STRUCTURAL RELAXATION AND INTERNAL FRICTION PHENOMENA IN THE Fe40Ni38Mo4B18 AMORPHOUS ALLOY

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STRUCTURAL RELAXATION AND INTERNAL FRICTION PHENOMENA IN THE Fe40Ni38Mo4B18

AMORPHOUS ALLOY

E. Bonetti, E. Evangelista, G. Riontino, P. Allia, F. Vinai

To cite this version:

E. Bonetti, E. Evangelista, G. Riontino, P. Allia, F. Vinai. STRUCTURAL RELAXATION AND

INTERNAL FRICTION PHENOMENA IN THE Fe40Ni38Mo4B18 AMORPHOUS ALLOY. Journal

de Physique Colloques, 1983, 44 (C9), pp.C9-133-C9-138. �10.1051/jphyscol:1983915�. �jpa-00223361�

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JOURNAL DE PHYSIQUE

Colloque C9, suppl6ment au n012, Tome 44, decembre 1983 page C9-133

STRUCTURAL RELAXATION AND INTERNAL F R I C T I O N PHENOMENA I N THE F e 4 0 N i 3 8 M 0 4 B 1 8 AMORPHOUS ALLOY

E . B o n e t t i , E . Evangelista, G .

iont ti no',

P . ~ l l i a ' ~ and F . v i n a i r r

I s t i t u t o d i F i s i c a deZ 2 'Universitd, Unit2 G . N , S.M. deZ C.N.R., Via I m e r i o , 4 6 , 40126 BoZogna, I t a l y

' ~ s t i t u t o d i Chimica Generale e Inorganica delZa Facolt2 d i Farmacia, Universitc? d i Torino, Torino, ItaZy

r r I s t i t u t o EZettrotecnico NazionaZe "GaZiZeo F e r r a r i s f : Unitd G.N.S.M. deZ C.N.R., Torino, ItaZy

R6sum6- Des mesures de f r o t t e m e n t i n t e r i e u r e t de module drnamique ont 6 t e rPa1isi.e~

s u r l ' a l l i a g e amorphe Fe,,lli,,Flo,Bl,obtenu par "melt spinning" avec d i f f e ' r e n t e s v i t e s s e s de trempe dans l e domaine de temperature compris e n t r e l a temperature anbiante e t cel l e oh cornmencent l e s transformations i r r 6 v e r s i b l e s de 1 'a1 1 ia g e . Les r g s u l t a t s concernant l e f r o t t e m e n t du fond o n t e t 6 compares avec l e s r e s u l

-

t a t s a e s mesures de r O s i s t i v i t e i n t e r p r i t e s en termes de volume l i b r e dans l ' a l - l i a g e . Des pics de f r o t t e m e n t o n t 6 t e observes dans l e s p e c t r e Q - l ( T ) . On a 2 t u d i 6 l ' i n f l u e n c e de l a v i t e s s e de trempe e t des t r a i t e m e n t s termiques s u r l e parametre c h a r a c t e r i s t i q u e de ces p i c s . Tous l e s r g s u l t a t s exp6rimentaux s o n t i n - t e r p r e t 6 s en termesde processus de r e l a x a t i o n s t r u c t u r a l e dans l a phase amorphe.

Abstract

-

I n t e r n a l f r i c t i o n and dynamic nodulus measurements were performed on t h e amorphous Fe,,Ni,,Mo,B,, a l l o y obtained by melt spinning with d i f f e r e n t quenching r a t e s from room temperature up t o t h e s t a r t i n g temperature of t h e i r r e - v e r s i b l e a l l o y transformations. The i n t e r n a l f r i c t i o n background d a t a were d i r e c t - l y compared with those of e l e c t r i c a l r e s i s t i v i t y measurements i n t e r p r e t e d i n terms of t h e f r e e volume degree p r e s e n t i n t h e a l l o y . Relaxation peaks were observed i n t h e Q-l vs. temperature spectrum and t h e i n f 1 u e n c e o f q u e n c h - ing r a t e and thermal treatments on t h e c h a r a c t e r i s t i c parameters of t h e s e peaks was i n v e s t i g a t e d . All t h e experimental r e s u l t s a r e i n t e r p r e t e d i n terms of struc- t u r a l r e l a x a t i o n processes ~ c c u r r i n g i n t h e amorphous s t a t e .

Introduction

-

I t i s now well e s t a b l i s h e d t h a t s t r u c t u r a l r e l a x a t i o n processes occur- r i n g i n t h e amorphous a l l o y s i n a wide temperature range below g l a s s t r a n s i t i o n tem- peratureareaccompanied by d r a s t i c modifications of many physical p r o p e r t i e s 11-31.

