RELAXATION STUDY OF Ni-P-B METALLIC GLASSES

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RELAXATION STUDY OF Ni-P-B METALLIC GLASSES

B. Fogarassy, A. Böhönyey, A. Cziráki, I. Szabó, L. Gránásy, A. Lovas, I.

Bakonyi

To cite this version:

B. Fogarassy, A. Böhönyey, A. Cziráki, I. Szabó, L. Gránásy, et al.. RELAXATION STUDY OF Ni-P-B METALLIC GLASSES. Journal de Physique Colloques, 1985, 46 (C8), pp.C8-473-C8-477.

�10.1051/jphyscol:1985873�. �jpa-00225217�

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JOURNAL DE PHYSIQUE

Colloque C8, supplément au n°12, Tome 46, décembre 1985 page C8-473

RELAXATION STUDY OF N i - P - B METALLIC GLASSES

B. F o g a r a s s y , A. Bohonyey, A. C z i r a k i , I . Szabo, L. G r l n a s y * , A. L o v a s * and I . Bakonyi* +

Eotvos University, Institute for Solid State Physios, H-1088 Budapest, Muzeum-krt. 6-8, Hungary

*Central Research Institute of Physios, H-1525 Budapest, P.O.B. 49, Hungary Résumé - La relaxation structurale des alliages amorphes Ni„, rP,„ _ B

°^r 81.5 18.5-x x (0 — x - 18.5) obtenues par trempe rapide a été étudiée par les mesures de résistivité électrique et le module dynamique de Young par les méthodes de calorimétrie différetielle et la tnicroscopie d'électrons. Nous avons établi des spectres d'énergie d'activation par les mesures de résistivité et aussi de module de Young. Pour ce système amorphe, la résistivité est uniquement sensible aux processus de relaxation de type chimique tandis que le module de Young est aussi sensible à d'autres mécanismes de relaxation.

Abstract - The structural relaxation of the melt-quenched Ni„, rP,„ . B 81.5 18.5-x x (0 - x - 18.5) amorphous system was investigated by means of electrical resistivity and dynamical Young's modulus measurements, differential scanning calorimetry and electron microscopy. Activation energy spectra were determined from both resistivity and dynamical Young's modulus measurements which have revealed that in this amorphous alloy system the resistivity is sensitive only to chemical type relaxation processes whereas the Young's modulus is sensitive to other relaxation mechanisms as well.

I - INTRODUCTION

In previous work jj \ the crystallization processes of NiO I _ P1 0 . B metallic

u J r 81.5 18.5-x x

glasses were studied. For x=0, 1.8 and 5.5 only Ni and Ni^P phases appeared in the crystallized samples. For x=ll.l, 14.8 and 16.7 Ni, NiqP and Ni,B were observed and for x=18.5 the final crystallization products were Ni and Ni.B. Supposing a quasi- crystalline model L^J this means that the short-range order of the amorphous state should change with the B-content. Furthermore) the appearance of two metal-metalloid phases in the crystallized samples at certain compositions suggests that these alloys may be phase-separated before the crystallization. If this phase-separation was not present in the as-quenched alloys but developed during heating of the samples substantial thermal relaxation (TR) effects are expected to occur. Therefore it is interesting to investigate the influence of thermal relaxation on different physical quantities as a function of the metalloid ratio B/P at constant metal-metalloid ratio since this may help to from a better understanding of the different kinds of relaxation processes. As transition metal constituent, Ni was chosen since this enables the pre- paration of a paramagnetic amorphous alloy system in the investigated range of con- centrations and temperatures in order to avoid complications arising from the effects due to ferromagnetism.

At present as an Alexander von Humboldt Fellow with the Institut fur Physikalische Chemie der Universitat. Sophienstrasse 11, D-8000 Munchen 2, F.R.G.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985873

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JOURNAL DE PHYSIQUE

I1 - EXPERIMENTAL

The amorphous alloy samples which were identical with those used in the previous crystallization study Il2were prepared by a single-roller melt-spinning method with the nominal compositions Ni P B (x=O, 1.8, 5.5, 11.1, 14.8, 16.7 and 18.5).

81.5 18.5-x x

The electrical resistivity, the energy of relaxation and the dynamical Young's modulus were measured by a DC four-point system, a Perkin-Elmer DSC-2 calorimeter and a vibrating-reed apparatus, respectively. All of the measuring equipment was computer-controlled and connected to a data-handling system. Transmission electron microscopy was performed on a JEOL 100-CX microscope.

