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Rapid annealing of metallic glasses under tension
Journal of Magnetism and Magnetic Materials 92 (1990) 181-184 North-Holland
181
Rapid annealing of metallic glasses under tension i~. K i s d i - K o s z 6 , L. P o t o c k #
a,
M. Hrab~.fik b, L. N o v f i k b a n d A. L o v a s
Central Research Institute for Physics H.1525 Budapest, P.O. Box 49. Hungao' P.J. Safjrik University, ndm. Februdrovdho vit. 9, 04154 Ko~iceo Czechoslovakia b Institute of Experimental Physics, ndm. Februdtrov$ho v|t. 9, 04154 Ko~ice. Czechoslovakia
Received 12 April 1990; in revised form 21 June 1990
Pulse heat treatment using 0.4 s current pulses was applied to FesoBlaSi6 amorphous ribbons above its Curie temperature in order to avoid magnetically induced anisotropy. After relaxation the pulse heat treatment was continued while applying 128
MPa mechanical stress to obtain induced anisotropy. The results of pulse annealing were monitored by coercive force and effective anisotropy measurements carried out between the pulses at room temperature. It is shown that pu!se annealing enables a magnetically soft relaxed state to be a0=hieved and if mechanical stress is applied during the process, induced aldsotropy can be developed.
1. Introduction
T h e magnetic properties of ferromagnetic lnetallic glasses can be varied by applying different heat a n d / o r mechanical treatments. If mechanical stress is applied during pulse heat treatment a large increase in induced anisotropy can be expected [1]. According to Lanotte et al. [2] and T a u b [3] pulse annealing reduces internal stresses and improves the magnetic properties. But higher temperature can also induce stresses as a consequence of the rapid heating and cooling or as the result of the onset of crystallization. There are several techniques for pulse annealing: passing the ribbon over a hot body [4] or over a quartz line heater [3]; using a continuous laser beam through which the ribbon can be moved [2]; usil~g infrared heat pulses [5] or electrical current pulse heating [6-8]. In this work current pulses were applied because this m e t h o d has some advantages for investigating the results of pul~,e heat treatment, viz. the pulse length can easily be controlled over a very wide time scale and heating is effective throughout the whole cross-section.
Another advantage is that the magnetization measurements can be performed in the same apparatus as the pulse heat treatments. If short current pulses are used for heating it is necessary to use high currents which have their own magnetic field perpendicular to the current direction [9]. This magnetic field perpendicular to the ribbon axis would induce transversal magnetic anisotropy if the pulse heat treatment is carried out below Tc. This transversal anisotropy would counteract the longitudinal one induced by the mechanical stress. Therefore it is really important which temperature is chosen. A magnetically soft state can be obtained by combining pulse heat treatment with applied mechanical stress. Pulse heat treatment can avoid crystallization also at very high applied peak temperatures. It does not affect the Curie temperature. Tc (except the relaxation effect which modifies Tc by only a few degrees centigrade). Using sufficiently short pulses, heat treatment can be provided at temperatures above the Curie temperature even in those metallic glasses which would crystallize at conventional heat treatments above
0304-8853/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)
182
~7. Kisdi-Koszb et aL / Rapid annealing of metallic glasses
T c . In this way one can achieve pure stress-induced anisotropy without the influence of any external or internal magnetic fields. Applied mechanical stress modifies the magnetization curve as was shown by Egami et al. [10] and Vfizquez et al. [11].
