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Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites
Accepted Manuscript Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites D.Q. Ma, W.T. Jiao, Y.F. Zhang, B.A. Wang, J. Li, X.Y. Zhang, M.Z. Ma, R.P. Liu PII: DOI: Reference:
S0925-8388(14)02747-9 http://dx.doi.org/10.1016/j.jallcom.2014.11.099 JALCOM 32653
To appear in:
Journal of Alloys and Compounds
Received Date: Revised Date: Accepted Date:
25 September 2014 23 October 2014 13 November 2014
Please cite this article as: D.Q. Ma, W.T. Jiao, Y.F. Zhang, B.A. Wang, J. Li, X.Y. Zhang, M.Z. Ma, R.P. Liu, Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.11.099
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Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites D.Q. Ma1, W.T. Jiao2, Y.F. Zhang1,3, B.A. Wang1, J. Li1, X.Y. Zhang1 , M.Z. Ma1*, R.P. Liu1 1
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University,
Qinhuangdao 066004, PR China 2
College of Education, Hebei Normal University of Science and Technology, Qinhuangdao 066004,
PR China 3
Hebei Vocational and Technical College of Building Materials, Qinhuangdao 066004, PR China
Abstract ： A series of TiZr-based bulk metallic glass matrix composites (BMGMCs) with distinguished mechanical properties are successfully fabricated by adding different volume fractions of Ta (Ti38.8Zr28.8 Cu6.2Be16.2Nb10 as the basic composition, denoted as Ta0.0–Ta8.0). Along with the growth of precipitated phase, typical dendritic morphology is fully developed in the TiZr-based BMGMCs of Ta8.0. Energy-dispersive spectrometry analysis of the dendrites and glass matrix indicates that the metallic elements of Nb and Ta should preferentially form solid solution into dendrites. The chaotic structure of high-temperature precipitate phase is trapped down by the rapid cooling of the copper-mould. The detected lattice distortions in the dendrites are attributed to the strong solid solution strengthening of the metallic elements of Ti, Zr, Nb, and Ta. These lattice distortions increase the resistance of the dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Dendrites create a strong barrier for the shear band propagation and generate multiple shear bands after solid solution strengthening, thereby providing the TiZr-based BMGMCs with greatly improved capacity to sustain plastic deformation and resistance to brittle fracture. Thus, the TiZr-based BMGMCs possess distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta0.5 possesses the largest plastic strain (εp) at 20.3% and ultimate strength (σmax) of 2613 MPa during compressive loading. In addition, the sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa during the tensile process, and then progressively softens until it fractures at a strain of 10.2%. Keywords ： Bulk metallic glass composites; Microstructure; Solid solution strengthening; Work-hardening; Shear bands; Lattice distortions
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*Corresponding author: Fax: +86 03358064504; E-mail address: [email protected]; Address: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, PR China. 1. Introduction The distinguished mechanical properties of bulk metallic glasses (BMGs) including ultrahigh high strength and hardness render them potential candidates as structural materials [1–5]. However, the room temperature brittleness has seriously limited their application as an engineering material [6–9]. Research on the plasticity of BMGs aimed at overcoming this drawback has resulted in the development of a series of BMG matrix composites (BMGMCs). Fortunately, a series of BMGMCs are successfully developed due to the efforts of many researchers [10–15]. The ZrTi-based BMGMCs reported by Hofmann et al. (2008) exhibits work-hardening properties of up to an ultrahigh tensile strength of 1500 MPa during the tensile process, and then progressively softens until it fractures at a strain of 8.1%, thereby creating a new era of amorphous materials [16]. Later for that, professor Qiao et al. summarized the deformation mechanism of ZrTi-based BMGMCs. Researchers believe that the precipitated phase of soften dendrite is considered crucial in impeding shear band propagation and generating multiple shear bands in the glass matrix that largely increase the plasticity of the BMGMCs [17,18]. Strong work-hardening behavior has been discovered recently in ZrTi-based and CuZr-based BMGMCs which is attributed to transformation-induced plasticity, such as metastable B2 crystals transformed to B19′ martensite and the body-centered cubic (bcc) β phase transformed to hexagonal close-packed (hcp) a′ martensite phases under applied stress [19-22]. However, the glass-forming ability (GFA) of these BMGMCs is so poor that the related application is greatly restricted. In this study, a series of TiZr-based BMGMCs (Ti38.8 Zr28.8Cu6.2Be16.2Nb10 as the basic composition, in Volume Fractions, denoted as Ta0.0–Ta8.0) with distinguished mechanical properties are successfully fabricated using the strong solid solution strengthening of dendrites. The thermal properties and mechanical properties, especially the deformation mechanisms are investigated in detail using differential scanning calorimetry (DSC), microscopic fracture images, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) studies.
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2. Experimental procedure Master alloy ingots of Ta0.0–Ta8.0 were prepared by arc melting the mixture of the high-purity Zr, Ti, Nb, Ta, Cu, and Be elements (>99.9 wt.%) under a Ti-gettered Ar atmosphere. In order to ensure the compositional homogeneity, Zr, Nb and Ta, which possess high melting points and large solid solubility at high temperatures, were fabricated before they are arc-melted into master alloy ingots with the remaining elemental components, such as Ti, Cu and Be [23]. Copper-mould suction casting synthesized the cylindrical rods with different diameters. X-ray diffraction was used to confirm the microstructure of the dendritic phases in the glassy matrix (D/max-2500/PC). Thermal analyses were conducted by DSC under the protection of high-purity Ar gas at a constant heating rate of 0.33 Ks –1. The hardness of the glass matrix and dendrites was measured by an ultra-micro Vickers hardness tester (FM-ARS 9000). Mechanical properties were characterized on an Instron 5982 mechanical testing machine at an initial strain rate of 5×10–4 s
–1
at room temperature. The geometry of the
compressive sample is a 6 mm-long rod with an aspect ratio of 2. All samples were carefully fabricated, ensuring that the ends were parallel with each other. The tension specimen was machined into a dumb-bell geometry which had a nominal gage diameter of 1.6 mm and gage length of 10 mm. Three specimens of each composition were tested under tension. The cross-section of the as-cast sample and the side surface of the deformed sample were investigated in detail using scanning electron microscopy with energy dispersive spectrometry (EDS) capability (SEM: Hitachi S-530). TEM and HRTEM images were obtained using a JEM-2010F instrument. The TEM samples were mechanically ground up to a thickness of 25 µm in thickness and prepared by ion milling. 3. Results and discussion Fig. 1(a) displays the XRD patterns of as-cast TiZr-based BMGMCs together with the magnified regions of the main peaks. The bcc β (Ti, Zr) (Nb, Ta) solid solution diffraction peaks are superimposed on a broad scattering feature, which is characteristic of an amorphous phase, similar to the Zr-based BMGMCs [16]. The inset picture indicates a rightward movement of the main peaks with an increase of Ta content. The experimental results demonstrate that the crystal structures of the dendrite in TiZr-based BMGMCs change after Ta has been added. According to the Bragg diffraction equation and the expression of interplanar spacing, lattice parameters of the β phase dendrite
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decrease after Ta addition. The crystal lattice parameters of the dendrite based on the XRD patterns is calculated by XRD refinement. Fig. 1(b) presents the change trend of the crystal lattice parameters of the β phase dendrite after Ta addition. It indicates that lattice parameters of the β phase dendrite decrease after Ta addition (Ta0.0: 0.3392 nm and Ta8.0: 0.3360 nm), in agreement with the analysis of XRD. Based on comparisons of the atomic radius (Ti
