Understanding the relationship between ...

Materials and Design 92 (2016) 1038–1045

Contents lists available at ScienceDirect

Materials and Design journal homepage: www.elsevier.com/locate/matdes

Understanding the relationship between microstructure and mechanical properties of Al–Cu–Si ultrafine eutectic composites Jeong Tae Kim a, Seoung Wan Lee a, Sung Hwan Hong a, Hae Jin Park a, Jun-Young Park a, Naesung Lee a, Yongho Seo b, Wei-Min Wang c, Jin Man Park d,⁎, Ki Buem Kim a,⁎ a

Hybrid Materials Center, Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea Graphene Research Institute (GRI) & HMC, Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747, Republic of Korea Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China d Global Production Technology Center, Samsung Electronics Co., Ltd, 129, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-742, Republic of Korea b c

a r t i c l e

i n f o

Article history: Received 5 September 2015 Received in revised form 11 November 2015 Accepted 14 December 2015 Available online 18 December 2015 Keywords: Ultrafine eutectic composite Microstructure Heterogeneity Deformation mechanism

a b s t r a c t Systematic investigations for the influence of the microstructural change derived from compositional tuning in Al-rich corner of Al–Cu–Si system on mechanical properties demonstrate that mechanical characteristic of ultrafine eutectic composites strongly depend on the crystallinity, length scale and volume fraction of constituent phases. Ultrafine eutectic composites can be divided into two categories: 1) whether primary phases exist or not and 2) the types of matrix phases, i.e., single eutectic or bimodal eutectic. The features of primary phases play a principal role on the macroscopic property. Ductile α-Al phase is very effective to improve the plasticity while brittle Al2Cu intermetallic phase deteriorates obviously mechanical performance. In addition, bimodal eutectic matrix alloys composed of eutectics with different length scale and morphology show superior mechanical properties than single eutectic matrix alloys. Based on the microstructural studies, it is believed that high strength is originated from ultrafine scale microstructure and enhanced plasticity is supported by strain gradient plasticity. These results reveal that mechanical properties of the ultrafine eutectic composites can be properly optimized via control of chemical and topological governing factors. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Nano-/ultrafine structured materials including bulk metallic glasses (BMGs) have been highlighted due to their remarkable high strength as contrasted with conventional coarse-structured materials [1–6]. However, the practical engineering applications are strictly limited due to their low level of plastic deformability and toughness at room temperature. Recently, nano-/ultrafine structured composites containing micrometer-scale dendrites in ultrafine eutectic matrix or bimodal ultrafine eutectic alloys composed of multi-scale eutectic microstructure have received comprehensive attention because of their improved plasticity and excellent damage tolerance [7–14]. Design concepts of these particular alloys are based on the construction of structural or chemical heterogeneities such as the combination of crystalline phases with different length scale and different physical characteristic [15–17]. The high strength is provided by the dislocation file up attributed to the hindering of dislocation movement from nano-/ultrafine scale eutectic matrix while large plasticity is due to the stress relaxation and strain accommodation during deformation [18–20]. Generation of ⁎ Corresponding authors. E-mail addresses: [email protected] (J.M. Park), [email protected] (K.B. Kim).

http://dx.doi.org/10.1016/j.matdes.2015.12.080 0264-1275/© 2015 Elsevier Ltd. All rights reserved.

inhomogeneous microstructure with uniform distribution can effectively minimize the plastic instability [21–24]. In more details, an achievement of global plastic deformation is originated from the summation of different plastic deformation mechanisms, i.e., dislocationbased slip activity in the ductile dendrites and constraint multiple shear banding in the hard ultrafine-structured matrix [25–29]. Therefore, it is noted that the characteristics of constituent phases containing dendrite and ultrafine-structured matrix, such as size, volume fraction, crystallinity, shape and distribution, are very important factors to determine the macroscopic strength and ductility [30–37]. Recently, Park et al. reported that Al81Cu13Si6 bimodal eutectic composite consisting of micrometer-sized cellular type binary eutectic colonies (α-Al + Al2Cu) and nanometer-sized ternary eutectic matrix (α-Al + Al2Cu + Si) presents a high strength of 1 GPa as well as high plasticity of 11% at ambient temperature [38–42]. However, there are only few studies related with microstructural modulation and its influence on mechanical properties via micro-alloying of additional elements [43–48]. It is worth noting that understanding of the relationship between microstructure and mechanical property in the ultrafine eutectic composites. In order to assessment of structure–property relationship, we explore the evolution of microstructure in Al-rich corner of simple ternary Al–Cu–Si system by fine-compositional tuning and investigate the corresponding mechanical properties.

