Preparation and mechanical properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy

Journal of Non-Crystalline Solids 352 (2006) 3936–3941 www.elsevier.com/locate/jnoncrysol

Preparation and mechanical properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy Baozhong Liu a

a,b

, Yaoming Wu a, Limin Wang

a,*

Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, CAS, 5625 Renmin Street, Changchun 130022, China b Graduate School of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China Received 8 December 2005; received in revised form 22 June 2006 Available online 28 August 2006

Abstract A bulk Ti45Zr35Ni17Cu3 alloy, which consisted of the icosahedral quasicrystalline phase, was prepared by mechanical alloying(MA) and subsequent pulse discharge sintering. Ti45Zr35Ni17Cu3 amorphous powders (with particle size <50 lm) were obtained after mechanical alloying for more than 150 h from the mixture of the elemental powder. The transformation temperature range from amorphous phase to the quasicrystalline phase was from 400 K to 900 K. The mechanical properties of the bulk quasicrystalline alloy have been examined at room temperature. The Vickers hardness and compressive fracture strength were 620 ± 40 and 1030 ± 60 MPa, respectively. The bulk quasicrystalline alloy exhibited the elastic deformation by the compressive test. The fracture mode was brittle cleavage fracture.  2006 Elsevier B.V. All rights reserved. Keywords: Alloys; Transition metals; Crystals; Quasicrystals; Fracture; Hardness

1. Introductions Since the icosahedral quasicrystalline phase was found, it has been reported that the quasicrystalline phase was formed in a number of Ti-based alloys [1–3]. The quasicrystalline phase was also characterized as well ordered and thermodynamically stable in the Ti–Zr–Ni system [4]. Furthermore, significant attention has been paid to the study of physical, chemical, mechanical properties and other specific characteristic performances of the stable quasicrystalline Ti–Zr–Ni alloys. It was important to investigate the formation [5,6], quasicrystalline phase transformation [7,8], hydrogen storage ability [9,10] and mechanical properties [11,12] of the alloys. However, it was difficult to fabricate a single bulk quasicrystalline alloy by casting or by annealing an as-cast alloy. The formation and crystallization of amorphous and quasicrystalline Ti–Zr–Ni–Cu alloys have been reported *

Corresponding author. Tel.: +86 431 5262447; fax: +86 431 5698041. E-mail address: [email protected] (L. Wang).

0022-3093/$ - see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.07.002

in previous works [13–15]. The compositional dependence of the structure as well as quasicrystalline phase forming ability by melt-spinning and casting techniques has been examined. An improvement in the forming ability of the amorphous phase and the quasicrystalline phase has been obtained by the addition of a small amount of Cu. Ti45Zr35Ni17Cu3 alloy rods of 1 or 2 mm in diameter, mainly consisting of the quasicrystalline phase, have been prepared. However, the single bulk quasicrystalline alloy has not been fabricated by using the conventional casting technique. In the present work, the single bulk quasicrystalline Ti45Zr35Ni17Cu3 alloy was prepared by mechanical alloying (MA) and subsequent pulse discharge sintering (PDS). The microstructure and mechanical properties of the bulk quasicrystalline alloy have been investigated. 2. Experimental procedures Elemental powders of Ti (100 mesh, 99.9%), Zr (100 mesh, 99.9%), Ni (150 mesh, 99.9%) and Cu (250 mesh, 99.99%) were used as starting materials for MA. The mixed

B. Liu et al. / Journal of Non-Crystalline Solids 352 (2006) 3936–3941

powders with a desired composition of Ti45Zr35Ni17Cu3 (at.%) were added into the milling container. MA was carried out in a vibratory ball mill under the vibration frequency of 25 Hz and amplitude of 2.5 mm. The milling was conducted in an argon atmosphere for 0–280 h. The powders after MA for 280 h were consolidated by the PDS system under 190 MPa and at 858 K for 30 min in vacuum (5 · 10 3 Pa). A cylindrical bulk sample was obtained with a diameter of 20 mm and a length of approximately 30 mm. The microstructure of the MA powders and the bulk sample were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Thermal stability of the MA powders was determined by differential scanning calorimetry (DSC). The mechanical properties were examined at room temperature. The compressive fracture strength (rf) was measured at a strain rate of 1.2 · 10 3 s 1 with the specimen dimension of about 3.5 · 3.5 · 7.0 mm3, and the Vickers hardness was examined using a microhardness tester for a loading time of 15 s under the load of 0.245–4.90 N. 3. Results 3.1. Amorphization behavior The SEM images and the XRD patterns of the Ti45Zr35Ni17Cu3 powders after MA for different times were shown

