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Amorphous transition metal-zirconium alloys prepared by milling
Materials Science and Engineering, 97(1988) 133 135
133
Amorphous Transition Metal-Zirconium Alloys Prepared by Milling* A. W. WEEBER and H. BAKKER
Natuurkundig Laboratorium der Universiteit van Amsterdam, Valckenierstraat 65, NL-1018 XE Amsterdam (The Netherlands)
Abstract
As an example of the mechanical alloying process, we prepared amorphous Ni62Zr38 powder. From the X-ray diffraction patterns taken after different milling periods, it is concluded that the amorphous alloy is formed directly from the elements when a ball mill on a vibrating frame is used. We also succeeded in preparing amorphous VzgZr 71 by mechanical alloying. The crystallization of this material to different intermetallic compounds was observed using a high temperature Guinier-Lennk camera. I. Introduction
In previous papers [I-5], we have reported the preparation of amorphous transition metal-zirconium alloys by mechanical alloying and also by grinding the crystalline alloy. During mechanical alloying of the elemental powders, more or less alternating crystalline elemental layers are formed, which decrease in thickness during the milling process [4]. The amorphization reaction occurs by interdiffusion at the boundaries of these layers. In this picture the amorphization is similar to the amorphization of multilayered thin films during heating [6]. Not all transition metals form an amorphous alloy with zirconium by mechanical alloying. For example, tungsten does not react at all with zirconium, whereas the alloying of zirconium with silicon results in crystalline zirconium silicides [3]. Using our results and those of Hellstern and Schultz [7, 8], we found the following as criteria for the occurrence of the solid state amorphization reaction with zirconium as the larger atom [3]. (1) The system must exhibit a negative heat of mixing. (2) The metal-to-zirconium volume ratio must be less than 0.58. For this the volumes are to be corrected for the effect of alloying following the semiempirical model of Miedema and Niessen [9].
*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3-7, 1987. 0025-5416/88/$3.50
Furthermore we found that different ball-milling techniques result in different amorphization reaction paths [5]. When our planetary ball mill is used, crystalline intermetallic compounds appear as intermediate products in the amorphization reaction. In contrast, when a ball mill on a vibrating frame is applied, the amorphous alloy is formed directly from the elements. In this paper, we shall present as an example of the mechanical alloying process the formation of amorphous Ni62Zr38 using the vibrating-frame equipment. Also, results on the formation and crystallization of amorphous V29Zr71will be discussed. 2. Experimental procedures
The elemental powders were weighed and mixed in a glove box under purified argon. The milling was carried out in a hardened steel vial with a tungsten carbide bottom which we constructed ourselves; this was mounted on a vibrating frame. One hardened steel ball with a diameter of 6 cm was used. To avoid oxidation, the milling was carried out in an argon flux outside the glove box. X-ray diffraction patterns were taken by means of a Philips vertical powder diffractometer with Cu K~ radiation. A high' temperature film scan was made. using a Guinier-Lenn6 camera, and the heating rate was 10 K h -~. For this high temperature scan the powder was embedded in a graphite foil. To avoid oxidation, the scan was carried out in a vacuum of 10 -6 Torr. Differential scanning calorimetry (DSC) measurements were made using a Setaram D S C l l l ( 10 K min-1). 3. Results and discussion
The X-ray diffraction pattern of Ni-Zr powder with a nominal composition of 62 at.% Ni after several milling periods is given in Fig. 1. It is clearly visible that the intensity of the Bragg reflections decreases and that the broad peak of the amorphous alloy appears during mechanical alloying. (The crystalline peaks observed in the X-ray pattern after 70 h © Elsevier Sequoia/Printed in The Netherlands
134
