Structural evolution of nano-scale icosahedral phase in novel multicomponent amorphous alloys

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Ki Buem Kim, Paul Warren, Brian Cantor, J Eckert. Structural evolution of nano-scale icosahedral phase in novel multicomponent amorphous alloys. Philosophical Magazine, Taylor & Francis, 2005, 86 (03-05), pp.281-286. �10.1080/14786430500228135�. �hal-00513554�

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Structural evolution of nano-scale icosahedral phase in novel multicomponent amorphous alloys

Journal: Philosophical Magazine & Philosophical Magazine Letters Manuscript ID: TPHM-05-May-0144.R1

Journal Selection: Philosophical Magazine Date Submitted by the

Author: 03-Jun-2005

Complete List of Authors: Kim, Ki Buem; Darmstadt Technical University, Department of Materials and Geo-science

Warren, Paul; Univeristy of Oxford, Materials

Cantor, Brian; University of York, Vice-chancellor's office

Eckert, J; Darmstadt Technical University, Department of Materials and Geo-science

Keywords: quasicrystalline alloys, amorphous alloys

Keywords (user supplied): multicomponenent, equiatomic substitution, devitrification

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Structural evolution of nano-scale icosahedral phase in novel multicomponent amorphous alloys

K. B. KIM^*1, P. J. WARREN², B. CANTOR³ and J. ECKERT¹

1 FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, Petersenstraße 23, D-64287 Darmstadt, Germany

2 Department of Materials, University of Oxford, Oxford, OX1 3PH, U.K.

3 Vice-Chancellor’s Office, University of York, Heslington, YO10 5DD, U.K.

Abstract

Novel (Ti33Zr33Hf33)70(Ni50Cu50)20Al10, (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10

and (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₃₃Cu₃₃Ag₃₃)₂₀Al₁₀multicomponent amorphous alloys developed by equiatomic substitution transform into a nano-scale icosahedral phase upon devitrification. However, the decomposition sequence of the nano-scale icosahedral phase at higher temperatures is significantly different for each alloy. The occurrence of the Zr2Cu-type phase during the decomposition of the devitrified icosahedral phase can enhance the thermal stability of the icosahedral phase.

Keywords: Multicomponent alloys; Equiatomic substitution; Devitirification; Nano- scale icosahedral phase

*Corresponding author: Dr. K. B. Kim, e-mail: k.b.kim@phm.tu-darmstadt.de

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1. Introduction

Recently, novel multicomponent metallic glasses based on well-known good glass forming Zr-Ni-Cu-Al alloys [1,2] have been developed using the equiatomic substitution. A variety of samples with different composition have been produced using melt-spinning [3-7] and mechanical alloying [8]. Furthermore, extensive investigations of their crystallisation behaviour have revealed the phase fields of these multicomponent alloys [6,9,10]. Among these, the amorphous alloys (Ti33Zr33Hf33)70(Ni50Cu50)20Al10, (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10 and (Ti33Zr33Hf33)70(Ni33Cu33Ag33)20Al10 are particularly interesting since their compositions are very similar to those previously developed Zr-based alloys which show devitrification of icosahedral phase [11-15]. This paper compares the crystallisation behaviour of these three alloys in order to understand the effect of equiatomically substituted Nb and Ag in (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₅₀Cu₅₀)₂₀Al₁₀alloy on devitirification of the icosahedral phase.

2. Results and Discussion

Melt-spun ribbons were prepared from pure metals by single roller melt- spinning and characterized by X-ray Diffraction (XRD) using Cu Kα radiation, Differential Scanning Calorimetry (DSC) with a heating rate of 20 K/min and Transmission Electron Microscopy (TEM). Details of the experimental conditions used are reported elsewhere [3-6].

XRD and DSC traces of the as-quenched amorphous ribbons are shown in Figs.