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volume fractions are determined by analyzing the contrast in SEM images. The average diameters of the dendrite in the sample Ta0.0–Ta8.0 increase with the Ta addition, and are approximately 0.6, 1.5, 3.3, 8.1 and, 11.2 µm, respectively; whereas the volume fractions of the dendrites are 53, 58, 61, 65 and 69 vol.%, respectively. The geometrical shape of precipitated phase in Fig. 3(a) and (b) is approximately spherical particle, indicating that the β phase has not been sufficiently developed because of the high cooling rate. Along with the growth of solid solution precipitated phase, a small amount of fine dendrites are embedded in the glass matrix, as presented in the inset picture of Fig. 3(c). Typical dendritic morphology (marked by ellipses) develops in the TiZr-based BMGMC of Ta8.0, as presented in Fig. 3(d). The addition of Ta raises the liquidus temperature that provides the dynamic condition for the growth of precipitated phase, which is consistent with the result of DSC. The microstructural analysis indicates that the solid solution strengthening changes the geometrical morphology and size of the precipitated phase. Fig. 3(e) and (f) are the EDS analysis of Ta0.0 and Ta8.0. EDS performed on the dendrites and glass matrix indicates that the metallic element of Nb and Ta should preferentially form solid solution into dendrites (marked by arrows). For example, the Ta content in dendrites is 6.6 at.% and in amorphous is 2.1 at.%, as presented in Fig. 3(f). Therefore, the hardness of dendrites should be increased through solid solution strengthening [25]. The room-temperature compressive engineering stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs are displayed in Fig. 4(a). The yielding strength (σy), the yielding strain (εy), the ultimate strength (σmax), and the plastic strain (εp) are summarized in Table 2. The samples of Ta0.0–Ta5.0 possess not only high fracture strength and large plasticity, but also a large stress increase after yielding. Similar results about the significant work-hardening capability in a Ti-based BMGMC has been reported [19,20]. Among these TiZr-based BMGMCs, the mechanical properties of Ta0.5 stand out at σy = 1602 MPa, εy = 2.1%, εp = 20.3%, and σmax = 2613 MPa. The decrease of the yield strength in Ta2.0 is attributed to the size effect, consistent with our previous research results [18]. Nevertheless, the σy of Ta8.0 alloy rod sharply declines to 815 MPa owing to the decrease of amorphous in the volume fractions after the increase of Ta content, as evident in Fig. 3(d). The values of work-hardening index (n) exhibit multiple changes with Ta addition, as presented by the inset picture in Fig. 4(a). The values of n can be estimated based on the Hollomon equation [26]:
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S = kε n
(1)
where S, K and ε are the true stress, strength factor and true strain, respectively. For example, the n values of Ta0.0, Ta0.5 and Ta8.0 are 0.19, 0.5, and 0.63, respectively. The degree of work-hardening is significantly improved after the addition of Ta. In encountering a ductile β phase dendrite, the shear band has to be either blocked or bypassed at the ductile phases because of the strong bonding between the dendrites and the glass matrix. Therefore, the capacity to resist deformation should be increased by the solid solution strengthening of β phase dendrites. A significant difference is notable between the TiZr-based BMGMC and traditional materials during the deformation process. The strengthening of traditional materials should be significantly increased after solid solution strengthening, whereas ductility should be decreased [27]. In this study, the strengthening and ductility of the TiZr-based BMGMCs simultaneously increased (discussed in nature). The plots of the mechanical properties were analyzed with respect to the dσ/dε and ε, which is considered as a good indicator of resistance of a material against brittle fracture, as presented in Fig. 4(b). The ε range is between εy and εp (the true plastic strain at where necking begins). All of the plots exhibit an initial transient region of rapid decrease in ε followed by a region of gradual decrease (isolated by straight) [28]. The fluctuations of Ta0.5 (marked by ellipses) at the final stage indicate that a large amount of stress concentration around the dendrites and glassy matrix is released by a dislocation glide, consistent with the distinguished mechanical properties of Ta0.5. The morphologies of the lateral surfaces and the fractured surfaces of the deformed TiZr-based BMGMCs are illustrated in Fig. 5. Primary shear bands are parallel to each other and terminate at the dendrites, as presented in Fig. 5(a), indicating that dendrites act as obstacles of the propagated shear bands and promote the branching of abundant secondary shear bands. Molten droplet patterns are dominant and accompanied by an apparent sliding trace (marked by arrow), as presented in Fig. 5(d); this observation is a typical ductile fracture mechanism. The fracture morphology for sample Ta2.0 and Ta5.0 is analogous to that for sample Ta0.0 (not presented here). Profuse shear bands are distributed on the lateral surface of the deformed sample of Ta0.5, as presented in Fig. 5(b). Fig. 5(e) is the enlarged area of the ellipse in Fig. 5(b) and indicates that the interface of dendrites and glass matrix suffer from serious distortion. A large number of regular bricks are obtained after the fracture
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of Ta8.0, as presented in Fig. 5(c). On the fractured surface of Ta8.0, cracks and molten droplet patterns are dominant, as presented in Fig. 5(f), indicating that Ta8.0 suffers from severe plastic deformation. The occurrence of fractures suggests that the failure process starts with the deformation of the soft dendrites (near the interface) upon yielding, after which, part of the load is transferred to the surrounding glassy matrix to generate multiple shear bands. As the number of shear bands reaches a certain value, cracks start and propagate along the direction of the primary shear bands because of the severe plastic deformation. As a result, a large stress increase after yielding in the TiZr-based BMGMCs should be obtained. Tensile experiments are applied to exhibit the mechanical properties of a series of TiZr-based BMGMCs. Fig. 6(a) presents the engineering stress–strain curves of the TiZr-based BMGMC upon tension, and Table 3 summarizes the mechanical properties. Compared with untreated samples, the mechanical properties of Ta0.5 are greatly improved by the solid solution strengthening. The yield strength (σy) and the yield strain (εy) are 1213 MPa and 2.1%, respectively. Macroscopic necking can be observed from the inset picture in Fig. 6(a), consistent with the distinguished mechanical properties of the sample Ta0.5. The sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa, and then progressively softens until it fractures at a strain of 10.2% that induced by premature necking. Nevertheless, the σmax of Ta8.0 alloy rods sharply declines to 1085 MPa, consistent with our previous studies [18]. Fig. 6(b) presents the micro-hardness of dendrite and amorphous phase; the micro-hardness of amorphous phase remained unchanged, whereas that of dendrite increased rapidly at approximately 68 HV from Ta0.0 to Ta 8.0 after solid solution strengthening. Given that if the volume fractures of dendrite are greater than 50 vol.%, the yield strength (σy) of the composites is obtained through the load-bearing model [29]:
σ Composite = σ Dendrite (1 + 0.5 f Glass )
(2)
where σComposite, σDendrite and fGlass are the yield strength of TiZr-based BMGMCs, yield strength of the dendrites during compressive loading and volume fractions of the glassy phase, respectively. In this case, the yield strength (σComposite) of the composite is mainly governed by σDendrite and fGlass. In this study, the hardness and size of the dendrites increase because of solid solution strengthening. The micro-hardness and the yield strength are positively related, hence the increase in σcomposite.
