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Precipitation of nano-scale icosahedral quasicrystalline phase in amorphous Hf70Ni10Pd20 alloy
Journal of Non-Crystalline Solids 289 (2001) 163±167
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Precipitation of nano-scale icosahedral quasicrystalline phase in amorphous Hf 70Ni10Pd20 alloy Chunfei Li a,*, Akihisa Inoue b a
Japan Science and Technology Exploratory Res. for Advanced Technology, Inoue Superliquid Glass Project, ERATO, JST, Yagiyamaminami 2-1-1, Taihaku-ku, Sendai 982-0807 Japan b Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan Received 12 October 2000; received in revised form 6 March 2001
Abstract An amorphous Hf 70 Ni10 Pd20 ternary alloy was prepared and its crystallization process was studied. The crystallization proceeds through two exothermic reactions, of which the low temperature one corresponds to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature leads to its decomposition to stable crystalline phases, indicating the metastable character of the initial icosahedral quasicrystalline phase. In comparison with the crystallization process of other Hf-based amorphous alloys, factors aecting the precipitation of the icosahedral quasicrystalline phase in Hf-based amorphous alloy were discussed. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 61.43.j; 64.70.Rh; 61.10.I; 61.16.Bg
1. Introduction In our previous papers, the crystallization process of amorphous Hf 65 Al7:5 Ni10 Cu17:5 and Hf 65 Al7:5 Ni10 Cu12:5 Pd5 alloys was reported [1,2]. The initial precipitation phases are a face-centered cubic Hf 2 Ni phase and an icosahedral quasicrystalline phase (I-phase) for Hf 65 Al7:5 Ni10 Cu17:5 [2] and Hf 65 Al7:5 Ni10 Cu12:5 Pd5 [1], respectively. Therefore, it was concluded that the addition of Pd is essential for the precipitation of I-phase in the Hf±Al±Ni±Cu amorphous alloy. However, it is not clear whether other elements are essential. To
* Corresponding author. Tel.: +81-22 243 7662; fax: +81-22 243 7616. E-mail address: [email protected] (C. Li).
clarify this problem, Hf±Ni±Pd ternary amorphous alloys were prepared and their crystallization process was studied. The precipitation of I-phase in an amorphous Hf 70 Ni10 Pd20 alloy has been revealed and the result is reported in this paper.
2. Experimental The alloy ingot was prepared by arc-melting a mixture of pure metals. From the alloy ingot, a ribbon with a cross-section of about 0:03 1 mm2 was prepared by a single roller melt-spinning method in an argon atmosphere. The melt-spun ribbon was annealed in an evacuated quartz tube. The structure was examined by X-ray diraction (XRD) and the thermal stability was investigated
0022-3093/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 0 1 ) 0 0 6 9 9 - 8
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C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
Fig. 1. DSC curve of the amorphous Hf 70 Ni10 Pd20 ribbon.
by dierential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The microstructure was examined by a transmission electron microscope (TEM) JEM-3000F, operated at 300 kV. The diameter of the electron beam was focused to 1.0 nm in the nano-beam diraction.
Fig. 2. XRD pattern of the Hf 70 Ni10 Pd20 ribbons annealed at 790 K for 0.6 ks. Diraction peaks are indexed as an I-phase.
3. Results and discussion XRD measurement veri®ed that the melt-spun ribbon is in an amorphous state. The DSC curve shown in Fig. 1 indicates that the crystallization
Fig. 3. Bright-®eld TEM image of the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. The precipitated particle size ranges from 3 to 7 nm.