T
(K)I 800~ 7001
2. Experimental procedures
600
FesoB14Si6 metallic glass ribbons (which have large magnetostriction) were prepared by the spinning wheel method, their amorphousness was checked by X-ray diffraction. The magnetic measurements were performed on straight ribbons using a magnetometer with FiSrster probes. Pulse heating and magnetization measurements were carried out in the same sample holder. Magnetostriction was measured by the small angle magnetization rotation (SAMR) method. The pulse heat treatment was as follows: about 10 A, 50 Hz electrical current pulses were passed through a 6 mm wide, about 30 ~m thick, metallic glass ribbon. Such a current produces a transverse magnetic field of ---800 A / m on the surface of the ribbon - the field decreases to zero in the midplane - so some transversal anisotropy could be induced by this magnetic field if the heat treatment is below T c . The duration of the ac current pulse was 0.4 s. The time dependence of the ribbon's mean temperature during such a current pulse is schematically shown in fig. 1. The maximum value of the curve is called T~,, the annealing temperature. The sample was heat treated in air without forced cooling therefore the estimated cooling rate is one order smaller ( = 100 K / s ) than the heating rate ( = 1000 K/s). One of the greatest problems in pulse heat treatment investigations is to determine the temperature of the sample during the pulse. Since u l l e c t m e a s u r e i l i e i i [ is Llllli~Ull.a'~. ee'- for tecnnlcal"'"' reasons, we accepted a simple method to set the required temperature. This method is reproducible, though it may have a large systematic error. This method is the following: the resistivity of the as-quenched sample was measured and the current was adjusted by equating the electrical power times
500
300 0
tls)
Fig. 1. Time dependence of the mean temperature of the amorphous ribbon during a current pulse.
the pulse length to the thermal energy needed for the sample to reach the required Ta. Heat losses due to radiation and conduction were not taken into account and the uneven temperature distribution of the ribbon was also ignored, so Ta is surely overestimated. A series of short electrical current pulses were applied to a 10 cm long ribbon. After each high temperature pulse the sample was allowed to cool to room temperature and the coercive force, H~ and effective anisotropy, Kef f w e r e determined from the magnetization curve (the latter as the energy required to reach saturation). The electrical resistivity was also monitored to ensure that no crystallization occurred. After relaxation, pulse heat treatment was continued while applying 128 MPa tensile stress.
3. Results and discussion "-rl_
_
~
•
_
t ne t, une and crystamzauon" "" temperatures of the investigated metallic glass were determined from the thermomagnetic curve: T c = 680 K, Tcryst = 790 K. With short pulses, amorphous alloys can be heat treated at much higher temperatures without crystallization than with conventional heat treatments. To estimate the onset of crystallization
~2. Kisdi-Koszb et al. / Rapid annealin~ of metallic glasses
temperature, we extrapolated the T~yst versus ln(ta) straight line (t, is the annealing time) determined for 10% crystallization by isothermal electrical resistance measurements [12] for Uae alloy in question. It was found that with one 0.4 s pulse no crystallization occurred till T~---900 K. As we wished to avoid crystallization after several pulses we chose a much lower annealing temperature, T~ --- 760 K. Applying a series of pulses without other magnetic field or mechanical stress the variation of H~. with the number of pulses, N shows that relaxation takes place during the first few pulses, when the coercive force decreases rapidly (see fig. 2). It then attains a practically constant and relatively low value. This small coercive force of 4 A / m shows the magnetic softness of the F e - S i - B metallic glass after pulse annealing. Because the accuracy of the estimation of T,, is not very high, it was advisable to verify wether the Ta > Tc condition is fulfilled. After relaxation, several heat pulses were applied to the sample in a longitudinal magnetic field of H = 4 k A / m with no effect on H c (and Kerr). Therefore it could be concluded that Ta is higher than the Curie temperature. This also verifies that, in spite of the not very high cooling rate, the applied longitudinal magnetic field could not induce measurable anisotropy during cooling down through Tc.
183
"1
[A/m)
,2 t /
~, /
10
H=0
H= 4kA/m
I
w I I
6
I
I I
I
I
I [ I I
2 l
0
20
l
Z,0
l
i
-.
169
l
80
N
Fig. 2. Coercive force as a function of the number of applied current pulses.
