INTERACTIONS BETWEEN DISLOCATIONS AND CRYSTALLINE DEFECTS DURING THE CYCLIC DEFORMATION OF A 0.7 Wt% Al-Li ALLOY

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INTERACTIONS BETWEEN DISLOCATIONS AND CRYSTALLINE DEFECTS DURING THE CYCLIC

DEFORMATION OF A 0.7 Wt% Al-Li ALLOY

J. Gentzbittel, C. Esnouf, R. Fougeres

To cite this version:

J. Gentzbittel, C. Esnouf, R. Fougeres. INTERACTIONS BETWEEN DISLOCATIONS AND CRYS- TALLINE DEFECTS DURING THE CYCLIC DEFORMATION OF A 0.7 Wt% Al-Li ALLOY.

Journal de Physique Colloques, 1987, 48 (C3), pp.C3-721-C3-727. �10.1051/jphyscol:1987384�. �jpa-

00226615�

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

INTERACTIONS BETWEEN DISLOCATIONS AND CRYSTALLINE DEFECTS DURING THE CYCLIC DEFORMATION OF A 0.7 Wt% A1-Li ALLOY

J.M. GENTZBITTEL, C. ESNOUF and R. FOUGERES

Groupe d l E t u d e s d e Metallurgie Physique et de Physique des

~ a t & r i a u x , f ~ ~ ~ , CNRS-UA 341, 20, Avenue Albert Einstein, F-69622 Vilfeurbanne Cedex, France

ABSTRACT I n t h e aerospace i n d u s t r y requirements f o r new m a t e r i a l s w i t h h i g h mechanical propepties and low d e n s i t y has s t i m u l a t e d research works i n RI-Li a1 loys. For t e n years numerous s t u d i e s have been developed i n order t o promote complex a l l o y s having convenient mechanical and p h y s i c a l p r o p e r t i e s , and a b l e t o r e p l a c e convent i ônal â1 l ôys11

1

and 12,'. From a fundamental p o i n t o f view b a s i c researchs t o study t h e microscopic mechanisms c o n t r o l l i n g t h e mechanical behaviour o f HI-Li a l l o y s have t o entered upon because several microscopic mechanisms are nut we1 l understood. Such invest i g a t ions were f i r s t conducted on b i n a r y RI-L-i a l l o y i n s o l i d s o l u t i o n s t a t e o r having a f i n e d i s t r i b u t i o n o f

& " ( R I ~ L ~ ) p r e c i p i t a t e s , according t o the amount o f l i t h i u m atoms.Tensile p r o p e r t i e s 131 o r c y c l i c behaviour /4/,15/ have been i n u e s t i g a t e d , The aim o f t h i s paper i s t o determine i n terms o f d i a l o c a t i o n - c r y s t a l l ine defect i n t e r a c t ions t h e m icroscopi c mechanisms inuol ued i n t h e c y c l i c deformat i o n o f a s o l i d s o l u t i o n o f a b i n a r y AI-Li a l l o y , c o n t a i n i n g 0.7 W t % o f l i t h i u m . T h i s work i s a p a r t o f a whole research progras devoted t o A l - L i b i n a r y a l loys i n our l a b o r a t o r y and t h e r e f o r e i s complementary t o s t u d i e s presented i n reference /51.

EXPER l i'lENTAL PROCEDURE

R b i n a r y AI-Li a l l o y c o n t a i n i n g 0 . 7 W t % o f l i t h i u m has been used i n t h i s present i n v e s t i g a t i o n . A f t e r h e a t i n g a t 530°C f o r two hours, then quenching

i n i c e water and f i n a l l y ageing a t room temperature f o r several months t h e 0.7 Ut W Rl-Li a l l o y i s kept i n a s o l i d s o l u t i o n s t a t e as can be i n f e r r e d by small angle X r a y s c a t t e r i n g experiments and TEn observations. Host o f f a t i g u e s t u d i e s presented here have been entered upon w i t h f a t i g u e specimen i n t h i s s o l i d s o l u t ion s t a t e , Some t e s t s have been c a r r i e d out w i t h samples a f t e r undergoing t o a s o l i d s o l u t ion heat treatment a t 320°C so as t o reduce t h e thermal vacancy r a t e and t o understand b e t t e r t h e r o l e o f s o l u t e l i t h i u m atoms.

