- Email: [email protected]
Enhancement of plasticity in Zr-Cu-Ni-Al-Ti bulk metallic glass by heterogeneous microstructure
Journal of Non-Crystalline Solids 481 (2018) 530–536
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Enhancement of plasticity in Zr-Cu-Ni-Al-Ti bulk metallic glass by heterogeneous microstructure
T
⁎
Wei Zhou , Jiaqi Hu, Wenping Weng, Lingyan Gao, Guangying Xu Shagang School of Iron and Steel, Soochow University, Suzhou 215021, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Zr-based metallic glass Icosahedral medium-range order cluster Free volume Plasticity
Icosahedral phase was found as a primary precipitated phase in the Zr70 − xCu12.5Ni10Al7.5Tix (x = 0–8) BMGs with two or three steps of crystallization process. Remarkable plasticity was realized in a wide range of alloy composition. The enhanced plasticity is attributed to the presence of icosahedral medium-range order clusters and the local heterogeneous distribution of free volume.
1. Introduction Bulk metallic glasses (BMGs) with long-range atomic disorder display outstanding physical, chemical, and mechanical properties [1–4]. Nevertheless, their plastic deformation is achieved by the formation of localized shear bands in contrast to the multiplication and slide of dislocations in conventional crystalline materials. Such localized shear event takes place around shear transformation zones (STZs) accompanied with the creation of free volume. Dilatation of free volume inside the shear band results in a local of lowering the viscosity. Thereby, shear localization and/or strain softening leads to an early and catastrophic failure of BMG along one dominant shear band [5,6]. The poor plasticity is a major hurdle to the range of their application. In accord, extensive efforts have been devoted to remedy such deficiency, such as extrinsically adding or in-situ precipitating crystalline phase to form BMG composites [7,8], increasing free volume stored in BMG [9,10], and producing structural heterogeneity [11,12]. Among them, producing structural heterogeneity is relatively simple and effective in the enhancement of plasticity of BMG, because there is no need to consider two aspects: (1) the wettability and interfacial reaction between the second phase and the glass matrix; (2) enhancing the cooling rate to produce more free volume stored in the BMG. Minor alloying has been widely used to produce heterogeneous structure in the BMG. Chen et al. [13] reported Zr60Cu17.5Ni13.5Al8.5Nb0.5 BMG exhibits a large plasticity (~ 19.7%) with formation of phase separation structure by the addition of 0.5 at% Nb. However, after the reduction of the amount of Nb addition, the plasticity of Zr60.2Cu17.5Ni13.5Al8.5Nb0.3 BMG dramatically decreased to 5.3%. This work indicates that the excellent plasticity is available within a narrow composition range in the ZrCuNiAlNb BMG, because it
⁎
is very sensitive to the alloy composition. Similar phenomenon was also found in the ZrCuAlY [14], ZrCuAlFe [15], ZrCuAlSn [16] and TiYNbZrBeCuNi [17] BMGs with phase separation structure or ZrCuAl [18] and TiCuNiZrSn [19] BMGs with chemical fluctuation in microregion. Therefore, maintaining excellent plasticity in a wide range of alloy composition is of great importance to the applications of BMGs. Besides phase separation and chemical fluctuation in micro-region, short- or medium-range atomic ordering cluster [20] is also a kind of structural heterogeneity. But little attention has been paid to it. Some important scientific problems remain to be solved, e.g. what kind of short- or medium-range atomic ordering cluster can enhance the plasticity and the mechanism for its effect on the plasticity is still unclear. In this paper, novel Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of icosahedral medium-range order (IMRO) were synthesized by partial substitution of Zr with Ti. The effects of IMRO on the mechanical properties were systematically investigated in order to unveil the origin of the excellent plasticity. 2. Experimental procedure A series of Zr70 − xCu12.5Ni10Al7.5Tix (x = 0, 1, 2, 4, 6, and 8) master alloy ingots were prepared by arc melting high-purity metals (Zr, 99.9%; Cu, 99.99%; Ni, 99.99%; Al, 99.99%; Ti, 99.99%) using a WS-4 vacuum nonconsumable arc furnace in a purified argon atmosphere. After six times remelting, BMG rods with 2 mm in diameter were produced by suction casting. A Thermo ARL X-ray diffractometer (XRD) with monochromatic Cu Kα radiation was used to examine the phase present in the sample. Thermal analyses were carried out on Perkin-Elmer Pyris Diamond differential scanning calorimeter at a constant heating rate of 20 K/min under a flow of high purity argon.
Corresponding author. E-mail address: [email protected] (W. Zhou).
https://doi.org/10.1016/j.jnoncrysol.2017.11.042 Received 24 June 2017; Received in revised form 18 November 2017; Accepted 22 November 2017 Available online 25 November 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 1. XRD patterns obtained from the as-cast Zr70 − xCu12.5Ni10Al7.5Tix rods of 2 mm in diameter.
Fig. 3. DSC traces of the Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys at a constant heating rate of 20 K/min.
The temperature and the heat flow were calibrated by measuring the melting temperatures and the heats of fusion of pure In and Zn, giving an accuracy of ± 0.2 K and ± 0.02 mW, respectively. The microstructure of the as-cast samples was examined using a JEOL JEM-2100F high-resolution transmission electron microscopy (HRTEM). The TEM foils were prepared by electrochemical twin-jet polishing in a solution of 5% perchloric acid and 95% ethanol at 233 K, followed by ion milling with liquid nitrogen cooling. The TEM foils were immediately observed under TEM since the thin foils readily oxidize upon exposure to air. The morphology and chemical compositions of the crystallined phases were studied using a JSM-6460 scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Prior to SEM observation, the annealed samples were mechanically polished to mirror finish, and then chemically etched in a solution of 35% HNO3 plus several drops of HF for around 40 s. Uniaxial compression tests were carried out on the 2 mm in diameter and 4 mm in length cylindrical as-cast and annealed rods using a Sans CMT 5105 testing machine under a strain rate of 2 × 10− 4 s− 1. The annealed sample was heated by a vacuum electric resistance furnace to 610 K at 20 K/min. Each rod was polished carefully to ensure parallelism. At least five compressive measurements were conducted for each alloy to obtain reliable results. After compression, fracture surfaces were examined by SEM. Olympus 5072R model ultrasonic system was carried out to measure the acoustic longitudinal velocity and shear velocity of the samples. The carrying frequency of longitudinal wave and shear wave was 15 MHz and 10 MHz, respectively. Based on Archimedean principles, density measurements of the samples were performed with a Mettler Toledo XS105 microbalance with a sensitivity of 0.01 mg. The Poisson's ratio (ν), shear modulus (G) and elastic modulus (E) were derived from the acoustic velocities and the density data. 3. Results and discussion Fig. 1 shows typical XRD patterns recorded from Zr70 − xCu12.5Ni10Al7.5Tix rods of 2 mm in diameter. A broad diffuse peak instead of sharp Bragg peaks corresponding to crystalline phase is detected for each as-cast sample. HRTEM images of the as-cast rods exhibit a homogeneous featureless contrast with the absence of distinguishable crystallite, as displayed in Fig. 2. The corresponding selected area electron diffraction (SAED) patterns taken from the region with a diameter of 130 nm consist of a broad halo, characteristic of a fully
Fig. 2. HRTEM images with the inset of SAED patterns for the as-cast Zr70Cu12.5Ni10Al7.5 (a) and Zr64Cu12.5Ni10Al7.5Ti6 (b) rods.
