STRESS DEPENDENT INTERNAL FRICTION AND MODULUS CHANGES IN IRON BASED METALLIC GLASSES

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STRESS DEPENDENT INTERNAL FRICTION AND MODULUS CHANGES IN IRON BASED METALLIC

GLASSES

G. Posgay, S. Kiss, F. Kedves, I. Harangozó, Z. Cseresnyés

To cite this version:

G. Posgay, S. Kiss, F. Kedves, I. Harangozó, Z. Cseresnyés. STRESS DEPENDENT INTERNAL

FRICTION AND MODULUS CHANGES IN IRON BASED METALLIC GLASSES. Journal de

Physique Colloques, 1987, 48 (C8), pp.C8-447-C8-450. �10.1051/jphyscol:1987868�. �jpa-00227172�

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JOURNAL DE PHYSIQUE

Colloque C8, supplement au n012, Tome 48, decembre 1987

STRESS DEPENDENT INTERNAL FRICTION AND MODULUS CHANGES IN IRON BASED METALLIC GLASSES

G. POSGAY, S. KISS, F.J. KEDVES, 1.2. HARANGOZO and

z .

C S E R E S N Y ~ S

Department of Solid State Physics, Kossuth University, PO Box 2 , H-4010 Debrecen, Hungary

Abstract, The measurements were m a d e in a torsional pendulum at about 0 . 1 c p s using bongitudinal s t r e s s (5 - 1 5 0 MPa) in the temperature r a n g e 2 0

-

^{6 0 0}C. The internal friction (i.f.) decreases and the modu- l u s increases monotonously with increasing longitudinal s t r e s s in the, amorphous state. T h i s i.f. c h a n g e i s more pronounced in the temperature r a n g e of structural relaxation. Changing the s t r e s s a t constant temperature the changesof the measured parameters were time andtemperature dependent. These effects can be explained by the diffusion controlled reversible ordering of the a t o m s due to the applied stress. Also the isothermal crystallization w a s accelerated by the stress.

Neasuring structural changes during increases in t e m p e r a t u r e , (struc- t u r a l relaxation 'and crystallization) in metallic g l a s s e s using internal friction proved to be effective [ I ] . In general the i.f. measure- m e n t s are made using low s'c~ess. One method of measuring the influence of mechanical s t r e s s i s the determination of the dependence of i.f. on re- l a t i v e deformation.8 disadvantage of this method i s t h e fact that the s t r e s s c h a n g e s with time. We examined the influence of tensile s t r e s s on t h e internal friction using constant r e l a t i v e maximal s t r e s s in tor- s i o n during measurements.

E x ~ e r i m e n t a l m e t h o d s

The i.f. w a s measured with a torsional pendulum in which a mirror was fastened on the movina element and the lioht reflected on it was re- gistered by a light-spot following recorder. The r e l a t i v e deformation of t h e 4 0 mm l o n g , 1 mm wide and 2 0 - 4 0 f i thick s p e c i m e n s w a s

during the

measurements.

The p r e s s u r e w a s P = 1 0 P a , the temperature r a n g e 2 0 - 6 0 0 C , and the frequency about 0 , l cps. The m a s s of the moving element w a s 2 5 grams. Using a manipulator w e were able to put f i v e further masses on it. This meant 5 - 1 5 0 MPa s t r e s s e s in the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987868

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JOURNAL DE PHYSIQUE

samples of a typical cross-section. The changed moment of inertia can be reproduced with the increase of the mass of the vibrating element which must be taken as a correction. A further correction is needed because of the additional torsional stress caused by the applied tensile stress which can be calculated froni the geometry of the sample.

Results and d i s c u s s i o ~

The i.f. and dynamic modulus (d.m.) changes caused by tensile stress were found to be similar for two-or multicomponent alloys. The stress dependence for an FeCoNiCrBSi metallic glass i s shown in Fig.1. It c a n be s e e n that the i.f. decreases and the d.m. increases with increasing applied stress. The equilibrium values of i.f. and d.m. shown in Fig.1

Fig.1.

