HYDROGEN RELATED INTERNAL FRICTION PEAKS IN METALLIC GLASSES

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HYDROGEN RELATED INTERNAL FRICTION

PEAKS IN METALLIC GLASSES

K. Agyeman, E. Armbruster, H. Künzi, A. das Gupta, H.-J. Güntherodt

To cite this version:

JOURNAL DE PHYSIQUE

CoZZoque C5, supplgment au nOIO, Tome 42, octobre 1981 _{page C5-535}

HYDROGEN RELATED INTERNAL FRICTION

PEAKS

I N METALLIC GLASSES

K. Agyeman, E. Armbruster, H.U. Kiinzi, A . Das ~ u ~ t a * and H.-J. Giintherodt

I n s t i t u t fiir Physik, UniversitZt BaseZ, CH-4056 BaseZ, mitzerZand

Abstract.- Dissolved hydrogen in amorphous Ni-Zr and Pd-Zr alloys gives rise to thermally activated internal friction peaks. These peaks are characterized by a relatively wide spectrum of relaxa- tion times. The width of this spectrum and thus the characteristics of the peaks depend strongly on the hydrogen concentration.

It is now well known that similar to crystalline metals amorphous metals may also dissolve a large amount of hydrogen, which has a consi- derable influence on their mechanicalproperties. This paper deals with measurements of internal friction in amorphous alloys Ni-Zr and Pd-Zr containing hydrogen. Crystalline metals provide many familiar examples

for stress induced structural relaxation. For exampletthe well known

S n ~ e k and Zener relaxations are associated with changes in the short

range order which occur through thermally activated atom movements over one or two atomic distances. Recent studies on metallic glasses have shown that similar relaxations giving rise to thermally activated inter-

nal friction peaks, may as well occur in an amorphous structure.(l-5). Even though metallic glasses differ in many respects from crystalline metals, such peaks may give valuable information on the kinetics of

atomic short range movements and long range diffusion. Such peaks also provide a tool to study the local atomic arrangements in crystalline so- Lids. In metallic glasses, however, structural models, e.g. the dense random packing of hard spheres,suggest a great variability of possible local arrangements of atoms. Consequently, an internal friction peak

caused by mobile atoms, e.g. solute H, should result from quite diffe-

rent relaxation centers. We would rather expect a braad peak than a

simple Debye peak. Nevertheless, the first results by Berry and Pritchet

(1,2)and our own measurements ( 5 ) on hydrogen related peaks showed ra-

ther narrow peaks having about 2-3 times the width of a simple Debye peak. From this observation it was concluded that in spite of the long range disorder the amorphous structure must contain structural units

(relaxation cermters),which exhibit a remarkable similarity. It is the purpose of this paper to show that other metallic glasses that dissolve larger quantities of hydrogen than the ones used for the first experi- ments indeed give results, which are in qualitative agreement with the present views on the variability of the local short range order in amor-

C5-536 JOURNAL DE PHYSIQUE

phous metals.

Metallic glasses were prepared in the form of long ribbons by the melt spinning technique, and in the form of splats by the anvil and pi- ston technique. The amorphous structure of all alloys was verified by

X-ray diffraction. Strips of about 15 mm length were cut directly from

the as prepared ribbons. The width of these ribbons was about 1 mm and

the thickness.40um. In the case of splats, samples of about the same dimensions could easily be cut out. Such samples were mechanically clamped at one end and tested in a vibrating reed apparatus starting at the temperature of liquid nitrogen up to the glass transition. The

glass transitions of the investigated alloys Ni24Zr76,Pd35Zr65 were at

about 300 and 480'~ respectively. Annealing of the samples and later on sorption and desorption of hydrogen were done in situ. Annealing treat- ments as well as the measurements were carried out in a vacuum of about

10-S mbar. Charging with hydrogen was done at approximately 1 atmos-

phere of hydrogen at 150-200~~. Contrary to prior studies on PdSi

alloys, the absorption kinetics of the Zr alloys proved to be much

slower. We have shown in Pds0Si2, alloys that the kinetics of atomic

jumps of hydrogen atoms, which give rise to internal friction peaks, obey the same kinetics as those which give rise to long range ddffu- sion. Since the internal friction peaks in Zr alloys occur at about the same temperatures as in Pd-Si alloys, we conclude that in the Pd-Zr and Ni-Zr alloys the absorption kinetics& limited by surface barriers rather than by the long range diffusion as in Pd alloys.This behavior appears to be similar to that in crystalline Zr and its alloys.

Results.- Fig. l shows internal friction peaks due to hydrogen in amor-

phous Ni24Zr76 alloys. The frequency of measurement was 270 Hz and cor-

responded to the first flexural mode of the sample. The entries in hours represent the total hydrogen charging time. Unforturnately, we did not yet succeed to correlate the peak heights with the exact con- centrations. The saturation concentration which was still not achieved after 60h may, however, be large. Spit et a1 (6) give a saturation

concentration ( H / M ) of 0.25 at 1 5 0 ~ ~ and atmospheric pressure for

towards the low temperature side 8 . 9 7 . 0 6 . 8 5 . 0 50 190 158 200 250 T C K I (lower activation energies) of the peak.