Cy l i n d r i c a l specimens w i t h 9 mm diameter and having a gauge length o f 40 mm have been used i n t h i s study

.

^Fati gue t e s t s have been performed i n a push p u l l mode u s i n g a s p e c i f i c f a t i g u e machine w i t h a v e r y h i g h displacement s e n s i t i v i t y , t h a t a l l o w s t o perform f a t i g u e s t u d i e s i n a very l a r g e range o f f a t i g u e str>ain amp1 i t u d e (10-6 i BEt i 10-2). I n f a c t , t h i s f a t i g u e machine i s very convenient f o r s t u d i ng a1 l types o f i n t e r a c t ions between d i s l ocat ions and c r y s t a l l i n e d e f e c t s t h a t occur d u r i n g c y c l i c deformation. Fatigue t e s t s are conducted by a PUP 11 D i g i t a l Computer w i t h a l i n e a r time deformation dependence and a frequency range between 0.2 and 10-3 Hz. Fat i gue t e s t s have been c a r r i e d out under t o t a l o r p l a s t i c s t r a i n c o n d i t i o n s , The .specimen deformat i o n i s recorded from a [ITS extensometer w i t h a measurement length o f 25 mm. The appl i e d s t r e s s i s deduced from data g i v e n by t h e loading c e l I . Both s t r a i n and load data

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987384

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C3-722 JOURNAL DE PHYSIQUE

a r e s t o r e d i n t h e computer memory. Then, parameters o f t h e f a t i g u e loop l f ig u r e 1 ) a r e determined by processing t h e s t o r e d mechanical data :

i ) t h e maximum f a t i g u e stress,

rH,

o f t h e f a t i g u e loop ( f i g u r e 1 ) . ( A symetr i ca l behav i our i n t r a c t i o n and compression i s observed)

.

i i ) t h e d i s s i p a t e d r e l a t i v e energy, 8 , g i v e n by :

a =

c y c l e aera RBCDR aera OBF +aera ODE

i i i ) t h e unloading s t i f f n e s s value R, determined by a least square method appl ied t o an unloading s t r e s s range,A

,

which i s d e f i n e d by : A A

=(rM

-

-'&CM)

figl

.

^I^{n add}ⁱ^ti o n cont i nuous acoust i c em i ss i on

(C .

^{A .}^E

.

) measurements have been c a r r i e d out i n r e a l time d u r i n g f a t i g u e c y c l i n g , i n order t o o b t a i n i n f o r m a t i o n s on t h e dynamic behaviour o f d i s l o c a t i o n s . Technical problems and t h e o r e t i c a l processing, concerning the a c o u s t i c emission phenomenon, are g i v e n

i n r e f e r e n c e /6/.

A t l a s t

,

d i s l ocat i on-structures have been i nuest i gated by TEfl observat ions u s i n g a 200 CX Jeo I Microscope

.

Thin f o i l s have been c u t o f f i n c y c l e d sample according a d i r e c t i o n p a r a l l e l o r perpendicular t o t h e t e n s i l e a x i s . Some i n s i t u t e n s i l e experiments have been performed i n t h e e l e c t r o n i c microscope i n order t o study t h e l o c a l movement o f d i s l o c a t i o n s w i t h i n d i s l o c a t i o n s t r u c t u r e s o f t h i n f o i l s obtained from a p r e v i o u s l y c y c l e d sample.

EXPER l HENTRL RESULTS

i ) Hechan i ca l p r o p e r t i es

The c y c l e d 0.7 Ut %' RI-Li b i n a r y a l l o y presents a c y c l i c hardening a t t h e beginning o f t h e f a t i g u e process. R f t e r some t e n o f f a t i g u e c y c l e s t h e maxi mum f a t i gue s t r e s s ,

CMJ

reaches a const ant ua l ue, 6 s J t h a t corresponds t o +he s t a b i l ized f a t i g u e range. However, a t low s t r a i n amp1 itude, a very weak cyc 1 i c hardening i s observed

<

5.10-5). On f i g u r e 2 , t h e dependence on b o t h maximum f a t i g u e s t r e s s

cM

and d i s s i p a t e d r e l a t i v e energy A, w i t h t h e amplitude o f t h e f a t i g u e p l a s t i c s t r a i n i s r e p o r t e d f o r t h e s t a b i l i z e d f a t i g u e range.