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in Figs. 1 and 2, respectively. After MA for 80 h, the powders exhibited approximately spherical particles (Fig. 1(b)), and the mixed structure of amorphous and a-(Zr, Ti) phases were observed (Fig. 2(b)). The particle size and the peak intensity of the a-(Zr, Ti) phase decreased gradually with increasing MA time. After MA for 150 h and 280 h, well proportioned powders were formed and the particle size was less than 50 lm (Fig. 1(c) and (d)). As shown in Fig. 2(c) and (d), which only a broad diffraction peak was observed, it suggested that the amorphous phase was formed. The TEM bright field image (a) and the area electron diffraction pattern (b) of the Ti45Zr35Ni17Cu3 powder after MA for 280 h were shown in Fig. 3. This further indicated that the MA milled powder was an amorphous phase. The amorphous powders after MA for 280 h were examined by DSC from room temperature to 930 K at a heating rate of 0.67 K s 1, and the result was shown in Fig. 4. It can be seen that the powders exhibited a broad exothermic peak, and the transformation temperature range was defined as the onset (Tonset) and ending (Tending) temperatures from the exothermic DSC event. The transformation temperature range was approximately from 400 to 900 K. The broad exothermic peak was attributed to the formation of the quasicrystalline phase. It should be pointed out that the above result was obtained based on the XRD and TEM analysis to be presented later.

Fig. 1. SEM images of the Ti45Zr35Ni17Cu3 powders after MA for different times, (a) MA for 0 h, (b) MA for 80 h, (c) MA for150 h and (d) MA for 280 h.

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Cu Kα

-1

0.67 K s Exothermic (arb. unit)

Intensity (arb. unit)

α - Zr,Ti

(d)

(c)

(b)

400

Zr

(a) 20

Tonset

Zr Zr Ti

30

Tending

500

600

700

800

900

Temperature (K) Ni Ti

40

Zr Ni Zr

50

Zr

60

Zr

Fig. 4. DSC heating trace of the Ti45Zr35Ni17Cu3 powders after MA for 280 h.

Ni

70

80

2θ (Degree) Fig. 2. XRD patterns of the Ti45Zr35Ni17Cu3 powders after MA for different times, (a) MA for 0 h, (b) MA for 80 h, (c) MA for 150 h and (d) MA for 280 h.

Fig. 5. XRD patterns of Ti45Zr35Ni17Cu3 alloy samples, (a) alloyed powders up to 930 K in the DSC cell, (b) fabricated bulk alloy by the PDS system under 190 MPa and at 858 K for 30 min.

Fig. 3. TEM bright field image, (a) and area electron diffraction pattern, (b) of the Ti45Zr35Ni17Cu3 powder after MA for 280 h.

3.2. Preparation of a bulk quasicrystalline alloy Fig. 5 showed XRD patterns of the Ti45Zr35Ni17Cu3 powders after MA for 280 h up to 930 K in the DSC cell (a) and the bulk sample fabricated by the PDS system under 190 MPa and at 858 K for 30 min (b), respectively. The XRD results suggested that the samples were icosahedral quasicrystalline alloys. Fig. 6 showed a TEM bright field image and the selected area electron diffraction pat-

terns of the hot-pressed Ti45Zr35Ni17Cu3 bulk alloy. Fig. 6(a) presented a typical bright field morphology, and (b), (c) and (d) showed the electron diffraction patterns corresponding to the quasicrystalline phase with two-, three- and fivefold symmetries, respectively. It was firmly determined from the results of XRD analysis and TEM observation that the bulk sample was an icosahedral quasicrystalline alloy. 3.3. Mechanical properties The representative compressive curve of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy was shown in Fig. 7. It was clear that the sample undergone the elastic

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Compressive fracture strength (σf) (MPa)

deformation without plastic deformation. The Vickers hardness (HV), compressive fracture strength (rf), deformation (e) and Young’s modulus (E) of the bulk and other alloys containing icosahedral quasicrystalline phase were listed in Table 1. It can be seen that the bulk Ti45Zr35Ni17Cu3 exhibited high HV (620 ± 40), rf (1030 ± 60 MPa) and e (8 ± 1.0%), and low E (12 ± 2.0 GPa). The typical indentation under the HV testing load of 4.90 N was shown in Fig. 8, a few cracks around the indenter mark can be observed. Fig. 9 showed the representative fracture surface of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy after compressive test. The obvious cracks and cleavage planes were observed, which suggested that the fracture mode was typical brittle fracture.

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1000

800

600

400

200

0

4. Discussion Recently, the mechanical properties of the Ti-based quasicrystalline alloys have been progressively studied, it was reported that Ti–Zr–Ni quasicrystalline alloy had high hardness and good strength [11,20]. In the present work, the mechanical properties of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy have been discussed. From Table 1, the similar characteristics (high HV and low E) were found

0

2

4

6

8

10

12

14

Deformation (ε) (%)

Fig. 7. The representative compressive curves of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy.

for the Ti-based quasicrystalline alloys. The HV of the investigated bulk quasicrystalline alloy was same to the hot-pressed bulk Ti41.5Zr41.5Ni17 quasicrystalline alloy [11], but higher than that of as-cast Ti40Zr40Ni20 bulk

Fig. 6. TEM bright field image, (a) and the selected electron diffraction patterns of the hot-pressed Ti45Zr35Ni17Cu3 bulk alloy, (b), (c) and (d) correspond to the two-, three- and five-fold symmetries of the quasicrystalline phase, respectively.