The i n t e r n a l f r i c t i o n techniques applied t o t h e study of t h e s e complex phenomena in amorphous a l l o y s f o r d i f f e r e n t chemical compositions and preparation techniques showed t h a t s t r u c t u r a l r e l a x a t i o n i c d u c e s i r r e v e r s i b l e modifications i n t h e i n t e r n a l f r i c t i o n and dynamic nodulus vs.T s p e c t r a 141. These changes regard t h e i n t e r n a l f r i c t i o n b a c k - ground a s well a s some r e l a x a t i o n peaks observed by various authors between room tem- p e r a t u r e and t h e g l a s s t r a n s i t i o n temperature 15-91 whose n a t u r e has not y e t been completely c l a r i f i e d .

On t h e o t h e r hand, a c r i t i c a l parameter i n determining t h e r e l a x a t i o n k i n e t i c s and the degreeofdisorder i n t h e amorphous s t r u c t u r e i s t h e quenching r a t e . This has been c l e a r l y shown i n r e c e n t s t r u c t u r a l r e l a x a t i o n measurements on a l l o y s obtained with d i f f e r e n t quenching r a t e s . These measurements /10,11/ r e f e r t o t h e determination of t h e Curie temperature v a r i a t i o n s and of t h e magnetic permeability r e l a x a t i o n .

I t appeared t h e r e f o r e i n t e r e s t i n g t o study i n t e r n a l f r i c t i o n and dynamic modulus vs.T,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983915

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C9-134 JOURNAL DE PHYSIQUE

and i n isothermal conditions in amorphous alloys in which the only varying parameter i s the quenching r a t e , t h a t i s tne degree of f r e e volume. Even though Egami e t a1 ./12/

have recently claimed t h a t the r o l e of f r e e volumes i n the p l a s t i c deformation of an amorphous metal should not be determining, an influence in the s t r u c t u r a l relaxation as well as in the a n e l a s t i c processes cannot be excluded.

Experimental

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The measurements of the internal f r i c t i o n c o e f f i c i e n t Q-land of the modulus Md were carried out on specimens of the Fe,,Ki,,Mo,E$,alloy obtained by a melt spinning technique with d i f f e r e n t quenching r a t e s , i . e . with d i f f e r e n t substrate wheel speed, in ribbon form -10-3m wide. The thickness of the samples was found t o be inversely proportional t o the wheel speed / I t / .

In t h i s study three s e r i e s of specimens were examined; quenching r a t e and ribbon thickness a r e as follows :

Series wheel speed ribbon thickness

m/sec m x

For the measurements the specimens were cantilever mounted on a specially designed support. Q-I and Md were obtained from the flexural vibration decay detected by a frequency modulation technique. The frequency range covered with specimens of d i f - f e r e n t lengths, using the fundamental and second overtone was 30

-

2000 Hz. All the measurements were made under a Pa vacuum. The heating r a t e f o r the Q-I and Md determination vs. T spectra was- 2K/min.

Results

-

Typical Q-I (T) and Md(T) trends of the specimens corresponding t o the ex- treme quenching r a t e s used a r e i l l u s t r a t e d i n Figs. la)-b). The thinner specimens show a higher value f o r the Q-l background f o r a1 1 the temperatures.

Fig. 1

-

Typical internal f r i c - ction Q" ( - ) and dynamic modulus Md

(--I

trends f o r specimens of s e r i e s A(a) and C(b). PI,: dynamic modulus a t room temperature f o r as-preprred s p e c i m e n s . Resonancefre-

quency $250 Hz.

The T ranges labelled I and I 1 r e f e r respectively t o the temperatures a t which revers- i b l e and i r r e v e r s i b l e Q-land Md variations a r e observed. Range I11 corresponds t o t h e onset of the primary c r y s t a l l i z a t i o n processes and i t will not be consideredhere.

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I t i s e v i d e n t t h a t the specimens obtained by f a s t quenching show a remarkable dynamic modulus increase i n a temperature range where t h e s l o w l y quenched specimens do n o t show appeciable v a r i a t i o n s . These show a s m a l l e r r e l a x a t i o n as i l l u s t r a t e d i n

Figs. 2a)-b) where the Md(t) spectra are r e p o r t e d a t t h e temperatures i n d i c a t e d f o r specimens o f type A and C, r e s p e c t i v e l y .

Discussion

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From t h e curves o f Fig. 1 which show t y p i c a l average trends (about t e n specimens f o r each s e r i e s ) i n t h e temperature range I, a l i n e a r r e l a t i o n s h i p between t h e Q-1 background values and t h e specimen thickness ( i . e . t h e r e c i p r o c a l quenching r a t e ) can be derived, as i l l u s t r a t e d i n Fig. 3b).

