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An internal friction peak in amorphous and microcrystalline Co33Zr67
Scripta M E T A L L U R G I C A
Vol. 23, pp. 471-476, 1989 Printed in the U.S.A.
AN INTERNAL FRICTION PEAK IN A M O R P H O U S
Pergamon Press plc All rights reserved
AND M I C R O C R Y S T A L L I N E
C033Zr~7
H.-R. Sinning, M. Nicolaus and F. Hae~ner Institut f~ir Werkstoffe, Technische Universitit Braunschweig, FR Germany (Received October 19, 1988) (Revised January 14, 1989) i. Introduction Although it is now widely accepted that atomic rearrangements within the amorphous structure of metallic glasses (e.g., during structural relaxation) can in general be described by a broad spectrum of activation energies (i), studies of the internal friction of these materials have often shown a well-defined peak at temperatures near or below room temperature (2-7). Recently, we have also discovered such a peak in amorphous Co3sZr6~ (8). Like in crystalline solids, a single (average) activation energy can be determined from these peaks in the usual way (9) by evaluating the change of the peak temperature with frequency. Most of these internal friction peaks have been associated with the thermally activated motion of hydrogen atoms as "interstitials" in the amorphous structure, in a way similar to the well-known Snoek relaxation of interstitials in bcc metals. However, based on the results for some binary metal-metal glasses, it has also been argued that such a relaxation effect may be intrinsic in the amorphous structure itself (Z). On the other hand, in crystalline metallic materials a Shock relaxation is usually observed only for heavier interstitials like carbon, nitrogen or oxygen but not for hydrogen (6). A rare exception from this rule is the alloy Pde2Sils, where a short-range reorientation (i.e. Snoek-type) relaxation of hydrogen has been found both in the amorphous state and after crystallization of the palladium silicide PdQSi 2 (with an orthorhombic defect structure based on Pd3Si ) (6). The position, height and shape of the internal friction peaks in Pds2Si18 in the amorphous and crystalline states are however very different from each other. In the present paper, new internal friction results on the alloy Co33Zre7 are presented which show for the first time a peak with nearly the same properties both in the amorphous and in the microerystalline state. Provided the microscopic mechanism underlying this surprising behaviour can be identified, interesting consequences for the understanding of the amorphous as well as of the microcrystalline structure can he expected from this observation. 2. Experimental A 2ram wide and about 35 pm thick amorphous ribbon of composition CossZrs7 was produced by melt-spinning under vacuum.* The amorphous and crystalline states of the material as well as the crystallization reactions were characterized using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The internal friction was obtained from the damping of flexural vibrations measured in a vibrating-reed apparatus with electrostatic ,excitation and a HF detection circuit. These measurements were performed under vacuum with the specimen clamped in a fixed holder at one end ("clamped-free" or "cantilever" mode of flexural vibration). As in this configuration thermal gradients along the specimen cannot be avoided completely, a temperature correction was applied to those internal friction data that were obtained by using harmonics. Without such a correction, the different distribution of strain along the specimen in the different vibration modes can " The production of the amorphous material was carried out at the "Kristallabor der physikalischen Institute" at the University of G~ttingen.
471 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
472
AMORPHOUS
Co-Zr
Vol.
23, No. 4
lead to a systematic error in the measured shift of the peak temperature with frequency and thus in activation energy (see below). The correction was obtained by comparing the fundamental mode of a short specimen with higher vibration modes of longer specimens at the same frequency; details of this procedure will be given elsewhere (I0). The heat treatments were performed in the vibrating-reed apparatus; the resonance frequency of the vibration was used to monitor the structural relaxation and crystallization reactions during these treatments. 3. Results
290
f[Hz] 280
FIG.I Change of the resonance frequency of a vibrating reed of Co33Zr67 during heating with 2 K/rain through crystallization. The arrows I and II indicate the positions of the two exothermic peaks obtained calorimetrically at the same heating rate.
