MICROPLASTICITY AND INTERNAL FRICTION IN PURE IRON

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MICROPLASTICITY AND INTERNAL FRICTION IN PURE IRON

J. San Juan, L. No, Gilbert Fantozzi, C. Esnouf, F. Vanoni

To cite this version:

J. San Juan, L. No, Gilbert Fantozzi, C. Esnouf, F. Vanoni. MICROPLASTICITY AND INTER- NAL FRICTION IN PURE IRON. Journal de Physique Colloques, 1981, 42 (C5), pp.C5-43-C5-48.

�10.1051/jphyscol:1981505�. �jpa-00220961�

page c5-43

MICROPLASTICITY AND INTERNAL FRICTION I N PURE IRON

J . San Juan, L. No, G . F a n t o z z i , C. Esnouf and F. vanonid

Groupe d l E t u d e s d e MdtaZZurgie P h y s i q u e e t P h y s i q u e d e s Mate'riam, E.R.A. 463 I.N.S.A. B E t . 5 0 2 , 69621 ViZZeurbanne Cedex, France

"c.E.N. GrenobZe, D.R.F., 85X, 38041 GrenobZe Cedex, France

Abstract.- We have s t ~ j d i e d t h e microdeformation behaviour o f pure i r o n a t low temperature (4K

-

^2501:). Two t h e r m a l l y a c t i v a t e d microdeformation stages a r e observed : one i s associated t o t h e a process observed by i n t e r n a l f r i c - t i o n , t h e o t h e r i s l i n k e d t o t h e 6, peak. A c t i v a t i o n parameters determined f o r t h e a component are i n good agreement w i t h double-kink f o r m a t i o n on non screw d i s l o c a t i o n s .

8,

component i s due t o d i s l o c a t i o n depinning from an extended atmosphere.

1. I n t r o d u c t i o n . - Generally, t h e r e l a x a t i o n s p e c t r a o f p l a s t i c a l l y b.c.c. metals a r e composed o f t h r e e bands o f i n t e r n a l f r i c t i o n peaks according t o t h e Chambers no- menclature : a ,

B

and y [I, 2, 3,

41.

Peak a i s g e n e r a l l y a t t r i b u t e d t o double-

k i n k n u c l e a t i o n on non screw d i s l o c a t i o n s , Peak

B

t o p o i n t d e f e c t - d i s l o c a t i o n i n t e r - a c t i o n and peak y t o double k i n k generation on screw d i s l o c a t i o n s . Each r e l a x a t i o n process i s c h a r a c t e r i z e d by s p e c i f i c a c t i v a t i o n energies and volumes, which can be determined by i n t e r n a l f r i c t i o n and microdeformation experiments.

I n t h i s paper, we study t h e microdeformation and t h e i n t e r n a l f r i c t i o n o f a pure i r o n . :~lany experiments were performed on i r o n [2]. S e n e r a l l y a peak a i s ob- served around 30K ( l h z ) , w i t h a shoulder a' a t lower temperatures. The a peak i s a t t r i b u t e d by H i v e r t e t a l . [5] and by A s t i e e t a l .

[a]

t o t h e k i n k generation on non screw d i s l o c a t i o n s . Furthermore, f o r low p l a s t i c deformation, a

Ba

peak i s observed by X i t c h i e e t a1

.

^[6] and Dufresne e t a1

. 171,

a t t r i b u t e d t o thermo-me- chanical unpinning o f d i s l o c a t i o n .

2. Experimental procedure.- Experiments were c a r r i e d o u t w i t h w i r e s (lmm i n diameter, 40mni i n l e n g t h ) o f CEllG pure i r o n , annealed 10 h a t 400°C under p u r i f i e d hydrogen.

P l a s t i c deformations were performed i n t o r s i o n a t room temperature. I n t e r n a l f r i c - t i o n and microdeformation were measured w i t h an i n v e r t e d t o r s i o n a l pendulum, w i t h a magnetic f i e l d o f 200 Oe LC]. The i n t e r n a l f r i c t i o n s o e c t r a were made a t about 0.8 Hz w i t h an o s c i l l a t i n g v i b r a t i o n amplitude

E,,, = We have v e r i f i e d t h a t t h e s t a t i c stresses used do n o t g i v e permanent s t r a i n s .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981505

C5-44 JOURNAL DE PHYSIQUE

3. Experimental r e s u l t s

3.1 Internal f r i c t i o n Fig. 1 presents the internal f r i c t i o n spectra as a func- tion of the p l a s t i c deformation amount. After mounting (curve I ) , a broad peak i s a observed around 130K

:

t h i s peak i s labelled 8, according to the nomenclature of Ritchie e t a l . [6]. After 0 . 5

%

deformation (curve 2 ) , t h i s peak growths strongly, s h i f t s towards low temperature

(115K)

and presents a shoulder between 30 and 50K a t t r i b u t e d t o the a ?eak. For 2 and 4

%

deformation, the peak s i t u a t e d a t 105K decreases and the peak a appears a t about 30K and increases with the deforma- t i o n amount.