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045 Table 1 The detail compositions of the currently investigated Al–Cu–Si alloys. Alloy

A1 (at.%)

Cu (at.%)

Si (at.%)

#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19 #20 #21 #22 #23 #24 #25 #26 #27 #28

75 75 76 78 80 80 80 80 81 81 81 81 81 81 81 82 82 83 83 84 84 85 85 86 86 88 88 88

10 18 22 15 5 8 13 16 7 10 11 12 13 14 15 8 11 11 12 9 14 5 10 7 12 6 8 10

15 7 2 7 15 12 7 3 12 9 8 7 6 5 4 10 7 6 5 7 2 10 5 7 2 6 4 2

2. Materials and methods Al–Cu–Si alloys were prepared by arc melting the pure elements under an argon atmosphere. Alloy ingots were re-melted at least four times to guarantee compositional homogeneity. Cylindrical rod samples with 3 mm diameter and 50 mm length were fabricated using suction

1039

casting facility. Phase identification of the alloys was performed by X-ray diffraction (XRD, Rigaku-D/MAX-2500/PC) with Cu Kα radiation (λ = 1.5406 Å). Scanning electron microscopy (SEM: JEOL JSM-6390) equipped with an energy-dispersive spectrometer (EDX) was used for microstructure observation. Cylindrical specimens with a 2:1 aspect ratio for compression tests were prepared. The room temperature mechanical properties were carried out under uniaxial compression and tension loading using an initial strain rate of 10− 3 s− 1 at room temperature. 3. Result and discussion To investigate the evolution of microstructure in Al-rich corner of Al–Cu–Si system during solidification, 28 alloys were designed and fabricated via suction casting method. All investigated alloys are listed in Table 1 and they are superimposed on the Al–Cu–Si ternary phase diagram in Al-rich corner, as shown in Fig. 1 [49]. Open numbered circles in Fig. 1 display the composition of present studied alloys. Based on the phase diagram, it is simply supposed that several types of eutectic composites with different phase constitution can be prepared. Possible phase constitutions are α-Al, Al2Cu, and Si. From the experimental results (see Figs. 2 and 3), currently studied alloys can be roughly categorized into two groups depending on the types of matrix morphology. One is the bimodal eutectic matrix alloy and the other is single eutectic matrix alloy. Moreover, each group can also be classified according to the existence of primary precipitated phases, e.g. α-Al solid solution, intermetallic Al2Cu, and Si phases. Among currently studied alloys, we selected representative 7 alloys in accordance with phase constitution and microstructural feature and investigated their corresponding mechanical properties. Fig. 2 shows the XRD patterns of representative (a) bimodal eutectic matrix alloys and (b) single eutectic matrix alloys. As depicted by Fig. 2, XRD patterns consist of three phases such as a face-centered cubic (fcc) α-Al solid solution phase (Fm3m, a = 0.4049 nm), body-centered tetragonal (bct) Al2Cu phase (I4/mcm, a = 0.6067 nm, c = 0.4877 nm)

Fig. 1. Compositional map of currently studied Al–Cu–Si ultrafine eutectic composites superimposed on the Al–Cu–Si ternary phase diagram in Al-rich corner.

1040

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045

Fig. 2. XRD patterns of representative (a) bimodal eutectic matrix alloys and (b) single eutectic matrix alloys.

and diamond cubic (dc) Si phase (Fd3m, a = 0.5430 nm). Although they show the similar XRD patterns due to same comprising phases, but intensity of XRD peaks is slightly different. This is attributed to the difference of volume fraction of constituent phases. In particular, the diffraction peaks of Si phases are more clearly shown in the bimodal eutectic matrix alloys due to exclusive existence of Si phases in anomalous ternary eutectic regions (see Fig. 3). In other words, it is supposed that the distinction of XRD patterns can be caused by the phase constitution and volume fraction of constituent phases. Fig. 3(a)–(d) show the SEM back scattering electron (BSE) images of the as-cast Al–Cu–Si bimodal eutectic matrix alloys. As shown in Fig. 3(a), Alloy #19 exhibits typical hypoeutectic-like structure consisting of micron-scale primary dendrite and fine scale eutectic matrix. Primary dendrites are homogeneously embedded and distributed in the bimodal eutectic matrix. The inset image in Fig. 3(a) obtained at higher magnification clearly indicates the bimodal eutectic structure composed of cellular eutectic and ultrafine structured matrix. From the analyses of XRD patterns and SEM BSE image, dark contrast dendrites are identified as