270
260 250 T
2/,0 300
I
i
I
~oo
soo
600
I
~oo
I
T[K]
eoo
To characterize the thermal behaviour of the as-quenched Co33Zre7 glass, Fig.l shows the change of the resonance frequency (due to the change of the elastic modulus) of a vibrating sample during heating with a constant heating rate of 2 K/min, together with the positions of two exothermic peaks (I and If) obtained in DSC. Whereas the slow increase of the frequency between 400 and 650 K is due to structural relaxation of the amorphous alloy, the following sharp steps at the positions of the DSC peaks indicate two reactions corresponding to the crystallization of the material. Detailed studies of these reactions (ii14) have shown that the first one (1) is identical with the polymorphic crystallization of (metastable) CoZr 2 (with some differences with respect to the question of whether the
FIG.2 Dark field electron mlcrograph (left) and diffraction pattern (right) of Co33Zrs7 after a heat treatment of 20 rain at 693 K.
Vol.
23, No.
4
AMORPHOUS
Co-Zr
473
resulting phase is tetragonal or cubic), whereas the second one (II) is due to a transformation within the crystalline state. After completion of the first reaction, the material is fully crystalline (12) and shows an extremely small grain size of about i0 n m difficult to detect even in T E M (14). An example for this microstructure is given in Fig.2. The internal friction peak of this alloy has been extensively studied at different frequencies and after different heat treatments; typical examples are shown in Figs.3 and 4. It is seen from Fig.3 that the peak remains nearly unaffected by heat treatments as long as the material is amorphous, even though considerable structural relaxation takes place in this range (Fig.l). A surprising result is, however, the fact that the peak is still existing after heating to 723 K, when the material has passed the first crystallization reaction and is microcrystalline (Fig.2). The peak is then only shifted by about 15 to 20 K to higher temperatures and somewhat reduced in height. However, this difference becomes smaller at higher frequencies as in the amorphous state a decrease of the peak height with increasing frequency is observed (Fig.4). (A similar behaviour has also been observed by Agyeman et al. (3) for the hydrogen peak in glassy Ni24ZrTs; an explanation for this effect is still missing.)
Heat treatment:
/ / ",k
---::'< 3 x
9
..... ........
FIG.3 Internal friction peak in Co33Zrs7 at a frequency of f=100 Hz after subtraction of the background and after different heat treatments (linear heating with 1 K/rain up to the temperatures indicated). The three upper curves correspond to the amorphous state, whereas after heating to 723 K the material is microcrystalline.
sn K
I.i
\~\
Ii
723 K
.,.-.:~.%.(...
I
,02 •~
./
"._
"\ -...
......<:."....~,'-"
/
\<.,,. -..,,/
200
TIK]
300
4
~3 K
/
i
"02
I
1 0
~.-
150
, 200
/
/
I
/
/'%593 ~'"~%3283 Hz (o)
/
l
!\,,. b"
~ ...~.
/.,~.~ .,~'4.J" (~:3592Hz /..~ ....,r.~ss2 ,'... ./ ,'.:>%~I07~ .\ \'...
FIG.4 Frequency dependence of the internal friction in the amorphous (a) and microcrystalline (c) state.
(c)
F
,Z' ,Yi %\ ~ - ,"....
\x ',":.",, '.....
\ \ \,',,, ..
.
~ 250
k\.
~ 300
,,
'".,
350
400
,,,
-... T[K]
450
474
AMORPHOUS
Co-Zr
Vol.
Z3, No.
The average activation energy E= and the preexponential time constant to of the internal friction peak have been obtained by the usual frequency shift method (9) from the AzThenius plot shown in Fig.5. The results for the various different heat treatments in the amorphous state (i.e. different amounts of structural relaxation) cannot be distinguished from each other. As the scatter is much larger for "as-quenched" specimens, the values obtained on "relaxed" samples give a more reliable characterization of the amorphous state. It should be noted from Fig.5 that the difference in E= and to between the amorphous and the microcrystalline state is very small and within the experimental scatter. It is therefore not possible to say which of these parameters has in fact changed by a very small amount to produce the small shift of the internal friction peak in temperature observed after crystallization in Fig.3. First attempts to look for dissolved hydrogen as a possible origin of the internal friction peak in Co33Zrs7 did not give a clear result: by heat extraction, certain amounts of hydrogen (0.3 at% at maximum) were indeed found, but only after extreme heating up to 1600"C. However, we do not know whether this hydrogen was really dissolved in the amorphous or microcrystalline matrix. After a more moderate heating of the samples, no hydrogen could be detected at all.