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
165
Fig. 4. Nano-beam electron diraction patterns of the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. (a), (b) and (c) correspond to the ®ve, three and two fold symmetries of I-phase, respectively. (d) shows the halo-ring from the residual amorphous matrix.
process proceeds through two exothermic reactions. Annealing of the specimen caused the precipitation of an I-phase in the initial crystallization process followed by the decomposition to regular crystalline phases. The XRD pattern of the specimen annealed at 790 K for 0.6 ks is shown in Fig. 2. The diraction peaks are identi®ed as an I-phase and their intensity is stronger as compared to those from the specimens annealed under other conditions, implying that 790 K for 0.6 ks is an optimum annealing condition for the precipitation of I-phase. It should be pointed out that the two maxima in the XRD pattern of specimen annealed at 790 K for 0.6 ks can also be indexed by considering other crystalline phase, e.g., Hf (hexagonal, P63 =mmc, a 0:320 nm and c 0:506 nm). The abovementioned indexing was performed by considering both the results of XRD and TEM observation to be illustrated later.
The above XRD result was con®rmed by TEM observation. Fig. 3 shows a bright-®eld TEM image of the specimen annealed at 790 K for 0.6 ks. The precipitated particle size ranges approximately from 3 to 7 nm. Figs 4(a)±(c) show the nano-beam electron diraction patterns, corresponding to the ®ve, three and two fold symmetries, respectively. These results indicate that the initial precipitation phase is an I-phase. The halo-ring shown in Fig. 4(d) implies the existence of residual amorphous phase. A high-resolution image of the precipitated I-phase particle taken with the incident electron beam parallel to the ®ve fold symmetry axis is shown in Fig. 5. The size of this particle is the largest one found in the experiment. The inlet shows the selected area electron diraction pattern. The main spots marked with arrows are from the particle in the center of the high-resolution image and show ®ve fold symmetry. The contrast within the particle is homogeneous, ruling out the
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C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
Fig. 5. High-resolution image of a precipitated I-phase particle in the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. The main spots marked with arrows are from the particle in the center of the high-resolution image and show ®ve fold symmetry.
possibility that the ®ve fold symmetry is from twinned crystalline approximants. Fig. 6 shows the XRD pattern of the specimen annealed at 1000 K for 1.2 ks. The diraction peaks are identi®ed as Hf 2 Pd, HfPd2 and Hf 2 Ni, implying that the initial I-phase is in a metastable state. The present result provides us new information on the precipitation of I-phase in Hf-based amorphous alloys. First, it is recognized that the Iphase can be formed in the Hf-based alloys containing no Al and Cu. Further, the maximum particle size of the I-phase depends on the content of the added Pd. Under an optimum annealing condition, the particle size of the precipitated Iphase ranges from 10 to 20 nm for the Hf 65 Al7:5 Ni10 Cu12:5 Pd5 alloy [1]. Such a size distribution for the present Hf 70 Ni10 Pd20 alloy is from 3 to 7 nm, indicating that the particle size of the precipitated I-phase decreases with increasing
Pd content. A similar tendency was also observed in the well-known Zr-based amorphous alloys [3,4].
Fig. 6. XRD patterns of the Hf 70 Ni10 Pd20 ribbon annealed at 1000 K for 1.2 ks. Diraction peaks corresponding to the initially precipitated I-phase are not observed, indicating that the I-phase is in a metastable state.
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
The addition of Pd is considered to promote the nucleation of the I-phase. It is well known that the center site of the icosahedral atomic cluster can be occupied by atoms or can remain empty [5]. The atomic radius of atoms occupying the center site should be approximately 5% smaller than that occupying the apex site. Noticing the fact that the Ti-based I-phase belongs to the center site occupied type [6], and Hf and Ti are located in the same group in the periodic table, the icosahedral center site of the present I-phase is presumed to be occupied by atoms. The apex sites should be occupied mainly by Hf atoms because of the alloy composition. Considering the atomic radii of Hf (0.160 nm), Ni (0.125 nm) and Pd (0.137 nm), it is suggested that the center site of icosahedron is occupied by Pd, forming a Hf 12 Pd icosahedral atomic cluster. Such a Hf 12 Pd atomic cluster may also exist in the amorphous state. This speculation is supported by the analysis of atomic radius of the constituent elements as explained above. It is also supported by the strong atomic binding of Hf±Pd atomic pair, which is evidenced by the large negative heat ()80 kJ/mol) of mixing [7]. The Hf 12 Pd cluster may serve as the seeds for the precipitation of the I-phase. The number density of such a Hf 12 Pd atomic cluster will increase with increasing Pd content, which explains why the precipitated particle size tends to decrease with increasing Pd content.