The i.f. and d.m. versus tensile stress for

FeCoNiCrBSi metallic glass at room temperature

were achieved after a transient process (Fig.2.).

At the transition between the different stress states i.f. showed an extra damping which ceased after a while. Moreover i n connection with this the modulus showed a decrease, too. This transient process depended to a great extent o n the temperature (Fig.3.). The extra damping w a s greater at higher temperatures and the process was faster.

Fig. 2. The time dependence of i .f. Fig.3. The changes during the al -+ .a and of d.m. after stress

changes for FeCoNiCrBSi metallic transition at different temper- olass at room temoerature.

7%

⁼ ^{5 MPa,} ^{= '}⁹⁰^MPa)

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The Q - ~ ( T ,6) and G/GO(T

,s)

measurements of metallic glasses w e r e carried out on the s a m e s a m p l e during continuous heating with periodi- cal loading

-

unloading. This w a s necessary because G/G (T) showed rather marked differences in the relaxation range even ijlthe s a m p l e s takzn from the sane material. As c a n be s e e n in Fig.4. Q (T) dccrcasad

Fig. 4.

The temperature dependence of i.f.

and d.m. a t different stresses.

with s t r e s s ; w e had the greatest difference during the structural relaxation and crystallization. The modulus increasing effect of the s t r e s s ceased after either the crystallization or the phase-transfor- mations following the crystallization. The extent of the modulus in- c r e a s e caused by the s t r e s s showed differences in the relaxation range in the s a m p l e s taken from the s a m e material similar to the above men- tioned dependence on temperature. The s t r e s s induced d.m. changes are greater for the sample having higher relaxation.

During continuous heating measuring of a s a m p l e under s t r e s s w e did not find any change in the crystallization temperature. However, during isothermal testing the stress accelerated the crystallization although

it did not change the extent of the modulus change during crystallization.

We a l s o examined a f e w metal wires. We c h o s e the diameters s o that their moments (i.e. the frequencies) would be characteristic of metallic glasses. Our results obtained i n s o m e s a m p l e s can be seen in Fig.5.

The i.f. increased and d.m. decreased with the s t r e s s in the s t e e l A

<'.lo4

35. 0

Fig.5.

30. The stress dependence of

i.f. and d.m. for s t e e l , Ni and Mo wires at room temperature.

A Mo

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JOURNAL DE PHYSIQUE

wires of 0.12 mm diameter and in the Ni wires of 0.35 mm diameter. The behaviour of the sintered Mo wire of 0.10 diameter w a s different at lower stresses. However these d.m. c h a n g e s are rather s m a l l , maximum 2-7%.

We m u s t try to find the reasons f o r the behaviour of metallic glasses contradicting the crystalline metals in their amorphous structure.

Under the influence of mechanical s t r e s s they s h o w reversible ordering

[ 2 ] . This ordering c a n have a time and temperature dependent part con-

trolled by diffusion which c a u s e s i.f. increase and d.m. decrease. The dependence of the stress-effect on temperature s h o w s that the influence of s t r e s s i s greatest where other (thermally activated) structural changes also take place in the material: during structural relaxation and cry tallization. It c a n e b e s e e n clearly in Fig.6. w h e r e w e compared the Q ( T ,

Ff 6 )

and Q-'(T,T) c u r v e s belonging to the F e 8 metallic glass. The acceleration of crystallization c a n be explained by t h i s stress-induced ordering.

v 6;',20ymjn

0 6 0 , 2 0 C / m ~ n o 6,,10C m i n

Fig.6.

The i.f. behaviour similar (decrease) lower heating rate higher s t r e s s

(c,,=

61 = 1 5 0 MPa)

is for or for 1 0 M P a ,

References

[I] 5 . K i s s , G . Posgay, Cs. Kopasz, F. J. K e d v e s , I.Z. H a r a n g o z o , Journal d e Physique 44 (1983)

[2] T. Y a m a s a k i , H. I z u m i , H. S u n a d a , Y. Kondo, J . Inst. Met. 45 No7., 1981.