%[K]
340 -6
,
,
,
300
,
280
,
,
In "t"
,,,
,,,,,4(
-7
,. /,"
-8
,,"
/
,"
,,"
,
S/~
/
o /^/
/,o,
O o
~/•
o Z~
/~// O
//
o J/./ / // ,,
3.2
3.4
3.6
lO}'tp[K-']
"as-quenched" state (Ea=0.420 eV, ~o=i.i •10-Zls) "relaxed" amorphous state (different heat treatments between 373 and 673 K; Ea=0.465 eV, ~o=2.2-i0-IIs)
#/#
3.0
FIG.5 Arrhenius plot of the relaxation time t = i/2]rf against the reciprocal peak temperature i/Tp after different heat treatments:
o/// ,F? .//
// -9
260
,
3.8
microcrystalline state (1 K/min to 723 K; Ea=0.475 eV, ro=3.4.10-Z2s)
4
Vol.
23, No.
4
AMORPHOUS
Co-Zr
475
4. Discussion The observation of so closely related internal friction peaks described by almost the same average activation energy and preexponential factor both in amorphous and microcrystaline Cos3Zrs7 strongly suggests that in both cases the same anelastic relaxation mechanism is operating, This can be assumed to be an atomic rearrangement interacting with the applied stress by an anisotropic elastic distortion (9). It is remarkable that this rearrangement is obviously the same in an amorphous as well as in a microcrystalline material. This can already be stated as an important result of this study: apparently there are relaxation centers in the material which have almost identical local atomic surroundings both in the amorphous and in the microcrystalline state. With respect to the microscopic nature of the relaxation mechanism, there are two principal possibilities to be discussed: a rearrangement of the Co and Zr atoms themselves, i.e. a stress-induced directional short range ordering. In crystalline alloys, this could be the Zener relaxation (9), but also more complicated processes like that proposed by Berry for age-hardened A1 alloys (15) (based on clusters with built-in excess vacancies). Similar mechanisms can be imagined for amorphous alloys as well. the thermally activated motion of impurities dissolved as "interstitials" in the amorphous or microcrystalline matrix. This would then probably be hydrogen as those internal friction p h e n o m e n a in metallic glasses that are k n o w n to be due to hydrogen (3-7) are very similar to the peak observed here. Within the same class of materials, it seems unlikely that heavier "interstitials" like oxygen could give rise to a relaxation effect in the same temperature range and with similar activation parameters as hydrogen. At present it is not yet possible to decide between these two possibilities as the experimental evidence is too small: For the first, intrinsic process we do not k n o w of any examples on comparable systems from the literature with clear evidence with respect to the relaxation mechanism. From the values of the activation energy, a mechanism involving excess vacancies or free volume seems more likely than the normal Zener relaxation (9,15). With respect to the hydrogen mechanism, the activation energy does also fit well to the values k n o w n for the amorphous state from the literature (3-7). The frequency factor ~o -I is somewhat lower than the literature values; however, this comparison is very sensitive to the applied temperature gradient correction (i0) and therefore has to be examined more critically from the experimental side. The stability of the peak against annealing is in contrast to observations on the hydrogen peak in Pd- and Fe-based glasses (3,4); a similar behaviour has been used by K~inzi et.al. (2) as an argument against the hydrogen mechanism. Nevertheless, an explanation of our results by hydrogen is possible by assuming that both the desorption of hydrogen from the Co-Zr glass is prevented and the local atomic configuration and symmetry around a hydrogen atom is insensitive to structural relaxation of the amorphous material. The most unexpected feature of the observed internal friction peak with respect to the hydrogen mechanism is however the fact that it appears also in the microcrystalline state, with the same kinetic parameters (in contrast to Pd82Si18 (6)). If hydrogen were responsible for this effect, this would be an outstanding result both for the relaxation of point defects in crystalline materials and for the study of the amorphous structure. To get a better answer to these open questions, a detailed study of the behaviour of hydrogen in amorphous and microcrystalline Co33Zr67 is necessary. Such work is in progress. If the anelastic relaxation process responsible for the observed internal friction behaviour could then be identified, it could be used as a probe to study both amorphous and microcrystalline materials.