531
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Table 1 Thermal, mechanical and elastic properties of the Zr70 − xCu12.5Ni10Al7.5Tix (x = 0, 1, 2, 4, 6 and 8) glassy alloys. x (at%Ti)
Tg (K)
Tx (K)
ΔTx (K)
Er (J/g)
σy (MPa)
0 1 2 4 6 8 6 (annealed)
616 617 618 619 620 622 620
703 687 672 666 663 660 663
87 70 54 47 43 38 43
5.1 4.9 5.4 4.7 5.0 5.2 0.1
1473 1535 1578 1640 1703 1744 1756
± ± ± ± ± ± ±
33 47 29 44 39 35 48
εp (%)
ν
7.7 ± 1.9 11.8 ± 3.4 12.5 ± 2.8 10.3 ± 2.1 17.8 ± 4.6 6.9 ± 1.7 5.5 ± 1.1
0.384 0.376 0.377 0.383 0.374 0.367 0.367
G (GPa) ± ± ± ± ± ± ±
0.009 0.012 0.010 0.009 0.005 0.014 0.007
26.2 26.5 26.7 26.6 27.0 27.4 27.3
± ± ± ± ± ± ±
E (GPa) 0.9 0.7 1.1 0.2 0.8 0.4 0.6
72.5 72.9 73.5 73.6 74.2 74.9 74.6
± ± ± ± ± ± ±
0.4 0.3 0.4 0.2 0.3 0.5 0.3
atomic arrangement in I-phase (Fig. 5c) can be found. Similar structure has been found in the as-cast Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys as well (Fig. 2), indicating that icosahedral medium-range order (IMRO) structure exists in the glassy phase for the Zr70 − xCu12.5Ni10Al7.5Tix alloys. Similar phenomenon has been observed in the Zr65Cu7.5Ni10Al7.5Pd10, Hf65Cu12.5Ni10Al7.5Pd5, Zr70Pd30 and Hf73Pd27 metallic glasses (MGs) [21,22]. Under SEM observation of the sample after heating to the first peak temperature, as shown in Fig. 6, spherical primary particles identified as an I-phase are uniformly dispersed in the glass matrix. The I-phase particles are systematically varied in sizes from 1000, 500 and 200 nm to 1200, 700 and 400 nm for the alloys with x = 0, 2 and 6, respectively. As increasing Ti content, the particles size of I-phase decreases but the number of I-particles increases. Therefore, the partial substitution of Zr with Ti is effective for the increase in nucleation rate and the decrease in growth rate for the I-phase. Similar effects were also found in the ZrCuNiAlPd [23] and ZrCuNiAlAg [24] BMGs, where the addition of alloying elements such as Pd and Ag leads to a homogeneous precipitation of nanoscale icosahedral particles in the amorphous matrix during heating. The elastic and mechanical properties of the Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys0020were investigated by ultrasonic measurements and room temperature compression tests, respectively. The corresponding test results are listed in Table 1. As is seen, the Zr70 − xCu12.5Ni10Al7.5Tix alloys possess high Poisson's ratio (ν: 0.367–0.384). With increasing the Ti content, the elastic modulus (E) monotonically increases. Fig. 7 presents the compressive stress-strain curves of Zr70 − xCu12.5Ni10Al7.5Tix rods performed at a strain rate of 2 × 10− 4 s− 1. As is seen, a large elastic elongation followed by yielding and an obvious serrated flow in the plastic region is found for each alloy in the curves. Yield strength σy and plastic strain εp for Tifree BMG are measured as 1473 MPa and 7.7%, respectively. After adding Ti element, the σy monotonously increases from 1535 MPa at x = 1 to 1744 MPa at x = 8, the εp initially displays large strain up to about 10.3%–17.8% at x = 1–6, but then decreases to 6.9% at x = 8. The compression results reveal that an appropriate amount of Ti addition is effective to improve the mechanical properties of the Zr70 − xCu12.5Ni10Al7.5Tix BMGs including both strength and plasticity. Shear band distribution and fracture morphology for the alloy were investigated by SEM shown in Fig. 8. A high density of shear bands can be observed on the surface of the alloy with x = 6, in which many secondary shear bands intersect with the primary shear bands. The highly branched shear bands accounting for many multiple shear bands formation accommodate the large plastic strain [25], instead of rapid propagation along the preferential shear bands. The fracture surface for the alloy displays mixed morphologies composed of vein-like and intermittent smooth regions. The vein-like pattern is originated from local viscous flow during shear deformation, separated by smooth regions, presenting the discontinuous distribution. Similar fracture morphology has been reported in some heterogeneous structure BMGs [26,27]. The crystallization of BMG can be considered to be a competing process among various crystals. According to the classical nucleation theory, the nucleation of crystals is mainly controlled by the interfacial energy δ [28]. Considering that the interfacial energy between the I-
Fig. 4. XRD pattern of the Zr64Cu12.5Ni10Al7.5Ti6 alloy heated to the end temperature (Te) of the first exothermic reaction.
amorphous phase. Fig. 3 presents the DSC traces of the alloys heating at 20 K/min. Each sample displays an endothermic event and two or three exothermic peaks, corresponding to glass transition and crystallization. Thermal parameters of glass transition temperature (Tg) and initial crystallization temperature (Tx) marked with arrows in the DSC curves are summarized in Table 1. It can be found that the Tg is increased with Ti addition from 616 K at x = 0 to 622 K at x = 8, while the Tx monotonously decreases from 703 K at x = 0 to 660 K at x = 8. As a result, the supercooled liquid region width ΔTx defined by the difference between Tg and Tx, decreases from 87 K at x = 0 to 38 K at x = 8, indicating that the partial replacement of Zr with Ti is detrimental to the thermal stability of the glassy alloy. The primary precipitated phase during the crystallization process was examined via XRD, SEM and TEM. The XRD patterns of the glassy alloys with x = 6 annealed at the end temperature of the first exothermic peak, as presented in Fig. 4, exhibit several sharp diffraction peaks corresponding to an icosahedral phase (I-phase). Fig. 5a presents the bright-field TEM image for the alloy with x = 6 heated up to the peak temperature of the first exothermic reaction. Nanoscale spherical particles precipitate in the glass matrix. Nanobeam diffraction pattern taken from the region with diameter of 2.4 nm reveals a five-fold rotational symmetry, confirming the I-phase nature of these nanoparticles. The HRTEM image (Fig. 5b) obtained from the local region containing I-phase and glassy phase shows quite sharp boundary between these two phases. Fig. 5c is the Inverse Fourier Transfer (IFT) image obtained from the I-phase (area I as shown in Fig. 5a). The fivefold symmetries of the atomic arrangement can be obviously observed. Fig. 5d is the IFT image from the glassy phase (area II as shown in Fig. 5a). As is seen, except for the disorder atomic structure, some regions with 1–2 nm scale medium-range order structure similar to the 532
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 5. Bright-field TEM image with the inset of SAED pattern (a) and corresponding HRTEM image (b) for Zr64Cu12.5Ni10Al7.5Ti6 alloy heated to peak point (Tp) of the first exothermic reaction. (c) and (d) are the IFT images of the area I and area II, respectively.
