QH p r i o r gaseous hydrogen c h a r g i n g was measured t o be a b o u t 1 0 ppm. P a r t l y f o r t h i s r e a s o n and c e r t a i n l y due

t o

t h e e f f e c t i v e n e s s o f s u r f a c e o x i d e s , no s i g n i f i c a n t e m b r i t t l i n g e f f e c t o f hydrogen could be evidenced, f i g u r e 6 .

DISCUSSION

The results show that we have introduced high concentrations of hydrogen in A1 -Li alloy by using the molten s a l t s b a t h technique a t the optimum ageing temperature. To the best of our knowledge, no attempt has been done t o measure the hydrogen diffusion coefficient DH in A1-Li alloys

a t

190°C. However, NAKASHIMA and coll. (13) have measured DH in binary A1-Li system as a function of Li percentage and of temperature. Their results show great scattering and DH i

s

^estimated

as

about 1

o - ~

cm2. s-1 in the temperature range 1 80

t o

480°C, i ndependentl y of Li%. I n our conditions, hydrogen

may

diffuse

a t

a distance d from the surface of the metal equal t o about 85 t o 150

pm

for charging time vary'ing from 10 t o 30 h r respectively and according t o t h e relation : d 5

.

That i s t o say hydrogen may diffuse up t o or behind lithium depletion zone (14) ( S 100

pm),

which i s far beyond the oxide thickness (032

pm)

(14).

As mentionned above, S1 phase i s initiated on dislocations sites. Knowing that internal hydrogen promotes dislocations density (1 5, 1 6 ) , the probabil i ty of S' formation i s then more important in the presence of hydrogen than without hydrogen. Tensile stresses are increased when the A1 -Li a1 loy i s cathodical ly hydrogen charged. This increase does depend on hydrogen concentration, namely the polarisqtion time a t 190°C. Table I1 gives the percentage increase in t e n s i l e properties due

t o

hydrogen charging for two durations 15 and 30 h r . The reference alloy i s taken as t h a t heat treated in furnace under vacuum.

Table I I : Relative variation in the mechanical properties due to time of hydrogen charging (ageing time) a t -3.0 V/Ag.

...

I ^{t, hr} I

^{A Re%}

I

^{A R ~ %}

I

^F%*

I

1----_--1__---_--_1---I--- I

1 1 5 1 6 1 5 1 2 3

1

\

³⁰

1

¹¹⁵

1

¹⁹

1

75

1

The effect of internal hydrogen on the mechanical properties i s very important when the alloy i s in an overaged condition (190°C, 30 hr).klithout internal hydrogen and ageing heat treatment, the fai 1 ure surfaces show ductile rupture with f l a t surfaces containing s l i p lines, figure 7a. Figure 7b

shows

t h a t

when

the alloy i s aged heat treatment

a t

190°C during 30 hr in the

C3-592 JOURNAL DE PHYSIQUE

f u r n a c e under vacuum,

a

mixed r u p t u r e t y p e o c c u r s . Deep c r a c k s i n t h e s u b - g r a i n b o u n d a r i e s and many t e a r i n g s t h r o u g h o u t t h e m a t r i x a r e observed.

T h i s r e s u l t p o i n t s o u t t h a t c o a r s e d

6'

p a r t i c l e s ( 8 ) and S ' p h a s e w i t h i n t h e m a t r i x ( 9 ) and a l s o , S ' ( ~ 1 2CuMg) ( 9 ) , T2 ( A 1 2 C u ~ i ) ( 1 7) and A16(Fe, Cu) ( 1 8 ) p a r t i c l e s may b e p r e s e n t i n t h e sub-grain boundaries. With i n t e r n a l hydrogen and a t 500

pm

from t h e s u r f a c e , t h e r u p t u r e t y p e changes from i n t e r g r a n u l a r (10 h r ) t o mixed ( i n t e r