167
4. Conclusion In summary, the precipitation of the I-phase was revealed in the initial crystallization process of the amorphous Hf 70 Ni10 Pd20 alloy. Comparing with the previous results, it is recognized that the maximum size of the precipitated I-phase particle decreases with the increasing Pd content. The formation of a Hf 12 Pd atomic cluster with the center site occupied by Pd and the apex site by Hf in the amorphous matrix is addressed as the reason for the precipitation of the I-phase and the size dependence of precipitated I-phase particle on the added Pd content.
References [1] C. Li, M. Matsushita, J. Saida, A. Inoue, Appl. Phys. Lett. 77 (2000) 528. [2] C. Li, A. Inoue, Physica Status Solidi 184 (2001) 291. [3] A. Inoue, T. Zhang, J. Saida, M. Matsushita, M.W. Chen, T. Sakurai, Mater. Trans. JIM. 40 (1999) 1181. [4] J. Saida, M. Matsushita, C. Li, A. Inoue, Appl. Phys. Lett. 76 (2000) 3558. [5] S. Takeuchi, K. Etakawa, in: Crystalline, Quasicrystalline and Amorphous Solid, 1997, Uchitaroukakuho, Tokyo, p. 87. [6] C. Dong, Z.K. Hei, L.B. Wang, Q.H. Song, Y.K. Wu, K.H. Kuo, Scr. Metall. 20 (1986) 1155. [7] F.R. De Boer, R. Boom, W.C.M. Mattens, A.R. Miedema, A.K. Niessen, Cohesion in Metals, Elsevier, Amsterdam, 1989.
www.elsevier.com/locate/jnoncrysol
Precipitation of nano-scale icosahedral quasicrystalline phase in amorphous Hf 70Ni10Pd20 alloy Chunfei Li a,*, Akihisa Inoue b a
Japan Science and Technology Exploratory Res. for Advanced Technology, Inoue Superliquid Glass Project, ERATO, JST, Yagiyamaminami 2-1-1, Taihaku-ku, Sendai 982-0807 Japan b Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan Received 12 October 2000; received in revised form 6 March 2001
Abstract An amorphous Hf 70 Ni10 Pd20 ternary alloy was prepared and its crystallization process was studied. The crystallization proceeds through two exothermic reactions, of which the low temperature one corresponds to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature leads to its decomposition to stable crystalline phases, indicating the metastable character of the initial icosahedral quasicrystalline phase. In comparison with the crystallization process of other Hf-based amorphous alloys, factors aecting the precipitation of the icosahedral quasicrystalline phase in Hf-based amorphous alloy were discussed. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 61.43.j; 64.70.Rh; 61.10.I; 61.16.Bg
1. Introduction In our previous papers, the crystallization process of amorphous Hf 65 Al7:5 Ni10 Cu17:5 and Hf 65 Al7:5 Ni10 Cu12:5 Pd5 alloys was reported [1,2]. The initial precipitation phases are a face-centered cubic Hf 2 Ni phase and an icosahedral quasicrystalline phase (I-phase) for Hf 65 Al7:5 Ni10 Cu17:5 [2] and Hf 65 Al7:5 Ni10 Cu12:5 Pd5 [1], respectively. Therefore, it was concluded that the addition of Pd is essential for the precipitation of I-phase in the Hf±Al±Ni±Cu amorphous alloy. However, it is not clear whether other elements are essential. To
* Corresponding author. Tel.: +81-22 243 7662; fax: +81-22 243 7616. E-mail address: [email protected] (C. Li).
clarify this problem, Hf±Ni±Pd ternary amorphous alloys were prepared and their crystallization process was studied. The precipitation of I-phase in an amorphous Hf 70 Ni10 Pd20 alloy has been revealed and the result is reported in this paper.
