RELATION BETWEEN MAGNETOMECHANICAL INTERNAL FRICTION AND BARKHAUSEN NOISE IN COLD WORKED CoPt ALLOY

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RELATION BETWEEN MAGNETOMECHANICAL

INTERNAL FRICTION AND BARKHAUSEN NOISE

IN COLD WORKED CoPt ALLOY

B. Augustyniak, Gilbert Fantozzi, A. Vannes

To cite this version:

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RELATION BETWEEN MAGNETOMECHANICAL INTERNAL FRICTION ANV,BARKHAUSEN NOISE IN COLD WORKED Copt ALLOY

B. AUGUSTYNIAK, G. FANTOZZI' AND A. VANNES+

Institute

of Physics , Technical University of ~ d a h s k , 80-952 Gdansk , Pol and

+GEMPPM

-

INSA de Lyon, Bdt.502. 69621 Villeurbanne Cedex, France

R6sum6

-

Le bruit Barkhausen (BN) a Ct6 mesure sur des 6prouvettes de Copt m o n n 6 . Les mesures ont btt? effectubes sous contrainte (contrainte maxi- mum de 480 MPa) et apres suppression de la contrainte. Le BN apres suppres- sion de la contrainte est compare avec le frottement interieur magn6tom6- canique (MIF) des 6prouvettes qui ont 6t6 d6formees plastiquement en torsion de 0,5 %. Le BN et le MIF ont une dependence identique vis-8-vis de la contrainte appliqu6e.

Abstract

-

The Barkhaussen noise (BN) was measured for stressed (up to 480

'

n

a

n

d

unstressed sample of dissordered Copt alloy. The BN of unstressed sample is compared with magnetomechanical internal friction (MIF) of Copt sample which was strained up to 0.5 % by torsion. It was proved that BN and MIF have the similar dependence on the applied stress.

I

-

INTRODUCTION

The Barkhausen noise phenomenon (BN) is used in order to estimate the evolution of internal stresses ( ~ i ) . Internal stresses influence magnetic and magnetomechanic loop. Magnetomechanical loop leads to the magnetomechanical internal friction (MIF). Phenomenological model of MIF, as proposed by Birchak and Smith, makes possible to determine Gi value from MIF amplitude dependence /1,2/. The aim of this paper is to present BN of deformed Copt alloy and to compare the BN properties with the MIF properties of cold-worked alloy, /3/. Plastic deformation was used in order to change the

i

parameter value.

I1

-

EXPERIMENTAL RESULTS

The Copt alloy samples were made in wire of 1

mn

in diameter and of 50 mn length. Alloy was in disordered state as quenched, /3/.

1. Barkhausen noise measurements. Sample was welded to the iron plates which were connected with an electromagnet. Low frequency (f = 0.050 Hz) magnetic field had an amplitude of H = 8 KA/m. Electric signal from sensor coil was analysed by electronic set, /4/, and two functions, Us(H) and U(H) were recoved. The Us function is propor- tional to the average value of the BN signal voltage within the frequency range from 0.1 KHz to 100 KHz. The U function, as proportional to low frequency magnetic flux derivative, was used to calculate the magnetic loop and coercivity Hc. BN measure- ments were performed for stressed sample (stress b up to 480 MPa) and for unstressed state, after reduction of the previous stress

(Gal.

Fig. 1 shows t h e G ( ~ ) dependence from which the Young's modulus

(E

= 190

+

10 GPa) and elastic limit

(tYe

= 310 + 5 MPa) were estimated. Fig. 2 shows Us(H) records as measured for unstressed sampTe. Maximal value of Us function (Usm) appears at magnetic field H which is close to Hc. Plastic deformation

(Ga

>

be) decreases the Us(H) dependence and shifts its maximum to higher values of H, (Hc increases). This is shown on Fig. 3 by curves 1 and 4 respectively.