+

t r a n s c r i s t a l l i n e ) (1 5 and 2 0 h r ) and f i n a l l y becomes i n t e r g r a n u l a r ( 3 0 h r ) , f i g u r e 8. However, a t 100

pm

from t h e s u r f a c e , t h e f a i l u r e h a s an i n t e r g r a n u l a r f e a t u r e , i n d e p e n d e n t l y o f t i m e of ageing. The l a s t r e s u l t s prove t h a t hydrogen has d i f f u s e d and e m b r i t t l e d t h e metal a t a d i s t a n c e e q u a l t o o r g r e a t e r than 100

pm

from t h e m e t a l l i c s u r f a c e . The s u r f a c e o x i d e s i s t h e n overcome d u r i n g c a t h o d i c c h a r g i n g i n molten s a l t s b a t h . T h i s i s

not

t h e c a s e w h i l e gaseous hydrogen charging. However t h e r e s t r i c t e d number o f d i s k s l e f t a v a i l a b l e d i d n o t allow t h e n e c e s s a r y i n v e s t i g a t i o n o f t h e p r e s s u r e i n c r e a s e r a t e i n f l u e n c e . T h e r e f o r e , t h e s c a r c e

tests

on d i s k s hydrogen charged by t h i s t e c h n i q u e a r e i n c o n c l u s i v e b u t ought

t o

b e resumed

more

c o n s i s t e n t l y

,

e s p e c i a l 1 y w i t h t h i c k e r d i s k s .

CONCLUSION

I n t h i s work

we

have i n v e s t i g a t e d t h e hydrogen e r n b r i t t l e m e n t o f an A1-Li a1 l o y (8090). The r e s u l t s o b t a i n e d l e a d t o t h e f o l l o w i n g c o n c l u s i o n s :

1 ) Using t h e molten s a l t s b a t h t e c h n i q u e and c a t h o d i c a l l y hydrogen c h a r g e d t h e 8090

-

T351 a1 l o y a t t h e peak t e m p e r a t u r e (1 90°C). The outgased q u a n t i t y of hydrogen i s an i n c r e a s i n g f u n c t i o n

as

t h e t i m e of c h a r g i n g ( a g e i n g t i m e ) and c a t h o d i c p o t e n t i a l l e v e l i n c r e a s e . Molecular hydrogen t r a p p i n g i s p o i n t e d out.

2) Hydrogen may promote d i s l o c a t i o n s d e n s i t y which a r e t h e i n i t i a t i o n s i t e s o f S ' phase. T e n s i l e

stresses

and d u c t i l i t y l o s s a r e t h e n i n c r e a s e d . The e f f e c t of hydrogen i s i m p o r t a n t when t h e a l l o y i s i n t h e overaged c o n d i t i o n .

3 ) Hydrogen promotes a l s o i n t e r g r a n u l a r f a i l u r e , e s p e c i a l 1 y i n t h e overaged c o n d i t i o n . P r e c i p i t a t i o n o f S ' , T2 and A16(Fe, Cu) p a r t i c i e s i n t h e s u b - g r a i n b o u n d a r i e s may i n t e r a c t w i t h hydrogen atoms and t h e embri t t l e m e n t i

s

favoured.

REFERENCES

( 1 ) 5. NOBLE, G.E. THOMSON

-

Metal S c i . J. 5, 114, (1 971).

( 2 ) T.H. SANDERS, E.A. STARKE

-

Acta M e t a l l . 30, 927, (1982).

( 3 ) 8. NgBLE, S.J. HARRIS, K . DINSDALE

-

Metal S c i . J . 16, 425, (1982).

(4) T.H. SANDERS

-

Proc. 1 s t I n t . A1-Li Conf., p. 63, M e t a l l . Soc. AIME, (1981).

(5) H.M. FLOWER, P.J. GREGSON, C.N.J. TITE, A.K. MUKHOPADHYAY

-

P ~ o c . Al-A1 loys, t h e i r physical and mechanical p r o p e r t i e s

-

E d i t o r s E.A. STARKE J r and T.H. SANDERS J r , U n i v e r s i t y o f V i r g i n i a , C h a r l o t t e s v i l l e , USA, June (1986), p . 743.

( 6 ) I.M. LIFSHITZ, V.V. SLYOZOV

-

J. Phys. Chem. S o l i d s , 19, 35, (1961).

(7) K. DINSDALE, S.J. HARRIS, B. NOBLE

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I b i d . 4, p. 101.

(8) P.J.E. BISCHLER, J.W. MARTIN

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I b i d . 5, p. 963.

(9) S.J. HARRIS, B. NOBLE, K. DINSDALE, M. PRIDHAM

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I b i d . 5, p. 755.

(10) G.M. SCAMANS - Proc. Hydrogen E f f e c t s i n Metals, e d i t e d by I.M. BERNSTEIN and A.W. THOMPSON, The M e t a l l . Soc. o f AIME, Carnegie-Mellon U n i v e r s i t y , PIH, PENNSYLVANIA (1980), p. 467.