with the as-cast sample before deformation. The corresponding SAED pattern taken from the region with a diameter of 130 nm presents halo diffraction intensity. These results indicate that no phase transformation such as phase separation or nanocrystallization was detected during the deformation of the alloy. Plastic deformation of the BMG is accomplished by the operation and formation of shear transformation zone (STZ) associated with free volume. Thereby, introducing more free volume trapped in the BMG is effective to enhance the plasticity. Here, we use the relaxation energy to quantitatively characterize the free volume content stored in the BMG, which was developed by Beukel and Sietsma [33]. The relaxation energy Er for each alloy was estimated to be about 4.7–5.4 J/g. No positive correlation between the plasticity and free volume content was found among the samples. But after heating the 6 at% Ti alloy to the temperature below Tg, intrinsic structural relaxation accompanied with the annihilation of free volume results in the remarkable reduction of the plasticity (~ 5.5%), as presented in Fig. 10. Therefore, it can be concluded that the introduction of a certain amount of free volume into the BMG plays a beneficial role in the plasticity besides the existence of IMRO. Then, the key question addresses as to how the IMRO and free volume affect the shear banding behavior. Considering that the high densely packed IMRO have no or little free volume, the introduction of IMRO into the BMG causes the heterogeneous distribution of free volume, resulting in nanoscale structural heterogeneity. A structural model proposed by Liu et al. [34] supports such point, in which the ISRO serves as the core, and the surrounding loose region is the shell. The Zr70 − xCu12.5Ni10Al7.5Tix BMGs can be seen as composite structure consisting of high densely packed core of IMRO surrounded by loosely packed region, as presented in Fig. 11. Upon loading, the STZ preferentially nucleates in the loose region and then evolves into shear
phase and the glass phase is much lower than that of other crystals which possess face centered cubic structure or body centered cubic structure, the IMRO embedded in the glass phase for the as-cast Zr70 − xCu12.5Ni10Al7.5Tix BMG, acting as nuclei, causes the preferential precipitation of I-phase during the primary crystallization. From the structural and mechanical perspectives, the Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of IMRO display excellent plasticity. This feature in microstructure is distinctly different from that of most BMGs with poor plasticity such as Zr55Cu30Ni5Al10 or Zr65Cu17.5Ni10Al7.5 BMG [29,30], since no sign of IMRO was detected. It can be deduced that the excellent plasticity of the Zr70 − xCu12.5Ni10Al7.5Tix BMGs correlates with the existence of IMRO. Densely packed IMRO is however not easy to shear transformation. Zhang et al. [31] reported that the increase of Zr content in the Zr-Cu-Al BMG contributes to the decrease of yield strength and the enhancement of plasticity, due to the reduction in the number of icosahedral shortrange order (ISRO) clusters. In this case, the alloy with lower Zr content, and hence more numbers of IMRO cluster for the Zr70 − xCu12.5Ni10Al7.5Tix BMGs, would display a higher resistance to plastic flow and a lower plastic strain. However, the plasticity does not decrease, and even increases for some Ti-bearing BMGs in the compressive measurement. Therefore, it can be presumed that other factors also affect the deformation behavior of the BMG upon loading. Recently, Setyawan et al. [32] reported Zr65Cu12.5Ni10Al7.5Nb5 BMG with the presence of strong ISRO exhibits a large plastic strain, owing to deformation-induced structural transformation of glass phase into fccZr2Ni phase. Therefore, the possibility of deformation-induced crystallization was checked by HRTEM image recorded from the fracture Zr64Cu12.5Ni10Al7.5Ti6 rod near the main shear band. As shown in Fig. 9, except for a bright shear band with 5–10 nm in width, neither obvious contrast nor lattice fringe was found in the fracture sample as compared 533
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 7. Compressive stress-strain curves of the Zr70 − xCu12.5Ni10Al7.5Tix rods.
Fig. 6. SEM secondary electron images of Zr70Cu12.5Ni10Al7.5 (a), Zr68Cu12.5Ni10Al7.5Ti2 (b), and Zr64Cu12.5Ni10Al7.5Ti6 (c) BMGs after being annealed up to the peak point of the first exothermic reaction.
band. The propagation of shear band is however blocked by the core. With further increasing load, multiplication and branching of shear bands are activated. In other words, the heterogeneous structure can effectively impedes shear band from propagating catastrophically at the onset of the plastic deformation and promotes the generation of profuse multiple shear bands, accommodating more plastic strain. The present work indicates that the Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of IMRO possess large plasticity within a wide composition span. Therefore, the introduction of IMRO into the glassy phase, which causes the heterogeneity of free volume distribution, is believed to be effective for the design of a new series of BMGs with large plastic strain.
Fig. 8. SEM secondary electron images of the outer appearance (a) and fracture surface (b) for the Zr64Cu12.5Ni10Al7.5Ti6 rod after compression test.
Zr70 − xCu12.5Ni10Al7.5Tix BMGs, but does not change the initial crystallization phase. Icosahedral phase with spherical morphology was found to appear as a primary phase in the BMGs with two or three steps of crystallization process. (2) An appropriate amount of Ti addition can significantly improve the mechanical performance of the BMG. The yield strength tends to increase with the Ti content. The BMGs with x = 0–8 exhibit large compressive plastic strain of 6.9%–17.8%. The enhanced plasticity is attributed to structural heterogeneity resulted from the presence of IMRO and heterogeneous distribution of free volume, which
4. Conclusions (1) The
addition
of
Ti
reduces
the
thermal
stability
of 534
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 11. Schematic of microstructure evolution of Zr70 − xCu12.5Ni10Al7.5Tix BMGs during the plastic deformation.