α-Al phase. Fig. 3(b) shows similar morphology but inversed microstructure compared with that of Fig. 3(a) [Alloy #8]. Bright contrast primary phases are identified as Al2Cu phase. The inset image in Fig. 3(b) indicates the hierarchical morphology in length scale of constituent phases, which is micrometer-sized Al2Cu phase, ultrafine scaled eutectic, and nanostructured matrix. Fig. 3(c) exhibits the microstructure of Alloy #4, which composed of primary Si phases and bimodal eutectic matrix. The primary Si phases exhibit the typical facet morphology. The inset image exhibits the primary Si phases and bimodal eutectic structure. For Alloy #13, Fig. 3(d) reveals fully bimodal eutectic structure with length-scale difference in eutectic phase (coarse eutectic colony and fine eutectic matrix) and there is no micron-scale primary phase. It is worth noting that coarse eutectic colony structure with cellular morphology is surrounded by the fine eutectic matrix structure. The formation of composite-type novel microstructure based on homogeneous distribution of a heterogeneous structure is possible because of high cooling rate and compositional undercooling effect of Si addition during solidification. From previous studies, it was clearly identified that coarse eutectic colonies consist of α-Al and Al2Cu phases and fine eutectic matrix is composed of α-Al, Al2Cu and Si phases [38]. Coarse eutectic colony region has shown the cellular type morphology relating to the compositional undercooling, fine eutectic matrix region seems as the complex anomalous eutectic structure [39]. Fig. 3(e)–(g) present the microstructure of the as-cast Al–Cu–Si single eutectic matrix alloys. It was founded that the single eutectic matrix alloys can be classified with types of primary phase, e.g. α-Al, Al2Cu, and α-Al + Si. Particularly, the single eutectic matrix alloys exhibit relatively higher volume fraction of dendrites rather than that of the bimodal eutectic matrix alloys. Fig. 3(e) shows the Alloy #3 which is composed of single eutectic matrix and Al2Cu primary phases. The microstructure of Alloy #28 demonstrates the typical hypoeutectic structure with large volume fraction of α-Al dendrite phases embedded in eutectic matrix (Fig. 3(f)). Alloy #5 is composed of micron-scale dendrite (dark contrast) and eutectic matrix (gray contrast) [Fig. 3(g)]. In more details, morphological difference in the dark contrast areas is observed with rounded and angular blocky morphology. The EDX results reveal that rounded and angular blocky dendrites was identified as Al83.51Cu11.11Si5.38 (α-Al solid solution phase) and Al16.32Cu0.53Si83.14 (Si phase), respectively. Primary Si phases exhibit the facet morphology which similar to that of Alloy #7. Therefore, it is clear that the alloy #5 is incorporated by two difference dendrites (α-Al + Si) and eutectic matrix. According to variation of composition, the sort of primary phase and matrix type are summarized in Table 2. The fully eutectic microstructure among present studied alloys can obtain from alloys #13, #14, and #15, which include no primary phases. Alloys #1, #4, #7, #8, #10, #11, #12, #17, #18 and #19 reveal the microstructure of bimodal eutectic composite with primary phases. Furthermore, the primary α-Al phase is verified at Alloys #1, #10, #11, #17, #18 and #19 and primary Si phase is founded in Alloys #1, #4, #7, #10, #11, #12, #17 and #18. The primary Al2Cu phase with bimodal eutectic structure is identified at Alloy #8. On the other hand, the composites having a microstructure of single eutectic + primary phase were observed in Alloys #2, #3, #5, #6, #9, #16, #20, #21, #22, #23, #24, #25, #26, #27 and #28. Similarly, Alloys #5, #6, #9, #16, #20, #21, #22, #23, #24, #25, #26, #27 and #28 include the primary α-Al phase and Alloys #2, #5, #6, #9, #16, #20, #22 and #24 contain the primary Si phase. Besides, Alloys #2 and #3 involve the primary Al2Cu phase. This suggests that the evolution of primary phase and matrix is affected by controlling the contents of all three elements. Fig. 4 shows engineering and true compressive stress–strain curves of the nominated Al–Cu–Si eutectic composite alloys at room temperature. Fig. 4(a) exhibits the stress–strain curves of representative bimodal eutectic matrix alloys under compression. Alloy #8 (Al80Cu17Si3) consisting of primary Al2Cu phase and bimodal eutectic matrix shows reasonable yield strength of 750 MPa with insufficient for plasticity of 1.9%. Similarly, Alloy #4 (Al78Cu15Si7) included primary Si phase

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045

1041

Fig. 3. Secondary electron SEM images of bimodal eutectic matrix alloys (a)–(d) and of single eutectic matrix alloys (e)–(g): (a) Alloy #19, (b) Alloy #8, (c) Alloy #4, (d) Alloy #13, (e) Alloy #3, (f) Alloy #28, and (g) Alloy #5.

shows high strength of 807 MPa and limited plasticity of 3.5%, respectively. Alloy #19 (Al83Cu12Si5) composing of primary α-Al phase shows decreased yield strength (569 MPa) and low plasticity (3.5%). On the other hand, the fully bimodal eutectic alloy, Alloy #13 (Al81Cu13Si6), exhibits the excellent mechanical properties such as high yield strength of 773 MPa as well as reasonable plastic deformability of 8%. Fig. 4(b) shows the stress–strain curves of selected single eutectic matrix alloys under compressive condition. Similar to the bimodal eutectic alloys, the primary Al2Cu phase and eutectic

matrix composite alloy, Alloy #3 (Al76Cu22Si2), exhibits the high yield strength of 774 MPa and very limited plasticity of 0.2%. Alloy #2 (Al75Cu18Si7) consisting of primary Al2Cu and Si phases also shows very high yield strength of 810 MPa and low plasticity of 1.3%. On the other hand, Alloy #28 (Al88Cu10Si2, including primary α-Al phase) and Alloy #5 (Al80Cu5Si15, including primary α-Al and Si phases) have low yield strength about ~520 MPa and large plasticity of ~20%, relatively. The detail values of yield strength and plastic strain for all present alloys are summarized in Table 2. The inset true stress–strain curves in