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However, the volume fractions of the amorphous phase decrease, considered as the most important factors, decrease and cause a sharp decrease in yield strength. Thus, a critical size and volume fractions of dendrites corresponding to the best mechanical properties of the TiZr-based BMGMCs should exist [18]. The fracture morphology of Ta0.5 is typical of a ductile fracture mechanism, characterized as cupand cone-shaped fractures, as presented in Fig. 7(a). Fiber regions and shear lips dominate the deformation behavior. Cracks originated in the fiber regions, and ductile shear lip areas develop up to final fracture. The fracture mode of the fiber area is a microporous gathered type, described as different sizes and depths of dimples, as presented in Fig. 7(b). Shear lips start accompanied with molten droplets and sliding traces, as presented in Fig. 7(c). Shear bands are angled at 36° with respect to the loading direction, as presented in the inset picture of Fig. 6(a). Profuse shear bands are distributed near the fracture surface, as presented in Fig. 7(d). Dimples and shear lips indicate that the deformation behavior of Ta0.5 is typical of a ductile fracture pattern. TEM and HRTEM analyses are necessary to understand the mechanism of the solid solution strengthening of dendrite, resulting in a large stress increase after yielding. In this study, Ta0.5 is selected as a typical sample. Fig. 8(a) presents a TEM bright-field image and the selected area electronic diffraction (SAED) pattern of the glass matrix and dendrites. The dark and light areas indicate the dendrites and glass matrix, respectively. The SAED pattern is identified as the [0 1 1] zone axis of bcc β-(Ti, Zr) (Nb, Ta) with a lattice parameter a= 0.3392 nm, as presented in the inset picture of Fig. 8(a). The results demonstrate that a fine dual-phase structure is fabricated. The spacing of (011) crystal plane is 0.233 nm, obtained from an HRTEM image in dendrites, as presented in the inset of Fig. 8(b). The inverse fast-Fourier transform (IFFT) patterns of the dendrite suffering from rapid cooling are presented in Fig. 8(b–d). Along with the addition of Ta, the degree of lattice distortion (labeled as arrows) has been exacerbated by the strong solid solution strengthening of dendrites. Similar results are obtained in high-entropy alloy and β-Ti3Nb alloy [30,31]. Lattice distortions increase the resistance of dislocation motion and then pin the dislocations, thereby resulting in increased dendrite strength and hardness [32]. Local disordered amorphization in dendrites is also found and labeled as ellipses [33]. The strong solid solution strengthening has
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prompted the simultaneous increase in the strength and ductility of the sample Ta0.5, thereby implying that: (i) dendrites are crucial in impending shear band propagation and generating multiple shear bands in TiZr-based BMGMCs; (ii) the hardness and strength values of dendrite after solid solution strengthening are still lower than the values of the amorphous phase, as presented in Fig. 6(b), which means that the dendrites still play the role of a plastic phase; and (iii) dendrites increase the resistance of deformation in TiZr-based BMGMCs after strengthening. 4. Conclusions In this study, the effect of the solid solution strengthening of dendrite on the microstructure and mechanical properties are investigated in detail. The following conclusions are drawn based on the results: (1) A series of TiZr-based BMGMCs with distinguished mechanical properties are successfully fabricated by the solid solution strengthening of dendrites. The average diameters and sizes of the dendrite increase with the Ta addition. In addition, the hardness and strength values of dendrite increase by solid solution strengthening, whereas the volume fractions of amorphous decrease after the addition of Ta. (2) The TiZr-based BMGMCs (Ta0.0-Ta8.0) manifest distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta0.5 possesses the largest plastic strain (εp) of 20.3% and ultimate strength (σmax) of 2613 MPa during compressive loading. In addition, the sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa during tensile process, and then progressively softens until it fractures at a strain of 10.2%. The distinguished mechanical properties should be attributed to the solid solution strengthening of dendrites. (3) Solid solution strengthening distorts the lattice of dendrites. Lattice distortions increase the resistance of dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Therefore, dendrites after solid solution strengthening create a strong barrier for the shear band propagation and generate multiple shear bands, which provide the TiZr-based BMGMCs with remarkably improved capacity to sustain plastic deformation and resistance to brittle fracture.
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Acknowledgments This work was supported by the SKPBRC (grant no.2013CB733000) and NSFC (grant no. 51171163/51434008/51171160). References [1] W.L. Johnson, MRS Bull, 24 (1999) 42. [2] A.L. Greer, Mate01r Today, 12 (2009) 14–22. [3] A. Inoue, Takeuchi, Int’l J Appl Glass Sci. 1 (2010) 273. [4] A. Inoue, X.M. Wang, W. Zhang, Rev Adv Mater Sci. 18 (2008) 1. [5] T. Mizushima, H. Koshiba, Y. Naito, A. Inoue, J Jpn Soc Powder Metall. 55 (2008) 146. [6] H. Ma, J. Xu, E. Ma, Appl. Phys. Lett. 83 (2003) 2793. [7] Y.K. Xu, H. Ma, J. Xu, E. Ma, Acta Mater. 53 (2005) 1857. [8] H.A. Bruck, T. Chrictman, A.J. Rosakis, W.L. Johnson, Scr. Metall.Mater. 30 (1994) 429. [9] A. Inoue, B.L. Shen, H. Koshiba, H. Kato, A.R. Yavari, Nat. Mater. 2 (2003) 661. [10] H.T. Zong, M.Z. Ma, X.Y. Zhang, B.W. Bai, P.F. Yu, Li. Q, et al., J Alloys Comp. 504S (2010) S106-S109. [11] H. Choi-Yim, R.D. Conner, F. Szuecs, W.L. Johnson, Acta Mater. 50 (2002) 2737–2745. [12] J.W. Qiao, Y. Zhang, G.L. Chen, Mater Design. 30 (2009) 3966–3971. [13] C. Fan, D.C. Qiao, T.W. Wilson, H. Choo, P.K. Liaw, Mater Sci Eng A, 431 (2006) 158–165. [14] C.C. Hays, C.P. Kim, W.L. Johnson, Phys Rev Lett. 84 (2000) 2901–2904. [15] H.M. Fu, H. Wang , H.F. Zhang, Z.Q. Hu, Scripta Mater. 54 (2006) 1961–1966. [16] D.C. Hofmann, J.Y. Suh, A. Wiest, G. Duan, M.L. Lind, M.D. Demetriou, et al., Nature, 451 (2008) 1085. [17] J.W. Qiao, Y. Zhang, P.K. Liaw, G.L. Chen, Scripta Mater. 61 (2009) 1087–1090. [18] D.Q. Ma, J.Li, Y.F. Zhang, X.Y. Zhang, M.Z. Ma, R.P. Liu, Mater Sci Eng A 612 (2014) 310–315. [19] Z.Y. Zhang, Y. Wu, J. Zhou, H. Wang, X.J. Liu , Z.P. Lu, Scripta Mater. 69 (2013) 73–76. [20] Choongnyun Paul Kim, Yoon S. Oh, Sunghak Lee, Nack J. Kim, Scripta Mater. 65 (2011) 304–307.
