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APFIM and TEM study of the oxygen behavior during crystallization of Zr65Cu27.5Al7.5 metallic glass
Materials Science and Engineering A304–306 (2001) 706–709
APFIM and TEM study of the oxygen behavior during crystallization of Zr65Cu27.5Al7.5 metallic glass B.S. Murty a,∗ , D.H. Ping a , K. Hono a , A. Inoue b a
Materials Physics Division, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan b lnstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Abstract The influence of oxygen on the crystallization behavior of Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) metallic glasses has been studied. The supercooled liquid regime (1Tx ) decreases with increase in oxygen. At low oxygen level (0.14%), the alloy crystallizes in a single stage by the formation of Zr2 (Cu, Al). At higher oxygen content, the amorphous phase crystallizes in two stages by the precipitation of a quasicrystalline phase first and subsequently the stable Zr2 (Cu, Al). The present paper is the first evidence of icosahedral phase formation in ternary Zr–Cu–Al system. The temperature and time window for the formation of quasicrystalline phase is quite narrow. Three-dimensional atom probe studies have shown that the quasicrystalline phase has a composition of Zr65 Cu27.5 Al7.5 suggesting that it is rich in Zr and O and is depleted in Cu. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Zr65 Cu27.5 Al7.5 metallic glasses; Alloy; Quasicrystalline phase
1. Introduction Multi-component metallic glasses with excellent glass forming ability and high thermal stability have attracted much attention in recent years due to the feasibility of obtaining bulky samples using conventional solidification techniques at cooling rates as low as 1–100 K/s [1,2]. Among the bulk metallic glasses, Zr based alloys exhibit large supercooled liquid regime, 1Tx (Tx −Tg ), where Tx and Tg are the crystallization and glass transition temperatures, respectively [3–5]. However, the glass forming ability of theses metallic glasses appears to be strongly affected by the possible contamination of oxygen during processing [6–8]. In addition, oxygen is shown to enhance the crystallization process [9–12]. In the case of binary Zr–Ni [9] and quaternary Zr–Ni–Cu–Al [10,11] systems, it has been shown that oxygen induces the formation of metastable fcc NiZr2 , thus reducing the thermal stability of the glass. It has also been shown that the 1Tx of Zr65 Cu27.5 Al7.5 metallic glasses decreases with increase in oxygen content of the alloy, mainly by a change in crystallization sequence from single to double step process [11]. Köster et al. [13,14] have reported the formation of icosahedral phase in the Zr–Cu–Ni–Al metallic glasses during crystallization. Recent reports [10,15] indi∗ Corresponding author. Present address: Department of Metallurgical Materials Engineering, Indian Institute of Technology, Kharagpur 721 302, India. Tel.: +91-3222-77689; fax: +91-3222-55303. E-mail address: [email protected] (B.S. Murty).
cate that the quasicrystal formation is induced by the presence of oxygen in the Zr–Ni–Cu–Al alloy. However, quasicrystalline phase formation has not been reported so far in the ternary Zr–Cu–Al system. Chen et al. [16] and Ping et al. [17] have recently attempted to map the oxygen distribution in Zr–Cu–Al–Pd metallic glass during crystallization by three dimensional atom probe (3DAP) studies. Since the crystallization products could not be identified completely in the Zr based multicomponent systems in the previous studies, a simplified ternary composition Zr65 Cu27.5 Al7.5 with the highest supercooled liquid regime [4] has been chosen in the present study, to study the influence of oxygen on the crystallization behavior of Zr based metallic glass. Transmission electron microscopy and 3DAP have been extensively used in order to understand the behavior of oxygen. The present paper is the first direct evidence of oxygen stabilization of icosahedral phase in Zr based metallic glass. 2. Experimental Details Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) alloys have been produced by arc melting of high purity metals (99.9% Zr, 99.99% Cu and Al) and CuO of 99.9% purity. The composition of the alloys was analyzed using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Amorphous ribbons were obtained from these alloys by single roller melt spinning at a velocity of 20 m/s. The thermal stability of the amorphous alloys was studied using
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 5 7 6 - 8
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
Fig. 1. DSC traces of Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) at a heating rate of 10 K/s.