Taking another sample, after relaxation heat treatment, tensile stress was applied and the pulse heat treat,~,ent was continued. The coercive force decreased, then remained constant and in this case also. no significant change could be observed due to the application of tensile stress.
Keff
{kjm'3)t
~:128MPo
1.2 6"--O O 0 O 0 OOOeo00000OO0000
0.8 0.6
I
t00
~e
0
0
a
0
@ @ 0
0
@ @ @ @ @ 0
@ @ B
@ 0
@
07,
0.2
Fig. 3. Effective anisotropy constant versus number of pulses during relaxation and stress annealing
E. Kisdi-Koszb et al. / Rapid annealing of metallic glasses
184
J(T) [ ..,..
I
--6.8
I
'~
-3.4
'
I
I
6.8
H(kAlm)
°°~I
cause stress was also applied during the measurements. In fig. 4 the effect of applied tensile stress on the magnetization curve is shown. F r o m that we estimated the decrease of effective anisotropy constant due to 85 M P a applied stress during measurement to be 51%. Thus, the induced anisotropy is about 170 J / m 3, which is a resonable value. From fig. 3 it can also be seen that after the first pulse the change is very slow. This is in agreement with the observation of Kraus et al. [13], who showed, using conventional heat treatment, that pre-annealing generally reduces the anisotropy induced by subsequent stress annealing because it slows down the kinetics.
References Fig. 4. Magnetization curve of as-quenched sample (full line), after relaxation due to 10 pulses (dashed line) and of the same sample measured under a tensile stress of 85 MPa (dotted line). In fig. 3 the change of Keff is shown during relaxation and stress annealing. The effective anisotropy constant also decreased during relaxation and the magnetization curve became steeper (see fig. 4). This supports the idea that using pulse heat treatment, good magnetic softness can be achieved by removing the quenched-in stresses. If tensile stress is applied, Kef f decreases further showing that stress-induced longitudinal anisotropy is developed (the magnetization curve is almost squared). The measured saturation magnetostriction of this material is very high, 41.1 × 10 -6. The total change of Kef f due to the applied tensile stress during pulse annealing and measurement is about 340 J / m 3. The initial change on application of tensile stress is the major part (290 J / m 3) of the total change but that is partly be-
[I] J. Gonzhlez, M. Vhzquez, J.M. Barandiarfin,V. Madurga and A. Hernando, J. Magn. Magn. Mat. 68 (1987) 151. [2] L. Lanotte, P. Matteazzi and V. Tagliaferri, J. Magn. Magn. Mat. 42 (I984) 183. [3] A.J. Taub, IEEE Trans. Magn. M A G - 2 0 (1984) 564. [4] H. Senno, H. Sakakima, Y. Yanagiuchi, T. Inoue, M. Yamaguchi and E. Hirota, U S Patent 4 288 260 (8 September 1981). [5] A. Mitra and S.K. Ghatak, J. Magn. Magn. Mat. 74 (1988) 285. [6] T. Jagielinski,IEEE Trans. Magn. M A G - 1 9 (1983) 1925. [7] M.R.J. Gibbs, D.-H. Lee and J.E. Evetts, IEEE Trans. Magn. M A G - 2 0 (1984) 1373.
[8] A. Zaluska, D. Zaluski, R. Petryk, P.G. Zielinski and H. Matyja, Rapidly Quenched Metals, eds. S. Steeb and H. Warlimont (North-Holland, Amsterdam, 1985)p. 235. [9] J.D. Livingston, W.G. Morris and T. Jagielinski, J. Appl. Phys. 55 (1984) 1790. [10] T. Egami, P.J. Flanders and C.D. Graham, AIP Conf. Proe. 24 (1974) 697. [11] M. V~quez, W. Fernengei and H. Kronmiiller, Phys. Star. Sol. (a) 80 (1983) 195. [12] J. T6th, Mater. Res. Bull. 13 (1978) 691. [13] L. Kraus, N. Z:~rubovfi, K. Zhv~ta and P. Duhaj, J. Magn. Magn. Mat. 72 (1988) 199.