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Table Captions: Table 1 Thermal parameters of as cast TiZr-based BMGMCs (denoted as Ta0.0–Ta8.0). The errors of the temperatures are at ±1K. Table 2 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during compressive loading. Table 3 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during tensile process.
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Table 1 Thermal parameters of as cast TiZr-based BMGMCs (denoted as Ta0.0–Ta8.0). The errors of the temperatures are at ±1K. Tg (K)
Tx1 (K)
∆Tx (K)
Tm (K)
Tl (K)
Trg
∆Hx (J/k)
Ta0.0 (VF)
644
726
82
932
1042
0.618
-31.6
Ta0.5 (VF)
636
716
80
936
1056
0.602
-30.6
Ta2.0 (VF)
577
715
138
957
1085
0.532
-29.3
Ta5.0 (VF)
561
716
155
969
1116
0.503
-25.5
Ta8.0 (VF)
595
718
123
984
1132
0.526
-22.8
Composition (at.%): Ti38.8 Zr28.8Cu6.2Be16.2Nb10
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Table 2 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during compressive loading. Composition (at.%):
σy (MPa)
εy (%)
σmax(MPa)
εp (%)
Ta0.0 (VF)
1510
2.3
2150
12.0
Ta0.5 (VF)
1517
2.1
2610
20.3
Ta2.0 (VF)
1433
2.1
2464
16.2
Ta5.0 (VF)
1581
1.9
2453
16.7
Ta8.0 (VF)
815
1.8
2032
27.2
Ti38.8Zr28.8Cu6.2Be16.2Nb10
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Table 3 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during tensile process. Composition (at.%):
σy (MPa)
εy (%)
σmax(MPa)
εp (%)
Ta0.0 (VF)
1238
2.2
1526
3.9
Ta0.5 (VF)
1280
2.1
1680
10.2
Ta8.0 (VF)
961
1.9
1082
6.8
Ti38.8Zr28.8Cu6.2Be16.2Nb10
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Figure Captions: Fig. 1. (a) XRD patterns of as cast TiZr-based BMGMCs and inset presents the enlarged regions of main peaks; (b) crystal lattice parameters of the β-(Ti, Zr)(Nb, Ta) phase dendrite. Fig. 2. (a) DSC curves of 3 mm-diameter of as cast TiZr-based BMGMCs at a heating rate of 0.33Ks–1 ; (b) the change trend of Tg, Tl, and Trg. Fig. 3. Edge micrograph of (a) Ta0.0; (b) Ta0.5;(c) Ta5.0 (the inset is a fine dendrite); (d) Ta8.0; EDS analysis of (e) Ta0.0 and (f) Ta8.0. Fig. 4. (a) Engineering compressive stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs at room temperature and inset picture presents the work-hardening index n; (b) relationship between the dσ/dε and ε; the inset picture is an enlarged area of the true stress–strain curves obtained through appropriate adjustment. Fig. 5. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during compressive loading: (a) the lateral surface of Ta0.0; (b) the lateral surface of Ta0.5; (c) the lateral surface of Ta8.0; (d) the fracture surface of Ta0.0; (e) the enlarged area of lateral surface of Ta0.5; (f) the fracture surface of Ta8.0. Fig. 6. (a) Engineering tensile stress–strain curves of the TiZr-based BMGMCs and the inset are macroscopic necking of Ta0.5 and schematic drawing of the tensile specimen (mm); (b) micro-hardness of amorphous and dendrites. Fig. 7. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during tensile loading: (a) the fracture surface of Ta0.5; (b) the enlarged area of fiber regions; (c) the enlarged area of shear lips; (d) the lateral surface of Ta0.5. Fig. 8. (a) BF TEM image of the composites and the insets are corresponding to SAED patterns of glass matrix and dendrites; (b) IFFT image of Ta0.0 in the dendrites obtained from inset picture at crystal plane (011) and the inset picture is an HRTEM image (c) IFFT image of Ta0.5 in the dendrites at crystal plane (011); (d) IFFT image of Ta8.0 in the dendrites indicating pile-ups of dislocations after solid solution strengthening.
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Fig. 1. (a) XRD patterns of as cast TiZr-based BMGMCs and inset presents the enlarged regions of main peaks; (b) crystal lattice parameters of the β-(Ti, Zr)(Nb, Ta) phase dendrite.
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Fig. 2. (a) DSC curves of 3 mm-diameter of as cast TiZr-based BMGMCs at a heating rate of 0.33Ks–1 ; (b) the change trend of Tg, Tl, and Trg.
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Fig. 3. Edge micrograph of (a) Ta0.0; (b) Ta0.5;(c) Ta5.0 (the inset is a fine dendrite); (d) Ta8.0; EDS analysis of (e) Ta0.0 and (f) Ta8.0.
19
Fig. 4. (a) Engineering compressive stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs at room temperature and inset picture presents the work-hardening index n; (b) relationship between the dσ/dε and ε; the inset picture is an enlarged area of the true stress–strain curves obtained through appropriate adjustment.
20
Fig. 5. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5, and Ta8.0) during compressive loading: (a) the lateral surface of Ta0.0; (b) the lateral surface of Ta0.5; (c) the lateral surface of Ta8.0; (d) the fracture surface of Ta0.0; (e) the enlarged area of lateral surface of Ta0.5; (f) the fracture surface of Ta8.0.
21
Fig. 6. (a) Engineering tensile stress–strain curves of the TiZr-based BMGMCs and the inset are macroscopic necking of Ta0.5 and schematic drawing of the tensile specimen (mm); (b) micro-hardness of amorphous and dendrites.
22
Fig. 7. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during tensile loading: (a) the fracture surface of Ta0.5; (b) the enlarged area of fiber regions; (c) the enlarged area of shear lips; (d) the lateral surface of Ta0.5.
23
Fig. 8. (a) BF TEM image of the composites and the insets are corresponding to SAED patterns of glass matrix and dendrites; (b) IFFT image of Ta0.0 in the dendrites obtained from inset picture at crystal plane (011) and the inset picture is an HRTEM image (c) IFFT image of Ta0.5 in the dendrites at crystal plane (011); (d) IFFT image of Ta8.0 in the dendrites indicating pile-ups of dislocations after solid solution strengthening.
24
Highlights： ： Hardness of dendrite of TiZr-based BMGMCs increases. Strong work-hardening behavior is obtained after solid solution strengthening. Lattice distortions of dendrite suffering from rapid cooling are detected.