476
AMORPHOUS Co-Zr
Vol.
23, No. 4
Acknowledgement Some parts of this work have been supported by the Deutsche Forschungsgemeinschaft. References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
(12) (13) (14) (15)
M.R.J. Gibbs, J.E. Evetts and J.A. Leake, J.Mat.Sci 18, 278 (1983). H.U. Kiinzi, K. Agyeman and H.-J. G~intherodt, Solid--State Comm. 32, 711 (1979). K. Agyeman, E. Armbruster, H.U. K~inzi, A. Das Gupta and H.-J. G~-ntherodt, J. de Physique 42, C5-535 (1981). B.S. Berry and W.C. Pritchet, Scripta Met. 15, 637 (1981). O. Yoshinari, M. Koiwa, A. Inoue and T. Mas-umoto, Acta Met. 31, 2063 (1983). B.S. Berry and W.C. Pritchet, in: Nontraditional Methods in D1~[fusion, eds. G.E. Murch, H.K. Birnbaum and J.R. Cost, The Metallurgical Society of AIME, Warrendale/Pa. 1984, pp. 83-109. U. Stolz, M. Weller and R. Kirchheim, Scripta Met. 20, 1361 (1986). H.-R. Sinning, E. Woldt and F, Hae~ner, Mat.Sci.Eng797, 501 (1988). A.S. Nowick and B.S. Berry, Anelastic Relaxation in C--rystalline Solids, Academic Press, New York 1972. H.-R. Sinning, to be published. K.H.J. Buschow, J. Less C o m m o n Metals 85, 221 (1982) and J.Phys.F: Metal Physics 14, 593 (1984). K. Jansson, M. Nygren and A. ~Jstiund, Mat.Res.Bu11. 19, 1091 1984). M. Blank-Bewersdorff and U. KSster, Mat.Sci.Eng. 9/7, 313 (1988) M. Nicolaus, current research. B.S. Berry, Acta Met. _7, 741 (1959).
Vol. 23, pp. 471-476, 1989 Printed in the U.S.A.
AN INTERNAL FRICTION PEAK IN A M O R P H O U S
Pergamon Press plc All rights reserved
AND M I C R O C R Y S T A L L I N E
C033Zr~7
H.-R. Sinning, M. Nicolaus and F. Hae~ner Institut f~ir Werkstoffe, Technische Universitit Braunschweig, FR Germany (Received October 19, 1988) (Revised January 14, 1989) i. Introduction Although it is now widely accepted that atomic rearrangements within the amorphous structure of metallic glasses (e.g., during structural relaxation) can in general be described by a broad spectrum of activation energies (i), studies of the internal friction of these materials have often shown a well-defined peak at temperatures near or below room temperature (2-7). Recently, we have also discovered such a peak in amorphous Co3sZr6~ (8). Like in crystalline solids, a single (average) activation energy can be determined from these peaks in the usual way (9) by evaluating the change of the peak temperature with frequency. Most of these internal friction peaks have been associated with the thermally activated motion of hydrogen atoms as "interstitials" in the amorphous structure, in a way similar to the well-known Snoek relaxation of interstitials in bcc metals. However, based on the results for some binary metal-metal glasses, it has also been argued that such a relaxation effect may be intrinsic in the amorphous structure itself (Z). On the other hand, in crystalline metallic materials a Shock relaxation is usually observed only for heavier interstitials like carbon, nitrogen or oxygen but not for hydrogen (6). A rare exception from this rule is the alloy Pde2Sils, where a short-range reorientation (i.e. Snoek-type) relaxation of hydrogen has been found both in the amorphous state and after crystallization of the palladium silicide PdQSi 2 (with an orthorhombic defect structure based on Pd3Si ) (6). The position, height and shape of the internal friction peaks in Pds2Si18 in the amorphous and crystalline states are however very different from each other. In the present paper, new internal friction results on the alloy Co33Zre7 are presented which show for the first time a peak with nearly the same properties both in the amorphous and in the microerystalline state. Provided the microscopic mechanism underlying this surprising behaviour can be identified, interesting consequences for the understanding of the amorphous as well as of the microcrystalline structure can he expected from this observation. 2. Experimental A 2ram wide and about 35 pm thick amorphous ribbon of composition CossZrs7 was produced by melt-spinning under vacuum.* The amorphous and crystalline states of the material as well as the crystallization reactions were characterized using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The internal friction was obtained from the damping of flexural vibrations measured in a vibrating-reed apparatus with electrostatic ,excitation and a HF detection circuit. These measurements were performed under vacuum with the specimen clamped in a fixed holder at one end ("clamped-free" or "cantilever" mode of flexural vibration). As in this configuration thermal gradients along the specimen cannot be avoided completely, a temperature correction was applied to those internal friction data that were obtained by using harmonics. Without such a correction, the different distribution of strain along the specimen in the different vibration modes can " The production of the amorphous material was carried out at the "Kristallabor der physikalischen Institute" at the University of G~ttingen.