I11 - QUASI-ISOCHRONAL HEAT TREATMENTS

The electrical resistivity q was measured as a function of the temperature T with a constant heating rate (quasl-isochronal process) up to the crystallization. In Fig.1 the quantity %=?(T)-(: [l+d(~-~~).l is plotted for the Ni-P-B series where T =O CO

and yo and o( are the rgsistivity and the temperature coefficient of resistikty (TCR), respectively, at T=To. Apparently, two different processes (upturn and downturn of

ap) appear below the crystallization and with increasing B-content x the downturn e fect becomes more and more dominant.

The quasi-isochronal heat treatments were performed also by stopping the heating before the start of the crystallization- and then cooling the sample down to room temperature. Representative curves of and of the corresponding quantity for the dynamical Young's modulus E are shown og Fig.2. The ap/o vs T plot demonstra- tes that only the downturn effect in the resistivity (see ~ig.2)Ois irreversible and therefore it must be connected with some TR. It is also obvious from Fig.2 that the

L

- 1 . 5 0 , . . , ! . . , ! . . * ! . , .

4 198 288 388 T [CI

Fig. 1 - Resistivity difference ag ^(as

defined in the text) vs temperature T for the Ni-P-B alloy series obtained with 2 K/min heating rate

- V . @ B 4 I

t

. . ¹ . ^! ^, ^, ^, ⁴

1

- 1 . 3

P 1 b@ 280 T CCI

Fig.2 - Typical curves for tne variation of the dynamical Young's modulus and the resistivity with temperature T obtained with 2 K/min heating rate. The cooling branch of the resistivity goes under the first heating branch for each composition.

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Young'modulus is much more sensitive to this relaxation process. The upturn effect in the resistivity present in both the as-quenched and relaxed samples is reversible and this means that the TCR does not remain constant in the investigated range of temperature. Furthermore, according to the isothermal measurements,the effect of TR is always a resistivity decrease for each composition.

The energy of relaxationAQ was estimated as follows: approximately 15 mg of as- -quenched sample was heated in DSC from 350 K up to a temperature 20 K below the crystallization point, then it was immediately quenched down to 350 K and again re- heated. The area between the two DSC scans (AH vs T) recorded with 40 K/min heating rates was used as a measure of the relaxation energy. A typical heat-release (LIH vs T) curve is shown on Fig.3. The relaxation energyAQ can be seen as a function of x on Fig.4 where AQmax gives the relaxation energies obtained by considering the total area under the AH vs T curve andhQ500 gives the values when the area was measured only up to 500 K. It is probable that the former quantity overestimates and the latter one underestimates the true value of the relaxation energy but it seems to be well established that bQ is a monotonous function of the B-content. Since the average ribbon thickness was found to be 13+1 ,urn for each composition, the quenching rate can be assumed to be constant for the whole alloy series. Therefore, the observed dependence of &Q on x cannot be a quenching rate effect L31, it is more probably connected to phase separation processes.

Fig.3 - Typical heat-release curve Fig.4 - Relaxation energy (AQ) and TCR (d) as a function of B-content (x)

IV - ISOTHERMAL HEAT TREATMENTS

The electrical resistivity and dynamical Young's modulus were measured at constant temperature as a function of time in two different ways: either the temperature was immediately changed from T I to T or the sample was rapidly cooled from T 1 down to room temperature and then it was heated up to T2. Both methods gave the same func- 2 tional dependence of the measured physical quantity on time. The heat-treatment time was typically 1200 min. Representative curves can be seen on Fig.5 and the change

(AP) of some physical quantities (P) is shown as a function of the logarithm of the time (In t) on Fig.6 where AP is the change at a given constant temperature T and t is measured from that time when the temperature reached T defined by the break points on Fig.5. As it can be seen the TR follows a logarithmic kinetics in the investigated amorphous Ni-P-B system (the deviation from linearity as t+O is not due to experimental error but it is a consequence of the explicit functional form of the logarithmic kinetics as it will be clear from the discussion in Section V).

V - DISCUSSION

An obvious contribution to the TR is the decrease of the free volume and the. term

"volume thermal relaxation" (VTR) will be used for this process. The effect of VTR

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C8-476 JOURNAL DE PHYSIQUE

Fig.5 - Typical isothermal resistivity Fig.6 - Isothermal annealing steps from and dynamical Young's modulus curves the data of Fig.5 plotted against In t on resistivity can be tentatively discussed within the extended Ziman theory. By considering that the TCR (o<) is a monotonously increasing function of the B-content

(see Fig.4) we have for the present Ni-P-B alloy series that 2kF<k for all values of x (here,kF and k are the Fermi-momentum and the peak position 8f the structure factor, respectivele). Therefore,the influence of VTR on the resistivity would always be an upturn effect. In this manner the downturn effect observed in the resistivity

(see Figs. 1 and 2) can be attributed to a kind of chemical thermal relaxation (CTR).