1042

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045

Table 2 Phase constitution and mechanical properties of Al–Cu–Si ultrafine eutectic composites: Yield strength σy, plastic strain %, constitution of primary phase and eutectic matrix. Alloy

Yield strength (MPa)

Plastic strain (MPa)

Primary phase

Matrix feature

#1 : Al75Cu10Si15 #2 : Al75Cu18Si7 #3 : Al76Cu22Si2 #4 : Al78Cu15Si7 #5 : Al80Cu5Si15 #6 : Al80Cu8Si12 #7 : Al80Cu13Si7 #8 : Al80Cu17Si3 #9 : Al81Cu7Si12 #10 : Al81Cu10Si9 #11 : Al81Cu11Si8 #12 : Al81Cu12Si7 #13 : Al81Cu13Si6 #14 : Al81iCu14Si5 #15 : Al81Cu15Si4 #16 : Al82Cu8Si10 #17 : Al82Cu11Si7 #18 : Al83Cu11Si6 #19 : Al83Cu12Si5 #20 : Al84Cu9Si7 #21 : Al84Cu14Si2 #22 : Al88Cu5Si10 #23 : Al85Cu10Si5 #24 : Al86Cu7Si7 #25 : Al86Cu12Si2 #26 : Al88Cu6Si6 #27 : Al88Cu8Si4 #28 : Al88Cu10Si2

620 810 774 807 520 650 762 750 542 653 648 732 773 719 760 635 575 589 596 541 650 462 551 615 547 460 542 518

2.5 1.3 0.2 3.5 13.7 13 8 1.9 4.1 4.7 8.5 8.7 8 8.3 8.6 6.2 2.2 4.6 3.5 9.3 11.5 12.3 13.7 21.5 15.8 21.5 19.2 16.1

α-Al + Si A12Cu + Si A12Cu Si α-Al + Si α-Al + Si Si Al2Cu α-Al + Si α-Al + Si α-Al + Si Si – – – α-Al + Si α-Al + Si α-Al + Si α-Al α-Al + Si α-Al α-Al + Si α-Al α-Al + Si α-Al α-Al α-Al α-Al

Bimodal eutectic Single eutectic Single eutectic Bimodal eutectic Single eutectic Single eutectic Bimodal eutectic Bimodal eutectic Single eutectic Bimodal eutectic Bimodal eutectic Bimodal eutectic Bimodal eutectic Bimodal eutectic Bimodal eutectic Single eutectic Bimodal eutectic Bimodal eutectic Bimodal eutectic Single eutectic Single eutectic Single eutectic Single eutectic Single eutectic Single eutectic Single eutectic Single eutectic Single eutectic

Fig. 4(a)–(b) show the similar deformation behaviors comparing with engineering stress–strain curves. One can find that the bimodal eutectic matrix alloys show higher yield strength than single eutectic matrix alloys due to the existence of nano-scale ternary anomalous eutectic structure composed by α-Al, Al2Cu and Si. Moreover, the large plasticity above 10% is only achieved in the single eutectic alloys with primary α-Al dendrites. These tendencies indicate that the development of bimodal eutectic alloys without primary phase is successful strategy for avoiding tradeoff between the strength and plasticity. The microstructural features and mechanical diagram of present studied alloys are illustrated in the partial ternary phase diagrams of Al–Cu–Si system (Fig. 5). The microstructural features of present studied alloys display in Fig. 5(a), which the Al–Cu–Si alloys containing each primary phase denoted by different colors and symbols, such as α-Al: Blue, Si: Yellow, Al2Cu: Green and no primary phase: Red. The alloys including two primary phases are expressed by the two-tone. Moreover, the single eutectic matrix alloys are represented as inverted triangle and the bimodal eutectic matrix alloys are described using the circle. The distribution of mechanical properties is shown in Fig. 5(b). The red color covered area indicates the compositions with high strength above 700 MPa and the blue color covered areas show alloy compositions with high plasticity (N8%). It is well-known that the mechanical properties of dendrite-ultrafine eutectic composites are strongly governed by phase selection and their volume fraction of primary precipitate [7,8,10–12]. Eckert et al. reported that micrometer scale solid-solution phases act as a barrier for suppression of catastrophic failure [50]. In this study, primary α-Al phase plays a critical role in significant improvement of plastic deformability, even though which can result in inevitable reduction of strength. At the early stage of plastic deformation, the ductile dendrites plastically deform with formation of slip bands by dislocation activation and the local stress concentrates on the dendrite-ultrafine eutectic matrix interface. And then, the part of stress is transferred to the neighboring ultrafine eutectic matrix. As depicted in Fig. 6(a), localized stress leads