181
Rapid annealing of metallic glasses under tension i~. K i s d i - K o s z 6 , L. P o t o c k #
a,
M. Hrab~.fik b, L. N o v f i k b a n d A. L o v a s
Central Research Institute for Physics H.1525 Budapest, P.O. Box 49. Hungao' P.J. Safjrik University, ndm. Februdrovdho vit. 9, 04154 Ko~iceo Czechoslovakia b Institute of Experimental Physics, ndm. Februdtrov$ho v|t. 9, 04154 Ko~ice. Czechoslovakia
Received 12 April 1990; in revised form 21 June 1990
Pulse heat treatment using 0.4 s current pulses was applied to FesoBlaSi6 amorphous ribbons above its Curie temperature in order to avoid magnetically induced anisotropy. After relaxation the pulse heat treatment was continued while applying 128
MPa mechanical stress to obtain induced anisotropy. The results of pulse annealing were monitored by coercive force and effective anisotropy measurements carried out between the pulses at room temperature. It is shown that pu!se annealing enables a magnetically soft relaxed state to be a0=hieved and if mechanical stress is applied during the process, induced aldsotropy can be developed.
1. Introduction
T h e magnetic properties of ferromagnetic lnetallic glasses can be varied by applying different heat a n d / o r mechanical treatments. If mechanical stress is applied during pulse heat treatment a large increase in induced anisotropy can be expected [1]. According to Lanotte et al. [2] and T a u b [3] pulse annealing reduces internal stresses and improves the magnetic properties. But higher temperature can also induce stresses as a consequence of the rapid heating and cooling or as the result of the onset of crystallization. There are several techniques for pulse annealing: passing the ribbon over a hot body [4] or over a quartz line heater [3]; using a continuous laser beam through which the ribbon can be moved [2]; usil~g infrared heat pulses [5] or electrical current pulse heating [6-8]. In this work current pulses were applied because this m e t h o d has some advantages for investigating the results of pul~,e heat treatment, viz. the pulse length can easily be controlled over a very wide time scale and heating is effective throughout the whole cross-section.
Another advantage is that the magnetization measurements can be performed in the same apparatus as the pulse heat treatments. If short current pulses are used for heating it is necessary to use high currents which have their own magnetic field perpendicular to the current direction [9]. This magnetic field perpendicular to the ribbon axis would induce transversal magnetic anisotropy if the pulse heat treatment is carried out below Tc. This transversal anisotropy would counteract the longitudinal one induced by the mechanical stress. Therefore it is really important which temperature is chosen. A magnetically soft state can be obtained by combining pulse heat treatment with applied mechanical stress. Pulse heat treatment can avoid crystallization also at very high applied peak temperatures. It does not affect the Curie temperature. Tc (except the relaxation effect which modifies Tc by only a few degrees centigrade). Using sufficiently short pulses, heat treatment can be provided at temperatures above the Curie temperature even in those metallic glasses which would crystallize at conventional heat treatments above
0304-8853/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)
182
~7. Kisdi-Koszb et aL / Rapid annealing of metallic glasses
T c . In this way one can achieve pure stress-induced anisotropy without the influence of any external or internal magnetic fields. Applied mechanical stress modifies the magnetization curve as was shown by Egami et al. [10] and Vfizquez et al. [11].