affect the shear band formation and propagation, and promote the activation of multiple shear bands. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant No. 51401139) and the Natural Science Foundation of Jiangsu Province (No. BK20151221). References [1] B.A. Sun, W.H. Wang, The fracture of bulk metallic glasses, Prog. Mater. Sci. 74 (2015) 211–307. [2] M.M. Trexler, N.N. Thadhani, Mechanical properties of bulk metallic glasses, Prog. Mater. Sci. 55 (2010) 759–839. [3] A. Inoue, A. Takeuchi, Recent development and application products of bulk glassy alloys, Acta Mater. 59 (2011) 2243–2267. [4] C.A. Schuh, T.C. Hufnagel, U. Ramamurty, Mechanical behavior of amorphous alloys, Acta Mater. 54 (2007) 4067–4109. [5] A.L. Greer, Y.Q. Cheng, E. Ma, Shear bands in metallic glasses, Mater. Sci. Eng. R 74 (2013) 71–132. [6] W. Zhou, Y.B. Guo, B.F. Lu, L.T. Kong, J.F. Li, Y.H. Zhou, Microstructure and mechanical property of Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass subjected to rolling, J. Mater. Sci. 47 (2012) 2206–2212. [7] H. Choi-Yim, R.D. Conner, F. Szuecs, W.L. Johnson, Processing, microstructure and properties of ductile metal particulate reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass composites, Acta Mater. 50 (2002) 2737–2745. [8] H.M. Zhai, H.F. Wang, F. Liu, Effect of Sn addition on mechanical properties of Tibased metallic glass composites, Mater. Des. 110 (2016) 782–789. [9] Y.J. Huang, J. Shen, J.F. Sun, Buk metallic glasses: smaller is softer, Appl. Phys. Lett. 90 (2007) 081919. [10] L.Y. Chen, Z.D. Fu, G.Q. Zhang, X.P. Hao, Q.K. Jiang, X.D. Wang, Q.P. Cao, H. Franz, Y.G. Liu, H.S. Xie, S.L. Zhang, B.Y. Wang, Y.W. Zeng, J.Z. Jiang, New class of plastic bulk metallic glass, Phys. Rev. Lett. 100 (2008) 075501. [11] T. Nagase, Y. Umakoshi, Amorphous phase formation in Co-Cu-Zr-B-based immiscible alloys, J. Alloys Compd. 649 (2015) 1174–1181. [12] D.H. Kim, W.T. Kim, E.S. Park, N. Mattern, J. Eckert, Phase separation in metallic glasses, Prog. Mater. Sci. 58 (2013) 1103–1172. [13] S.S. Chen, I. Todd, Enhanced plasticity in the Zr-Cu-Ni-Al-Nb alloy system by in-situ formation of two glassy phases, J. Alloys Compd. 646 (2015) 973–977. [14] E.S. Park, D.H. Kim, Phase separation and enhancement of plasticity in Cu-Zr-Al-Y bulk metallic glasses, Acta Mater. 54 (2006) 2597–2604. [15] J. Pan, K.C. Chan, Q. Chen, N. Li, S.F. Guo, L. Liu, The effect of microalloying on mechanical properties in CuZrAl bulk metallic glass, J. Alloys Compd. 504S (2010) S74–S77. [16] W. Zhou, J.X. Hou, W.P. Weng, Microstructure, thermal stability and mechanical properties of Zr-Cu-Al-Sn bulk metallic glass, J. Non-Cryst. Solids 429 (2015)
Fig. 9. Bright-field TEM images with the inset of SAED patterns and corresponding HRTEM images for the fracture Zr64Cu12.5Ni10Al7.5Ti6 rod near the main shear band.
Fig. 10. Compressive stress-strain curves of the as-cast and annealed Zr64Cu12.5Ni10Al7.5Ti6 rods. The inset shows comparison of specific heats of the as-cast and annealed samples.
535
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
[26] J.M. Park, J.H. Han, N. Mattern, D.H. Kim, J. Eckert, Designing Zr-Cu-Co-Al bulk metallic glasses with phase separation mediated plasticity, Metall. Mater. Trans. A 43 (2012) 2598–2603. [27] E.S. Park, H.J. Chang, J.S. Kyeong, D.H. Kim, Role of minor addition of metallic alloying elements in formation and properties of Cu-Ti-rich bulk metallic glasses, J. Mater. Res. 23 (2008) 1995–2002. [28] K.F. Kelton, Crystallization of liquids and glasses to quasicrystals, J. Non-Cryst. Solids 317 (2003) 97–105. [29] Y. Hu, L.F. Li, T. Lin, Y.H. Zhou, Plasticity improvement of Zr55Al10Ni5Cu30 bulk metallic glass by remelting master alloy ingot, J. Mater. Res. 24 (2009) 3590–3595. [30] Q.S. Zhang, W. Zhang, X.M. Wang, Y. Yokoyama, K. Yubuta, A. Inoue, Structure, thermal stability and mechanical properties of Zr65Al7.5Ni10Cu17.5 glassy alloy rod with a diameter of 16 mm produced by tilt casting, Mater. Trans. 49 (2008) 2141–2146. [31] L. Zhang, Y.Q. Cheng, A.J. Cao, J. Xu, E. Ma, Bulk metallic glasses with large plasticity: composition design from the structural perspective, Acta Mater. 57 (2009) 1154–1164. [32] A.D. Setyawan, J. Saida, H. Kato, M. Matsushita, A. Inoue, Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys, J. Mater. Res. 25 (2010) 1149–1158. [33] A. van den Beukel, J. Sietsma, The glass transition as a free volume related kinetic phenomenon, Acta Metall. 38 (1990) 383–389. [34] X.J. Liu, G.L. Chen, X. Hui, T. Lu, Z.P. Liu, Ordered clusters and free volume in a ZrNi metallic glass, Appl. Phys. Lett. 93 (2008) 011911.
208–212. [17] E.S. Park, H.J. Chang, J.Y. Lee, D.H. Kim, Improvement of plasticity by tailoring combination of constituent elements in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses, J. Mater. Res. 22 (2007) 3440–3447. [18] K.B. Kim, J. Das, F. Baier, M.B. Tang, W.H. Wang, J. Eckert, Heterogeneity of a Cu47.5Zr47.5Al5 bulk metallic glass, Appl. Phys. Lett. 88 (2006) 051911. [19] K.B. Kim, J. Das, S. Venkataraman, S. Yi, J. Eckert, Work hardening ability of ductile Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 bulk metallic glasses, Appl. Phys. Lett. 89 (2006) 071908. [20] Z.W. Zhu, H.F. Zhang, W.S. Sun, B.Z. Ding, Z.Q. Hu, Processing of bulk metallic glasses with high strength and large compressive plasticity in Cu50Zr50, Scr. Mater. 54 (2006) 1145–1149. [21] J. Saida, C. Li, M. Matsushita, A. Inoue, Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior, J. Mater. Res. 16 (2001) 3389–3401. [22] J. Saida, A. Inoue, Quasicrystals from glass devitrification, J. Non-Cryst. Solids 317 (2003) 97–105. [23] A. Inoue, High strength and ductile bulk quasi-crystalline alloys, Adv. Eng. Mater. 3 (2001) 669–673. [24] A. Inoue, T. Zhang, M.W. Chen, T. Sakurai, J. Saida, M. Matsushita, Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility, J. Mater. Res. 10 (2000) 2195–2208. [25] J. Pan, L. Liu, K.C. Chan, Enhanced plasticity by phase separation in CuZrAl bulk metallic glass with micro-addition of Fe, Scr. Mater. 60 (2009) 822–825.