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1. The as-quenched (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₅₀Cu₅₀)₂₀Al₁₀ ribbon exhibits a wide supercooled liquid region ∆T = Tx - Tg = 61 K, with crystallisation onset temperature Tx = 676 K and glass transition temperature T_g = 615 K. On the other hand, the Nb-containing ribbons exhibit ∆T = 70 K, with Tx = 742 K and Tg = 672 K. The Ag-containing ribbons exhibit

∆T = 31 K with Tx = 681 K and Tg = 650 K. From these results, it appears that Nb significantly enhances both of the thermal stability and glass-forming ability of the amorphous phase. [inset Fig. 1 about here]

XRD traces after various heat treatments to investigate the crystallisation products are shown in Fig. 2. The (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy initially decomposes to form icosahedral phase, possibly with some minor unidentified phase. At higher temperatures (i.e. at 873 K without holding time) the icosaheral phase coexists with Zr2Cu-type (C16) phase. After heat treatment above all three exothermic reactions (i.e. at 973 K without holding time) it is possible to identify the crystalline phases as a mixture of the icosahedral, Zr₂Cu-type (C16) and β-(Ti,Zr,Hf) phases. In contrast, in the Nb-containing alloy the diffraction peaks after the first exothermic reaction (i.e. at 873 K for 5 min) are very broad similar to that of the as-quenched sample in Fig. 1 (a). At higher temperatures (i.e. at 936 K without holding time) the icosaheral phase coexists with Ti2Ni-type phase. After further increase of heat treatment temperature (i.e. 973 K for 10 min) the diffraction peaks are identified as a mixture of MgZn₂-type and Ti₂Ni- type phases. The Ag-containing alloy initially decomposes into icosahedral phase, similar to the base alloy. Increasing the heat treatment temperature (i.e. at 873 K without holding time) also shows the icosahedral phase coexists with Zr2Cu-type (C16) phase.

However, the icosahedral phase decomposes entirely into a mixture of the Zr2Cu-type (C16) and Ti₂Ni-type phases after heat treatment at 973 K without holding time. [inset

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Fig. 2 about here]

Microstructural investigation by TEM confirmed the phase identification of the heat treated samples by XRD in Fig. 2. The microstructure of (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy in Fig. 3 (a) after heat treatment at 813 K for 5 min is predominantly small grains 10-20 nm in size distributed homogeneously throughout the sample. In addition a small fraction of big particles 80-100 nm in size are randomly distributed throughout the sample, identifed as Zr2Cu-type (C16) phase.

Figure 3 (b) shows a HREM image of the nano-scale icosahedral phase. After heat treatment at 973 K without holding time, Fig. 3 (c), three types of grains are distinguishable by TEM image contrast; defect-free grains (as indicated by the black TEM pointer), mottled grains and sharp linear defective grains. The detailed phase identification and chemistry of these crystalline phases using TEM [16] also confirmed a mixture of the icosaheral, Zr₂Cu-type (C16) and β-(Ti,Zr,Hf) phases as identified in the XRD pattern in Fig. 1 (a). [inset Fig. 3 about here]

The microstructure of the Nb-containing alloy in Fig. 4 (a) after heat treatment at 873 K for 5 min reveals a homogeneous distribution of icosahedral grains less than 10 nm in size. As previously reported [17] the addition of the Nb is also effective to decrease the grain size of the devitrified icosahedral phase. After heat treatment at 936 K without holding time, Fig. 4 (b), small icosahedral grains (20-30 nm) coexist with large Ti2Ni-type grains (50-80 nm), all distributed homogeneously. After heat treatment at 973 K for 10 min the icosahedral phase in this alloy has transformed into a mixture of MgZn2-type grains 200-300 nm in size and Ti2Ni-type phase 50-100 nm in size. [inset Fig. 4 about here]

The microstructure of the Ag-containing alloy in Fig. 5 (a) after heat treatment

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at 843 K for 5 min shows a homogeneous distribution of icosahedral phase 10-20 nm in size. After heat treatment at 873 K without holding time, Fig. 5 (b), spherical particles of Zr₂Cu-type (C16) phase 30-40 nm in size are dispersed among the icosahedral phase.

After heat treatment at 973 K without holding time, Fig. 5 (c), two types of grains are distinguishable by TEM image contrast; defective Zr2Cu-type (C16) and defect-free Ti₂Ni-type grains. Furthermore, these crystalline phases have an orientation relationship as shown in the inset microbeam diffraction pattern i.e. [111]Ti2Ni-type//[331]Zr2Cu-type [10].

No icosahedral phase was observed after heat treatment at 973 K without holding time.

Therefore, it appears that the equiatomically substituted Ag in (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy can retard the formation of the Zr2Cu-type (C16) phase from the nano-scale icosahedral phase. [inset Fig. 5 about here]

These results suggest that the thermal stability of the icosahedral phase can be enhanced by forming the Zr₂Cu-type (C16) phase. In contrast the formation of MgZn₂- type and Ti₂Ni-type phases reduces the thermal stability of the devitrified icosahedral phase. Since it is known that both of the MgZn2-type and the Ti2Ni-type phases have the local icosahedral clusters [18], a small driving force will be necessary for the decomposition of the devitrified icosahedral phase.