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C10-734 JOURNAL DE PHYSIQUE

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-

DISCUSSION

From d i r e c t comparison o f the BN r e s u l t s (Fig. 2) w i t h those o f the MIF (Fig. 4), the assumption o f a c o r r e l a t i o n between these two phenomena appears t o be correct. I n order t o prove t h i s assumption, the MIF r e s u l t s are r e l a t e d also t o the

G

parameter. For MIF experiment the G a parameter corresponds t o maximal

torsions?

6 t r a i n

rO.

The Ca (f0) dependence was calculated using the

U

(&) data from Fig. 1 by assuming t h a t

E

and .r" s t r a i n s are equalized by & = 0.574

$

r e l a t i o n , /5/. It was Pound t h a t t h e maximal value

&-,

= 1.2 % corresponds t o the p l a s t i c deformation ,g

=

0.48 %. The main r e s u l t s concerning the MIF experiment are shown on Fig. 5 as r e l a t e d t o the Ga parameter values. The Q-lm parameter (curve 1 ) presents maximal values o f Q-l($) dependence, shown on Fig. 4. The Gi parameter values (curve 3) were c a l c u l a t e d according t o Smith and B i r c h a k o s model o f MIF, /3/. The Q-1s parameter (curve 2) i s t h e i n t e r n a l f r i c t i o n o f Copt a l l o y as measured a t s a t u r a t i n g magnetic f i e l d ( f o r

f =

8.10e5),/3/. This parameter value i s assumed t o be proportional t o d i s l o c a t i o n density

9 .

The f i r s t data p o i n t s on Fig. 5. ( f o r G a = 100 MPa) were c a l c u l a t e d from the experimental curve 1 on Fig. 4. The l i n e a r increase o f Gi and

Q;I

appears f o r

O

a > G e e

The s i m i l a r dependence on Qa o f the Usm values (Fig. 3, curve

1)

and o f the 9-lm values (Fig. 5, curve 1) i s evident. I n both cases, one can observe the decrease of BN and MIF ( f o r G a

>

6,) and t h e increase o f these functions f o r a C 0.5 Gee

500:

,

4 /

'I

-

400

-

E a I U I I I I I I I ,

,

I a a 200 '

j

I I I I I _I I 0 I 100 '

_,:

I. I 0 I I I I I I I O U ~ . . ~ ~ . : . . . ~ . ~ ~ ~ ' . , . . ~ . . ~ . '

The r e s u l t s o f the BN measurements f o r s t r e s s e d sample a r e presented a l s o on Fig. 3

,

(curves 2 f o r Usm and curve 3 f o r Hc). The Usm

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dependence o f stressed sample i s d i f - f e r e n t from t h a t o f the unstressed one. The Usm value decreases and the Hc value increases f o r CC 0.3 Gee For v a l u e f r o m 0 . 3 & e t o

Ge,

Usm increases and Hc i s constant. For the higher stress (

G

>$) the decrease o f Usm and increase o f Hc are observed. We s h a l l compare the BN r e s u l t s f o r unstressed sample ( f i g . 2) w i t h the MIF r e s u l t s which were obtained f o r 0 1 2 3 4 5 c o l d worked C o l t a l l o y . Sample was

&

'I%

I

deformed by t o r s i o n i n pendulum. 2. I n t e r n a l f r i c t i o n measurements. Fig. 1. S t r e s s - s t r a i n dependence Results o f i n t e r n a l f r i c t i o n me,asure- o f Copt a l l o y . ments f o r c o l d worked C o l t a l l o y were _{d e s c r i b e d p r e v i o u s l y , /3/.} _{F i g . 4}

shows the p a r t o f those r e s u l t s which

50 concern t h e MIF measurements. The

3

LO amp1 i t u d e dependence Q - l ( r ) was

U measured a f t e r t o r s i o n a l deformation.