25
S0925-8388(14)02747-9 http://dx.doi.org/10.1016/j.jallcom.2014.11.099 JALCOM 32653
To appear in:
Journal of Alloys and Compounds
Received Date: Revised Date: Accepted Date:
25 September 2014 23 October 2014 13 November 2014
Please cite this article as: D.Q. Ma, W.T. Jiao, Y.F. Zhang, B.A. Wang, J. Li, X.Y. Zhang, M.Z. Ma, R.P. Liu, Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.11.099
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Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites D.Q. Ma1, W.T. Jiao2, Y.F. Zhang1,3, B.A. Wang1, J. Li1, X.Y. Zhang1 , M.Z. Ma1*, R.P. Liu1 1
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University,
Qinhuangdao 066004, PR China 2
College of Education, Hebei Normal University of Science and Technology, Qinhuangdao 066004,
PR China 3
Hebei Vocational and Technical College of Building Materials, Qinhuangdao 066004, PR China
Abstract ： A series of TiZr-based bulk metallic glass matrix composites (BMGMCs) with distinguished mechanical properties are successfully fabricated by adding different volume fractions of Ta (Ti38.8Zr28.8 Cu6.2Be16.2Nb10 as the basic composition, denoted as Ta0.0–Ta8.0). Along with the growth of precipitated phase, typical dendritic morphology is fully developed in the TiZr-based BMGMCs of Ta8.0. Energy-dispersive spectrometry analysis of the dendrites and glass matrix indicates that the metallic elements of Nb and Ta should preferentially form solid solution into dendrites. The chaotic structure of high-temperature precipitate phase is trapped down by the rapid cooling of the copper-mould. The detected lattice distortions in the dendrites are attributed to the strong solid solution strengthening of the metallic elements of Ti, Zr, Nb, and Ta. These lattice distortions increase the resistance of the dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Dendrites create a strong barrier for the shear band propagation and generate multiple shear bands after solid solution strengthening, thereby providing the TiZr-based BMGMCs with greatly improved capacity to sustain plastic deformation and resistance to brittle fracture. Thus, the TiZr-based BMGMCs possess distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta0.5 possesses the largest plastic strain (εp) at 20.3% and ultimate strength (σmax) of 2613 MPa during compressive loading. In addition, the sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa during the tensile process, and then progressively softens until it fractures at a strain of 10.2%. Keywords ： Bulk metallic glass composites; Microstructure; Solid solution strengthening; Work-hardening; Shear bands; Lattice distortions
1
*Corresponding author: Fax: +86 03358064504; E-mail address: [email protected]; Address: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, PR China. 1. Introduction The distinguished mechanical properties of bulk metallic glasses (BMGs) including ultrahigh high strength and hardness render them potential candidates as structural materials [1–5]. However, the room temperature brittleness has seriously limited their application as an engineering material [6–9]. Research on the plasticity of BMGs aimed at overcoming this drawback has resulted in the development of a series of BMG matrix composites (BMGMCs). Fortunately, a series of BMGMCs are successfully developed due to the efforts of many researchers [10–15]. The ZrTi-based BMGMCs reported by Hofmann et al. (2008) exhibits work-hardening properties of up to an ultrahigh tensile strength of 1500 MPa during the tensile process, and then progressively softens until it fractures at a strain of 8.1%, thereby creating a new era of amorphous materials [16]. Later for that, professor Qiao et al. summarized the deformation mechanism of ZrTi-based BMGMCs. Researchers believe that the precipitated phase of soften dendrite is considered crucial in impeding shear band propagation and generating multiple shear bands in the glass matrix that largely increase the plasticity of the BMGMCs [17,18]. Strong work-hardening behavior has been discovered recently in ZrTi-based and CuZr-based BMGMCs which is attributed to transformation-induced plasticity, such as metastable B2 crystals transformed to B19′ martensite and the body-centered cubic (bcc) β phase transformed to hexagonal close-packed (hcp) a′ martensite phases under applied stress [19-22]. However, the glass-forming ability (GFA) of these BMGMCs is so poor that the related application is greatly restricted. In this study, a series of TiZr-based BMGMCs (Ti38.8 Zr28.8Cu6.2Be16.2Nb10 as the basic composition, in Volume Fractions, denoted as Ta0.0–Ta8.0) with distinguished mechanical properties are successfully fabricated using the strong solid solution strengthening of dendrites. The thermal properties and mechanical properties, especially the deformation mechanisms are investigated in detail using differential scanning calorimetry (DSC), microscopic fracture images, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) studies.
2
2. Experimental procedure Master alloy ingots of Ta0.0–Ta8.0 were prepared by arc melting the mixture of the high-purity Zr, Ti, Nb, Ta, Cu, and Be elements (>99.9 wt.%) under a Ti-gettered Ar atmosphere. In order to ensure the compositional homogeneity, Zr, Nb and Ta, which possess high melting points and large solid solubility at high temperatures, were fabricated before they are arc-melted into master alloy ingots with the remaining elemental components, such as Ti, Cu and Be [23]. Copper-mould suction casting synthesized the cylindrical rods with different diameters. X-ray diffraction was used to confirm the microstructure of the dendritic phases in the glassy matrix (D/max-2500/PC). Thermal analyses were conducted by DSC under the protection of high-purity Ar gas at a constant heating rate of 0.33 Ks –1. The hardness of the glass matrix and dendrites was measured by an ultra-micro Vickers hardness tester (FM-ARS 9000). Mechanical properties were characterized on an Instron 5982 mechanical testing machine at an initial strain rate of 5×10–4 s
–1
at room temperature. The geometry of the
compressive sample is a 6 mm-long rod with an aspect ratio of 2. All samples were carefully fabricated, ensuring that the ends were parallel with each other. The tension specimen was machined into a dumb-bell geometry which had a nominal gage diameter of 1.6 mm and gage length of 10 mm. Three specimens of each composition were tested under tension. The cross-section of the as-cast sample and the side surface of the deformed sample were investigated in detail using scanning electron microscopy with energy dispersive spectrometry (EDS) capability (SEM: Hitachi S-530). TEM and HRTEM images were obtained using a JEM-2010F instrument. The TEM samples were mechanically ground up to a thickness of 25 µm in thickness and prepared by ion milling. 3. Results and discussion Fig. 1(a) displays the XRD patterns of as-cast TiZr-based BMGMCs together with the magnified regions of the main peaks. The bcc β (Ti, Zr) (Nb, Ta) solid solution diffraction peaks are superimposed on a broad scattering feature, which is characteristic of an amorphous phase, similar to the Zr-based BMGMCs [16]. The inset picture indicates a rightward movement of the main peaks with an increase of Ta content. The experimental results demonstrate that the crystal structures of the dendrite in TiZr-based BMGMCs change after Ta has been added. According to the Bragg diffraction equation and the expression of interplanar spacing, lattice parameters of the β phase dendrite
3
decrease after Ta addition. The crystal lattice parameters of the dendrite based on the XRD patterns is calculated by XRD refinement. Fig. 1(b) presents the change trend of the crystal lattice parameters of the β phase dendrite after Ta addition. It indicates that lattice parameters of the β phase dendrite decrease after Ta addition (Ta0.0: 0.3392 nm and Ta8.0: 0.3360 nm), in agreement with the analysis of XRD. Based on comparisons of the atomic radius (Ti
4