[::;I)

%to6 I 1.0 2

I n Fig. 3a) t h e data obtained by A l l i a e t a l . /13/ w i t h e l e c t r i c a l r e s i s t i v i t y measurements (p) on samples obtained from t h e sameribbons used i n t h e present work, have been p l o t t e d vs. Qijick. The l i n e a r t r e n d obtained, on account o f t h e analogous p dependence on t h e f r e e volume degree of t h e a1 1 oy / I 1 ,13/ i n d i c a t e s t h a t t h e d i s s i - p a t i v e processes near room temperature a r e c o n d i t i o n e d by t h i s s t r u c t u r a l parameter.

F i g .

thermal 2

-

anneal Dynamic i ngs modulus

.

vs. time d u r i n g i s o - a : sample o f s e r i e s A, T

anneal ⁼430K b : sample o f s e r i e s B, Tanneal ' = 460K Resonance frequency 200Hz.

T2y:

^CI

[>T,<]

^{F i g .}^{t i o n}vs. r e s i s t i v i t y Q3

-

Background ' . a t a) ~room in t e r n a l temperature ~ ~ f r i c - - : ~ ~

. 3

0 20 vs. specimens thickness b),

-

f o r specimens obtained w i t h d i f f e r -

I r e n t quenching r a t e s (Table I ) .

120 140 10 3 0

e f p g cml T h i c k n e s s ( r n x 1 W 6 )

M,: dynamic modulus a t t h e annealing tempera- t u r e a t t h e s t a r t o f t h e anneal.

1.02

The ^Q-ltrends i n t h e range I depend on t h e quenching r a t e a s shown i n F i g . 1 a n d i n F i g . 4 w h i c h r e f e r s t o t h e M d ( T ) t r e n d s . The q u e n c h i n g r a t e e f - f e c t i s s i m i l a r t o t h a t produced by d i f f e r e n t annealing treatments on specimens j u s t as prepared: t h e s l o w l y quenched samples behave as those annealed f o r a l o n g e r time ( i .e. l i k e the more r e l a x e d ones).

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JOURNAL DE PHYSIQUE

The t r a n s i t i o n temperature between range I and I 1 depends, f o r c o n s t a n t heating r a t e , on t h e quenching r a t e and, f o r specimens of equal t h i c k n e s s , on t h e measurement frequency. The structural r e l a x a t i o n process involved i s c h a r a c t e r i z e d by an ap- p a r e n t a c t i v a t i o n energy

"

40

-

60 KJ/mole ( A and C samples) obtained by t h e s h i f t with frequency of t h e t r a n s i t i o n temperature. As shown i n Fig. l a n d u n d e r isothermal c o n d i t i o n s i n Fig. 2 t h e Md v a r i a t i o n s i n range 2 s t r o n g l y depend on t h e quenching r a t e . These Md i n c r e a s e s a r e connected t o s t r u c t u r a l r e l a x a t i o n processes i n t h e amorphous s t a t e not linked t o t h e modulus i n c r e a s e due t o primary c r y s t a l l i z a t i o n of t h e a l l o y t h a t s t a r t s a t about 580 K.

Fig. 4

-

Typical Md v s . T t r e n d s i n t h e temperature range I ( s e e f i g . 1 ) f o r specimens of s e r i e s A

( - - . I ,

B ( - - - ) , C (-). Resonance f r e - quency %200 Hz. Mo i n every c a s e i s t h e dynamic modulus a t room temperature.

".., .-

- - _-

ff

0.9 8

-

. .

.

With regard t o t h e mechanisms r e s p o n s i b l e f o r t h e r e l a x a t i o n i t must be considered t h a t a l l t h e specimens examined have t h e sane nominal chemical composition, t h e r e f o r e

t h e d i f f e r e n c e s observed between specimens of t h e d i f f e r e n t s e r i e s m u s t depend, a t l e a s t t o a c e r t a i n e x t e n t , on t h e d i f f e r e n t f r e e volume content.

300 3 50 4 0

T ( K )

-

k-

I 0.96 0.94

In t s m s of s t r u c t u r a l d e f e c t s defined by t h e atomic l e v e l s t r e s s e s , (Egami e t a l . / 3 , 1 4 / ) t h e r e l a x a t i o n process i n range I 1 could be l a r g e l y determined by annealing of p-n d e f e c t p a i r s . p and n a r e r e s p e c t i v e l y t h e l o c a l h y d r o s t a t i c press-

. . _..

.. .