Fig. 4. Engineering and true compressive stress–strain curves of the as-cast Al–Cu–Si ultrafine eutectic composites: (a) bimodal eutectic matrix alloys and (b) single eutectic matrix alloys.

to the generation of shear bands in the ultrafine eutectic matrix [51]. Here the ductile dendrite phase can act as both a nucleation site of shear bands and hampering site for propagation of shear bands (inset image in Fig. 6(a)). With further increasing strain, multiple shear bands are extensively developed in overall region to accommodate the excessive strain. For that reason, the ductile dendrites obviously contribute to improved macroscopic plasticity. In contrast, the Al–Cu– Si alloys containing primary Al2Cu intermetallic phase exhibit the high yield strength, but no reasonable plasticity (Fig. 4(b)). Moreover, the increasing of plastically incompatible phases contributes to decrease the cavitation resistance of the ultrafine eutectic matrix leading to micro-cracking and hence the reduced ductility [52,53]. Fig. 6(b) shows some cracks on the lateral surface morphology of deformed sample. The brittle intermetallic phases can easily initiate the cracks due to their low level of strain accommodation ability. As denoted by red circle in Fig. 5(a), the bimodal eutectic alloys in Al-rich corner of Al–Cu–Si system show an outstanding combination of high strength and reasonable plasticity. This indicates that the well-designed microstructural heterogeneities are effective to enhance the plastic deformation, together with maintaining the high strength [54–58]. The geometrically favorable morphology of eutectic colony can effectively dissipate the shear stress and suppress the localization of deformation using the rotational motion (see Fig. 6(c)). Hence, the bimodal eutectic structure can accommodate the much higher strain than single eutectic structure (#2, #3). In turn, the origin of outstanding mechanical properties of spatially modulated ultrafine composites in Al–Cu–Si system can

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045

1043

Fig. 5. (a) Microstructural and (b) mechanical characteristic maps of Al–Cu–Si ultrafine eutectic composites.

be supposed to their combined effect of ultrafine lamellar structure and microstructural heterogeneity, e.g. length scale, phase selection and colony morphology (rotational motion). Based on this understanding, it is noted that intrinsic characteristics of comprising phases and structure as well as their harmonic distribution are crucial factor to control

the mechanical properties of Al–Cu–Si ultrafine composites. In view of that, the relationship between microstructure and mechanical property of ultrafine eutectic composites can be properly demonstrated and novel physical/chemical/mechanical properties can be tailor-made [59–61].

1044

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045

mechanical strength than single eutectic matrix alloys. In particular, bimodal eutectic composites composed of two eutectics with different length scale (alloys 13, 14, and 15) exhibit the well optimized mechanical properties, i.e., high yield strength (N 700 MPa) and large plasticity (N8%), due to unique topological distribution termed as harmonic structure. Here it is feasible that strategies for strengthening and toughening mechanism of ultrafine eutectic composites can be suggested from the understanding of relationship between structural distribution characteristic and mechanical properties.

Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science, ICT & Future Planning) (No. 2013R1A2A2A05006550), the framework of international cooperation program managed by National Research Foundation of Korea (Grant Number NRF-2015K2A2A2002583) and the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, industry & Energy (No. 20154030200630). One of the authors, Y. Seo, specially thanks the support from Priority Research Centers Program through the National Research Foundation of Korea (NRF) (No. 2010-0020207).

References

Fig. 6. SEM images of lateral surface morphologies of deformed samples and schematic propagation behavior of shear bands in ultrafine eutectic composites with different microstructural characteristics: (a) α-Al dendrite + eutectic structure, (b) Al2Cu dendrite + eutectic structure, (c) bimodal eutectic structure.

4. Conclusions Influence of the microstructural feature including phase constitution, length scale, volume fraction and distribution of component phases on mechanical properties of Al–Cu–Si alloys in Al-rich corner was systematically investigated through fine compositional tuning. The currently studied alloys were roughly classified into two types depending on the matrix structure as follows: 1) bimodal eutectic matrix alloys and 2) single eutectic matrix alloys. In addition, they were further distinguished by existence of primary solidified phases such as α-Al, Al2Cu and Si. The macroscopic mechanical properties of ultrafine eutectic composites strongly depend on the phase selection and volume fraction of primary phase. Ductile α-Al solid-solution phase has a fabulous effect on the plasticity whereas the intermetallic Al2Cu and Si phases have a difficulty in accommodation of plastic strain. Moreover, bimodal eutectic matrix alloys generally show better