536
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Enhancement of plasticity in Zr-Cu-Ni-Al-Ti bulk metallic glass by heterogeneous microstructure
T
⁎
Wei Zhou , Jiaqi Hu, Wenping Weng, Lingyan Gao, Guangying Xu Shagang School of Iron and Steel, Soochow University, Suzhou 215021, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Zr-based metallic glass Icosahedral medium-range order cluster Free volume Plasticity
Icosahedral phase was found as a primary precipitated phase in the Zr70 − xCu12.5Ni10Al7.5Tix (x = 0–8) BMGs with two or three steps of crystallization process. Remarkable plasticity was realized in a wide range of alloy composition. The enhanced plasticity is attributed to the presence of icosahedral medium-range order clusters and the local heterogeneous distribution of free volume.
1. Introduction Bulk metallic glasses (BMGs) with long-range atomic disorder display outstanding physical, chemical, and mechanical properties [1–4]. Nevertheless, their plastic deformation is achieved by the formation of localized shear bands in contrast to the multiplication and slide of dislocations in conventional crystalline materials. Such localized shear event takes place around shear transformation zones (STZs) accompanied with the creation of free volume. Dilatation of free volume inside the shear band results in a local of lowering the viscosity. Thereby, shear localization and/or strain softening leads to an early and catastrophic failure of BMG along one dominant shear band [5,6]. The poor plasticity is a major hurdle to the range of their application. In accord, extensive efforts have been devoted to remedy such deficiency, such as extrinsically adding or in-situ precipitating crystalline phase to form BMG composites [7,8], increasing free volume stored in BMG [9,10], and producing structural heterogeneity [11,12]. Among them, producing structural heterogeneity is relatively simple and effective in the enhancement of plasticity of BMG, because there is no need to consider two aspects: (1) the wettability and interfacial reaction between the second phase and the glass matrix; (2) enhancing the cooling rate to produce more free volume stored in the BMG. Minor alloying has been widely used to produce heterogeneous structure in the BMG. Chen et al. [13] reported Zr60Cu17.5Ni13.5Al8.5Nb0.5 BMG exhibits a large plasticity (~ 19.7%) with formation of phase separation structure by the addition of 0.5 at% Nb. However, after the reduction of the amount of Nb addition, the plasticity of Zr60.2Cu17.5Ni13.5Al8.5Nb0.3 BMG dramatically decreased to 5.3%. This work indicates that the excellent plasticity is available within a narrow composition range in the ZrCuNiAlNb BMG, because it
⁎
is very sensitive to the alloy composition. Similar phenomenon was also found in the ZrCuAlY [14], ZrCuAlFe [15], ZrCuAlSn [16] and TiYNbZrBeCuNi [17] BMGs with phase separation structure or ZrCuAl [18] and TiCuNiZrSn [19] BMGs with chemical fluctuation in microregion. Therefore, maintaining excellent plasticity in a wide range of alloy composition is of great importance to the applications of BMGs. Besides phase separation and chemical fluctuation in micro-region, short- or medium-range atomic ordering cluster [20] is also a kind of structural heterogeneity. But little attention has been paid to it. Some important scientific problems remain to be solved, e.g. what kind of short- or medium-range atomic ordering cluster can enhance the plasticity and the mechanism for its effect on the plasticity is still unclear. In this paper, novel Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of icosahedral medium-range order (IMRO) were synthesized by partial substitution of Zr with Ti. The effects of IMRO on the mechanical properties were systematically investigated in order to unveil the origin of the excellent plasticity. 2. Experimental procedure A series of Zr70 − xCu12.5Ni10Al7.5Tix (x = 0, 1, 2, 4, 6, and 8) master alloy ingots were prepared by arc melting high-purity metals (Zr, 99.9%; Cu, 99.99%; Ni, 99.99%; Al, 99.99%; Ti, 99.99%) using a WS-4 vacuum nonconsumable arc furnace in a purified argon atmosphere. After six times remelting, BMG rods with 2 mm in diameter were produced by suction casting. A Thermo ARL X-ray diffractometer (XRD) with monochromatic Cu Kα radiation was used to examine the phase present in the sample. Thermal analyses were carried out on Perkin-Elmer Pyris Diamond differential scanning calorimeter at a constant heating rate of 20 K/min under a flow of high purity argon.
Corresponding author. E-mail address: [email protected] (W. Zhou).
https://doi.org/10.1016/j.jnoncrysol.2017.11.042 Received 24 June 2017; Received in revised form 18 November 2017; Accepted 22 November 2017 Available online 25 November 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 1. XRD patterns obtained from the as-cast Zr70 − xCu12.5Ni10Al7.5Tix rods of 2 mm in diameter.
Fig. 3. DSC traces of the Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys at a constant heating rate of 20 K/min.
The temperature and the heat flow were calibrated by measuring the melting temperatures and the heats of fusion of pure In and Zn, giving an accuracy of ± 0.2 K and ± 0.02 mW, respectively. The microstructure of the as-cast samples was examined using a JEOL JEM-2100F high-resolution transmission electron microscopy (HRTEM). The TEM foils were prepared by electrochemical twin-jet polishing in a solution of 5% perchloric acid and 95% ethanol at 233 K, followed by ion milling with liquid nitrogen cooling. The TEM foils were immediately observed under TEM since the thin foils readily oxidize upon exposure to air. The morphology and chemical compositions of the crystallined phases were studied using a JSM-6460 scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Prior to SEM observation, the annealed samples were mechanically polished to mirror finish, and then chemically etched in a solution of 35% HNO3 plus several drops of HF for around 40 s. Uniaxial compression tests were carried out on the 2 mm in diameter and 4 mm in length cylindrical as-cast and annealed rods using a Sans CMT 5105 testing machine under a strain rate of 2 × 10− 4 s− 1. The annealed sample was heated by a vacuum electric resistance furnace to 610 K at 20 K/min. Each rod was polished carefully to ensure parallelism. At least five compressive measurements were conducted for each alloy to obtain reliable results. After compression, fracture surfaces were examined by SEM. Olympus 5072R model ultrasonic system was carried out to measure the acoustic longitudinal velocity and shear velocity of the samples. The carrying frequency of longitudinal wave and shear wave was 15 MHz and 10 MHz, respectively. Based on Archimedean principles, density measurements of the samples were performed with a Mettler Toledo XS105 microbalance with a sensitivity of 0.01 mg. The Poisson's ratio (ν), shear modulus (G) and elastic modulus (E) were derived from the acoustic velocities and the density data. 3. Results and discussion Fig. 1 shows typical XRD patterns recorded from Zr70 − xCu12.5Ni10Al7.5Tix rods of 2 mm in diameter. A broad diffuse peak instead of sharp Bragg peaks corresponding to crystalline phase is detected for each as-cast sample. HRTEM images of the as-cast rods exhibit a homogeneous featureless contrast with the absence of distinguishable crystallite, as displayed in Fig. 2. The corresponding selected area electron diffraction (SAED) patterns taken from the region with a diameter of 130 nm consist of a broad halo, characteristic of a fully
Fig. 2. HRTEM images with the inset of SAED patterns for the as-cast Zr70Cu12.5Ni10Al7.5 (a) and Zr64Cu12.5Ni10Al7.5Ti6 (b) rods.