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be noted that this is the first non-fast-diffusing system [10] in which the solid state amorphization reaction occurs. When V-Zr with a vanadium concentration of 50 at. % is mechanically alloyed, the Bragg reflections of vanadium are still visible. However, reducing the vanadium concentration to 29at.% results in an amorphous alloy without the Bragg reflections of the elements. The X-ray pattern of VE9Zr71after 140 h of mechanical alloying is shown in Fig. 2. The peak of the amorphous alloy with a maximum at K = 2.52 ~ - ~ is clearly visible. The small reflection at K = 3.12 ,~ ~could not be identified. The onset crystallization temperature of the amorphous V29Zr71 alloy, using a heating rate of 1 0 K m i n -~, is 895K. Figure 3 shows an X-ray scan with increasing temperature from 298 to 1273 K and a heating rate of 10 K h 1. The Bragg reflections that do not change in this temperature range originate from the graphite foil in which the amorphous powder is embedded. At low temperatures the broad band of the amorphous alloy is visible around K = 2.5/~-~. The first transition occurs around 750 K where, apart from the broad band of the amorphous alloy, weak lines from a crystalline compound become visible. These lines do not correspond to any of the compounds that are expected on the basis of the phase diagram [ 1l], i.e. :t-Zr o r VEZr. So, these lines are Bragg reflections from a probably metastable compound. The second transition is around 850 K. Here, the band of the amorphous alloy has almost disappeared. The lines appearing at this temperature are the Bragg reflections from ~-Zr, one of the products expected after crystallization. At the third transition, around 940 K, intense Bragg reflections appear. These lines also can-
,.o
K [A-'] Fig. 1. X-ray diffraction patterns of Ni62Zr38 after several milling periods: curve a, after 4.8 h; curve b, after 9 h; curve c, after 18 h; curve d, after 35.5 h; curve e, after 70 h.
of alloying are from tungsten carbide impurities from the bottom of the vial.) From the diffraction patterns, it can be concluded that the elements nickel and zirconium are transformed directly into the amorphous alloy. This reaction path is similar to that found by Hellstern and Schultz [7], but it differs from the reaction path in our planetary ball mili, where crystalline intermetallic compounds are intermediate products in the amorphization reaction [5]. Another system that obeys the criteria for the occurrence of the solid state amorphization reaction is V-Zr. As presented previously [3], we prepared amorphous V29Zr71 by mechanical alloying using the vibrating-flame apparatus as a milling tool. It should
V oo
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Fig. 2. X-ray diffraction pattern of amorphous 140 h of milling.
e.o
V29Zr71after
135 powder is lost. Figure 4 shows the X-ray diffraction pattern of a m o r p h o u s V29Zr71 after heating in an argon-filled quartz ampoule at 1273 K for 1 h. The peaks in the pattern (apart from some weak zirconia reflections) correspond to the lines on the film obtained using the Guinier-Lenn6 camera. F r o m the fact that no reflections o f both elemental vanadium and zirconium are present during and after heating, it must be concluded that vanadium and zirconium were really alloyed to an amorphous alloy during the milling.
1200-
1100-
1000
900-
800-
700-
4. Conclusions
600-
5001 L,00300
t 1
1 2
/ 3
I ~
I 5
K(~-~)
V29Zr71 using a
Fig. 3. High temperature X-ray scan of Guinier-Lenn6 camera.
not be identified and are p r o b a b l y due to metastable c o m p o u n d s too. At the last transition a r o u n d 1030 K the intensity o f the Bragg reflections appearing around 850 K ( o f ~-Zr) decreases and new reflections appear. This transition will be due to a transition o f zirconium. The new phase does not exhibit the b.c.c. structure, and so it is not the transition o f ~-Zr to fl-Zr. Because of the strong reflections of the graphite foil, some information of the eventually obtained
A m o r p h o u s Ni62Zr38 powder can be prepared by mechanical alloying. By using a ball mill mounted on a vibrating frame, elemental nickel and zirconium are directly transformed into the a m o r p h o u s alloy. Amorphous V29Zr71 could also be prepared by ball milling. F r o m the high temperature X-ray scan, it is concluded that amorphous V29Zr71 first crystallizes around 850 K to ~-Zr and a metastable V - Z r compound. Further heating to 1273 K results in the transition o f ~-Zr to an unidentified phase.