differential scanning calorimetry (DSC) at different heating rates in the range of 10–40 K/min. The amorphous ribbons were heat treated in vacuum (10−5 Torr) at 380 and 400◦ C for periods ranging from 5 to 90 min. Transmission electron microscopy (TEM) has been carried out using Philips CM200 and Jeol 4000EX. Sharp needle shaped samples for atom probe field ion microscopic (APFIM) study have been prepared by first mechanical polishing of the melt spun and heat treated ribbons to square rods of about 20 m × 20 m cross section followed by electropolishing. 3DAP equipped with a CAMECA tomographic atom probe detection system has been used in the present study.
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beyond which no significant change has been observed (Table 1). The alloy containing the lowest amount of oxygen (0.14%) crystallized in a single stage with an exothermic peak at 452◦ C. The alloy showed a large supercooled liquid regime (1T x = 79◦ C) which is comparable to that reported by Inoue et al. [4] for Zr65 Cu27.5 Al7.5 (1T x = 89◦ C). The larger 1Tx value of the earlier report [4] could be attributed to the higher heating rate used in their study (40 K/s). The present results showed that the 1Tx decreases with the increase in oxygen content of the alloy (Table 1). This is partly due to the increase in the Tg and also due to the additional first crystallization peak observed in case of alloys containing 0.43 and 0.82%O before the main second crystallization event. Interestingly, the enthalpy of the first crystallization peak for the alloy containing 0.43%O is almost double to that of the alloy with 0.82%O, while the activation energy is marginally smaller in the former case (Table 1). The temperature of the second crystallization is quite similar for all the three alloys suggesting that the first crystallization peak observed in case of oxygen rich alloys could be due to the precipitation of a metastable phase. Eckert et al. [10] and Gebert et al. [11] have also reported the observation of additional crystallization peak with increasing oxygen content in Zr65 Cu27.5 Al7.5 which was attributed to the co-formation of quasicrystalline phase and metastable NiZr2 . It is interesting that the first crystal-
3. Results and Discussion All the three alloys Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%)) were amorphous in the melt spun condition. The X-ray diffraction (XRD) study has shown that the amorphous broad peak is slightly shifted to lower angle by about 0.2◦ (in 2θ ) in case of 0.43 and 0.82%O alloys, suggesting that the interatomic distances are marginally modified in oxygen rich alloys. Fig. 1 shows the DSC traces of the three alloys at a heating rate of 10 K/s. The Tg increased from 373 to 381◦ C with the increase in oxygen from 0.14 to 0.43%,
Fig. 2. TEM bright field image of alloy containing 0.14%O heat treated at 400◦ C for 15 min.
Table 1 DSC results of Zr65−x Cu27.5 Al7.5 Ox alloys at a heating rate of 10 K/s Oxygen level (at.%)
Tg (◦ C)
1Tx (◦ C)
First crystallization peak Tx
0.14 0.43 0.82
373 381 382
79 59 57
(◦ C)
– 440 439
Second crystallization peak
1H (kJ/mol)
Q (kJ/mol)
Tx (◦ C)
1H (kJ/mol)
Q (kJ/mol)
– 0.91 0.47
– 220 270
452 453 450
4.6 2.5 2.5
205 275 245
708
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
Fig. 3. (a) TEM bright field image and (b) five-fold microdiffraction pattern of icosahedral phase in the alloy with 0.82%O, heat treated at 400◦ C for 10 min.