[1] H. Gleiter, Nanostructured materials: basic concepts and microstructure, Acta Mater. 48 (2000) 1–29. [2] E. Ma, Recent progress in improving ductility of ultra-high strength nanostructured metals, Met. Mater. Int. 10 (2004) 527–531. [3] W.L. Johnson, Bulk glass-forming metallic alloys: science and technology, MRS Bull. 24 (1999) 42–56. [4] A. Inoue, Stabilization of metallic supercooled liquid and bulk amorphous alloys, Acta Mater. 48 (2000) 279–306. [5] M. Telford, The case for bulk metallic glass, Mater. Today 7 (2004) 36–43. [6] J.R. Greer, Nanotwinned metals: it's all about imperfections, Nat. Mater. 12 (2013) 689–690. [7] G. He, J. Eckert, W. Löser, L. Schultz, Novel Ti-base nanostructure-dendrite composite with enhanced plasticity, Nat. Mater. 2 (2003) 33–38. [8] E. Ma, Nanocrystalline materials: controlling plastic instability, Nat. Mater. 2 (2003) 7–8. [9] P.V. Liddicoat, X.Z. Liao, Y. Xhao, Y. Zhu, M.Y. Murashkin, E.J. Lavernia, R.Z. Valiev, S.P. Ringer, Nanostructural hierarchy increases the strength of aluminium alloys, Nat. Commun. 1 (2010) 63–67. [10] D.V. Louzguine-Luzgin, L.V. Louzguina-Luzgina, H. Kato, A. Inoue, Investigation of Ti– Fe–Co bulk alloys with high strength and enhanced ductility, Acta Mater. 53 (2005) 2009–2017. [11] G. Liu, G.J. Zhang, F. Jiang, X.D. Ding, Y.J. Sun, J. Sun, E. Ma, Nanostructured highstrength molybdenum alloys with unprecedented tensile ductility, Nat. Mater. 12 (2013) 344–350. [12] J.M. Park, K.B. Kim, W.T. Kim, M.H. Lee, J. Eckert, D.H. Kim, High strength ultrafine eutectic Fe–Nb–Al composites with enhanced plasticity, Intermetallics 16 (2008) 642–650. [13] L.H. Liu, C. Yang, F. Wang, S.G. Qu, X.Q. Li, W.W. Zhang, Y.Y. Li, L.C. Zhang, Ultrafine grained Ti-based composites with ultrahigh strength and ductility achieved by equiaxing microstructure, Mater. Des. 79 (2015) 1–5. [14] J.T. Kim, S.H. Hong, H.J. Park, Y.S. Kim, G.H. Park, J.-Y. Park, N. Lee, Y. Seo, J.M. Park, K.B. Kim, Improving the plasticity and strength of Fe–Nb–B ultrafine eutectic composite, Mater. Des. 76 (2014) 190–195. [15] Y.M. Wang, M. Chen, F. Zhou, E. Ma, High tensile ductility in a nanostructured metal, Nature 419 (2002) 912–915. [16] C.C. Koch, Optimization of strength and ductility in nanocrystalline and ultrafine grained metals, Scr. Mater. 49 (2004) 657–662. [17] C.H. Lee, S.H. Hong, J.T. Kim, H.J. Park, G.A. Song, J.M. Park, J.Y. Suh, Y. Seo, M. Qian, K.B. Kim, Chemical heterogeneity-induced plasticity in Ti–Fe–Bi ultrafine eutectic alloys, Mater. Des. 60 (2014) 363–367. [18] K.B. Kim, J. Das, W. Xu, Z.F. Zhang, J. Eckert, Microscopic deformation mechanism of a Ti66.1Nb13.9Ni4.8Cu8Sn7.2 nanostructure-dendrite composite, Acta Mater. 54 (2006) 3701–3711. [19] J.M. Park, S.W. Sohn, D.H. Kim, K.B. Kim, W.T. Kim, J. Eckert, Propagation of shear bands and accommodation of shear strain in the Fe56Nb4Al40 ultrafine eutecticdendrite composite, Appl. Phys. Lett. 92 (2008) 091910. [20] R.Z. Valiev, Nanostructured alloys: large tensile elongation, Nat. Mater. 12 (2013) 289–291. [21] G.H. Cao, R. Schneider, D. Gerthsen, R. Scharrschuch, C.G. Oertel, W. Skrotzki, Sn and Nb modified ultrafine Ti-based bulk alloys with high-strength and enhanced ductility, Appl. Phys. Lett. 102 (2013) 061908.