( 1 1 ) A. ELKHOLY, J. GALLAND, P. AZOU, P. BASTIEN

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^C.R. Acad. Sci., 284, s 6 r i e C, (1977), p. 363.

(12) J.P. FIDELLE

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"Hydrogen embrittlement t e s t i n g " ASTM STP 543, 31 (1974), p. 243.

(13) M. NAKASHIMA, M. SAEKI, Y. ARATONO, E. TACHIKAWA

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Journal o f Nuclear M a t e r i a l s , 116, (1983), p. 141.

(14) F. DEEREVE, Ph. MEYER, N. THORNE

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Pertes en 1 i t h i u m des a l l i a g e s A1-Li-X, Rapport i n t e r n e de PECHINEY, mars ( 1 986).

(15) J. EASTMAN, T. MATSUMOTO, N. NARITA, F. HEUBAUM, H.K. BIRNBAUM

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Conf.

Proc. on "Hydrogen i n Metals" E d i t e d by I. M. BERNSTEIN, A.W. THOMPSON Carnegie

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Me1 l o n U n i v e r s i t y , P i t t s b u r g h , Pennsylvania, U.S.A. (1980), p. 397.

(16) K.S. SHIN, C.G. PARK, M. MESH11

-

I b i d 15, p.209.

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Met. Trans. 13A (1982), p. 401.

(18) N.J. OWEN, D.J. FIELD, E.P. BUTLER

-

I b i d . 4, p. 1217.

JOURNAL DE PHYSIQUE

Figure 1 : V a r i a t i o n of Q 5 2 0 ' ~ and 1000

B

C desorded a t as a f u n c t i o n of c a t h o d i c p o t e n t i a l l e v e l and of hydrogen charging (ageing time) ; hydrogen charging temperature = 19O0C.

0 1151 (0lDITlOl DLIW sun ur* s I, 11w~cl + mna sun urn AT -1 114 (1W.O

.

^{N U T S "1- .IW 1I)O.O}

0 ,mu([ "IT"ILY(IWC1

I , h r

F i g u r e 3 : V a r i a t i o n of maximum t r u e s t r e s s a s a f u n c t i o n of e i t h e r t h e hydrogen charging time ( w i t h and w i t h o u t c a t h o d i c p o l a r i z a t i o n ) o r a g e i n g time : peak temperature = 190°C.

t . h r

Figure 2 : V a r i a t i o n of y i e l d s t r e n g t h a s a f u n c t i o n of e i t h e r t h e hydrogen charging time (with and without c a t h o d i c p o l a r i z a t i o n ) o r ageing time ; peak temperature = 190°C.

Figure 4 : V a r i a t i o n of maximum s t r a i n a s a f u n c t i o n of e i t h e r t h e hydrogen charging time (with and without c a t h o d i c p o l a r i z a t i o n ) o r ageing time ; peak temperature = 190°C.

F i g u r e 5 : View of a d i s k f a i l u r e by i n c r e a s i n g hydrogen gas- 1 p r e s s u r e a t 0.1 MPa.min

.

1

F i g u r e 6 : Disk f a i l u r e p r e s s u r e of hydrogen o r helium gas v e r s u s t h e f a t e of i n c r e a s i n g of t h e g a s and of p r i o r i n t e r n a l hydrogen c h a r g i n g : i s t s e r i e s c o r r e s p o n d s t o n a t u r a l a g e i n g u n t i l 1985, 2nd s e r i e s c o r r e s p o n d s t o n a t u r a l a g e i n g u n t i l 1986.

F i g u r e 7a : S u r f a c e f a i l u r e b y t e n s i l e _Figure 7b ^: Surface failure by tensile t e s t a t room t e m p e r a t u r e o f t e s t a t room t e m p e r a t u r e of 8090-~351 a l l o y . 8090 a l l o y aged a t 190°C

d u r i n g 30 h r .

JOURNAL DE PHYSIQUE H CHARGING T I M E ( - 3 V / A g , 1 9 0 ° C )

F i g u r e 8 : V a r i a t i o n of t h e t y p e of r u p t u r e i n 8090 a l l o y c a t h o d i c a l l y h y d r o g e n a t e d

(-3V/Ag) a s a f u n c t i o n of lo hr time of h y d r o g e n a t i o n

and t h e d e p t h from t h e specimen s u r f a c e ; peak t e m p e r a t u r e = 190°c.