lization peak observed in the present study disappeared on increasing the heating rate to 40 K/s in DSC suggesting that the formation of the metastable phase is quite sensitive to the heat treatment conditions. The activation energy for the first crystallization peak of the present study is comparable with that reported for the quasicrystalline phase formation in a Zr–Cu–Ni–Al alloy [14]. In order to understand the crystallization behavior, the alloys were heat treated in the supercooled liquid regime. The alloy with 0.14%O has remained amorphous up to 60 min at 380◦ C and 10 min at 400◦ C, after which formation of Zr2 (Cu, Al) has been observed (Fig. 2). The XRD and TEM studies of the various heat treated specimen have confirmed the polymorphous crystallization of the amorphous phase
for the alloy containing 0.14%O. In case of alloy containing 0.82%O, precipitation of spherical icosahedral particles in the nanocrystalline state has been observed within 10 and 30 min at 400 and 380◦ C. The size of the icosahedral particles ranged widely between 10 and 100 nm. Fig. 3a and b show the TEM bright field image and five-fold microdiffraction pattern from an icosahedral particle of the alloy heated at 400◦ C for 10 min. This is the first evidence of the quasicrystalline phase formation in ternary Zr–Cu–Al metallic glass. Longer annealing resulted in the nucleation of polymorphic Zr2 (Cu, Al) phase from the residual amorphous phase with the concurrent disappearance of the quasicrystalline phase. The quasicrystalline phase appears to be quite unstable and within 15 min at 400◦ C the density of these
Fig. 4. (a) 3DAP elemental mapping and (b) composition profiles of Zr, Cu, Al and O in the alloy with 0.82%O after heat treatment at 400◦ C for 10 min.
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
particles has remarkably decreased. In fact, longer exposure of the icosahedral particles to the electron beam in TEM resulted in the disappearance of the particles. The temperature and time window for the formation of quasicrystalline phase appears to be quite narrow (30–60 and 10–15 min at 380 and 400◦ C, respectively, for 0.82%O). The fact that icosahedral phase has been observed only at higher oxygen levels suggests that it is stabilized by oxygen. APFIM is the ideal tool to characterize the distribution of various elements during crystallization of the amorphous alloy at the nanoscale. The 3DAP study of the alloy containing 0.82%O has shown that the amorphous alloy is quite homogeneous and no clustering tendency of any element has been observed. After quasicrystallization at 400◦ C for 10 min, partitioning of elements is clearly evident and the icosahedral phase was found to be enriched in Zr and O and depleted in Cu and Al, while the residual amorphous phase has negligible oxygen. Fig. 4a and b shows the elemental mapping and composition profiles, respectively, of Zr, Cu, Al and O in a small volume of the alloy. The composition of the icosahedral phase is close to Zr72 Cu16 Al8 O4 and that of the amorphous matrix was Zr63 Cu23 Al13 . Thus, the present study presents the first direct evidence of oxygen stabilization of the icosahedral phase in the Zr based metallic glasses.
4. Conclusions 1. Zr65−x Cu27.5 Al7.5 Ox amorphous alloys with 0.43 and 0.82%O crystallize in two stages with the initial precipitation of quasicrystalline phase and subsequent formation of stable Zr2 (Cu, Al), while at low oxygen level (0.14%) polymorphous crystallization of amorphous phase to Zr2 (Cu, Al) has been observed. 2. Formation of quasicrystalline phase has been observed for the first time in a ternary Zr alloy.