J.T. Kim et al. / Materials and Design 92 (2016) 1038–1045 [22] Z.P. Chen, H. Yu, Y. Wu, H. Wang, S.J. Liu, Z.P. Lu, Nano-network mediated high strength and large plasticity in an Al-based alloy, Mater. Lett. 84 (2014) 59–62. [23] D. Yu, H. Bei, Y. Chen, E.P. George, K. An, Phase-specific deformation behavior of a relatively tough NiAl–Cr(Mo) lamellar composite, Scr. Mater. 84-85 (2014) 52–55. [24] Y.Z. Tian, Z.F. Zhang, Bulk eutectic Cu–Ag alloys with abundant twin boundaries, Scr. Mater. 66 (2012) 65–68. [25] J.M. Park, T.E. Kim, S.W. Sohn, D.H. Kim, K.B. Kim, W.T. Kim, J. Eckert, High strength Ni–Zr binary ultrafine eutectic-dendrite composite with large plastic deformability, Appl. Phys. Lett. 93 (2008) 031903. [26] H. Ma, L.L. Shi, J. Xu, E. Ma, Chill-cast in situ composites in the pseudo- ternary Mg–(Cu,Ni)–Y glass-forming system: microstructure and compressive properties, J. Mater. Res. 22 (2007) 314–325. [27] T. Maity, B. Roy, J. Das, Mechanism of lamellar deformation and phase rearrangement in ultrafine b-Ti/FeTi eutectic composites, Acta Mater. 97 (2015) 170–179. [28] C.S. Tiwary, S. Kashyap, K. Chattopadhyay, Development of alloys with high strength at elevated temperature by tuning the bimodal microstructure in the Al–Cu–Ni eutectic system, Scr. Mater. 93 (2014) 20–23. [29] L. Wang, J. Shen, Z. Shang, H. Fu, Microstructure evolution and enhancement of fracture toughness of NiAl–Cr(Mo)-(Hf, Dy) alloy with a small addition of Fe during heat treatment, Scr. Mater. 80 (2014) 1–4. [30] J. Das, K.B. Kim, F. Baier, W. Löser, J. Eckert, High strength Ti-base ultrafine eutectic with enhanced ductility, Appl. Phys. Lett. 87 (2005) 161907. [31] J.M. Park, D.H. Kim, K.B. Kim, W.T. Kim, Deformation induced rotational eutectic colonies containing length-scale heterogeneity in an ultrafine eutectic Fe83Ti7Zr6B4 alloy, Appl. Phys. Lett. 91 (2007) 131907. [32] J.T. Kim, S.H. Hong, H.J. Park, G.H. Park, J.Y. Suh, J.M. Park, K.B. Kim, Influence of microstructural evolution on mechanical behavior of Fe–Nb–B ultrafine composites with a correlation to elastic modulus and hardness, J. Alloys Compd. 647 (2015) 886–891. [33] L. Shi, H. Ma, T. Liu, J. Xu, E. Ma, Microstructure and compressive properties of chillcast Mg–Al–Ca alloys, J. Mater. Res. 21 (2006) 613–622. [34] D.V. Louzguine, L.V. Louzguina, H. Kato, A. Inoue, Investigation of high strength metastable hypereutectic ternary Ti–Fe–Co and quaternary Ti–Fe–Co–(V, Sn) alloys, J. Alloys Compd. 32 (2007) 434–435. [35] J.M. Park, D.H. Kim, K.B. Kim, M.H. Lee, W.T. Kim, J. Eckert, Influence of heterogeneities with different length scale on the plasticity of Fe-base ultrafine eutectic alloys, J. Mater. Res. 23 (2008) 2003–2008. [36] Y.H. Zhao, X.Z. Liao, S. Cheng, E. Ma, Y.T. Zhu, Simultaneously increasing the ductility and strength of nanostructured alloys, Adv. Mater. 18 (2006) 2280–2283. [37] L. Zhuo, H. Wang, T. Zhang, Hierarchical ultrafine-grained network mediated high strength and large plasticity in an Al-based alloy, Mater. Lett. 124 (2014) 28–31. [38] J.M. Park, N. Mattern, U. Kühn, J. Eckert, K.B. Kim, W.T. Kim, K. Chattopadhyay, D.H. Kim, High-strength bulk Al-based bimodal ultrafine eutectic composite with enhanced plasticity, J. Mater. Res. 24 (2009) 2605–2609. [39] S.W. Lee, J.T. Kim, S.H. Hong, H.J. Park, J.Y. Park, N.S. Lee, Y. Seo, J.Y. Suh, J. Eckert, D.H. Kim, J.M. Park, K.B. Kim, Micro-to-nano-scale deformation mechanisms of a bimodal ultrafine eutectic composite, Sci. Rep. 4 (2014) 1–5. [40] X. Ma, L. Liu, Solidification microstructures of the undercooled Co–24 at.%Sn eutectic alloy containing 0.5 at.%Mn, Mater. Des. 83 (2015) 138–143. [41] G.C. Pettan, C.R.M. Afonso, J.E. Spinelli, Microstructure development and mechanical properties of rapid solidified Ti–Fe and Ti–Fe–Bi alloys, Mater. Des. 86 (2015) 221–229. [42] J.M. Park, K.B. Kim, N. Mattern, R. Li, G. Liu, J. Eckert, Multi-phase Al-based ultrafine composite with multi-scale microstructure, Intermetallics 19 (2011) 536–540.