471 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
472
AMORPHOUS
Co-Zr
Vol.
23, No. 4
lead to a systematic error in the measured shift of the peak temperature with frequency and thus in activation energy (see below). The correction was obtained by comparing the fundamental mode of a short specimen with higher vibration modes of longer specimens at the same frequency; details of this procedure will be given elsewhere (I0). The heat treatments were performed in the vibrating-reed apparatus; the resonance frequency of the vibration was used to monitor the structural relaxation and crystallization reactions during these treatments. 3. Results
290
f[Hz] 280
FIG.I Change of the resonance frequency of a vibrating reed of Co33Zr67 during heating with 2 K/rain through crystallization. The arrows I and II indicate the positions of the two exothermic peaks obtained calorimetrically at the same heating rate.
270
260 250 T
2/,0 300
I
i
I
~oo
soo
600
I
~oo
I
T[K]
eoo
To characterize the thermal behaviour of the as-quenched Co33Zre7 glass, Fig.l shows the change of the resonance frequency (due to the change of the elastic modulus) of a vibrating sample during heating with a constant heating rate of 2 K/min, together with the positions of two exothermic peaks (I and If) obtained in DSC. Whereas the slow increase of the frequency between 400 and 650 K is due to structural relaxation of the amorphous alloy, the following sharp steps at the positions of the DSC peaks indicate two reactions corresponding to the crystallization of the material. Detailed studies of these reactions (ii14) have shown that the first one (1) is identical with the polymorphic crystallization of (metastable) CoZr 2 (with some differences with respect to the question of whether the
FIG.2 Dark field electron mlcrograph (left) and diffraction pattern (right) of Co33Zrs7 after a heat treatment of 20 rain at 693 K.
Vol.
23, No.
4
AMORPHOUS
Co-Zr
473
resulting phase is tetragonal or cubic), whereas the second one (II) is due to a transformation within the crystalline state. After completion of the first reaction, the material is fully crystalline (12) and shows an extremely small grain size of about i0 n m difficult to detect even in T E M (14). An example for this microstructure is given in Fig.2. The internal friction peak of this alloy has been extensively studied at different frequencies and after different heat treatments; typical examples are shown in Figs.3 and 4. It is seen from Fig.3 that the peak remains nearly unaffected by heat treatments as long as the material is amorphous, even though considerable structural relaxation takes place in this range (Fig.l). A surprising result is, however, the fact that the peak is still existing after heating to 723 K, when the material has passed the first crystallization reaction and is microcrystalline (Fig.2). The peak is then only shifted by about 15 to 20 K to higher temperatures and somewhat reduced in height. However, this difference becomes smaller at higher frequencies as in the amorphous state a decrease of the peak height with increasing frequency is observed (Fig.4). (A similar behaviour has also been observed by Agyeman et al. (3) for the hydrogen peak in glassy Ni24ZrTs; an explanation for this effect is still missing.)
Heat treatment:
/ / ",k
---::'< 3 x
9
..... ........