T
(K)I 800~ 7001
2. Experimental procedures
600
FesoB14Si6 metallic glass ribbons (which have large magnetostriction) were prepared by the spinning wheel method, their amorphousness was checked by X-ray diffraction. The magnetic measurements were performed on straight ribbons using a magnetometer with FiSrster probes. Pulse heating and magnetization measurements were carried out in the same sample holder. Magnetostriction was measured by the small angle magnetization rotation (SAMR) method. The pulse heat treatment was as follows: about 10 A, 50 Hz electrical current pulses were passed through a 6 mm wide, about 30 ~m thick, metallic glass ribbon. Such a current produces a transverse magnetic field of ---800 A / m on the surface of the ribbon - the field decreases to zero in the midplane - so some transversal anisotropy could be induced by this magnetic field if the heat treatment is below T c . The duration of the ac current pulse was 0.4 s. The time dependence of the ribbon's mean temperature during such a current pulse is schematically shown in fig. 1. The maximum value of the curve is called T~,, the annealing temperature. The sample was heat treated in air without forced cooling therefore the estimated cooling rate is one order smaller ( = 100 K / s ) than the heating rate ( = 1000 K/s). One of the greatest problems in pulse heat treatment investigations is to determine the temperature of the sample during the pulse. Since u l l e c t m e a s u r e i l i e i i [ is Llllli~Ull.a'~. ee'- for tecnnlcal"'"' reasons, we accepted a simple method to set the required temperature. This method is reproducible, though it may have a large systematic error. This method is the following: the resistivity of the as-quenched sample was measured and the current was adjusted by equating the electrical power times
500
300 0
tls)
Fig. 1. Time dependence of the mean temperature of the amorphous ribbon during a current pulse.
the pulse length to the thermal energy needed for the sample to reach the required Ta. Heat losses due to radiation and conduction were not taken into account and the uneven temperature distribution of the ribbon was also ignored, so Ta is surely overestimated. A series of short electrical current pulses were applied to a 10 cm long ribbon. After each high temperature pulse the sample was allowed to cool to room temperature and the coercive force, H~ and effective anisotropy, Kef f w e r e determined from the magnetization curve (the latter as the energy required to reach saturation). The electrical resistivity was also monitored to ensure that no crystallization occurred. After relaxation, pulse heat treatment was continued while applying 128 MPa tensile stress.
3. Results and discussion "-rl_
_
~
•
_
t ne t, une and crystamzauon" "" temperatures of the investigated metallic glass were determined from the thermomagnetic curve: T c = 680 K, Tcryst = 790 K. With short pulses, amorphous alloys can be heat treated at much higher temperatures without crystallization than with conventional heat treatments. To estimate the onset of crystallization
~2. Kisdi-Koszb et al. / Rapid annealin~ of metallic glasses
temperature, we extrapolated the T~yst versus ln(ta) straight line (t, is the annealing time) determined for 10% crystallization by isothermal electrical resistance measurements [12] for Uae alloy in question. It was found that with one 0.4 s pulse no crystallization occurred till T~---900 K. As we wished to avoid crystallization after several pulses we chose a much lower annealing temperature, T~ --- 760 K. Applying a series of pulses without other magnetic field or mechanical stress the variation of H~. with the number of pulses, N shows that relaxation takes place during the first few pulses, when the coercive force decreases rapidly (see fig. 2). It then attains a practically constant and relatively low value. This small coercive force of 4 A / m shows the magnetic softness of the F e - S i - B metallic glass after pulse annealing. Because the accuracy of the estimation of T,, is not very high, it was advisable to verify wether the Ta > Tc condition is fulfilled. After relaxation, several heat pulses were applied to the sample in a longitudinal magnetic field of H = 4 k A / m with no effect on H c (and Kerr). Therefore it could be concluded that Ta is higher than the Curie temperature. This also verifies that, in spite of the not very high cooling rate, the applied longitudinal magnetic field could not induce measurable anisotropy during cooling down through Tc.
183
"1
[A/m)
,2 t /
~, /
10
H=0
H= 4kA/m
I
w I I
6
I
I I
I
I
I [ I I
2 l
0
20
l
Z,0
l
i
-.
169
l
80
N
Fig. 2. Coercive force as a function of the number of applied current pulses.
Taking another sample, after relaxation heat treatment, tensile stress was applied and the pulse heat treat,~,ent was continued. The coercive force decreased, then remained constant and in this case also. no significant change could be observed due to the application of tensile stress.