-I

- -

ure and t e n s i o n linked t o t h e l o c a l atomic volume and t h e r e f o r e t o t h e l o c a l d e n s i t y . On t h e o t h e r hand, t h e apparent a c t i v a t i o n energy value f o r t h i s process i s of t h e order of 150 KJ/mole

/ l a /

i.e. substantially higher than t h e ones obtained from isotherms l i k e t h o s e of Fig. 2a) f o r specimens of s e r i e s A i n t h e T range 370

-

⁴⁷⁰K t h a t a r e of t h e o r d e r of 50 KJ/mole.

Moreover isothermal r e s i s t i v i t y measurements on a l l o y s similar t o t h e one underconsider- ation /15/ showed t h a t r e s i s t i v i t y relaxation, a t temperatures below 550Kwas dominated by compositional short range ordering processes and t h a t topological ordering e f f e c t s were observed a t higher temperatures. Although no reliable estimation of the a c t i v a t i o n energies involved i n t h e relaxation was possible i n t h a t c a s e , the s h i f t observed in t h e temperature Mween topological and compositional ordering e f f e c t s c l e a r l y showed t h a t t h e l a t t e r a r e charac- t e r i z e d by a lower average a c t i v a t i o n energy.

%eMd increase observed i n the T-range 11, could be re1 a t e d to topological ordering with f r e e volume reduction; in t h e same range, however, resistivity measurements clearly indicated the existence of a strong compositional ordering. On t h e other hand, pure chemical ordering gives r i s e t o slight Md i n c r e a s e s in some amorphous a l l o y s / l 6 / ; such effects were observed i n rib- bons previously t r e a t e d to achieve ccmplete topological s h o r t range orderlng r e l a x a t i o n . I t cannot be excluded that in our alloys annealed f r m the a s - c a s t conditions c k n g e s of compositional short rangeorderingcould be s i g n i f i c a n t l y l a r g e r than the ones reported i n /16/.In any c a s e t h e n a t u r e of t h e r e l a x a t i o n obser\fed i n T-range I 1 i n t h e f a s t quenched specimens remains t o be c l a r i f i e d .

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Measurements c a r r i e d o u t a t d i f f e r e n t frequencies have shown t h a t t h e peaks a r e of thermally a c t i v a t e d type; s t i l l a c t i v a t i o n energy e v a l u a t i o n s do not lead t o repro- d u c i b l e values (of t h e o r d e r of 100 KJ/mole): i n p a r t i c u l a r , t h e s e values depend on t h e previous thermal treatments. This behaviour could be c o n s i s t e n t with a dependence of t h e a c t i v a t i o n energy and/or r e l a x a t i o n time on t h e s t r u c t u r a l r e l a x a t i o n degree of t h e samples. This problem has r e c e n t l y been examined by Berry / I T / ; moreover, a s i m i l a r behaviour has been observed f o r some Q-l peaks c h a r a c t e r i z i n g t h e i n t e r n a l f r i c t i o n spectrum before t h e g l a s s t r a n s i t i o n temperature on some e l e c t r o - l e s s deposited amorphous a1 loys / I $ / .

1.00

1

^{Fig. 5}

^-

Annealing e f f e c t on t h e Q - ~ ( T ) , Md(T) s p e c t r a f o r a sample of s e r i e s A.

r"

0,98> a , a ' f i r s t measurement,

t b , b l second measurement a f t e r a 5 min anneal a t 410 K.

>lo: dynamic modulus a t room temperature before t h e f i r s t measurement.

Conclusions

-

The r e s u l t s reported show t h a t t h e s t r u c t u r a l d i s o r d e r degree induced by d i f f e r e n t quenching r a t e s , i . e . d i f f e r e n t f r e e volume content a f f e c t t h e Q - ~ and Md t r e n d s considerably.

In p a r t i c u l a r :

-

t h e s t r o n g Md r e l a x a t i o n observed i n t h e f a s t quenched specimens ( s e r i e s A) i n t h e temperature range I1 should be determined by compositional ordering processes occurring through s h o r t range atomic d i f f u s i o n and f r e e volume a s s i s t e d ;

-

t h e Q-I peaks observed i n range I a r e probably determined by s t r e s s induced s h o r t range ordering processes linked t o t h e d i f f e r e n t atomic s p e c i e s of t h e alloy.

In t h i s c a s e t h e influence of t h e d i f f e r e n t f r e e volume contents should only be i n d i r e c t i n t h e sense t h a t i t should determine t h e degree of topological s t r u c - t u r a l r e l a x a t i o n and thus t h e c h a r a c t e r i s t i c parameters of t h e peaks, i . e . a c t i v a - t i o n energy and r e l a x a t i o n times.

Acknowledgments

-

This work was c a r r i e d o u t with CNR/GNSM funds. The c o l l a b o r a t i o n of miss. I . Zucchi i s g r a t e f u l l y acknowledged.

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