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3. The supercooled liquid regime (1Tx ) decreases from 79 to 57◦ C with the increase of oxygen from 0.14 to 0.83%. 4. 3DAP study has given the first direct evidence of oxygen stabilization of the icosahedral phase in Zr based metallic glasses. References [1] A. Inoue, Bulk amorphous alloys — preparation and fundamental characteristics, Materials Science Foundations, Vol. 4, 1998, Trans Tech Publications, Enfield, NH. [2] A. Inouc, Bulk amorphous alloys — practical characteristics and applications, Materials Science Foundations, Vol. 6, 1998, Trans Tech Publications, Enfield, NH. [3] T. Zhang, A. Inoue, T. Masumoto, Mater. Trans. JIM 32 (1991) 1005. [4] A. Inoue, D. Kawase, A.P. Tsai, T. Zhang, T. Masumoto, Mater. Sci. Eng. A l78 (1994) 255. [5] A. Peker, W.L. Johnson, Appl. Phys. Lett. 63 (1993) 2342. [6] A. Inoue, Y. Shinohara, Y. Yokayama, T. Masumoto, Mater. Trans. JIM 36 (1995) 1276. [7] X.H. Lin, W.L. Johnson, W.K. Rhim, Mater. Trans. JIM 38 (1997) 473. [8] A. Kubler, J. Eckert, A. Gabert, L. Schultz, J. Appl. Phys. 83 (1998) 3438. [9] Z. Altounian, E. Batalla, J.O. Strom-Olsen, J.L. Walter, J. Appl. Phys. 6 (1987) 149. [10] J. Eckert, N. Mattern, M. Zinkevitch, M. Seidel, Mater. Trans. JIM 39 (1999) 623. [11] A. Gebert, J. Eckert, L. Schultz, Acta Mater. 46 (1998) 5475. [12] U. Köster, A. Rudiger, J. Meinhardt, Mater. Sci. Forum 307 (1999) 9. [13] U. Köster, J. Meinhardt, S. Roos, H. Liebertz, Appl. Phys. Lett. 69 (1996) 179. [14] U. Köster, J. Meinhardt, S. Roos, R. Busch, Mater. Sci. Eng. A 226–228 (1997) 995. [15] D. Zander, R. Janleeing, A. Rudiger, U. Kosster, Mater. Sci. Forum 307 (1999) 25. [16] M.W. Chen, A. Inoue, T. Sakurai, D.H. Ping, K. Hono, Appl. Phys. Lett. 74 (1999) 812. [17] D.H. Ping, K. Hono, A. Inoue, Mater. Sci. Forum 307 (1999) 31.
APFIM and TEM study of the oxygen behavior during crystallization of Zr65Cu27.5Al7.5 metallic glass B.S. Murty a,∗ , D.H. Ping a , K. Hono a , A. Inoue b a
Materials Physics Division, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan b lnstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Abstract The influence of oxygen on the crystallization behavior of Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) metallic glasses has been studied. The supercooled liquid regime (1Tx ) decreases with increase in oxygen. At low oxygen level (0.14%), the alloy crystallizes in a single stage by the formation of Zr2 (Cu, Al). At higher oxygen content, the amorphous phase crystallizes in two stages by the precipitation of a quasicrystalline phase first and subsequently the stable Zr2 (Cu, Al). The present paper is the first evidence of icosahedral phase formation in ternary Zr–Cu–Al system. The temperature and time window for the formation of quasicrystalline phase is quite narrow. Three-dimensional atom probe studies have shown that the quasicrystalline phase has a composition of Zr65 Cu27.5 Al7.5 suggesting that it is rich in Zr and O and is depleted in Cu. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Zr65 Cu27.5 Al7.5 metallic glasses; Alloy; Quasicrystalline phase
1. Introduction Multi-component metallic glasses with excellent glass forming ability and high thermal stability have attracted much attention in recent years due to the feasibility of obtaining bulky samples using conventional solidification techniques at cooling rates as low as 1–100 K/s [1,2]. Among the bulk metallic glasses, Zr based alloys exhibit large supercooled liquid regime, 1Tx (Tx −Tg ), where Tx and Tg are the crystallization and glass transition temperatures, respectively [3–5]. However, the glass forming ability of theses metallic glasses appears to be strongly affected by the possible contamination of oxygen during processing [6–8]. In addition, oxygen is shown to enhance the crystallization process [9–12]. In the case of binary Zr–Ni [9] and quaternary Zr–Ni–Cu–Al [10,11] systems, it has been shown that oxygen induces the formation of metastable fcc NiZr2 , thus reducing the thermal stability of the glass. It has also been shown that the 1Tx of Zr65 Cu27.5 Al7.5 metallic glasses decreases with increase in oxygen content of the alloy, mainly by a change in crystallization sequence from single to double step process [11]. Köster et al. [13,14] have reported the formation of icosahedral phase in the Zr–Cu–Ni–Al metallic glasses during crystallization. Recent reports [10,15] indi∗ Corresponding author. Present address: Department of Metallurgical Materials Engineering, Indian Institute of Technology, Kharagpur 721 302, India. Tel.: +91-3222-77689; fax: +91-3222-55303. E-mail address: [email protected] (B.S. Murty).
