⇦Chinese Physics Letters, 2020, Vol. 37, No. 8, Article code 086401 A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties Dong-Mei Li (李冬梅)1, Lan-Sheng Chen (陈澜生)1, Peng Yu (余鹏)1*, Ding Ding (丁鼎)2, and Lei Xia (夏雷)2 Affiliations 1Chongqing Key Laboratory of Photo-Electric Functional Materials, College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China 2Laboratory for Microstructure & Institute of Materials, Shanghai University, Shanghai 200072, China Received 1 June 2020; accepted 28 June 2020; published online 28 July 2020 Supported by the Chongqing Research Program of Basic Research and Frontier Technology (Grant Nos. cstc2018jcyjAX0329 and cstc2018jcyjAX0444), and the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJZD-K201900501).
*Corresponding author. Email: pengyu@cqnu.edu.cn Citation Text: Li D M, Chen L S, Yu P, Ding D and Xia L et al. 2020 Chin. Phys. Lett. 37 086401    Abstract A new Cu-based bulk metallic glass composite of nominal composition (at.%) Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation, which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications. DOI:10.1088/0256-307X/37/8/086401 PACS:64.70.pe, 77.84.Lf, 62.20.F- © 2020 Chinese Physics Society Article Text Bulk metallic glasses (BMGs) with large elastic strain limit, ultrahigh strength, and good corrosion resistance have attracted significant attention as potential engineering materials.[1–4] Nevertheless, the homogeneous amorphous microstructure of BMGs results in their catastrophic failure under tension mode, especially an apparently brittle manner in unconstrained loading geometries, which restricts their structural applications.[5] In order to circumvent this restriction, BMG composites with inhomogeneous microstructure, such as nano/micrometer-sized ductile phase embedded in a BMG matrix, have been fabricated recently, which have been found to prevent the unlimited extension of shear bands and to be beneficial for the enhancement of macroscopic deformability.[6–9] Moreover, BMG composites can retain the positive structural features exhibited by BMGs, while the enhanced tensile ductility, fracture toughness, and fatigue endurance can also be obtained, which makes them desirable as potential engineering materials.[10–15] Crystallization kinetics can be used to design a metallic glass composite during the process of solidifying the glass-forming liquid. Typically, the in situ BMG composites consisting of crystal phase formed from their melts during appropriate solidification have advanced deformation behavior including large plasticity and high strength originating from the mechanical characteristics of both phases, which is superior to those of ex situ BMG composites.[16–19] These excellent mechanical properties place in situ BMG composites among the most promising engineering materials. However, disadvantages of these BMG composites are also been revealed, such as obvious working-softening behavior during the tensile test and the low repetitiveness of these composites. Therefore, designing crystal phase-reinforced BMGs to broaden and improve their properties are significant to develop excellent engineering materials. Referring to the strategy of performance improvement of in situ BMG composites, we designed and fabricated a Cu-based BMG composite of Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ in this work. In the process of rapid solidification, the crystal phase formed from the melts and imparts an appreciable work-hardening capability resulting from their intrinsic deformability. Therefore, the designed Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ alloy combines the advantages of BMG and crystal phase. Moreover, most of the existing Cu-based BMG and their composites contain zirconium, which is high cost and unsuitable for their industrial applications. All elements contained in this composite of Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ are cheap and low cost, therefore, it can be priority considered for industrial application. Our current finding offers a new paradigm for developing BMG composites with improved ductility as practical engineering material. Ingots of nominal composition (at.%) Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ were prepared by arc-melting a mixture of high purity metal. Cylindrical specimens with different diameters of 2–5 mm and a length of 70 mm were synthesized by copper mold suction casting. The structure of the specimens was analyzed by the x-ray diffraction (XRD) in a SHIMADZU XRD-6100 diffractometer. The cross-section and side surface of the samples were investigated by scanning electron microscopy (SEM). The microstructures of the deformed samples were also analyzed by the high-resolution transmission electron microscopy (HR TEM) of JEOL JSM-7800F. The thermal properties of the as-cast rods were measured by differential scanning calorimetry (DSC) in a Perkin-Elmer DSC-8000. Uniaxial compression and tensile tests were performed on the RGM-300 materials testing machine at room temperature with a strain rate of $1\times 10^{-4}$ s$^{-1}$.
cpl-37-8-086401-fig1.png
Fig. 1. (a) SEM image of the cross section of Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ with the contrast that has been reversed and increased to differentiate the two phases. (b) XRD pattern and (c) DSC results of Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$. High-resolution TEM images for (d) the interface between the two phases, (e) the crystal phase, and (f) the glass phase, with their corresponding diffraction patterns shown in the insets.