Corresponding curves o f pure p o l y c r y s t a l l ine alum i n i um (5N) and o f RI-flg d i l u t e a l l o y (100 ppm flg) a r e a l s o r e p o r t e d i n f i g u r e 3. I t can be seen i n f i g u r e 3 s i m i l a r v a r i a t i o n s independently o f t h e n a t u r e o f m a t e r i a l s except i n t h e low s t r a i n amp1 i t u d e range, Therefore, a " c y c l i c y i e l d s t r e n g t h " have been determined i n order t o reveal a s i m i l a r behaviour i n a l l t h e s t r a i n amplitude range. The c y c l i c y i e l d s t r e n g t h i s determined as f o l l o w : from r e s u l t s o f f a t i g u e t e s t s a t d i f f e r e n t s t r a i n amplitudes i n t h e s t a b i l i z e d f a t i g u e range, t h e t o t a l deformation

EL,,

corresponding t o a p l a s t i c d e f o r m a t i o n E p equal t o zero, i s obtained by e x t r a p o l a t i o n i n t h e (Et,EP) p l o t ( f i g u r e 4 ) . The " c y c l i c y i e l d strengthm,tCO

,

i s t h e p a r t i c u l a r s t r e s s value corresponding t o t h e e x t r a p o l a t e d s t r a i n vaiuef&-For t h e t h r e e m a t e r i a l s t h e s t r e s s value, CO

,

^{i s}

g i v e n i n table.

I n f i g u r e 5 i s reported, f o r t h e t h r e e p r e v i o u s m a t e r i a l s , t h e d i f f e r e n c e between t h e s t a b i l i z e d s t r e s s value,

rj ,

and t h e c y c l i c y i e l d strength,Cib, as a f u n c t i o n o f p l a s t i c s t r a i n amplitude. In t h i s p a r t i c u l a r p l o t ,

~ C I(UPa) 0 . 7 I t % R l - L i

11.5

RI-Mg 2.3

A l 5N 1 .l

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composi t i o n o f invest i gated a l l o y s .

The F i g u r e 6 shows the v a r i a t i o n o f t h e s t i f f n e s s value, R, versus t h e f a t i g u e s t r a i n amp1 i t u d e a f t e r c y c l i n g i n t h e s t a b i l i z e d s t r e s s range. I n f a c t , we have r e p o r t e d a reduced s t i f f n e s s value R/Ro i n order t o r e l e a s e from s c a t t e r i n g e f f e c t s r e s u l t i n g o f t h e use o f d i f f e r e n t specimens, For a g i v e n sample, Rg i s determined from a f a t i g u e loop having a t zero s t r e s s a width o f 1 .lo-6. R t low s t r a i n amp l i t ude t h e reduced s t i f fness remains approx i mat i ve l y a t a constant ualue, q u i t e c l o s e t o one. Rlso a very weak l e v e l o f d i s s i p a t e d r e l a t i v e energy i s observed. From a s t r a i n amplitude o f ~ E p , ' 2 = 5.10-5 a s t r o n g decrease i n t h e reduced s t i f fness var i a t i o n can be shown i n f i g u r e 4 . I t i s r e l a t e d w i t h a marked increase i n t h e value o f t h e r e l a t i v e d i s s i p a t e d energy A .

I n s p i t e o f f a t i g u e t e s t s c a r r i e d out i n a l a r g e frequency range

0 . 2 -10-3 Hz and w i t h d i f f e r e n t s t r a i n amplitude h i g h e r than 5.10-5, no s i g n i f i c a n t v a r i a t i o n s i n t h e maximum s t r e s s o r i n t h e r e l a t i v e d i s s i p a t e d energy has been obserued. Therefore, one may be considered t h a t t h e f a t i gue behaviour o f t h e 0.7 % RI-Li a1 l o y presents a very pronounced athermal character

.

F i n a l l y , a decrease i n the temperature o f t h e s o l i d s o l u t i o n treatment leads t o an increase i n t h e c y c l i c hardening a t t h e beginning o f t h e f a t i gue process. However, a f t e r severa l thousands o f f a t i gue cyc I es t h e f a t i gue s t r e s s I eve l becomes independent on t h e temperature o f t h e s o l i d s o l u t i o n heat treatment.

i i ) Continuous Rcoust i c Emission (C.R,E.)