A s

observed by Dufresne e t a l .

r 7

1, ^the

^@a

peak temperature depends strongly on the vibration amp1 i tude.

3.2 Microdeformation Figures

2 , 3 ,

4 and

5

show the variation of micro deforma- tion versus temperature according t o the method used by Esnouf and Fantozzi

_{[ 9 ]}

( t h e microdeformation plotted

E

i s corrected from the shear modulus variation with temperature

E =

'real a). Nhen the s t a t i c s t r e s s

o,

i s applied a t 4K, an e l a s t i c s t r a i n

AB

i s observed. Then, during the l i n e a r heating, an extra amount of microstrain

BC

occurs. Subsequently, the specimen i s cooled down t o 4K (CD) and the s t a t i c s t r e s s i s removed

:

microdeformation recovered during the suppression of the s t r e s s i s

DE.

During a subsequent heating without s t r e s s , we observe a recovery of the s t r a i n

( E F ) .

\le have obtained similar r e s u l t s f o r d i f f e r e n t values of s t a t i c s t r e s s . The essential features of f i g . 2 t o 5 a r e as follows

:

( 1 ) - During the f i r s t heatl'ng with the s t a t i c s t r e s s

as,

microdeformation

BC

occurs i n two stages

:

stage

a

between 10 and

50K

and stage 6 between

70

and

l l O K .

Stage a s h i f t s towards low temperatures and increases strongly with the p l a s t i c deformation. The 6 conponent i s lower than the one and shows only a s l i g h t increase with the p l a s t i c deforn:ation amount.

( 2 ) - The recovery

DE

obtained

by

suppressing the s t r e s s a t 4K is nearly equal t o the e l a s t i c deformation

AB.

( 3 ) - Luring the successive heating without s t r e s s (EF), recovery of the s t r a i n occurs in two stages

ar

and 6,. Stage

ar

takes place a t lower temperature than

a

stage and i s more important f o r deformed specimens. Stage Br occurs up t o high temperatures and another recovery phenomenon takes place beyond about 200K. Recovery i s complete towards 220K f o r non-deformed specimens and towards 250% f o r deformed specimens.

The derivative curves versus temperature a r e used t o locate the

a

stage of

microdeformation. Fig.6a shows the obtained r e s u l t s f o r the non-deformed specimen

:

we observe a big s h i f t of t h e maximum (from

53K

t o 26K) when t h e bias s t r e s s increa-

s e s . Fig.

6b

shows the derived curves f o r a

2 %

deformed specimen. Only a low

med specimens, a substructure of the

a

stage occurs.

In order t o determine the activation vol ume , we must normal i ze the mi crodeforrna- tion curves

E ( T ) [g].

From the observed s h i f t of the curves versus s t a t i c s t r e s s , we can obtain the a c t i v a t i o n volume from the following r e l a t i o n

:

T

da

v

= E/(G

-

^-)

with

E =

constant

dT

The a c t i v a t i o n energy

E

f o r the a peak i s about

Q.G6

eV

[5].

Tile activation volumes measured f o r d i f f e r e n t amounts of p l a s t i c deformation and f o r a value of

U s

equal t o about 4.5 x 1 0 - ~ v a r e given by the following t a b l e .

Fig.

1 :

Internal f r i c t i o n spectra of Iron ( E ~

= (1)

a f t e r niounting

;

( 2 ) a f t e r 0.5

%

p l a s t i c deformation a t

₆₀

+ 11; 7 + 5 RT;(3) a f t e r 2% deformation;(4) a f t e r

4% deformation.

We observe a l s o a decrease of the activation voluine when the s t a t i c s t r e s s increases f o r the non-deformed specimen (from

60 b3

t o

20 b 3

when os increases from 2 I O - ~ ~ to 7.5

I O - ~ ~ ) .

4 . -

Discussion.-

a

process

:

?.licrodeformation experiments are i n t e r e s t i n g because they can s h w an

a

cofiiponent though no a peak i s observed on the internal f r i c t i o n curve f o r t h e non deformed specimen. This r e s u l t seems t o indicate t h a t i n the very broad spectrum of

Ba

obtained f o r t h i s specimen, the low temperature range of the spec- t r u m i s certainly linked t o an i n t r i n s i c process a .

Stage

a observed by microdeformation has the same characteristics than the

one observed i n f . c . c metals 191: a stage takes place a t higher temperature than

the recovery stage a, obtained without stress. The decrease of the activation vo-

lume when the p l a s t i c deformation increases and the importance of stage

_a,

should

indicate t h a t the local internal s t r e s s i s large (much l a r g e r than i n f . c . c . metals)

and increases with the amount of p l a s t i c deformation. This conclusion i s similar t o

t h e one of Astie' e t a l .