volume fractions are determined by analyzing the contrast in SEM images. The average diameters of the dendrite in the sample Ta0.0–Ta8.0 increase with the Ta addition, and are approximately 0.6, 1.5, 3.3, 8.1 and, 11.2 µm, respectively; whereas the volume fractions of the dendrites are 53, 58, 61, 65 and 69 vol.%, respectively. The geometrical shape of precipitated phase in Fig. 3(a) and (b) is approximately spherical particle, indicating that the β phase has not been sufficiently developed because of the high cooling rate. Along with the growth of solid solution precipitated phase, a small amount of fine dendrites are embedded in the glass matrix, as presented in the inset picture of Fig. 3(c). Typical dendritic morphology (marked by ellipses) develops in the TiZr-based BMGMC of Ta8.0, as presented in Fig. 3(d). The addition of Ta raises the liquidus temperature that provides the dynamic condition for the growth of precipitated phase, which is consistent with the result of DSC. The microstructural analysis indicates that the solid solution strengthening changes the geometrical morphology and size of the precipitated phase. Fig. 3(e) and (f) are the EDS analysis of Ta0.0 and Ta8.0. EDS performed on the dendrites and glass matrix indicates that the metallic element of Nb and Ta should preferentially form solid solution into dendrites (marked by arrows). For example, the Ta content in dendrites is 6.6 at.% and in amorphous is 2.1 at.%, as presented in Fig. 3(f). Therefore, the hardness of dendrites should be increased through solid solution strengthening [25]. The room-temperature compressive engineering stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs are displayed in Fig. 4(a). The yielding strength (σy), the yielding strain (εy), the ultimate strength (σmax), and the plastic strain (εp) are summarized in Table 2. The samples of Ta0.0–Ta5.0 possess not only high fracture strength and large plasticity, but also a large stress increase after yielding. Similar results about the significant work-hardening capability in a Ti-based BMGMC has been reported [19,20]. Among these TiZr-based BMGMCs, the mechanical properties of Ta0.5 stand out at σy = 1602 MPa, εy = 2.1%, εp = 20.3%, and σmax = 2613 MPa. The decrease of the yield strength in Ta2.0 is attributed to the size effect, consistent with our previous research results [18]. Nevertheless, the σy of Ta8.0 alloy rod sharply declines to 815 MPa owing to the decrease of amorphous in the volume fractions after the increase of Ta content, as evident in Fig. 3(d). The values of work-hardening index (n) exhibit multiple changes with Ta addition, as presented by the inset picture in Fig. 4(a). The values of n can be estimated based on the Hollomon equation [26]:
5
S = kε n
(1)
where S, K and ε are the true stress, strength factor and true strain, respectively. For example, the n values of Ta0.0, Ta0.5 and Ta8.0 are 0.19, 0.5, and 0.63, respectively. The degree of work-hardening is significantly improved after the addition of Ta. In encountering a ductile β phase dendrite, the shear band has to be either blocked or bypassed at the ductile phases because of the strong bonding between the dendrites and the glass matrix. Therefore, the capacity to resist deformation should be increased by the solid solution strengthening of β phase dendrites. A significant difference is notable between the TiZr-based BMGMC and traditional materials during the deformation process. The strengthening of traditional materials should be significantly increased after solid solution strengthening, whereas ductility should be decreased [27]. In this study, the strengthening and ductility of the TiZr-based BMGMCs simultaneously increased (discussed in nature). The plots of the mechanical properties were analyzed with respect to the dσ/dε and ε, which is considered as a good indicator of resistance of a material against brittle fracture, as presented in Fig. 4(b). The ε range is between εy and εp (the true plastic strain at where necking begins). All of the plots exhibit an initial transient region of rapid decrease in ε followed by a region of gradual decrease (isolated by straight) [28]. The fluctuations of Ta0.5 (marked by ellipses) at the final stage indicate that a large amount of stress concentration around the dendrites and glassy matrix is released by a dislocation glide, consistent with the distinguished mechanical properties of Ta0.5. The morphologies of the lateral surfaces and the fractured surfaces of the deformed TiZr-based BMGMCs are illustrated in Fig. 5. Primary shear bands are parallel to each other and terminate at the dendrites, as presented in Fig. 5(a), indicating that dendrites act as obstacles of the propagated shear bands and promote the branching of abundant secondary shear bands. Molten droplet patterns are dominant and accompanied by an apparent sliding trace (marked by arrow), as presented in Fig. 5(d); this observation is a typical ductile fracture mechanism. The fracture morphology for sample Ta2.0 and Ta5.0 is analogous to that for sample Ta0.0 (not presented here). Profuse shear bands are distributed on the lateral surface of the deformed sample of Ta0.5, as presented in Fig. 5(b). Fig. 5(e) is the enlarged area of the ellipse in Fig. 5(b) and indicates that the interface of dendrites and glass matrix suffer from serious distortion. A large number of regular bricks are obtained after the fracture
6
of Ta8.0, as presented in Fig. 5(c). On the fractured surface of Ta8.0, cracks and molten droplet patterns are dominant, as presented in Fig. 5(f), indicating that Ta8.0 suffers from severe plastic deformation. The occurrence of fractures suggests that the failure process starts with the deformation of the soft dendrites (near the interface) upon yielding, after which, part of the load is transferred to the surrounding glassy matrix to generate multiple shear bands. As the number of shear bands reaches a certain value, cracks start and propagate along the direction of the primary shear bands because of the severe plastic deformation. As a result, a large stress increase after yielding in the TiZr-based BMGMCs should be obtained. Tensile experiments are applied to exhibit the mechanical properties of a series of TiZr-based BMGMCs. Fig. 6(a) presents the engineering stress–strain curves of the TiZr-based BMGMC upon tension, and Table 3 summarizes the mechanical properties. Compared with untreated samples, the mechanical properties of Ta0.5 are greatly improved by the solid solution strengthening. The yield strength (σy) and the yield strain (εy) are 1213 MPa and 2.1%, respectively. Macroscopic necking can be observed from the inset picture in Fig. 6(a), consistent with the distinguished mechanical properties of the sample Ta0.5. The sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa, and then progressively softens until it fractures at a strain of 10.2% that induced by premature necking. Nevertheless, the σmax of Ta8.0 alloy rods sharply declines to 1085 MPa, consistent with our previous studies [18]. Fig. 6(b) presents the micro-hardness of dendrite and amorphous phase; the micro-hardness of amorphous phase remained unchanged, whereas that of dendrite increased rapidly at approximately 68 HV from Ta0.0 to Ta 8.0 after solid solution strengthening. Given that if the volume fractures of dendrite are greater than 50 vol.%, the yield strength (σy) of the composites is obtained through the load-bearing model [29]:
σ Composite = σ Dendrite (1 + 0.5 f Glass )
(2)
where σComposite, σDendrite and fGlass are the yield strength of TiZr-based BMGMCs, yield strength of the dendrites during compressive loading and volume fractions of the glassy phase, respectively. In this case, the yield strength (σComposite) of the composite is mainly governed by σDendrite and fGlass. In this study, the hardness and size of the dendrites increase because of solid solution strengthening. The micro-hardness and the yield strength are positively related, hence the increase in σcomposite.