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Table 1 Mechanical properties of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy and other alloys containing quasicrystalline phase Alloys

Phase constituent

Vickers hardness (HV)

Compressive strength (rf) (MPa)

Deformation (e) (%)

Young’s modulus (E) (GPa)

References

Ti45Zr35Ni17Cu3 Al62Cu25.5Fe12.5 Al70Pd20Mn10 Al93Fe3Cr2Ti2 Ti60Zr20Ni20 Ti60Zr25Ni15 Ti40Zr40Ni20 Ti53Zr27Ni20 Ti41.5Zr41.5Ni17

I I I I I + C14 + a I+a I I I

620 ± 40 – – – 546 504 520 360 600

1030 ± 60 250 520 660 750 960 542 – –

8 ± 1.0 0.35 0.38 4.5 2.1 4.2 1.25 – –

12 ± 2.0 68 200 – 35.7 22.9 43 – –

This work [17] [18] [19] [12] [12] [20] [23] [11]

I: icosahedral quasicrystalline phase; C14: C14 Laves phase; a: a solid solution phase.

Fig. 9. The fracture surface appearance of the compressive tested bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy. Fig. 8. The typical indentation of the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy under a load of 4.90 N.

quasicrystalline alloy [20] and about two times higher than that of the conventional Ti alloy [16]. The rf of the investigated bulk quasicrystalline alloy was higher than that of the other Al-based and Ti-based bulk quasicrystalline alloys [17–20]. In addition, the bulk alloy exhibited lower Young’s modulus comparing with Al-based [17–19] and other Ti-based [12,20] bulk alloys, which may be related to the Poisson’s ratio. Ponkratz et al. [22] reported that the Ti–Zr–Ni quasicrystalline alloy had high Poisson’s ratio of 0.48 ± 0.015, and the Young’s modulus range of the Ti–Zr–Ni quasicrystalline alloy was 5–35 GPa. It was in agreement with the present result for the bulk Ti45Zr35Ni17Cu3 quasicrystalline alloy. The brittleness is a well known characteristic of the quasicrystalline alloys and the hardness indentation can generate cracks. Mykhopadhyay et al. [21] have reported that the crack could occur at the edge of the indention of the Al-based bulk quasicrystalline alloy when the HV testing load was larger than 0.49 N. Yi et al. [11] have investigated the HV of the Ti41.5Zr41.5Ni17 bulk quasicrystalline

alloy prepared by hot-pressing method through mechanical alloyed powders. The cracks were observed when the hardness testing load was more than 1.0 N, and obvious radial and lateral cracks appeared at a load of 2 or 10 N. In the present work, no crack was observed when the hardness testing load was lower than 0.98 N, but several radial cracks were observed near the corner of the indenter mark when the load increased to 4.90 N (Fig. 8). This indicated that the deformation ability of the Ti45Zr35Ni17Cu3 bulk quasicrystalline alloy was similar to that of the other Tibased quasicrystalline alloys. 5. Summary Amorphous Ti45Zr35Ni17Cu3 alloy powders, with particle sizes less than 50 lm, were prepared by mechanical alloying for 150–280 h. A single bulk quasicrystalline Ti45Zr35Ni17Cu3 alloy was formed when the powders were hot-pressed at 858 K for 30 min under a pressure of 190 MPa by the pulse discharge sintering method. The bulk quasicrystalline alloy exhibited a high Vickers hard-

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ness (HV = 620 ± 40), a significant compressive fracture strength (rf = 1030 ± 60 MPa) and a low Young’s modulus (E = 12 ± 2.0 GPa). The bulk quasicrystalline alloy showed the elastic deformation and high deformation stability (e = 8 ± 1.0%) at room temperature under compression. The fracture mode was brittle cleavage fracture. Acknowledgement The Project Sponsored by the Scientific Research Foundation for National Natural Science Foundations of China (50571094) and Chinese Academy of Science for Distinguished Talents Program. References [1] Z. Zhang, H.Q. Ye, K.H. Kuo, Philos. Mag. A 52 (1985) L49. [2] C. Dong, Z.K. Hei, L.B. Wang, Q.H. Song, Y.K. Wu, K.H. Kuo, Scr. Metall. 20 (1986) 1155. [3] K.F. Kelton, P.C. Gibbons, P.N. Sabes, Phys. Rev. B 38 (1988) 7810. [4] K.F. Kelton, W.J. Kim, R.M. Stround, Appl. Phys. Lett. 70 (1997) 3230. [5] J.B. Qiang, Y.M. Wang, D.H. Wang, M. Kramer, C. Dong, Philos. Mag. Lett. 83 (2003) 467. [6] G.W. Leey, T.K. Croat, A.K. Gangopadhyay, K.F. Kelton, Philos. Mag. Lett. 82 (2002) 199. [7] S. Yi, D.H. Kim, J. Mater. Res. 15 (2000) 892.

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