FIG.3 Internal friction peak in Co33Zrs7 at a frequency of f=100 Hz after subtraction of the background and after different heat treatments (linear heating with 1 K/rain up to the temperatures indicated). The three upper curves correspond to the amorphous state, whereas after heating to 723 K the material is microcrystalline.
sn K
I.i
\~\
Ii
723 K
.,.-.:~.%.(...
I
,02 •~
./
"._
"\ -...
......<:."....~,'-"
/
\<.,,. -..,,/
200
TIK]
300
4
~3 K
/
i
"02
I
1 0
~.-
150
, 200
/
/
I
/
/'%593 ~'"~%3283 Hz (o)
/
l
!\,,. b"
~ ...~.
/.,~.~ .,~'4.J" (~:3592Hz /..~ ....,r.~ss2 ,'... ./ ,'.:>%~I07~ .\ \'...
FIG.4 Frequency dependence of the internal friction in the amorphous (a) and microcrystalline (c) state.
(c)
F
,Z' ,Yi %\ ~ - ,"....
\x ',":.",, '.....
\ \ \,',,, ..
.
~ 250
k\.
~ 300
,,
'".,
350
400
,,,
-... T[K]
450
474
AMORPHOUS
Co-Zr
Vol.
Z3, No.
The average activation energy E= and the preexponential time constant to of the internal friction peak have been obtained by the usual frequency shift method (9) from the AzThenius plot shown in Fig.5. The results for the various different heat treatments in the amorphous state (i.e. different amounts of structural relaxation) cannot be distinguished from each other. As the scatter is much larger for "as-quenched" specimens, the values obtained on "relaxed" samples give a more reliable characterization of the amorphous state. It should be noted from Fig.5 that the difference in E= and to between the amorphous and the microcrystalline state is very small and within the experimental scatter. It is therefore not possible to say which of these parameters has in fact changed by a very small amount to produce the small shift of the internal friction peak in temperature observed after crystallization in Fig.3. First attempts to look for dissolved hydrogen as a possible origin of the internal friction peak in Co33Zrs7 did not give a clear result: by heat extraction, certain amounts of hydrogen (0.3 at% at maximum) were indeed found, but only after extreme heating up to 1600"C. However, we do not know whether this hydrogen was really dissolved in the amorphous or microcrystalline matrix. After a more moderate heating of the samples, no hydrogen could be detected at all.
%[K]
340 -6
,
,
,
300
,
280
,
,
In "t"
,,,
,,,,,4(
-7
,. /,"
-8
,,"
/
,"
,,"
,
S/~
/
o /^/
/,o,
O o
~/•
o Z~
/~// O
//
o J/./ / // ,,
3.2
3.4
3.6
lO}'tp[K-']
"as-quenched" state (Ea=0.420 eV, ~o=i.i •10-Zls) "relaxed" amorphous state (different heat treatments between 373 and 673 K; Ea=0.465 eV, ~o=2.2-i0-IIs)
#/#
3.0
FIG.5 Arrhenius plot of the relaxation time t = i/2]rf against the reciprocal peak temperature i/Tp after different heat treatments:
o/// ,F? .//
// -9
260
,
3.8
microcrystalline state (1 K/min to 723 K; Ea=0.475 eV, ro=3.4.10-Z2s)
4
Vol.
23, No.