531
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Table 1 Thermal, mechanical and elastic properties of the Zr70 − xCu12.5Ni10Al7.5Tix (x = 0, 1, 2, 4, 6 and 8) glassy alloys. x (at%Ti)
Tg (K)
Tx (K)
ΔTx (K)
Er (J/g)
σy (MPa)
0 1 2 4 6 8 6 (annealed)
616 617 618 619 620 622 620
703 687 672 666 663 660 663
87 70 54 47 43 38 43
5.1 4.9 5.4 4.7 5.0 5.2 0.1
1473 1535 1578 1640 1703 1744 1756
± ± ± ± ± ± ±
33 47 29 44 39 35 48
εp (%)
ν
7.7 ± 1.9 11.8 ± 3.4 12.5 ± 2.8 10.3 ± 2.1 17.8 ± 4.6 6.9 ± 1.7 5.5 ± 1.1
0.384 0.376 0.377 0.383 0.374 0.367 0.367
G (GPa) ± ± ± ± ± ± ±
0.009 0.012 0.010 0.009 0.005 0.014 0.007
26.2 26.5 26.7 26.6 27.0 27.4 27.3
± ± ± ± ± ± ±
E (GPa) 0.9 0.7 1.1 0.2 0.8 0.4 0.6
72.5 72.9 73.5 73.6 74.2 74.9 74.6
± ± ± ± ± ± ±
0.4 0.3 0.4 0.2 0.3 0.5 0.3
atomic arrangement in I-phase (Fig. 5c) can be found. Similar structure has been found in the as-cast Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys as well (Fig. 2), indicating that icosahedral medium-range order (IMRO) structure exists in the glassy phase for the Zr70 − xCu12.5Ni10Al7.5Tix alloys. Similar phenomenon has been observed in the Zr65Cu7.5Ni10Al7.5Pd10, Hf65Cu12.5Ni10Al7.5Pd5, Zr70Pd30 and Hf73Pd27 metallic glasses (MGs) [21,22]. Under SEM observation of the sample after heating to the first peak temperature, as shown in Fig. 6, spherical primary particles identified as an I-phase are uniformly dispersed in the glass matrix. The I-phase particles are systematically varied in sizes from 1000, 500 and 200 nm to 1200, 700 and 400 nm for the alloys with x = 0, 2 and 6, respectively. As increasing Ti content, the particles size of I-phase decreases but the number of I-particles increases. Therefore, the partial substitution of Zr with Ti is effective for the increase in nucleation rate and the decrease in growth rate for the I-phase. Similar effects were also found in the ZrCuNiAlPd [23] and ZrCuNiAlAg [24] BMGs, where the addition of alloying elements such as Pd and Ag leads to a homogeneous precipitation of nanoscale icosahedral particles in the amorphous matrix during heating. The elastic and mechanical properties of the Zr70 − xCu12.5Ni10Al7.5Tix glassy alloys0020were investigated by ultrasonic measurements and room temperature compression tests, respectively. The corresponding test results are listed in Table 1. As is seen, the Zr70 − xCu12.5Ni10Al7.5Tix alloys possess high Poisson's ratio (ν: 0.367–0.384). With increasing the Ti content, the elastic modulus (E) monotonically increases. Fig. 7 presents the compressive stress-strain curves of Zr70 − xCu12.5Ni10Al7.5Tix rods performed at a strain rate of 2 × 10− 4 s− 1. As is seen, a large elastic elongation followed by yielding and an obvious serrated flow in the plastic region is found for each alloy in the curves. Yield strength σy and plastic strain εp for Tifree BMG are measured as 1473 MPa and 7.7%, respectively. After adding Ti element, the σy monotonously increases from 1535 MPa at x = 1 to 1744 MPa at x = 8, the εp initially displays large strain up to about 10.3%–17.8% at x = 1–6, but then decreases to 6.9% at x = 8. The compression results reveal that an appropriate amount of Ti addition is effective to improve the mechanical properties of the Zr70 − xCu12.5Ni10Al7.5Tix BMGs including both strength and plasticity. Shear band distribution and fracture morphology for the alloy were investigated by SEM shown in Fig. 8. A high density of shear bands can be observed on the surface of the alloy with x = 6, in which many secondary shear bands intersect with the primary shear bands. The highly branched shear bands accounting for many multiple shear bands formation accommodate the large plastic strain [25], instead of rapid propagation along the preferential shear bands. The fracture surface for the alloy displays mixed morphologies composed of vein-like and intermittent smooth regions. The vein-like pattern is originated from local viscous flow during shear deformation, separated by smooth regions, presenting the discontinuous distribution. Similar fracture morphology has been reported in some heterogeneous structure BMGs [26,27]. The crystallization of BMG can be considered to be a competing process among various crystals. According to the classical nucleation theory, the nucleation of crystals is mainly controlled by the interfacial energy δ [28]. Considering that the interfacial energy between the I-
Fig. 4. XRD pattern of the Zr64Cu12.5Ni10Al7.5Ti6 alloy heated to the end temperature (Te) of the first exothermic reaction.
amorphous phase. Fig. 3 presents the DSC traces of the alloys heating at 20 K/min. Each sample displays an endothermic event and two or three exothermic peaks, corresponding to glass transition and crystallization. Thermal parameters of glass transition temperature (Tg) and initial crystallization temperature (Tx) marked with arrows in the DSC curves are summarized in Table 1. It can be found that the Tg is increased with Ti addition from 616 K at x = 0 to 622 K at x = 8, while the Tx monotonously decreases from 703 K at x = 0 to 660 K at x = 8. As a result, the supercooled liquid region width ΔTx defined by the difference between Tg and Tx, decreases from 87 K at x = 0 to 38 K at x = 8, indicating that the partial replacement of Zr with Ti is detrimental to the thermal stability of the glassy alloy. The primary precipitated phase during the crystallization process was examined via XRD, SEM and TEM. The XRD patterns of the glassy alloys with x = 6 annealed at the end temperature of the first exothermic peak, as presented in Fig. 4, exhibit several sharp diffraction peaks corresponding to an icosahedral phase (I-phase). Fig. 5a presents the bright-field TEM image for the alloy with x = 6 heated up to the peak temperature of the first exothermic reaction. Nanoscale spherical particles precipitate in the glass matrix. Nanobeam diffraction pattern taken from the region with diameter of 2.4 nm reveals a five-fold rotational symmetry, confirming the I-phase nature of these nanoparticles. The HRTEM image (Fig. 5b) obtained from the local region containing I-phase and glassy phase shows quite sharp boundary between these two phases. Fig. 5c is the Inverse Fourier Transfer (IFT) image obtained from the I-phase (area I as shown in Fig. 5a). The fivefold symmetries of the atomic arrangement can be obviously observed. Fig. 5d is the IFT image from the glassy phase (area II as shown in Fig. 5a). As is seen, except for the disorder atomic structure, some regions with 1–2 nm scale medium-range order structure similar to the 532
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 5. Bright-field TEM image with the inset of SAED pattern (a) and corresponding HRTEM image (b) for Zr64Cu12.5Ni10Al7.5Ti6 alloy heated to peak point (Tp) of the first exothermic reaction. (c) and (d) are the IFT images of the area I and area II, respectively.