3-

30 The _{s t a t i c t o r s i o n a l s t r a i n . According t o}

ro

parameter i s t h e value o f Birchak and Smith's theory, the maxi-

20 _{ma1 value.}_Q-lm _{o f Q - l ( r ) dependence}

i s r e l a t e d t o the

Gi

parameter v a l e

10 _{by the simple r e l a i o n :}

_Q-'?a~i-'.

0 P o s i t i o n o f Q - I ( $ ) maximum i s .8 - b -4 -2 ,2 * 4 + + 8 p r p o r t i o n a l t o

q.

Fig. 4 shows t h a t

P

Q- m decreases and i s s h i f t e d t o

H

IF]

h i g h e r v a , l u e s o f

$

w h e n

ro

>

0.2%.Such f e a t u r e o f M I F

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(rs)

and unstressed (Fa) sample. o f deformed sample, /3/.

Fig. 5. S t r e s s dependence o f MIF Fig. 6. R e l a t i o n between BN and MIF

parameters. w i t h 6, as parameter.

The f i n a l example o f t h e t e s t e d c o r r e l a t i o n i s shown

pn

Fig. 6. That f i g u r e shows t h e p o i n t s which a r e c a l c u l a t e d f r o m Usm (Ga) .and Q- m (Ga) dependences f o r t h e same values o f t h e C j a parameter. The c o r r e l a t i o n between EN and MIF phenomena i s found t o be s a t i s f a c t o r y f o r a l l values o f G a stress.

The discussed f e a t u r e s o f BN and MIF, as measured f o r u n s t r e s s e d sample, a r e c o n s i s t e n t w i t h magneto and magnetomechanical l o o p t h e o r i e s . A f t e r q u a n t i t i v e a n a l y s i s o f t h e r e s u l t s shown on Fig. 4 and Fig. 5, i t can be concluded t h a t both MIF and BN phenomena f o r 6, 5

6,

dependent t o t h e

Gi

parameter which i s p r o p o r t i o n a l t o d i s l o c a t i o n d e n s i t y as ki

--

.

The increase o f BN and MIF f o r

ba C 0.5 de can be explained by t h e i r r e v e r s i b l e change o f t h e domain s t r u c t u r e .

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C10-736 JOURNAL DE PHYSIQUE

I t was found t h a t r e l a t i v e l y small stress

(G

>100NPa) a c t i n g along

<loo>

d i r e c t i o n

can r o t a t e t h e magnetization vector from i t s :Ill> easy direction, (2100 = 210

.

10-6) /6/.

By existence o f the r o t a t i o n process one can explain also the increase o f BN f o r

stressed sample f o r

G

> l o 0 MPa (Fig. 3, curve 2). The BN o f such stressed Copt

a l l o y appears l i k e the BN o f m a t e r i a l s w i t h the p o s i t i v e magnetostriction along the

easy magnetization direction. For C C 100 MPa the BN o f stressed sample decreases,

(Fig. 3, curve 2) because o f the negative value o f A l l 1 magnetostriction ( h i l l =

-

32.106, /6/). CONCLUSIONS

1. Barkhausen noise and magnetomecanical i n t e r n a l f r i c t i o n phenomena depend on the

comnon Gi parameter.

2. Barkhausen noise features f o r stressed Copt sample can be explained by assuming

t h a t small stress r o t a t e s magnetization vector.

The authors l i k e t o thank M. C. Flombard from Centre Technique des I n d u s t r i e s

Mecaniques f o r support and s t i m u l a t i n g discussion. REFERENCES

/1/ Smith, G.W., Birchak, J.R., J. Appl. Phys.

41

(1970) 3315.

/2/ Oegauque, J. These, Toulouse (1977).

/3/ Augustyniak, B., J? de Phys. C9,

44

(1983) 455.

/4. Vannes, A., Cousinou, E., Augustyniak, B., Flambard, C., Journ6e National du

COFREND, SCER, P a r i s (1985) 209.

/5/ Ada, V., e t al., Elements de M e t a l l u r g i e Physique, CEN, Saclay (1977).