cate that the quasicrystal formation is induced by the presence of oxygen in the Zr–Ni–Cu–Al alloy. However, quasicrystalline phase formation has not been reported so far in the ternary Zr–Cu–Al system. Chen et al. [16] and Ping et al. [17] have recently attempted to map the oxygen distribution in Zr–Cu–Al–Pd metallic glass during crystallization by three dimensional atom probe (3DAP) studies. Since the crystallization products could not be identified completely in the Zr based multicomponent systems in the previous studies, a simplified ternary composition Zr65 Cu27.5 Al7.5 with the highest supercooled liquid regime [4] has been chosen in the present study, to study the influence of oxygen on the crystallization behavior of Zr based metallic glass. Transmission electron microscopy and 3DAP have been extensively used in order to understand the behavior of oxygen. The present paper is the first direct evidence of oxygen stabilization of icosahedral phase in Zr based metallic glass. 2. Experimental Details Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) alloys have been produced by arc melting of high purity metals (99.9% Zr, 99.99% Cu and Al) and CuO of 99.9% purity. The composition of the alloys was analyzed using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Amorphous ribbons were obtained from these alloys by single roller melt spinning at a velocity of 20 m/s. The thermal stability of the amorphous alloys was studied using
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 5 7 6 - 8
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
Fig. 1. DSC traces of Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%) at a heating rate of 10 K/s.
differential scanning calorimetry (DSC) at different heating rates in the range of 10–40 K/min. The amorphous ribbons were heat treated in vacuum (10−5 Torr) at 380 and 400◦ C for periods ranging from 5 to 90 min. Transmission electron microscopy (TEM) has been carried out using Philips CM200 and Jeol 4000EX. Sharp needle shaped samples for atom probe field ion microscopic (APFIM) study have been prepared by first mechanical polishing of the melt spun and heat treated ribbons to square rods of about 20 m × 20 m cross section followed by electropolishing. 3DAP equipped with a CAMECA tomographic atom probe detection system has been used in the present study.
707
beyond which no significant change has been observed (Table 1). The alloy containing the lowest amount of oxygen (0.14%) crystallized in a single stage with an exothermic peak at 452◦ C. The alloy showed a large supercooled liquid regime (1T x = 79◦ C) which is comparable to that reported by Inoue et al. [4] for Zr65 Cu27.5 Al7.5 (1T x = 89◦ C). The larger 1Tx value of the earlier report [4] could be attributed to the higher heating rate used in their study (40 K/s). The present results showed that the 1Tx decreases with the increase in oxygen content of the alloy (Table 1). This is partly due to the increase in the Tg and also due to the additional first crystallization peak observed in case of alloys containing 0.43 and 0.82%O before the main second crystallization event. Interestingly, the enthalpy of the first crystallization peak for the alloy containing 0.43%O is almost double to that of the alloy with 0.82%O, while the activation energy is marginally smaller in the former case (Table 1). The temperature of the second crystallization is quite similar for all the three alloys suggesting that the first crystallization peak observed in case of oxygen rich alloys could be due to the precipitation of a metastable phase. Eckert et al. [10] and Gebert et al. [11] have also reported the observation of additional crystallization peak with increasing oxygen content in Zr65 Cu27.5 Al7.5 which was attributed to the co-formation of quasicrystalline phase and metastable NiZr2 . It is interesting that the first crystal-
3. Results and Discussion All the three alloys Zr65−x Cu27.5 Al7.5 Ox (x = 0.14, 0.43 and 0.82%)) were amorphous in the melt spun condition. The X-ray diffraction (XRD) study has shown that the amorphous broad peak is slightly shifted to lower angle by about 0.2◦ (in 2θ ) in case of 0.43 and 0.82%O alloys, suggesting that the interatomic distances are marginally modified in oxygen rich alloys. Fig. 1 shows the DSC traces of the three alloys at a heating rate of 10 K/s. The Tg increased from 373 to 381◦ C with the increase in oxygen from 0.14 to 0.43%,
Fig. 2. TEM bright field image of alloy containing 0.14%O heat treated at 400◦ C for 15 min.