A comparison of the electron microscopic pictures of as-quenched and for 1200 min heat-treated alloys has revealed the development of a periodic structure in some parts of the relaxed samples indicating the effect of CTR. The observed composition dependence of CTR might be connected with the higher mobility and the lower chemical affinity of B to Ni in comparison with P in agreement with diffusion measurements 171.

The results of kinetic measurements can be interpreted in terms of a continuous spectrum of activation energies for the

relaxation processes [ 4 to 63. The change P [10l1 + + +

of a physical quantity P at the tempera-

ture T from the time ti to t; is given by " @ ' { ' ' I ' ! I *

kTln(Jt7)

h P = 1 ^pO(u)3u ^{( 1 )}

kTln(vt ;)

where k is the Boltzmann constant, the effective attack frequency of the process and p (U) the activation energy spectrum

of thg physical quantity P in question. I

At the beginning of an isothermal meas- -' ++*'

urement the alloy is, due to its pre- 1 + * +++*++*+++ ,

history, in a certain relaxed state charac- _*++ +.*+ I I

terized by an incubation time t. during ++++*+ I I

++

which the alloy could have reached the 8.84 ~ ~ . i ~ l . ~ ~ s ! ~ ~ ~ ' ! ' ' " ! " "

same relaxed state at the annealing tern- d 2 4 t i ~ b * i l 8 t' perature T after melt-quenching. If t is

the annealing time we have t'=t. and Fig.7 - Schematic plot of the logarithmic

1 1

t'=t+ti (Fig.7). By assuming that

2 kinetics of the TR for the quantity P

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Fig.8 - Activation energy spectrum obtained from resistivity (a) and Young' s modulus (b) measurements

p (U)=p =constant we obtain 4 P = pokTln(t/ti+l).

For t>>t. a plot of AF' against In t gives a straight line (Fig.6) with the slope pokT and intircept In ti which can be used for the determination of po and ti.

By successively annealing the sample at the temperatures T 1 and T2?Tl the attack frequency V and the relaxation energy spectrum p (U) can be determined [61. If the relaxed state reached after annealing for time ty at T 1 remains unchanged during the transition from T 1 to T2 then we have

T21n(vti2) = Tlln(v (tl+til)) from which V can be obtained.

The lowest activation energy U is connected with the first incubation time t. ₁₁ measured at T because in thisOcase the lower limit of the integral (1) is

1

Uo = kTlln(ytil).

From the first isothermal measurement at T 1 we have pol which is displaced at the energy U =U +AU /2 where AU,=AP1/po,. By performing isothermal measurements at sev-

l o 1

era1 temperatures above T1 we can now successively construct the spectrum p (U).

Such spectra determined from resistivity and Young's modulus measurements age shown on Fig.8 for different B-contents. The activation energy spectra start in both cases at U =1.1 to 1.2 eV but their composition-dependences are somewhat different. For zeroO~-content (x=O) the resistivity indicates almost no relaxation effects in con- trast to the Young's modulus for the same composition. This may be connected with the fact that the Young's modulus is sensitive not only to the CTR but also to VTR.

Similar results were published 181 for the activation energy spectra of a-Cu-Ti and Metglas 2826A.

REFERENCES [l

] Fogarassy, B., Cziraki, A., Bakonyi, I., Wetzig, K., Ziess, G. and Szabo, I., in:

Proc. 5th Int. Conf. on Rapidly Quenched Metals (Wurzburg, 1984)

121 Kemzny, T., Vincze, I., Fogarassy, B. and Arajs, S., Phys. Rev. B 0 (1979) 476.

I31 Granasy, L. and Lovas, A., J. Magn. Magn. Mater. 41 (1984) 113.

C41 Egami, T., J. Mater. Sci. 2 (1978) 2587.

[51 Gibbs, M.R.J. and Evetts, J.E., in: Proc. 4th Int. Conf. on Rapidly Quenched Metals (Sendai, 1981). Eds. T. Masumoto and K. Suzuki (The Japan Institute of Metals, Sendai, 1982). Vol. I, p. 479.

Bothe, K. and Neuhzuser, H., Scripta Met. 16 (1982) 1053.

17) - Cantor, B., ibid. 1 595.

C83 Bothe, K., ibid. 1 731.