Acknowledgments
We thank Mr. A. C. Moleman for technical assistence. We are obliged to Dr. P. I. Loeff for helpful discussion and a critical reading of the manuscript.
References
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Fig. 4. X-ray diffraction pattern of amorphous heating at 1273 K for 1 h.
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V29Zr71after
1 A. W. Weeber, K. van der Meer, H. Bakker, F. R. de Boer, B. J. Thijsse and J. F. Jongste, J. Phys. F, 16 (1986) 1897. 2 A. W. Weeber, H. Bakker and F. R. de Boer, Europhys. Lett., 2(1986) 445. 3 A. W. Weeber and H. Bakker, Proc. 6th Int. Conf. on Liquid and Amorphous Metals, Garmisch-Partenkirchen, 1986, in Z. Phys. Chem., 156-157(1987). 4 A. W. Weeber, H. Bakker, H. J. M. Heijligers and G. F. Bastin, Europhys. Len., 3 (1987) 1261. 5 A. W. Weeber, A. J. H. Wester, W. J. Haag and H. Bakker, Physica B, 145(1987) 349. 6 R. B. Schwarz and W. L. Johnson, Phys. Bey. Lett., 51 (1983) 281. 7 E. Hellstern and L. Schultz, Appl. Phys. Lett., 48 (1986) 124. 8 E. Hellstern and L. Schultz, Proc. 6th Int. Conf. on Liquid and Amorphous Metals, Garmisch-Partenkirchen, 1986, in Z. Phys. Chem., 156-157 (1987). 9 A. R. Miedema and A. K. Niessen, Physica B, 114 (1982) 367. 10 R. P. Agarwale, S. P. Murarka and M. C. Anand, Acta Metall., 16 (1967) 61. I1 M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 1965, Fig. 682.
133
Amorphous Transition Metal-Zirconium Alloys Prepared by Milling* A. W. WEEBER and H. BAKKER
Natuurkundig Laboratorium der Universiteit van Amsterdam, Valckenierstraat 65, NL-1018 XE Amsterdam (The Netherlands)
Abstract
As an example of the mechanical alloying process, we prepared amorphous Ni62Zr38 powder. From the X-ray diffraction patterns taken after different milling periods, it is concluded that the amorphous alloy is formed directly from the elements when a ball mill on a vibrating frame is used. We also succeeded in preparing amorphous VzgZr 71 by mechanical alloying. The crystallization of this material to different intermetallic compounds was observed using a high temperature Guinier-Lennk camera. I. Introduction
In previous papers [I-5], we have reported the preparation of amorphous transition metal-zirconium alloys by mechanical alloying and also by grinding the crystalline alloy. During mechanical alloying of the elemental powders, more or less alternating crystalline elemental layers are formed, which decrease in thickness during the milling process [4]. The amorphization reaction occurs by interdiffusion at the boundaries of these layers. In this picture the amorphization is similar to the amorphization of multilayered thin films during heating [6]. Not all transition metals form an amorphous alloy with zirconium by mechanical alloying. For example, tungsten does not react at all with zirconium, whereas the alloying of zirconium with silicon results in crystalline zirconium silicides [3]. Using our results and those of Hellstern and Schultz [7, 8], we found the following as criteria for the occurrence of the solid state amorphization reaction with zirconium as the larger atom [3]. (1) The system must exhibit a negative heat of mixing. (2) The metal-to-zirconium volume ratio must be less than 0.58. For this the volumes are to be corrected for the effect of alloying following the semiempirical model of Miedema and Niessen [9].