2. Experimental The alloy ingot was prepared by arc-melting a mixture of pure metals. From the alloy ingot, a ribbon with a cross-section of about 0:03 1 mm2 was prepared by a single roller melt-spinning method in an argon atmosphere. The melt-spun ribbon was annealed in an evacuated quartz tube. The structure was examined by X-ray diraction (XRD) and the thermal stability was investigated
0022-3093/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 0 1 ) 0 0 6 9 9 - 8
164
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
Fig. 1. DSC curve of the amorphous Hf 70 Ni10 Pd20 ribbon.
by dierential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The microstructure was examined by a transmission electron microscope (TEM) JEM-3000F, operated at 300 kV. The diameter of the electron beam was focused to 1.0 nm in the nano-beam diraction.
Fig. 2. XRD pattern of the Hf 70 Ni10 Pd20 ribbons annealed at 790 K for 0.6 ks. Diraction peaks are indexed as an I-phase.
3. Results and discussion XRD measurement veri®ed that the melt-spun ribbon is in an amorphous state. The DSC curve shown in Fig. 1 indicates that the crystallization
Fig. 3. Bright-®eld TEM image of the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. The precipitated particle size ranges from 3 to 7 nm.
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
165
Fig. 4. Nano-beam electron diraction patterns of the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. (a), (b) and (c) correspond to the ®ve, three and two fold symmetries of I-phase, respectively. (d) shows the halo-ring from the residual amorphous matrix.
process proceeds through two exothermic reactions. Annealing of the specimen caused the precipitation of an I-phase in the initial crystallization process followed by the decomposition to regular crystalline phases. The XRD pattern of the specimen annealed at 790 K for 0.6 ks is shown in Fig. 2. The diraction peaks are identi®ed as an I-phase and their intensity is stronger as compared to those from the specimens annealed under other conditions, implying that 790 K for 0.6 ks is an optimum annealing condition for the precipitation of I-phase. It should be pointed out that the two maxima in the XRD pattern of specimen annealed at 790 K for 0.6 ks can also be indexed by considering other crystalline phase, e.g., Hf (hexagonal, P63 =mmc, a 0:320 nm and c 0:506 nm). The abovementioned indexing was performed by considering both the results of XRD and TEM observation to be illustrated later.
The above XRD result was con®rmed by TEM observation. Fig. 3 shows a bright-®eld TEM image of the specimen annealed at 790 K for 0.6 ks. The precipitated particle size ranges approximately from 3 to 7 nm. Figs 4(a)±(c) show the nano-beam electron diraction patterns, corresponding to the ®ve, three and two fold symmetries, respectively. These results indicate that the initial precipitation phase is an I-phase. The halo-ring shown in Fig. 4(d) implies the existence of residual amorphous phase. A high-resolution image of the precipitated I-phase particle taken with the incident electron beam parallel to the ®ve fold symmetry axis is shown in Fig. 5. The size of this particle is the largest one found in the experiment. The inlet shows the selected area electron diraction pattern. The main spots marked with arrows are from the particle in the center of the high-resolution image and show ®ve fold symmetry. The contrast within the particle is homogeneous, ruling out the
166
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
Fig. 5. High-resolution image of a precipitated I-phase particle in the Hf 70 Ni10 Pd20 ribbon annealed at 790 K for 0.6 ks. The main spots marked with arrows are from the particle in the center of the high-resolution image and show ®ve fold symmetry.