3. Summary

A series of novel multicomponent amorphous (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₅₀Cu₅₀)₂₀Al₁₀, (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10 and (Ti33Zr33Hf33)70(Ni33Cu33Ag33)20Al10 alloys have been developed based on equiatomic substitution. Among these alloys the Nb- containing alloy exhibits the highest crystallisation temperature indicating the thermally

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most stable amorphous phase. These amorphous alloys transform into nano-scale icosahedral phases during the first exothermic reaction. The grain size of the devitrified icosahedral phase in the base and Ag-containing alloys (10-20 nm) is larger than that in the Nb-containing alloy (less than 10 nm). The icosahedral phase in (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy exists up to 973 K, coexisting with Zr2Cu-type (C16) and β-solid solution phases. However, the nano-scale icosahedral phase in the Nb-containing alloy transforms into a mixture of Ti2Ni-type and MgZn2-type phases during the second exothermic reaction around 936 K. In contrast the devitrified icosahedral phase in the Ag-containing alloy transforms partially into Zr2Cu-type (C16) phase during the second exothermic reaction and subsequently into a mixture of Zr2Cu (C16) and Ti₂Ni-type phase.

Acknowledgements

One of the authors K. B. Kim gratefully acknowledges financial support from The British Council. This research was carried out with support from EPSRC grant GR/M12971.

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References

[1] A. Inoue, T. Zhang, T. Masumoto, Mater. Trans. JIM 31 177 (1990).

[2] A. Inoue Bulk Amorphous Alloys: Preparation and Fundamental Characteristic (Trans Tech Publication Ltd, Swizerland, 1998), pp.17-25.

[3] B. Cantor, K. B. Kim and P. J. Warren, Mater. Sci. Forum 386-388 27 (2002).

[4] K. B. Kim, P. J. Warren and B. Cantor, J. Non-Cryst. Solids 317 17 (2003).

[5] K. B. Kim, P. J. Warren and B. Cantor, Mater. Trans. JIM 44 411 (2003).

[6] K. B. Kim, Y. Zhang, P. J. Warren, et al., Phil. Mag. 83 2371 (2003).

[7] L. C. Zhang and J. Xu, J. Non-Cryst. Solids 347 166 (2004).

[8] L. C. Zhang, Z. Q. Shen and J. Xu, J. Mater. Res. 18 2141 (2003).

[9] K. B. Kim, P. J. Warren and B. Cantor, Mater. Sci. Eng. A 375-377 317 (2004).

[10] K. B. Kim, P. J. Warren, B. Cantor, J. Metastable and Nanocrystalline Materials, 15-16 143 (2003).

[11] A. Inoue, T. Zhang, J. Saida, et al., Mater. Trans. JIM 40 1181(1999).

[12] A. Inoue, J. Saida, M. Matsushita, et al., Mater. Trans. JIM 41 362 (2000).

[13] A. Inoue, T. Zhang, M. W. Chen, et al., Appl. Phys. Lett. 76 967 (2000).

[14] J. Saida, M. Matsushita, C. Li, et al., Appl. Phys. Lett. 76 3558 (2000).

[15] L. Q. Xing, J. Eckert, W. Löser, et al., Apply. Phys. Lett. 74 664 (1999).

[16] K. B. Kim, D.Phil. thesis, University of Oxford, U. K. (2004)

[17] S. Scudino, U. Kuhn, L. Schultz, et al., J. Mater. Sci. 39 5483 (2004).

[18] W. J. Kim, Ph. D. thesis, Washington University in St. Louis, U.S.A. (1998).

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Figure captions

Figure 1. XRD patterns (a) and DSC traces (b) from as-quenched alloys

Figure 2. XRD patterns after heat treatment to various temperatures.

Figure 3. TEM micrographs of (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy after heat treatment at 813 K for 5 min (a) and (b), and 973 K without holding time (c).

Figure 4. TEM micrographs of (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10 alloy after heat treatment at 873 K for 5 min (a), 936 K without holding time (b), and 973 K for 10 min (c).

Figure 5. TEM micrographs of (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₃₃Cu₃₃Ag₃₃)₂₀Al₁₀ alloy after heat treatment at 843 K for 5 min (a), 873 K without holding time (b), and 973 K without holding time (c)

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Fig. 1. K. B. Kim et al.

http://mc.manuscriptcentral.com/pm-pml 3

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