The effect of this relaxation is also clearly observable in the elastic modu- lus, as shown in

Fig. 2. The sample

after 60h indicates already a relaxatio- nal strain of 7%.

Fig. 1. Internal. friction peaks of H-doped amor-

phous Ni2bZr76 alloys. Indications in hour give

total hydrogen charging times. The frequency was 270 Hz.

Fig. 3 shows the themally activated nature of the hydrogen relaxation after a charging time of 15h. Similar results were observed for other hydrogen concentrations. We do not yet understand why the peak heights depend so strongly on the measuring frequency. The observed variations are obsriously much stronger than the usual 1/T dependence. The frequen-

cy variation of the base line, visible above 300 K, is due to the ther-

moelastic effect. The Arrhenius repre- sentation of the re- laxation time T, de- termined from the re-

1.05

-

-

lation UT = 1 at the

peak temperature, is

shown in Fig. 4. With-

in the investigated 1.88

-

temperature range,the relaxation times for different hydrogen con-

I s e 2ea 256 TCKI

centrations closely follow the Arrhenius

' E / ~ T , where law r d 0 e

T~ is the preexponen- Fig. 2. Young's modulus in relative units for

JOURNAL DE PHYSIQUE

activation energy and k the Boltzmann con-

stant. Interestingly, the activation energy strongly depends on the hydrogen concen- tration. This finding is contrary to the typical behavior of point defect internal friction peaks in crystalline materials. Here the concentra-

Fig. 3. Internal friction peak of H-doped amor- tion dependence is

phous Ni,,Zr,, alloys after a 15h annealing treat-usually restricted to

0

ment in H-atmosphere at 200 C.

the peak height. Also the preexponential factor varies systematically with the H-concen- tration. Similar internal friction peaks and elastic modulus variation have been observed in PdZr alloys

as well after hydrogen charging. In this case the peak increadd by

r e l a x a t i o n

almost two orders of magnitude time CSI

above the baseline of hydrogen free samples. The anelastic deformation

increased to about 10% of the purely I E - ~

elastic strain at the 'highest con-

centration.

1E-04 .-

Discussion.

-

tion between hydrogen charging times and the peak height indica- tes that these relaxations are due to the presence of dissolved

1 E-86

hydrogen. The preexponential fac- 3 . 5 4 . 8 4 . 5 5 . 8 5 . 5 C lBOO/Tp I/K I

tors of order 10-I 3-10-1 sec are _{Fig. 4. Arrhenius plot of the}

characteristic for point defect relaxation time T .-Entries give

activation energies and preex-

relaxations

.

expected to be very low. Under these circumstances,dissolved H-atoms may create an anisotropic strain field (elastic dipole), which can be oriented to give rise to an anelastic strain by external constraints. Since an amorphous structure may offer a great variety of different

sites to H-atoms and since the relaxation time (activation energy and

T ~ ) depends on the local arrangement of atoms around these sites it is to be expected that the relaxation is characterized by a relatively broad spectrum of relaxation times. When, however, the activation ener-

gy, in addition, correlates with the binding-energy of the H-atom at

its site in the sense that deep potential wells (sites) have high acti-

vation energies, then the behavior observed in Fig. 4 is to be expected.

At low concentrations the H-atoms will occupy the deepest potential wells available, which correspond to high activation energies. At low concentrations the spectrum of relaxation times and the width of the internal friction peaks remain narrow as it was observed in Fig. l

(Oh) and in the H-peak of PdSi (5) where the maximum concentration is

about 1 at.% of H. However, at higher concentrations all the favorable sites with deep potential wells are occupied, and additional H-atoms have to go into energetically less favorable sites with smaller activa- tion energies. In this manner, the spectrum of possible hydrogen sta- tes representing the great variety of different local atomic arrange- ment becomes visible in the internal friction peak.

Financial support of the Swiss National Science Foundation and the Komrnission zur Forderung der wissenschaftlichen Forschung is gratefully acknowledged.

References.

-

1 B.S. Berry, W.C. Pritchet and C.C. Tsuei, Phys. Rev. Lett.

41

(1978)

2 B.S. Berry and W.C. Pritchet, in "Rapidly Quenched Metals III", Ed.

B. Cantor, The Metals Society, London, Vol 2 p 21 (1978)

3 H.U. Kiinzi, K. Agyeman and H.-J. Giintherodt, Solid State Commun.z

711 (1979)

4 H.U. Kunzi and K. Agyeman in "Internal Friction and Ultrasonic Atte-

nuation in Solids" Ed. C.C. Smith Pergamon Press p 371 (1980) (Pro- ceeding of the Manchester Conference)

5 H.U. Kunzi, E. Armbruster and K. Agyeman Proc.of Conf. on Metallic

Glasses: Science and Technology Budapest 1980 in press.

6 F.H.M. Spit, J.W. Drijver, W.C. Turkenburg and S. Radelaar,J.de Phy-