7
However, the volume fractions of the amorphous phase decrease, considered as the most important factors, decrease and cause a sharp decrease in yield strength. Thus, a critical size and volume fractions of dendrites corresponding to the best mechanical properties of the TiZr-based BMGMCs should exist [18]. The fracture morphology of Ta0.5 is typical of a ductile fracture mechanism, characterized as cupand cone-shaped fractures, as presented in Fig. 7(a). Fiber regions and shear lips dominate the deformation behavior. Cracks originated in the fiber regions, and ductile shear lip areas develop up to final fracture. The fracture mode of the fiber area is a microporous gathered type, described as different sizes and depths of dimples, as presented in Fig. 7(b). Shear lips start accompanied with molten droplets and sliding traces, as presented in Fig. 7(c). Shear bands are angled at 36° with respect to the loading direction, as presented in the inset picture of Fig. 6(a). Profuse shear bands are distributed near the fracture surface, as presented in Fig. 7(d). Dimples and shear lips indicate that the deformation behavior of Ta0.5 is typical of a ductile fracture pattern. TEM and HRTEM analyses are necessary to understand the mechanism of the solid solution strengthening of dendrite, resulting in a large stress increase after yielding. In this study, Ta0.5 is selected as a typical sample. Fig. 8(a) presents a TEM bright-field image and the selected area electronic diffraction (SAED) pattern of the glass matrix and dendrites. The dark and light areas indicate the dendrites and glass matrix, respectively. The SAED pattern is identified as the [0 1 1] zone axis of bcc β-(Ti, Zr) (Nb, Ta) with a lattice parameter a= 0.3392 nm, as presented in the inset picture of Fig. 8(a). The results demonstrate that a fine dual-phase structure is fabricated. The spacing of (011) crystal plane is 0.233 nm, obtained from an HRTEM image in dendrites, as presented in the inset of Fig. 8(b). The inverse fast-Fourier transform (IFFT) patterns of the dendrite suffering from rapid cooling are presented in Fig. 8(b–d). Along with the addition of Ta, the degree of lattice distortion (labeled as arrows) has been exacerbated by the strong solid solution strengthening of dendrites. Similar results are obtained in high-entropy alloy and β-Ti3Nb alloy [30,31]. Lattice distortions increase the resistance of dislocation motion and then pin the dislocations, thereby resulting in increased dendrite strength and hardness [32]. Local disordered amorphization in dendrites is also found and labeled as ellipses [33]. The strong solid solution strengthening has
8
prompted the simultaneous increase in the strength and ductility of the sample Ta0.5, thereby implying that: (i) dendrites are crucial in impending shear band propagation and generating multiple shear bands in TiZr-based BMGMCs; (ii) the hardness and strength values of dendrite after solid solution strengthening are still lower than the values of the amorphous phase, as presented in Fig. 6(b), which means that the dendrites still play the role of a plastic phase; and (iii) dendrites increase the resistance of deformation in TiZr-based BMGMCs after strengthening. 4. Conclusions In this study, the effect of the solid solution strengthening of dendrite on the microstructure and mechanical properties are investigated in detail. The following conclusions are drawn based on the results: (1) A series of TiZr-based BMGMCs with distinguished mechanical properties are successfully fabricated by the solid solution strengthening of dendrites. The average diameters and sizes of the dendrite increase with the Ta addition. In addition, the hardness and strength values of dendrite increase by solid solution strengthening, whereas the volume fractions of amorphous decrease after the addition of Ta. (2) The TiZr-based BMGMCs (Ta0.0-Ta8.0) manifest distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta0.5 possesses the largest plastic strain (εp) of 20.3% and ultimate strength (σmax) of 2613 MPa during compressive loading. In addition, the sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa during tensile process, and then progressively softens until it fractures at a strain of 10.2%. The distinguished mechanical properties should be attributed to the solid solution strengthening of dendrites. (3) Solid solution strengthening distorts the lattice of dendrites. Lattice distortions increase the resistance of dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Therefore, dendrites after solid solution strengthening create a strong barrier for the shear band propagation and generate multiple shear bands, which provide the TiZr-based BMGMCs with remarkably improved capacity to sustain plastic deformation and resistance to brittle fracture.
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Acknowledgments This work was supported by the SKPBRC (grant no.2013CB733000) and NSFC (grant no. 51171163/51434008/51171160). References [1] W.L. Johnson, MRS Bull, 24 (1999) 42. [2] A.L. Greer, Mate01r Today, 12 (2009) 14–22. [3] A. Inoue, Takeuchi, Int’l J Appl Glass Sci. 1 (2010) 273. [4] A. Inoue, X.M. Wang, W. Zhang, Rev Adv Mater Sci. 18 (2008) 1. [5] T. Mizushima, H. Koshiba, Y. Naito, A. Inoue, J Jpn Soc Powder Metall. 55 (2008) 146. [6] H. Ma, J. Xu, E. Ma, Appl. Phys. Lett. 83 (2003) 2793. [7] Y.K. Xu, H. Ma, J. Xu, E. Ma, Acta Mater. 53 (2005) 1857. [8] H.A. Bruck, T. Chrictman, A.J. Rosakis, W.L. Johnson, Scr. Metall.Mater. 30 (1994) 429. [9] A. Inoue, B.L. Shen, H. Koshiba, H. Kato, A.R. Yavari, Nat. Mater. 2 (2003) 661. [10] H.T. Zong, M.Z. Ma, X.Y. Zhang, B.W. Bai, P.F. Yu, Li. Q, et al., J Alloys Comp. 504S (2010) S106-S109. [11] H. Choi-Yim, R.D. Conner, F. Szuecs, W.L. Johnson, Acta Mater. 50 (2002) 2737–2745. [12] J.W. Qiao, Y. Zhang, G.L. Chen, Mater Design. 30 (2009) 3966–3971. [13] C. Fan, D.C. Qiao, T.W. Wilson, H. Choo, P.K. Liaw, Mater Sci Eng A, 431 (2006) 158–165. [14] C.C. Hays, C.P. Kim, W.L. Johnson, Phys Rev Lett. 84 (2000) 2901–2904. [15] H.M. Fu, H. Wang , H.F. Zhang, Z.Q. Hu, Scripta Mater. 54 (2006) 1961–1966. [16] D.C. Hofmann, J.Y. Suh, A. Wiest, G. Duan, M.L. Lind, M.D. Demetriou, et al., Nature, 451 (2008) 1085. [17] J.W. Qiao, Y. Zhang, P.K. Liaw, G.L. Chen, Scripta Mater. 61 (2009) 1087–1090. [18] D.Q. Ma, J.Li, Y.F. Zhang, X.Y. Zhang, M.Z. Ma, R.P. Liu, Mater Sci Eng A 612 (2014) 310–315. [19] Z.Y. Zhang, Y. Wu, J. Zhou, H. Wang, X.J. Liu , Z.P. Lu, Scripta Mater. 69 (2013) 73–76. [20] Choongnyun Paul Kim, Yoon S. Oh, Sunghak Lee, Nack J. Kim, Scripta Mater. 65 (2011) 304–307.
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[21] S. Pauly, J. Das, J. Bednarcik, N. Mattern, K.B. Kim, D.H. Kim, J. Eckert, Scripta Mater. 60 (2009) 432. [22] Y.F. Sun, H. Fuii, N. Tsuji, Y. Todaka, M. Umemoto, J Alloys Comp., 492 (2010) 149–152. [23] F. Szuecs, C.P. Kim, W.L Johnson, Acta Mater. 49 (2001) 1507–1513. [24] R.L. Narayan, P.S. Singh, D.C. Hofmann, N. Hutchinson, K.M. Flores, U. Ramamurty, Acta Mater. 60 (2012) 5089–5100. [25] R. Jing, S.X. Liang, C.Y. Liu, M.Z. Ma, X.Y. Zhang, R.P. Liu, Mater Sci Eng A 552 (2012) 295–300. [26] J.H. Hollomon, Trans. AIME 162 (1945) 268. [27] Q. Lu, W. Xu, Sybrand van der Zwaag, Acta Mater. 77 (2014) 310–323. [28] E. Isaac Samuel, B.K. Choudhary, K. Bhanu Sankara Rao, Scripta Mater. 46 (2002) 507–512. [29] S. Pauly, G. Liu, G. Wang, U. Kühn, N. Mattern, J. Eckert, Acta Mater. 57 (2009) 5445. [30] K.G. Pradeep, N. Wanderka, P. Choi, J. Banhart, B.S. Murty, D. Raabe, Acta Mater. 61 (2013) 4696–4706. [31] J.G. Niu, W.T. Geng, Acta Mater. 81 (2014) 194–203. [32] E.M. Parka, G.A. Songa, J.K. Leeb, M.H. Leec, H.S. Leec, J.Y. Parka, et al., J Alloys Comp. 509 (2011) 9015–9018. [33] K.B. Kim, J. Das, F. Baier, J. Eckert, Appl. Phys. Lett.86 (2005) 201909.