*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3-7, 1987. 0025-5416/88/$3.50
Furthermore we found that different ball-milling techniques result in different amorphization reaction paths [5]. When our planetary ball mill is used, crystalline intermetallic compounds appear as intermediate products in the amorphization reaction. In contrast, when a ball mill on a vibrating frame is applied, the amorphous alloy is formed directly from the elements. In this paper, we shall present as an example of the mechanical alloying process the formation of amorphous Ni62Zr38 using the vibrating-frame equipment. Also, results on the formation and crystallization of amorphous V29Zr71will be discussed. 2. Experimental procedures
The elemental powders were weighed and mixed in a glove box under purified argon. The milling was carried out in a hardened steel vial with a tungsten carbide bottom which we constructed ourselves; this was mounted on a vibrating frame. One hardened steel ball with a diameter of 6 cm was used. To avoid oxidation, the milling was carried out in an argon flux outside the glove box. X-ray diffraction patterns were taken by means of a Philips vertical powder diffractometer with Cu K~ radiation. A high' temperature film scan was made. using a Guinier-Lenn6 camera, and the heating rate was 10 K h -~. For this high temperature scan the powder was embedded in a graphite foil. To avoid oxidation, the scan was carried out in a vacuum of 10 -6 Torr. Differential scanning calorimetry (DSC) measurements were made using a Setaram D S C l l l ( 10 K min-1). 3. Results and discussion
The X-ray diffraction pattern of Ni-Zr powder with a nominal composition of 62 at.% Ni after several milling periods is given in Fig. 1. It is clearly visible that the intensity of the Bragg reflections decreases and that the broad peak of the amorphous alloy appears during mechanical alloying. (The crystalline peaks observed in the X-ray pattern after 70 h © Elsevier Sequoia/Printed in The Netherlands
134
Cl
a5 cv,
<
d
i
o.o
I
I
,o
I
I
'
be noted that this is the first non-fast-diffusing system [10] in which the solid state amorphization reaction occurs. When V-Zr with a vanadium concentration of 50 at. % is mechanically alloyed, the Bragg reflections of vanadium are still visible. However, reducing the vanadium concentration to 29at.% results in an amorphous alloy without the Bragg reflections of the elements. The X-ray pattern of VE9Zr71after 140 h of mechanical alloying is shown in Fig. 2. The peak of the amorphous alloy with a maximum at K = 2.52 ~ - ~ is clearly visible. The small reflection at K = 3.12 ,~ ~could not be identified. The onset crystallization temperature of the amorphous V29Zr71 alloy, using a heating rate of 1 0 K m i n -~, is 895K. Figure 3 shows an X-ray scan with increasing temperature from 298 to 1273 K and a heating rate of 10 K h 1. The Bragg reflections that do not change in this temperature range originate from the graphite foil in which the amorphous powder is embedded. At low temperatures the broad band of the amorphous alloy is visible around K = 2.5/~-~. The first transition occurs around 750 K where, apart from the broad band of the amorphous alloy, weak lines from a crystalline compound become visible. These lines do not correspond to any of the compounds that are expected on the basis of the phase diagram [ 1l], i.e. :t-Zr o r VEZr. So, these lines are Bragg reflections from a probably metastable compound. The second transition is around 850 K. Here, the band of the amorphous alloy has almost disappeared. The lines appearing at this temperature are the Bragg reflections from ~-Zr, one of the products expected after crystallization. At the third transition, around 940 K, intense Bragg reflections appear. These lines also can-
,.o
K [A-'] Fig. 1. X-ray diffraction patterns of Ni62Zr38 after several milling periods: curve a, after 4.8 h; curve b, after 9 h; curve c, after 18 h; curve d, after 35.5 h; curve e, after 70 h.
of alloying are from tungsten carbide impurities from the bottom of the vial.) From the diffraction patterns, it can be concluded that the elements nickel and zirconium are transformed directly into the amorphous alloy. This reaction path is similar to that found by Hellstern and Schultz [7], but it differs from the reaction path in our planetary ball mili, where crystalline intermetallic compounds are intermediate products in the amorphization reaction [5]. Another system that obeys the criteria for the occurrence of the solid state amorphization reaction is V-Zr. As presented previously [3], we prepared amorphous V29Zr71 by mechanical alloying using the vibrating-flame apparatus as a milling tool. It should
V oo
10
20
~o
~.a
~.o
Fig. 2. X-ray diffraction pattern of amorphous 140 h of milling.