1045

[43] N.A. Belov, E.A. Naumova, A.N. Alabin, I.A. Matveeva, Effect of scandium on structure and hardening of Al–Ca eutectic alloys, J. Alloys Compd. 646 (2015) 741–747. [44] J.M. Park, S. Pauly, N. Mattern, K.B. Kim, J. Eckert, Microstructural modulations enhance the mechanical properties in Al–Cu–(Si, Ga) ultrafine composite, Adv. Eng. Mater. 12 (2010) 1137–1141. [45] A. Darlapudi, S.D. McDonald, D.H. StJohn, The influence of ternary Cu additions on the nucleation of eutectic grains in a hypoeutectic Al–10 wt.%Si alloy, J. Alloys Compd. 646 (2015) 699–705. [46] M. Gogebakan, C. Kursun, K.O. Gunduz, M. Tarakci, Y. Gencer, Microstructural and mechanical properties of binary Ni–Si eutectic alloys, J. Alloys Compd. 643 (2015) S219–S225. [47] S.W. Sohn, J.M. Park, W.T. Kim, D.H. Kim, Micro-alloying effect on the microstructure and mechanical properties in Al–Cu based dendrite-ultrafine composites, J. Alloys Compd. 541 (2012) 14–17. [48] R. Li, S. Pang, M. Stoica, J.M. Park, U. Kühn, T. Zhang, J. Eckert, Mechanical properties of rapidly solidified Fe–Al–B ternary alloys, J. Alloys Compd. 504 (2010) S472–S475. [49] X.M. Pan, C. Lin, J.E. Morral, H.D. Brody, An assessment of thermodynamic data for the liquid phase in the Al-rich corner of the Al–Cu–Si system and its application to the solidification of a 319 Alloy, J. Phase Equilib. Diffus. 26 (2005) 225–233. [50] J. Eckert, J. Das, G. He, M. Calin, K.B. Kim, Ti-base bulk nanostructure-dendrite composite: microstructure and deformation, Mater. Sci. Eng. A 449–451 (2007) 24–29. [51] J.T. Kim, S.H. Hong, H.J. Park, Y.S. Kim, G.H. Park, N. Lee, J.-Y. Park, Y. Seo, J.-Y. Suh, J.K. Lee, J.M. Park, K.B. Kim, Enhancement of mechanical properties in a Fe81Nb9B10 ultrafine-eutectic composite with in-situ polygonal pro-eutectic and encapsulating eutectic structure, J. Alloys Compd. 643 (2015) S204–S208. [52] M. Gupta, S. Ling, Microstructure and mechanical properties of hypo/hyper-eutectic Al–Si alloys synthesized using a near-net shape forming technique, J. Alloys Compd. 287 (1999) 284–294. [53] A.L. Geiger, J.A. Walker, The processing and properties of discontinuously reinforced aluminum composites, J. Met. 43 (1991) 8–9. [54] I. Baker, F. Meng, Lamellar coarsening in Fe28Ni18Mn33Al21 and its influence on room temperature tensile behavior, Acta Mater. 95 (2015) 124–131. [55] D.K. Misra, S.W. Sohn, H. Gabrisch, W.T. Kim, D.H. Kim, High strength Ti–Fe–(In, Nb) composites with improved plasticity, Intermetallics 18 (2010) 342–347. [56] D.K. Misra, S.W. Sohn, W.T. Kim, D.H. Kim, High strength hypereutectic Ti–Fe–Ga composites with improved plasticity, Intermetallics 18 (2010) 254–258. [57] D.K. Misra, S.W. Sohn, W.T. Kim, D.H. Kim, Plastic deformation in nanostructured bulk glass composites during nanoindentation, Intermetallics 17 (2009) 11–16. [58] I.V. Okulov, U. Kühn, J. Romberg, I.V. Soldatov, J. Freudenberger, L. Schultz, A. Eschke, C.-G. Oertel, W. Skrotzki, J. Eckert, Mechanical behavior and tensile/compressive strength asymmetry of ultrafine structured Ti–Nb–Ni–Co–Al alloys with bi-modal grain size distribution, Mater. Des. 62 (2014) 14–20. [59] D.K. Misra, R.K. Rakshit, M. Singh, P.K. Shukla, K.M. Chaturvedi, B. Sivaiah, B. Gahtori, A. Dhar, S.W. Sohn, W.T. Kim, D.H. Kim, High yield strength bulk Ti based bimodal ultrafine eutectic composites with enhanced plasticity, Mater. Des. 58 (2014) 551–556. [60] S.M. Hoque, S.K. Makineni, A. Pal, P. Ayyub, K. Chattopadhyay, Structural and magnetic properties of ultra-small scale eutectic CoFeZr alloys, J. Alloys Compd. 620 (2015) 442–450. [61] J. Das, R. Mitra, S.K. Roy, Oxidation behaviour of Mo–Si–B–(Al, Ce) ultrafine-eutectic dendrite composites in the temperature range of 500–700 °C, Intermetallics 19 (2011) 1–8.