[lo]

obtained from microdeformation experl'ments i n theyrange

C5-46 JOURNAL DE PHYSIQUE

F i g . 2 : i l i c r o d e f o r m a t i o n i n i r o n w i t h o u t deformation w i t h o, = 3 x

uo.

F i g . 3 : Microdeformation i n I r o n a f t e r 0.5 % deformation w-i t h os = 6 x l 0 - ~ po

F i g . 4 : Microdeformation i n i r o n a f t e r F i g . 5 : ;'iicrodeforniation i n I r o n a f t e r 2 1 defomiation w i t h o, = 6 x po 4 % deformation w i t h os = 6 x

lo'5 uo

t h e given i n t e r p r e t a t i o n f o r t h e a peak i n i r o n . Furthermore, t h e microdeformation curves always seem t o present an a' component a t low temperature, which must be p r e c i sed.

8, process : t h e 8, peak i s g e n e r a l l y a t t r i b u t e d t o t h e thermomechanical unpinning o f non screw d i s l o c a t i o n s from i m p u r i t y i n t e r s t i t i a l s C and N. The m i - crodeformation experiments show t h a t 8, i s n o t a simple breakaway process from p i n n i n g p o i n t s s i t u a t e d on t h e d i s l o c a t i o n l i n e . Indeed, i n t h i s case, we should observe a microdeformation stage d u r i n g h e a t i n g w i t h t h e s t a t i c s t r e s s and a comple- t e recovery o f t h i s deformation d u r i n g t h e suppression o f o s a t 4K. I n f a c t , no recovery i s observed a t 4K when t h e s t r e s s i s removed ( t h e AB deformation i s equal t o DE deformation). Therefore, d i s l o c a t i o n s remain pinned d u r i n g t h e suppression o f as, p i n n i n g p o i n t s being immobile a t considered temperature. Thus, we can t h i n k t h a t 8, i s due t o a d i s l o c a t i o n depinning from an extended atmosphere. The microdeforma- t i o n associated t o t h e 8, peak occurs i n a broad range o f temperature as t h e

B,

peak. I t i s d i f f i c u l t t o observe a s h i f t when t h e a p p l i e d s t r e s s v a r i e s . This s i t u a - t i o n i s n o t f a v o r a b l e t o determine t h e c a r a c t e r i s t i c s o f t h e Ba process b u t i t i s necessary t o use a model o f d i s l o c a t i o n motion i n d i l u t e s o l i d s o l u t i o n as proposed by S c h l i p f

fill

and R i t c h i e C12-J.

Acknowledgements.- J. SAN JUAN and L. NO on leave o f t h e Physics department o f t h e l i n i v e r s i t y o f B i l b a o g r a t e f u l l y acknowledge t h e Universidad d e l Pais Vasco and t h e Departamento de Educacion d e l Gobierno Vasco f o r h i s f i n a n c i a l support.

References

111

R.H. Chambers, i n Phys. Acoustics ( V o l . I I I A ) , ed. by H.P. Nason, Acad. Press, N.Y. (1966), p. 123.

[2] G. Fantozzi, C. Esnouf, W. Benoit, I. R i t c h i e , t o be published, Progress i n ivlaterial s Science.

[3] H. Schultz, M. I;laul, Y . Rodrian and R. Gren, Proc. 5th. I n t e r n . Symp. on H i g h - P u r i t y E a t e r i a l s i n Science and technology, Vol. 111, Dresden (1980), p. 334.

[4] A. Seeger and C. WOthrich, Nuovo Cimento, 33 B, 33, 1976 L53 V . H i v e r t , P . G r o h , W . F r a n k , I . W i t c h i e a n d P . l ~ l o s e r .

Phys. S t a t . Sol., (a), 46, 89, 1978.

[6] ^I.G. R i t c h i e , J.F. Dufresne and P. Moser, Phys. S t a t . Sol., (a), 50, 617, 1378.

[7] Y.F. Dufresne, I.G. R i t c h i e and P. I.loser, ECIFUAS, Manchester (1979), p. 37.

[8] P. A s t i e , J.P. Peyrade and P. Groh, S c r i p t a hlet., 14, 611, 1980.

9

^C. Esnouf and G. Fantozzi, P h i l . Nag. A, 42, 63, 1980.

C5-48 JOURNAL DE PHYSIQUE

[lo] P.

A s t i e ,

J.P.

Peyrade and

P .

Groh, t h i s conference.

[ll] J .

S c l i l i p f , Proc. ICIFUAS-6, Ed.

2.K.

Hasiguti and

ii.

:"likshido.

1121

I .

R i t c h i e , t h i s conference.

Fig. 6

:

Derived microdeformation Fig.

7 :

Normalized microdeformation curves f o r i r o n . curves f o r i r o n .

a ) without defcrtnation ( 1 ) a,

=

wo

( 2 ) 0, = 3

x

11,

-

5 b)

a f t e r 2

%

deformation ( 1 )

0, = 3

x uo ( 2 )

0, =

6x10 u,