e.o
V29Zr71after
135 powder is lost. Figure 4 shows the X-ray diffraction pattern of a m o r p h o u s V29Zr71 after heating in an argon-filled quartz ampoule at 1273 K for 1 h. The peaks in the pattern (apart from some weak zirconia reflections) correspond to the lines on the film obtained using the Guinier-Lenn6 camera. F r o m the fact that no reflections o f both elemental vanadium and zirconium are present during and after heating, it must be concluded that vanadium and zirconium were really alloyed to an amorphous alloy during the milling.
1200-
1100-
1000
900-
800-
700-
4. Conclusions
600-
5001 L,00300
t 1
1 2
/ 3
I ~
I 5
K(~-~)
V29Zr71 using a
Fig. 3. High temperature X-ray scan of Guinier-Lenn6 camera.
not be identified and are p r o b a b l y due to metastable c o m p o u n d s too. At the last transition a r o u n d 1030 K the intensity o f the Bragg reflections appearing around 850 K ( o f ~-Zr) decreases and new reflections appear. This transition will be due to a transition o f zirconium. The new phase does not exhibit the b.c.c. structure, and so it is not the transition o f ~-Zr to fl-Zr. Because of the strong reflections of the graphite foil, some information of the eventually obtained
A m o r p h o u s Ni62Zr38 powder can be prepared by mechanical alloying. By using a ball mill mounted on a vibrating frame, elemental nickel and zirconium are directly transformed into the a m o r p h o u s alloy. Amorphous V29Zr71 could also be prepared by ball milling. F r o m the high temperature X-ray scan, it is concluded that amorphous V29Zr71 first crystallizes around 850 K to ~-Zr and a metastable V - Z r compound. Further heating to 1273 K results in the transition o f ~-Zr to an unidentified phase.
Acknowledgments
We thank Mr. A. C. Moleman for technical assistence. We are obliged to Dr. P. I. Loeff for helpful discussion and a critical reading of the manuscript.
References
F~
4
J
+-~ oo
.
, . . . . . io
, ~o
ao
K [A-']
~.o
50
Fig. 4. X-ray diffraction pattern of amorphous heating at 1273 K for 1 h.
6.0
V29Zr71after
1 A. W. Weeber, K. van der Meer, H. Bakker, F. R. de Boer, B. J. Thijsse and J. F. Jongste, J. Phys. F, 16 (1986) 1897. 2 A. W. Weeber, H. Bakker and F. R. de Boer, Europhys. Lett., 2(1986) 445. 3 A. W. Weeber and H. Bakker, Proc. 6th Int. Conf. on Liquid and Amorphous Metals, Garmisch-Partenkirchen, 1986, in Z. Phys. Chem., 156-157(1987). 4 A. W. Weeber, H. Bakker, H. J. M. Heijligers and G. F. Bastin, Europhys. Len., 3 (1987) 1261. 5 A. W. Weeber, A. J. H. Wester, W. J. Haag and H. Bakker, Physica B, 145(1987) 349. 6 R. B. Schwarz and W. L. Johnson, Phys. Bey. Lett., 51 (1983) 281. 7 E. Hellstern and L. Schultz, Appl. Phys. Lett., 48 (1986) 124. 8 E. Hellstern and L. Schultz, Proc. 6th Int. Conf. on Liquid and Amorphous Metals, Garmisch-Partenkirchen, 1986, in Z. Phys. Chem., 156-157 (1987). 9 A. R. Miedema and A. K. Niessen, Physica B, 114 (1982) 367. 10 R. P. Agarwale, S. P. Murarka and M. C. Anand, Acta Metall., 16 (1967) 61. I1 M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 1965, Fig. 682.