A t y p i c a l r e s u l t o f CRE measurements d u r i n g f a t i g u e t e s t s i s r e p o r t e d i n f i g u r e 7. The rootmean square { r . m . s ) u o l t a g e i s very s t r o n g l y increased j u s t as t h e f a t i g u e s t r e s s reaches t h e y i e l d s t r e n g t h i n t r a c t i o n as w e l l as i n compression. Then, a very marked peak i s obserued and t h e CRE evo l u t i o n i n t h e p l a s t i c domain i s c h a r a c t e r i z e d by a s l i g h t decrease o f t h e CRE l e v e l t h a t i s c l e a r l y h i g h e r the l e v e l t h a t o f t h e background n o i s e . During the quasi e l a s t i c unloading t h e r.m.s, v o l t a g e presents a very weak ualue corresponding approximatiuely t o t h e background n o i s e l e v e l . According t o t h e c y c l e number a decrement i s observed i n t h e l e v e l o f CAE. When t h e s t abi l ized s t r e s s domain i s reached, no v a r i a t ions o f a c o u s t i c parameters can be detected. Below a s t r a i n f a t i g u e amplitude o f 2.10-3

,

t h e v a r i a t i o n s o f t h e r.m.s, voltage have no p h y s i c a l s i g n i f i c a n c e b e i n g included i n the background n o i s e . It i s n o t i c e d t h a t a c o u s t i c emission r e s u l t s f o r t h e 0.7 Wt % R I - L i a l l o y , a r e q u i t e s i m i l a r t o those observed i n t h e case o f pure p o l y c r y s t a l l i n e aluminium /7/.

i i i ) MET observat ions

No s i g n i f i cant d i f ference a r e gernera l l y detected bet ween d i s l ocat i o n m i c r o s t r u c t u r e s o f the 0.7 W t % RI-Li a l l o y o r t h e pure p o l y c r y s t a l l i n e aluminium c y c l e d under t h e same condi t ions. The f i g u r e 8 shows d i s l o c a t i o n ce l I s corresponding t o t h e m i c r o s t r u c t ura l s t a t e o f f a t igue specimens c y c l e d a t s t r a i n amplitude between 4.10q9and 2 . 1 0 - ~

.

O i s l o c a t i o n s c e l l s o f 2-5 pm sized, having s t r a i g h t d i s l o c a t i o n w a l l s (" 0.5 pm l a r g e ) and a h i g h d e n s i t y o f t a n g l e d d i s l o c a t i o n s , e x h i b i t a very weak v a r i a t i o n i n s i z e as t h e c y c l e number o r t h e s t r a i n amp l i tude are increased. However a t t h e highest s t r a i n amp l i tude used i n t h i s study ( 2 . 1 0 - ~

1,

e q u i a x i s d i s l o c a t i o n s c e l l s have been simultaneously

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C3-724 JOURNAL DE PHYSIQUE

ctbserved w i t h very e l ongated c e l I s . They have very narrow wal I s arranged such as they form a very marked " l a b y r i n t h " s t r u c t u r e ( f i g 9). This s t r u c t u r e i s very s i m i l a r t o t h e one observed i n cooper s i n g l e c r y s t a l s c y c l e d under s i m i l a r cond i t ions, Rs a matter o f f a c t , we have a l s o observed o n l y two act i vated s i i p systems w i t h mainly screw d i s l o c a t i o n s components. I n s i t u t e n s i l e experiments c a r r i e d out on l a b y r i n t h s t r u c t u r e s obtained from a mossiue specimen p r e v i o u s \ y c y c l e d has shown t h a t t h e p l a s t i c deformat i o n occurs by c r e a t i o n o f edge d i s f o c a t i o n s and displacement o f screw components i n t h e channel between t h e u ~ a l l s [ f i g u r e 105.