with the as-cast sample before deformation. The corresponding SAED pattern taken from the region with a diameter of 130 nm presents halo diffraction intensity. These results indicate that no phase transformation such as phase separation or nanocrystallization was detected during the deformation of the alloy. Plastic deformation of the BMG is accomplished by the operation and formation of shear transformation zone (STZ) associated with free volume. Thereby, introducing more free volume trapped in the BMG is effective to enhance the plasticity. Here, we use the relaxation energy to quantitatively characterize the free volume content stored in the BMG, which was developed by Beukel and Sietsma [33]. The relaxation energy Er for each alloy was estimated to be about 4.7–5.4 J/g. No positive correlation between the plasticity and free volume content was found among the samples. But after heating the 6 at% Ti alloy to the temperature below Tg, intrinsic structural relaxation accompanied with the annihilation of free volume results in the remarkable reduction of the plasticity (~ 5.5%), as presented in Fig. 10. Therefore, it can be concluded that the introduction of a certain amount of free volume into the BMG plays a beneficial role in the plasticity besides the existence of IMRO. Then, the key question addresses as to how the IMRO and free volume affect the shear banding behavior. Considering that the high densely packed IMRO have no or little free volume, the introduction of IMRO into the BMG causes the heterogeneous distribution of free volume, resulting in nanoscale structural heterogeneity. A structural model proposed by Liu et al. [34] supports such point, in which the ISRO serves as the core, and the surrounding loose region is the shell. The Zr70 − xCu12.5Ni10Al7.5Tix BMGs can be seen as composite structure consisting of high densely packed core of IMRO surrounded by loosely packed region, as presented in Fig. 11. Upon loading, the STZ preferentially nucleates in the loose region and then evolves into shear
phase and the glass phase is much lower than that of other crystals which possess face centered cubic structure or body centered cubic structure, the IMRO embedded in the glass phase for the as-cast Zr70 − xCu12.5Ni10Al7.5Tix BMG, acting as nuclei, causes the preferential precipitation of I-phase during the primary crystallization. From the structural and mechanical perspectives, the Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of IMRO display excellent plasticity. This feature in microstructure is distinctly different from that of most BMGs with poor plasticity such as Zr55Cu30Ni5Al10 or Zr65Cu17.5Ni10Al7.5 BMG [29,30], since no sign of IMRO was detected. It can be deduced that the excellent plasticity of the Zr70 − xCu12.5Ni10Al7.5Tix BMGs correlates with the existence of IMRO. Densely packed IMRO is however not easy to shear transformation. Zhang et al. [31] reported that the increase of Zr content in the Zr-Cu-Al BMG contributes to the decrease of yield strength and the enhancement of plasticity, due to the reduction in the number of icosahedral shortrange order (ISRO) clusters. In this case, the alloy with lower Zr content, and hence more numbers of IMRO cluster for the Zr70 − xCu12.5Ni10Al7.5Tix BMGs, would display a higher resistance to plastic flow and a lower plastic strain. However, the plasticity does not decrease, and even increases for some Ti-bearing BMGs in the compressive measurement. Therefore, it can be presumed that other factors also affect the deformation behavior of the BMG upon loading. Recently, Setyawan et al. [32] reported Zr65Cu12.5Ni10Al7.5Nb5 BMG with the presence of strong ISRO exhibits a large plastic strain, owing to deformation-induced structural transformation of glass phase into fccZr2Ni phase. Therefore, the possibility of deformation-induced crystallization was checked by HRTEM image recorded from the fracture Zr64Cu12.5Ni10Al7.5Ti6 rod near the main shear band. As shown in Fig. 9, except for a bright shear band with 5–10 nm in width, neither obvious contrast nor lattice fringe was found in the fracture sample as compared 533
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 7. Compressive stress-strain curves of the Zr70 − xCu12.5Ni10Al7.5Tix rods.
Fig. 6. SEM secondary electron images of Zr70Cu12.5Ni10Al7.5 (a), Zr68Cu12.5Ni10Al7.5Ti2 (b), and Zr64Cu12.5Ni10Al7.5Ti6 (c) BMGs after being annealed up to the peak point of the first exothermic reaction.
band. The propagation of shear band is however blocked by the core. With further increasing load, multiplication and branching of shear bands are activated. In other words, the heterogeneous structure can effectively impedes shear band from propagating catastrophically at the onset of the plastic deformation and promotes the generation of profuse multiple shear bands, accommodating more plastic strain. The present work indicates that the Zr70 − xCu12.5Ni10Al7.5Tix BMGs with the presence of IMRO possess large plasticity within a wide composition span. Therefore, the introduction of IMRO into the glassy phase, which causes the heterogeneity of free volume distribution, is believed to be effective for the design of a new series of BMGs with large plastic strain.
Fig. 8. SEM secondary electron images of the outer appearance (a) and fracture surface (b) for the Zr64Cu12.5Ni10Al7.5Ti6 rod after compression test.
Zr70 − xCu12.5Ni10Al7.5Tix BMGs, but does not change the initial crystallization phase. Icosahedral phase with spherical morphology was found to appear as a primary phase in the BMGs with two or three steps of crystallization process. (2) An appropriate amount of Ti addition can significantly improve the mechanical performance of the BMG. The yield strength tends to increase with the Ti content. The BMGs with x = 0–8 exhibit large compressive plastic strain of 6.9%–17.8%. The enhanced plasticity is attributed to structural heterogeneity resulted from the presence of IMRO and heterogeneous distribution of free volume, which
4. Conclusions (1) The
addition
of
Ti
reduces
the
thermal
stability
of 534
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
Fig. 11. Schematic of microstructure evolution of Zr70 − xCu12.5Ni10Al7.5Tix BMGs during the plastic deformation.