Keff
{kjm'3)t
~:128MPo
1.2 6"--O O 0 O 0 OOOeo00000OO0000
0.8 0.6
I
t00
~e
0
0
a
0
@ @ 0
0
@ @ @ @ @ 0
@ @ B
@ 0
@
07,
0.2
Fig. 3. Effective anisotropy constant versus number of pulses during relaxation and stress annealing
E. Kisdi-Koszb et al. / Rapid annealing of metallic glasses
184
J(T) [ ..,..
I
--6.8
I
'~
-3.4
'
I
I
6.8
H(kAlm)
°°~I
cause stress was also applied during the measurements. In fig. 4 the effect of applied tensile stress on the magnetization curve is shown. F r o m that we estimated the decrease of effective anisotropy constant due to 85 M P a applied stress during measurement to be 51%. Thus, the induced anisotropy is about 170 J / m 3, which is a resonable value. From fig. 3 it can also be seen that after the first pulse the change is very slow. This is in agreement with the observation of Kraus et al. [13], who showed, using conventional heat treatment, that pre-annealing generally reduces the anisotropy induced by subsequent stress annealing because it slows down the kinetics.
References Fig. 4. Magnetization curve of as-quenched sample (full line), after relaxation due to 10 pulses (dashed line) and of the same sample measured under a tensile stress of 85 MPa (dotted line). In fig. 3 the change of Keff is shown during relaxation and stress annealing. The effective anisotropy constant also decreased during relaxation and the magnetization curve became steeper (see fig. 4). This supports the idea that using pulse heat treatment, good magnetic softness can be achieved by removing the quenched-in stresses. If tensile stress is applied, Kef f decreases further showing that stress-induced longitudinal anisotropy is developed (the magnetization curve is almost squared). The measured saturation magnetostriction of this material is very high, 41.1 × 10 -6. The total change of Kef f due to the applied tensile stress during pulse annealing and measurement is about 340 J / m 3. The initial change on application of tensile stress is the major part (290 J / m 3) of the total change but that is partly be-
[I] J. Gonzhlez, M. Vhzquez, J.M. Barandiarfin,V. Madurga and A. Hernando, J. Magn. Magn. Mat. 68 (1987) 151. [2] L. Lanotte, P. Matteazzi and V. Tagliaferri, J. Magn. Magn. Mat. 42 (I984) 183. [3] A.J. Taub, IEEE Trans. Magn. M A G - 2 0 (1984) 564. [4] H. Senno, H. Sakakima, Y. Yanagiuchi, T. Inoue, M. Yamaguchi and E. Hirota, U S Patent 4 288 260 (8 September 1981). [5] A. Mitra and S.K. Ghatak, J. Magn. Magn. Mat. 74 (1988) 285. [6] T. Jagielinski,IEEE Trans. Magn. M A G - 1 9 (1983) 1925. [7] M.R.J. Gibbs, D.-H. Lee and J.E. Evetts, IEEE Trans. Magn. M A G - 2 0 (1984) 1373.
[8] A. Zaluska, D. Zaluski, R. Petryk, P.G. Zielinski and H. Matyja, Rapidly Quenched Metals, eds. S. Steeb and H. Warlimont (North-Holland, Amsterdam, 1985)p. 235. [9] J.D. Livingston, W.G. Morris and T. Jagielinski, J. Appl. Phys. 55 (1984) 1790. [10] T. Egami, P.J. Flanders and C.D. Graham, AIP Conf. Proe. 24 (1974) 697. [11] M. V~quez, W. Fernengei and H. Kronmiiller, Phys. Star. Sol. (a) 80 (1983) 195. [12] J. T6th, Mater. Res. Bull. 13 (1978) 691. [13] L. Kraus, N. Z:~rubovfi, K. Zhv~ta and P. Duhaj, J. Magn. Magn. Mat. 72 (1988) 199.