DISCUSSION

: The a n a l y s i s o f t h e experimental r e s u l t s shou~s a d i s t i n c t i o n between low and h i g h f a t i g u e s t r a i n amplitude.

i ) R t low f a t i g u e s t r a i n amplitude

I n t h i s doma i n, a very ueak l e v e l o f the d i s s i pnted r e l a t i ve energy A and a smal l c y c l i c hardening suggest t h a t d i s i o c a t i o n c r e a t i o n i s probably not involved i n the f a t i g u e process. This hypothesis i s c o n s i s l e n t w i t h the f a c t t h a t t h e reduced s t i f f n e s s R/Ru

,

which i s s e n s i t i u e t o t h e mobile d i s l o c a t i o n s d e n s i t y

/S/

remains constant independently o f the s t r a i n amplitude, A l l t h e r e s u l t s suggest t h a t the microscopic mechanisms c o n t r o l l i n g t h e c y c l i c deformation o f t h e 0.7 llt X 81-Li a l l o y i s probably t h e i n t e r a c t i o n betreen d i s l o c a t i o n s and s o l u t e atoms as i n 5N p o l y c r y s t a l l i n e aluminium and Al-flg d i l u t e a l l o y . From t h e value o f t h e c y c l i c y i e l d s t r e n g t h determined i n

52

{ r o = 1 1 . 5 MPa) we have found a c y c l i c hardening value by atom per cent o f l i thium o f 5 flPa/at %. T h i s value i s i n good agreement w i t h t h e one determined by P.

SRINFORT /3/, i n t h e case o f t e n s i l e monotonous deformation, However, we have observed t h a t the f a t i g u e s t r e s s l e v e l i s s t r o n g l y dependent on t h e temperature o f t h e s o l i d s o l u t i o n heat treatment, Thus, i t seems t h a t t h e spat i a i d i s t r i b u t i o n o f l i t h i u m atoms i n t h e aluminium m a t r i x can p l a y an important r o l e e s p e c i a l l y o t t h e beginning o f t h e c y c l i c deformation,

i i ) R t h i g h s t r a i n amp1 i t u d e

This f a t i gue domain i s character i zed by a very. pronounced a t herma l behauiour and by a r a p i d increase i n t h e e v o l u t i o n o f d i s s i p a t e d r e l a t i v e enepgy versus t h e s t r a i n amp l i tude. As i t has been proposed by SL I RRN I and a I . /7/ i n the case o f pure a l um i n i urn t h e acoust i c emission peak, observed j u s t a t t h e beginning o f t h e p l a s t i c deformation, can be mainly i n t e r p r e t e d by a s t r o n g r a t e o f d i s l ocat i o n loop c r e a t i o n . A l l these cons i derat ions lead t o assume t h a t t h e i n t e r a c t i o n between d i s l o c a t ions c o n t r o l s t h e c y c l i c deformat i o n s f t h e 0.7 Ut % RI-Li a l l o y a t h i g h s t r a i n amplitude. The same c y c l i c behaviour i n t h e p l a s t i c deformat i o n domain beyond t h e c y c l i c y i e l d s t r e n g t h (see f i g u r e 3) may be probably r e l a t e d w i t h s i m i l a r d i s l o c a t i o n s t r u c t u r e s composed o f d i s l o c a t i o n c e l t s . Rs i n the case o f pure p o l y c r y s t a l l i n e aluminium /9/, / l o / we t h i n k t h a t the f a t i g u e s t r e s s i n the s t a b i l i z e d s t r e s s range can be understood from a composite type model w i t h a hard phase assumed t o be t h e c e l l w a l l s and a s o f t e r m a t r i x corresponding t o the i n t e r i o r o f c e l l s o r t o the channel o f l a b y r i n t h s t r u c t u r e .

The maximum f a t i g u e s t r e s s i s considered t o be t h e sum o f two components :

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t r e e s o f t h e d i s l o c a t i o n f o r e s t i n t h e w a l l s (as w e l l c e l l w a l l s than t h a t o f t h e l a b y r i n t h s t r u c t u r e ) .

i i ) t h e second component corresponds t o t h e i n t e r n a I s t r e s s e s necessary t o assume t h e s t r a i n c o m p a t i b i l i t y between t h e w a l l and t h e c e l l i n s i d e

,

these two r e g i o n s have not t h e same p l a s t i c behauiour.because t h e mechanical p r o p e r t i e s are s t r o n g l y dependent on t h e value o f d i s l o c a t i o n d e n s i t y t h a t depends i t s e l f on t h e respect i v e degree o f c r e a t i o n and o f anni h i l a t i o n o f d i s l ocat ions. The same behav i our r e n t i onned above f o r b o t h O. 7 Wt X a l I oy and aluminium suggest t h a t microscopic mechanisms wich c o n t r o l t h e c r e a t i o n and t h e a n n i h i l a t i o n o f d i s l o c a t i o n s are s l i g h t l y s e n s i t i v e t o t h e a d d i t i o n o f s o l u t e

l i t h i u m atoms.