Table 1 DSC results of Zr65−x Cu27.5 Al7.5 Ox alloys at a heating rate of 10 K/s Oxygen level (at.%)
Tg (◦ C)
1Tx (◦ C)
First crystallization peak Tx
0.14 0.43 0.82
373 381 382
79 59 57
(◦ C)
– 440 439
Second crystallization peak
1H (kJ/mol)
Q (kJ/mol)
Tx (◦ C)
1H (kJ/mol)
Q (kJ/mol)
– 0.91 0.47
– 220 270
452 453 450
4.6 2.5 2.5
205 275 245
708
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
Fig. 3. (a) TEM bright field image and (b) five-fold microdiffraction pattern of icosahedral phase in the alloy with 0.82%O, heat treated at 400◦ C for 10 min.
lization peak observed in the present study disappeared on increasing the heating rate to 40 K/s in DSC suggesting that the formation of the metastable phase is quite sensitive to the heat treatment conditions. The activation energy for the first crystallization peak of the present study is comparable with that reported for the quasicrystalline phase formation in a Zr–Cu–Ni–Al alloy [14]. In order to understand the crystallization behavior, the alloys were heat treated in the supercooled liquid regime. The alloy with 0.14%O has remained amorphous up to 60 min at 380◦ C and 10 min at 400◦ C, after which formation of Zr2 (Cu, Al) has been observed (Fig. 2). The XRD and TEM studies of the various heat treated specimen have confirmed the polymorphous crystallization of the amorphous phase
for the alloy containing 0.14%O. In case of alloy containing 0.82%O, precipitation of spherical icosahedral particles in the nanocrystalline state has been observed within 10 and 30 min at 400 and 380◦ C. The size of the icosahedral particles ranged widely between 10 and 100 nm. Fig. 3a and b show the TEM bright field image and five-fold microdiffraction pattern from an icosahedral particle of the alloy heated at 400◦ C for 10 min. This is the first evidence of the quasicrystalline phase formation in ternary Zr–Cu–Al metallic glass. Longer annealing resulted in the nucleation of polymorphic Zr2 (Cu, Al) phase from the residual amorphous phase with the concurrent disappearance of the quasicrystalline phase. The quasicrystalline phase appears to be quite unstable and within 15 min at 400◦ C the density of these
Fig. 4. (a) 3DAP elemental mapping and (b) composition profiles of Zr, Cu, Al and O in the alloy with 0.82%O after heat treatment at 400◦ C for 10 min.