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Table Captions: Table 1 Thermal parameters of as cast TiZr-based BMGMCs (denoted as Ta0.0–Ta8.0). The errors of the temperatures are at ±1K. Table 2 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during compressive loading. Table 3 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during tensile process.
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Table 1 Thermal parameters of as cast TiZr-based BMGMCs (denoted as Ta0.0–Ta8.0). The errors of the temperatures are at ±1K. Tg (K)
Tx1 (K)
∆Tx (K)
Tm (K)
Tl (K)
Trg
∆Hx (J/k)
Ta0.0 (VF)
644
726
82
932
1042
0.618
-31.6
Ta0.5 (VF)
636
716
80
936
1056
0.602
-30.6
Ta2.0 (VF)
577
715
138
957
1085
0.532
-29.3
Ta5.0 (VF)
561
716
155
969
1116
0.503
-25.5
Ta8.0 (VF)
595
718
123
984
1132
0.526
-22.8
Composition (at.%): Ti38.8 Zr28.8Cu6.2Be16.2Nb10
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Table 2 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during compressive loading. Composition (at.%):
σy (MPa)
εy (%)
σmax(MPa)
εp (%)
Ta0.0 (VF)
1510
2.3
2150
12.0
Ta0.5 (VF)
1517
2.1
2610
20.3
Ta2.0 (VF)
1433
2.1
2464
16.2
Ta5.0 (VF)
1581
1.9
2453
16.7
Ta8.0 (VF)
815
1.8
2032
27.2
Ti38.8Zr28.8Cu6.2Be16.2Nb10
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Table 3 Mechanical properties: the yielding strength (σy), the yielding strain (εy), the ultimate strength (σrmax) and the plastic strain (εp) during tensile process. Composition (at.%):
σy (MPa)
εy (%)
σmax(MPa)
εp (%)
Ta0.0 (VF)
1238
2.2
1526
3.9
Ta0.5 (VF)
1280
2.1
1680
10.2
Ta8.0 (VF)
961
1.9
1082
6.8
Ti38.8Zr28.8Cu6.2Be16.2Nb10
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Figure Captions: Fig. 1. (a) XRD patterns of as cast TiZr-based BMGMCs and inset presents the enlarged regions of main peaks; (b) crystal lattice parameters of the β-(Ti, Zr)(Nb, Ta) phase dendrite. Fig. 2. (a) DSC curves of 3 mm-diameter of as cast TiZr-based BMGMCs at a heating rate of 0.33Ks–1 ; (b) the change trend of Tg, Tl, and Trg. Fig. 3. Edge micrograph of (a) Ta0.0; (b) Ta0.5;(c) Ta5.0 (the inset is a fine dendrite); (d) Ta8.0; EDS analysis of (e) Ta0.0 and (f) Ta8.0. Fig. 4. (a) Engineering compressive stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs at room temperature and inset picture presents the work-hardening index n; (b) relationship between the dσ/dε and ε; the inset picture is an enlarged area of the true stress–strain curves obtained through appropriate adjustment. Fig. 5. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during compressive loading: (a) the lateral surface of Ta0.0; (b) the lateral surface of Ta0.5; (c) the lateral surface of Ta8.0; (d) the fracture surface of Ta0.0; (e) the enlarged area of lateral surface of Ta0.5; (f) the fracture surface of Ta8.0. Fig. 6. (a) Engineering tensile stress–strain curves of the TiZr-based BMGMCs and the inset are macroscopic necking of Ta0.5 and schematic drawing of the tensile specimen (mm); (b) micro-hardness of amorphous and dendrites. Fig. 7. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during tensile loading: (a) the fracture surface of Ta0.5; (b) the enlarged area of fiber regions; (c) the enlarged area of shear lips; (d) the lateral surface of Ta0.5. Fig. 8. (a) BF TEM image of the composites and the insets are corresponding to SAED patterns of glass matrix and dendrites; (b) IFFT image of Ta0.0 in the dendrites obtained from inset picture at crystal plane (011) and the inset picture is an HRTEM image (c) IFFT image of Ta0.5 in the dendrites at crystal plane (011); (d) IFFT image of Ta8.0 in the dendrites indicating pile-ups of dislocations after solid solution strengthening.
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Fig. 1. (a) XRD patterns of as cast TiZr-based BMGMCs and inset presents the enlarged regions of main peaks; (b) crystal lattice parameters of the β-(Ti, Zr)(Nb, Ta) phase dendrite.
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Fig. 2. (a) DSC curves of 3 mm-diameter of as cast TiZr-based BMGMCs at a heating rate of 0.33Ks–1 ; (b) the change trend of Tg, Tl, and Trg.
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Fig. 3. Edge micrograph of (a) Ta0.0; (b) Ta0.5;(c) Ta5.0 (the inset is a fine dendrite); (d) Ta8.0; EDS analysis of (e) Ta0.0 and (f) Ta8.0.
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Fig. 4. (a) Engineering compressive stress–strain curves of 3 mm-diameter of as-cast TiZr-based BMGMCs at room temperature and inset picture presents the work-hardening index n; (b) relationship between the dσ/dε and ε; the inset picture is an enlarged area of the true stress–strain curves obtained through appropriate adjustment.
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Fig. 5. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5, and Ta8.0) during compressive loading: (a) the lateral surface of Ta0.0; (b) the lateral surface of Ta0.5; (c) the lateral surface of Ta8.0; (d) the fracture surface of Ta0.0; (e) the enlarged area of lateral surface of Ta0.5; (f) the fracture surface of Ta8.0.
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Fig. 6. (a) Engineering tensile stress–strain curves of the TiZr-based BMGMCs and the inset are macroscopic necking of Ta0.5 and schematic drawing of the tensile specimen (mm); (b) micro-hardness of amorphous and dendrites.
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Fig. 7. Fractographs of the as-cast TiZr-based BMGMCs (Ta0.0, Ta0.5 and Ta8.0) during tensile loading: (a) the fracture surface of Ta0.5; (b) the enlarged area of fiber regions; (c) the enlarged area of shear lips; (d) the lateral surface of Ta0.5.
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Fig. 8. (a) BF TEM image of the composites and the insets are corresponding to SAED patterns of glass matrix and dendrites; (b) IFFT image of Ta0.0 in the dendrites obtained from inset picture at crystal plane (011) and the inset picture is an HRTEM image (c) IFFT image of Ta0.5 in the dendrites at crystal plane (011); (d) IFFT image of Ta8.0 in the dendrites indicating pile-ups of dislocations after solid solution strengthening.
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Highlights： ： Hardness of dendrite of TiZr-based BMGMCs increases. Strong work-hardening behavior is obtained after solid solution strengthening. Lattice distortions of dendrite suffering from rapid cooling are detected.
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