Rcknowledgements: The support o f t h i s work by t h e research c e n t e r o f CEGEDUR- PECH I NELt Company i n Uoreppe (France) i s g r a t e f u l l ^{y acknow}l ^eged

B. NOBLE, 5.1. HARRIS and K . ^DINDSDRLE

-

J . Hater. S c i , , 17, p.461, (1982) P. SRINFORT, B. DUBOST and P. HEVER

-

H.R.S. Europe, E d i t i o n de Physique, November p .45 ( 1 985)

P. SRINFORT Thesis, U n i v e r s i t e de Grenoble (1985)

Y . BRECHET, F . LOUCHET and J.L. UERGER-GAUGRY

-

Lowcycle f a t i g u e o f b i n a r y RI-Li a l l o y s : M i c r o s t r u c t u r a l c h a r a c t e r i z a t i o n and i n s i t u experiments.

This Congress

J.H. GENTZBITTEL, G . UlGlER and R. FOUGERES -The phenomenon o f s t r e s s i n s t a b i l i t y i n c y c l i c deformation o f RI-Li b i n a r y a l l o y s . This Congress.

J.ROUBY, P.FLEISCHMANN, C. OUUERGIER Phi I . Hay. R, 47, 5 . p.671, (1983) and P h i l Hay A, 47, 5 p.689 11983).

R . SLIBANI,

P.

FLEISCHHRNN and R. FOUGERES Proceeding o f non D e s t r u c t i v e Character i zat i o n o f m a t e r i a l s

-

Hontrea I, Canada. 21 -23 j u l y (1 986).

R. HRHEL, R. FOUGERES, A . UINCENT and P.F. GOBIN. R model f o r t h e unloading s t i f f n e s s change d u r i n g t h e f i r s t f a t i g u e stage o f p u r e a l u m i - nium. Proceedings o f ICHS, Beying, Chine, June - (1987).

J . CHlCOlS

,

R . FOUGERES, G. GUICHON, A . HRMEL e t R. FOUGERES Rcta.

Metal 1.34, 11 p.2157 (1986)

J.CHICOIS Thkse d ' E t a t Lyon-Mars (1987)

(7)

JOURNAL DE PHYSIQUE

1 ^stress

Fig 1 : D&finition of the relative dissipated energy and of the maximum fatigue stress on a fatigue loop.

Fig 3 : Maximum fatigue stress trersus plastic: strain for 3 materials. AL 5N ; Rl-Hg(100ppm) ; AI-Li 0,7 Ut8.

I I

1 0 to-' lo-"

PLASTIC STRAIN AEp/2 Fig 2 : Maximum fatigue stress (Tm and dissipated relative ertergy versus plastic stra i n amp I i tude JEp/2. Exper i mental values determined in the stabilized fatigue range.

Fig 4 : Detei-mination of the total deformation corresponding to a plastic deformation equal to zero.

3 0 .

-

^{2 0 -}

Fig 5 : gar iat ion of the stress increment in the plastic range of the stabilized

fatigue cycle versus plastic strain

G

amplitude. Observe the same behaviour 10

independently of the investigated alloys.

(Same curve for the three materials : A15#

AI-Hg and AI-Li alloys.)

x A \ - LI 0.7 ^'10 0 A I - 5 N

A A I - M g ( 1 0 0 p p m )

-

4

lo

l o - $ 1 0-0 PLASTIC STRAIN AEp12

(8)

mplitude IRiRo definition in the text)

Fig 7 : Continuous acoustic Emission recorded during a fatigue cycle . Test conducted in the stabilized range atACp/2 =

10.' 10-1

R A S T I C STRAIN AEp/2

Fig 8 : Fatigue cells in stabilized stress range ; Afpi? = 1.2 .10-3

cycle number N = 1000

Fig 9 : Labyrinth structwe Sample cycled at sEP/2 = 2.10- 3 Cycle number 1000

A -B :screw component

(oo') fl

^C^:edge ^component

Fig 10: In si tu tensile test . Displacement of the dislocations between the wa I Is .