B.S. Murty et al. / Materials Science and Engineering A304–306 (2001) 706–709
particles has remarkably decreased. In fact, longer exposure of the icosahedral particles to the electron beam in TEM resulted in the disappearance of the particles. The temperature and time window for the formation of quasicrystalline phase appears to be quite narrow (30–60 and 10–15 min at 380 and 400◦ C, respectively, for 0.82%O). The fact that icosahedral phase has been observed only at higher oxygen levels suggests that it is stabilized by oxygen. APFIM is the ideal tool to characterize the distribution of various elements during crystallization of the amorphous alloy at the nanoscale. The 3DAP study of the alloy containing 0.82%O has shown that the amorphous alloy is quite homogeneous and no clustering tendency of any element has been observed. After quasicrystallization at 400◦ C for 10 min, partitioning of elements is clearly evident and the icosahedral phase was found to be enriched in Zr and O and depleted in Cu and Al, while the residual amorphous phase has negligible oxygen. Fig. 4a and b shows the elemental mapping and composition profiles, respectively, of Zr, Cu, Al and O in a small volume of the alloy. The composition of the icosahedral phase is close to Zr72 Cu16 Al8 O4 and that of the amorphous matrix was Zr63 Cu23 Al13 . Thus, the present study presents the first direct evidence of oxygen stabilization of the icosahedral phase in the Zr based metallic glasses.
4. Conclusions 1. Zr65−x Cu27.5 Al7.5 Ox amorphous alloys with 0.43 and 0.82%O crystallize in two stages with the initial precipitation of quasicrystalline phase and subsequent formation of stable Zr2 (Cu, Al), while at low oxygen level (0.14%) polymorphous crystallization of amorphous phase to Zr2 (Cu, Al) has been observed. 2. Formation of quasicrystalline phase has been observed for the first time in a ternary Zr alloy.
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3. The supercooled liquid regime (1Tx ) decreases from 79 to 57◦ C with the increase of oxygen from 0.14 to 0.83%. 4. 3DAP study has given the first direct evidence of oxygen stabilization of the icosahedral phase in Zr based metallic glasses. References [1] A. Inoue, Bulk amorphous alloys — preparation and fundamental characteristics, Materials Science Foundations, Vol. 4, 1998, Trans Tech Publications, Enfield, NH. [2] A. Inouc, Bulk amorphous alloys — practical characteristics and applications, Materials Science Foundations, Vol. 6, 1998, Trans Tech Publications, Enfield, NH. [3] T. Zhang, A. Inoue, T. Masumoto, Mater. Trans. JIM 32 (1991) 1005. [4] A. Inoue, D. Kawase, A.P. Tsai, T. Zhang, T. Masumoto, Mater. Sci. Eng. A l78 (1994) 255. [5] A. Peker, W.L. Johnson, Appl. Phys. Lett. 63 (1993) 2342. [6] A. Inoue, Y. Shinohara, Y. Yokayama, T. Masumoto, Mater. Trans. JIM 36 (1995) 1276. [7] X.H. Lin, W.L. Johnson, W.K. Rhim, Mater. Trans. JIM 38 (1997) 473. [8] A. Kubler, J. Eckert, A. Gabert, L. Schultz, J. Appl. Phys. 83 (1998) 3438. [9] Z. Altounian, E. Batalla, J.O. Strom-Olsen, J.L. Walter, J. Appl. Phys. 6 (1987) 149. [10] J. Eckert, N. Mattern, M. Zinkevitch, M. Seidel, Mater. Trans. JIM 39 (1999) 623. [11] A. Gebert, J. Eckert, L. Schultz, Acta Mater. 46 (1998) 5475. [12] U. Köster, A. Rudiger, J. Meinhardt, Mater. Sci. Forum 307 (1999) 9. [13] U. Köster, J. Meinhardt, S. Roos, H. Liebertz, Appl. Phys. Lett. 69 (1996) 179. [14] U. Köster, J. Meinhardt, S. Roos, R. Busch, Mater. Sci. Eng. A 226–228 (1997) 995. [15] D. Zander, R. Janleeing, A. Rudiger, U. Kosster, Mater. Sci. Forum 307 (1999) 25. [16] M.W. Chen, A. Inoue, T. Sakurai, D.H. Ping, K. Hono, Appl. Phys. Lett. 74 (1999) 812. [17] D.H. Ping, K. Hono, A. Inoue, Mater. Sci. Forum 307 (1999) 31.