affect the shear band formation and propagation, and promote the activation of multiple shear bands. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant No. 51401139) and the Natural Science Foundation of Jiangsu Province (No. BK20151221). References [1] B.A. Sun, W.H. Wang, The fracture of bulk metallic glasses, Prog. Mater. Sci. 74 (2015) 211–307. [2] M.M. Trexler, N.N. Thadhani, Mechanical properties of bulk metallic glasses, Prog. Mater. Sci. 55 (2010) 759–839. [3] A. Inoue, A. Takeuchi, Recent development and application products of bulk glassy alloys, Acta Mater. 59 (2011) 2243–2267. [4] C.A. Schuh, T.C. Hufnagel, U. Ramamurty, Mechanical behavior of amorphous alloys, Acta Mater. 54 (2007) 4067–4109. [5] A.L. Greer, Y.Q. Cheng, E. Ma, Shear bands in metallic glasses, Mater. Sci. Eng. R 74 (2013) 71–132. [6] W. Zhou, Y.B. Guo, B.F. Lu, L.T. Kong, J.F. Li, Y.H. Zhou, Microstructure and mechanical property of Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass subjected to rolling, J. Mater. Sci. 47 (2012) 2206–2212. [7] H. Choi-Yim, R.D. Conner, F. Szuecs, W.L. Johnson, Processing, microstructure and properties of ductile metal particulate reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass composites, Acta Mater. 50 (2002) 2737–2745. [8] H.M. Zhai, H.F. Wang, F. Liu, Effect of Sn addition on mechanical properties of Tibased metallic glass composites, Mater. Des. 110 (2016) 782–789. [9] Y.J. Huang, J. Shen, J.F. Sun, Buk metallic glasses: smaller is softer, Appl. Phys. Lett. 90 (2007) 081919. [10] L.Y. Chen, Z.D. Fu, G.Q. Zhang, X.P. Hao, Q.K. Jiang, X.D. Wang, Q.P. Cao, H. Franz, Y.G. Liu, H.S. Xie, S.L. Zhang, B.Y. Wang, Y.W. Zeng, J.Z. Jiang, New class of plastic bulk metallic glass, Phys. Rev. Lett. 100 (2008) 075501. [11] T. Nagase, Y. Umakoshi, Amorphous phase formation in Co-Cu-Zr-B-based immiscible alloys, J. Alloys Compd. 649 (2015) 1174–1181. [12] D.H. Kim, W.T. Kim, E.S. Park, N. Mattern, J. Eckert, Phase separation in metallic glasses, Prog. Mater. Sci. 58 (2013) 1103–1172. [13] S.S. Chen, I. Todd, Enhanced plasticity in the Zr-Cu-Ni-Al-Nb alloy system by in-situ formation of two glassy phases, J. Alloys Compd. 646 (2015) 973–977. [14] E.S. Park, D.H. Kim, Phase separation and enhancement of plasticity in Cu-Zr-Al-Y bulk metallic glasses, Acta Mater. 54 (2006) 2597–2604. [15] J. Pan, K.C. Chan, Q. Chen, N. Li, S.F. Guo, L. Liu, The effect of microalloying on mechanical properties in CuZrAl bulk metallic glass, J. Alloys Compd. 504S (2010) S74–S77. [16] W. Zhou, J.X. Hou, W.P. Weng, Microstructure, thermal stability and mechanical properties of Zr-Cu-Al-Sn bulk metallic glass, J. Non-Cryst. Solids 429 (2015)
Fig. 9. Bright-field TEM images with the inset of SAED patterns and corresponding HRTEM images for the fracture Zr64Cu12.5Ni10Al7.5Ti6 rod near the main shear band.
Fig. 10. Compressive stress-strain curves of the as-cast and annealed Zr64Cu12.5Ni10Al7.5Ti6 rods. The inset shows comparison of specific heats of the as-cast and annealed samples.
535
Journal of Non-Crystalline Solids 481 (2018) 530–536
W. Zhou et al.
[26] J.M. Park, J.H. Han, N. Mattern, D.H. Kim, J. Eckert, Designing Zr-Cu-Co-Al bulk metallic glasses with phase separation mediated plasticity, Metall. Mater. Trans. A 43 (2012) 2598–2603. [27] E.S. Park, H.J. Chang, J.S. Kyeong, D.H. Kim, Role of minor addition of metallic alloying elements in formation and properties of Cu-Ti-rich bulk metallic glasses, J. Mater. Res. 23 (2008) 1995–2002. [28] K.F. Kelton, Crystallization of liquids and glasses to quasicrystals, J. Non-Cryst. Solids 317 (2003) 97–105. [29] Y. Hu, L.F. Li, T. Lin, Y.H. Zhou, Plasticity improvement of Zr55Al10Ni5Cu30 bulk metallic glass by remelting master alloy ingot, J. Mater. Res. 24 (2009) 3590–3595. [30] Q.S. Zhang, W. Zhang, X.M. Wang, Y. Yokoyama, K. Yubuta, A. Inoue, Structure, thermal stability and mechanical properties of Zr65Al7.5Ni10Cu17.5 glassy alloy rod with a diameter of 16 mm produced by tilt casting, Mater. Trans. 49 (2008) 2141–2146. [31] L. Zhang, Y.Q. Cheng, A.J. Cao, J. Xu, E. Ma, Bulk metallic glasses with large plasticity: composition design from the structural perspective, Acta Mater. 57 (2009) 1154–1164. [32] A.D. Setyawan, J. Saida, H. Kato, M. Matsushita, A. Inoue, Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys, J. Mater. Res. 25 (2010) 1149–1158. [33] A. van den Beukel, J. Sietsma, The glass transition as a free volume related kinetic phenomenon, Acta Metall. 38 (1990) 383–389. [34] X.J. Liu, G.L. Chen, X. Hui, T. Lu, Z.P. Liu, Ordered clusters and free volume in a ZrNi metallic glass, Appl. Phys. Lett. 93 (2008) 011911.
208–212. [17] E.S. Park, H.J. Chang, J.Y. Lee, D.H. Kim, Improvement of plasticity by tailoring combination of constituent elements in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses, J. Mater. Res. 22 (2007) 3440–3447. [18] K.B. Kim, J. Das, F. Baier, M.B. Tang, W.H. Wang, J. Eckert, Heterogeneity of a Cu47.5Zr47.5Al5 bulk metallic glass, Appl. Phys. Lett. 88 (2006) 051911. [19] K.B. Kim, J. Das, S. Venkataraman, S. Yi, J. Eckert, Work hardening ability of ductile Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 bulk metallic glasses, Appl. Phys. Lett. 89 (2006) 071908. [20] Z.W. Zhu, H.F. Zhang, W.S. Sun, B.Z. Ding, Z.Q. Hu, Processing of bulk metallic glasses with high strength and large compressive plasticity in Cu50Zr50, Scr. Mater. 54 (2006) 1145–1149. [21] J. Saida, C. Li, M. Matsushita, A. Inoue, Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior, J. Mater. Res. 16 (2001) 3389–3401. [22] J. Saida, A. Inoue, Quasicrystals from glass devitrification, J. Non-Cryst. Solids 317 (2003) 97–105. [23] A. Inoue, High strength and ductile bulk quasi-crystalline alloys, Adv. Eng. Mater. 3 (2001) 669–673. [24] A. Inoue, T. Zhang, M.W. Chen, T. Sakurai, J. Saida, M. Matsushita, Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility, J. Mater. Res. 10 (2000) 2195–2208. [25] J. Pan, L. Liu, K.C. Chan, Enhanced plasticity by phase separation in CuZrAl bulk metallic glass with micro-addition of Fe, Scr. Mater. 60 (2009) 822–825.
536