possibility that the ®ve fold symmetry is from twinned crystalline approximants. Fig. 6 shows the XRD pattern of the specimen annealed at 1000 K for 1.2 ks. The diraction peaks are identi®ed as Hf 2 Pd, HfPd2 and Hf 2 Ni, implying that the initial I-phase is in a metastable state. The present result provides us new information on the precipitation of I-phase in Hf-based amorphous alloys. First, it is recognized that the Iphase can be formed in the Hf-based alloys containing no Al and Cu. Further, the maximum particle size of the I-phase depends on the content of the added Pd. Under an optimum annealing condition, the particle size of the precipitated Iphase ranges from 10 to 20 nm for the Hf 65 Al7:5 Ni10 Cu12:5 Pd5 alloy [1]. Such a size distribution for the present Hf 70 Ni10 Pd20 alloy is from 3 to 7 nm, indicating that the particle size of the precipitated I-phase decreases with increasing
Pd content. A similar tendency was also observed in the well-known Zr-based amorphous alloys [3,4].
Fig. 6. XRD patterns of the Hf 70 Ni10 Pd20 ribbon annealed at 1000 K for 1.2 ks. Diraction peaks corresponding to the initially precipitated I-phase are not observed, indicating that the I-phase is in a metastable state.
C. Li, A. Inoue / Journal of Non-Crystalline Solids 289 (2001) 163±167
The addition of Pd is considered to promote the nucleation of the I-phase. It is well known that the center site of the icosahedral atomic cluster can be occupied by atoms or can remain empty [5]. The atomic radius of atoms occupying the center site should be approximately 5% smaller than that occupying the apex site. Noticing the fact that the Ti-based I-phase belongs to the center site occupied type [6], and Hf and Ti are located in the same group in the periodic table, the icosahedral center site of the present I-phase is presumed to be occupied by atoms. The apex sites should be occupied mainly by Hf atoms because of the alloy composition. Considering the atomic radii of Hf (0.160 nm), Ni (0.125 nm) and Pd (0.137 nm), it is suggested that the center site of icosahedron is occupied by Pd, forming a Hf 12 Pd icosahedral atomic cluster. Such a Hf 12 Pd atomic cluster may also exist in the amorphous state. This speculation is supported by the analysis of atomic radius of the constituent elements as explained above. It is also supported by the strong atomic binding of Hf±Pd atomic pair, which is evidenced by the large negative heat ()80 kJ/mol) of mixing [7]. The Hf 12 Pd cluster may serve as the seeds for the precipitation of the I-phase. The number density of such a Hf 12 Pd atomic cluster will increase with increasing Pd content, which explains why the precipitated particle size tends to decrease with increasing Pd content.
167
4. Conclusion In summary, the precipitation of the I-phase was revealed in the initial crystallization process of the amorphous Hf 70 Ni10 Pd20 alloy. Comparing with the previous results, it is recognized that the maximum size of the precipitated I-phase particle decreases with the increasing Pd content. The formation of a Hf 12 Pd atomic cluster with the center site occupied by Pd and the apex site by Hf in the amorphous matrix is addressed as the reason for the precipitation of the I-phase and the size dependence of precipitated I-phase particle on the added Pd content.
References [1] C. Li, M. Matsushita, J. Saida, A. Inoue, Appl. Phys. Lett. 77 (2000) 528. [2] C. Li, A. Inoue, Physica Status Solidi 184 (2001) 291. [3] A. Inoue, T. Zhang, J. Saida, M. Matsushita, M.W. Chen, T. Sakurai, Mater. Trans. JIM. 40 (1999) 1181. [4] J. Saida, M. Matsushita, C. Li, A. Inoue, Appl. Phys. Lett. 76 (2000) 3558. [5] S. Takeuchi, K. Etakawa, in: Crystalline, Quasicrystalline and Amorphous Solid, 1997, Uchitaroukakuho, Tokyo, p. 87. [6] C. Dong, Z.K. Hei, L.B. Wang, Q.H. Song, Y.K. Wu, K.H. Kuo, Scr. Metall. 20 (1986) 1155. [7] F.R. De Boer, R. Boom, W.C.M. Mattens, A.R. Miedema, A.K. Niessen, Cohesion in Metals, Elsevier, Amsterdam, 1989.