4
AMORPHOUS
Co-Zr
475
4. Discussion The observation of so closely related internal friction peaks described by almost the same average activation energy and preexponential factor both in amorphous and microcrystaline Cos3Zrs7 strongly suggests that in both cases the same anelastic relaxation mechanism is operating, This can be assumed to be an atomic rearrangement interacting with the applied stress by an anisotropic elastic distortion (9). It is remarkable that this rearrangement is obviously the same in an amorphous as well as in a microcrystalline material. This can already be stated as an important result of this study: apparently there are relaxation centers in the material which have almost identical local atomic surroundings both in the amorphous and in the microcrystalline state. With respect to the microscopic nature of the relaxation mechanism, there are two principal possibilities to be discussed: a rearrangement of the Co and Zr atoms themselves, i.e. a stress-induced directional short range ordering. In crystalline alloys, this could be the Zener relaxation (9), but also more complicated processes like that proposed by Berry for age-hardened A1 alloys (15) (based on clusters with built-in excess vacancies). Similar mechanisms can be imagined for amorphous alloys as well. the thermally activated motion of impurities dissolved as "interstitials" in the amorphous or microcrystalline matrix. This would then probably be hydrogen as those internal friction p h e n o m e n a in metallic glasses that are k n o w n to be due to hydrogen (3-7) are very similar to the peak observed here. Within the same class of materials, it seems unlikely that heavier "interstitials" like oxygen could give rise to a relaxation effect in the same temperature range and with similar activation parameters as hydrogen. At present it is not yet possible to decide between these two possibilities as the experimental evidence is too small: For the first, intrinsic process we do not k n o w of any examples on comparable systems from the literature with clear evidence with respect to the relaxation mechanism. From the values of the activation energy, a mechanism involving excess vacancies or free volume seems more likely than the normal Zener relaxation (9,15). With respect to the hydrogen mechanism, the activation energy does also fit well to the values k n o w n for the amorphous state from the literature (3-7). The frequency factor ~o -I is somewhat lower than the literature values; however, this comparison is very sensitive to the applied temperature gradient correction (i0) and therefore has to be examined more critically from the experimental side. The stability of the peak against annealing is in contrast to observations on the hydrogen peak in Pd- and Fe-based glasses (3,4); a similar behaviour has been used by K~inzi et.al. (2) as an argument against the hydrogen mechanism. Nevertheless, an explanation of our results by hydrogen is possible by assuming that both the desorption of hydrogen from the Co-Zr glass is prevented and the local atomic configuration and symmetry around a hydrogen atom is insensitive to structural relaxation of the amorphous material. The most unexpected feature of the observed internal friction peak with respect to the hydrogen mechanism is however the fact that it appears also in the microcrystalline state, with the same kinetic parameters (in contrast to Pd82Si18 (6)). If hydrogen were responsible for this effect, this would be an outstanding result both for the relaxation of point defects in crystalline materials and for the study of the amorphous structure. To get a better answer to these open questions, a detailed study of the behaviour of hydrogen in amorphous and microcrystalline Co33Zr67 is necessary. Such work is in progress. If the anelastic relaxation process responsible for the observed internal friction behaviour could then be identified, it could be used as a probe to study both amorphous and microcrystalline materials.
476
AMORPHOUS Co-Zr
Vol.
23, No. 4
Acknowledgement Some parts of this work have been supported by the Deutsche Forschungsgemeinschaft. References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
(12) (13) (14) (15)
M.R.J. Gibbs, J.E. Evetts and J.A. Leake, J.Mat.Sci 18, 278 (1983). H.U. Kiinzi, K. Agyeman and H.-J. G~intherodt, Solid--State Comm. 32, 711 (1979). K. Agyeman, E. Armbruster, H.U. K~inzi, A. Das Gupta and H.-J. G~-ntherodt, J. de Physique 42, C5-535 (1981). B.S. Berry and W.C. Pritchet, Scripta Met. 15, 637 (1981). O. Yoshinari, M. Koiwa, A. Inoue and T. Mas-umoto, Acta Met. 31, 2063 (1983). B.S. Berry and W.C. Pritchet, in: Nontraditional Methods in D1~[fusion, eds. G.E. Murch, H.K. Birnbaum and J.R. Cost, The Metallurgical Society of AIME, Warrendale/Pa. 1984, pp. 83-109. U. Stolz, M. Weller and R. Kirchheim, Scripta Met. 20, 1361 (1986). H.-R. Sinning, E. Woldt and F, Hae~ner, Mat.Sci.Eng797, 501 (1988). A.S. Nowick and B.S. Berry, Anelastic Relaxation in C--rystalline Solids, Academic Press, New York 1972. H.-R. Sinning, to be published. K.H.J. Buschow, J. Less C o m m o n Metals 85, 221 (1982) and J.Phys.F: Metal Physics 14, 593 (1984). K. Jansson, M. Nygren and A. ~Jstiund, Mat.Res.Bu11. 19, 1091 1984). M. Blank-Bewersdorff and U. KSster, Mat.Sci.Eng. 9/7, 313 (1988) M. Nicolaus, current research. B.S. Berry, Acta Met. _7, 741 (1959).