The backscattered SEM micrograph in Fig. 1(a) shows the microstructure of the cross section of the as-cast sample, where the light and dark contrast is from the glass matrix phase and the crystal phase, respectively. The flowery dendritic crystal phase is homogeneously distributed in the continuous matrix. As shown in Fig. 1(b), the XRD pattern indicates that the peaks of the crystal phase are superimposed on the broad diffraction hump, further identifying the two-phase structure. These sharp diffraction peaks probably correspond to metastable phases as they cannot be identified accurately. Figure 1(c) displays the continuous DSC trace of the Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ as-cast rod obtained at a heating rate of 20 K/min. The endothermic behavior before crystallization demonstrates a distinct glass transition with the onset temperature ($T_{\rm g}$) at about 560.4 K. The exothermic reaction occurs after the glass transition, which is associated with the transformation from the supercooled liquid state to equilibrium crystal phase. As the TEM micrograph is shown in Fig. 1(d), the clear interface of the metallic glass and dendritic phase was confirmed for this composite structure. Figures 1(e) and 1(f) show the TEM micrographs of the crystal phase and glassy matrix phase at high magnification, and the diffraction patterns for both phases are shown in the insets. The clear diffraction pattern and broad diffuse halo exhibit the typical features of the dendrite and glass matrix, respectively. Like pursuing the high strength of BMG composites, it is of importance to improve the plasticity of these materials, which is essential for their applications as engineering materials. The true compression and tension stress-strain curves of the prepared composite at ambient temperature are shown in Figs. 2(a) and 2(b), respectively. Under quasi-static compressive loading, the composite exhibits the yield strength of 1152.8 MPa. Upon further compression, the composite presents an approximately linear work-hardening until the fracture failure occurs with the fracture strength of 2010.5 MPa and plastic strain of 18.4%. Uniaxial compression tests are often used to assess the ductility of BMGs to distinguish them from other alloys, whereas their tensile ductility test is usually lacking and unsatisfactory. However, a quite considerable tensile ductility of this BMG composite was also observed in our work. As plotted in Fig. 2(b), the tensile yield strength and tensile fracture strength are about 1180.0 MPa and 1859.2 MPa, respectively, and plastic strain is 11.1%, which is significantly superior to that of most BMGs. As is known, tensile strain hardening is scarce for BMGs and BMG-composites, as most dendrite-enhanced BMG composites present hardening behavior under compression mode and softening behavior under tensile mode. Obviously, the fracture strength and plastic strain of this BMG composite are significantly superior to those of most high-strength alloys.[20–23] The excellent mechanical properties can be attributed to the high plastic deformation ability of the embedded crystal phase. Additionally, the crystal phase is homogeneously distributed in the glass matrix, which results in the larger strain and higher strength of this BMG composite.[24,25] Therefore, the composite can exhibit superior plasticity on both compressive and tensile loading.
cpl-37-8-086401-fig2.png
Fig. 2. True stress-strain curves of Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ rod under (a) compression and (b) tension mode at room temperature.
To explore the mechanism of the excellent mechanical properties, the morphology of the outer surface of the composite after deformation was analyzed. The SEM image for the compressed sample is shown in Fig. 3(a), and the designated areas are presented in Figs. 3(b)–3(d). The sample shows obvious lateral expansion and barrel shape, as shown in Fig. 3(a), which implies good plastic deformation ability. Stacked folds were densely distributed on the surface, as presented in Fig. 3(b). Two types of shear bands with different directions, namely SB1 and SB2, were clearly observed on the surface, as shown in Figs. 3(c) and 3(d). The SB1 represents the short and well-spaced shear bands that are parallel to the loading direction, while the SB2 represents the long and well-ranged shear bands at almost 45$^{\circ}$ to the loading direction. Moreover, the distinct wavy-edge crack was observed, as the arrows shown in Fig. 3(a), which could be attributed to the alternative distribution of SB1 and SB2. In fact, rapid propagation of either SB1 or SB2 type shear bands can be prevented by their staggered arrangement, which is beneficial to retard the crack propagation and enhance the global plastic deformation of the composite. Previous studies prove that the shear bands nucleated and grown in the amorphous matrix then arrested by the crystal phase.[26] The structural heterogeneity promotes the propensity of multiple shear bands and inhibits the free propagation of shear bands, resulting in the microscopic plasticity and work hardening of this composite.
cpl-37-8-086401-fig3.png
Fig. 3. (a) SEM micrographs for the Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ rod after compression. (b) Magnification of the oval region indicated in (a), (c), and (d) showing the magnification of rectangle regions indicated in (b).
In summary, a new Cu-based metallic glass composite with excellent mechanical properties has been designed and fabricated. The prepared composite can obtain great plasticity up to 11.1% and high strength of about 2000 MPa resulting from the coexistence of amorphous and crystal phases. Crystal phases embedded in the amorphous matrix have a dual role in response to mechanical loading. They serve as heterogeneous sites for the initiation of different types of shear bands. On the other hand, they also act as obstruction and inhibition centers for propagation of shear bands. Moreover, the two-phase microstructure leads to the multiplication of local shear bands. Ultimately, excellent mechanical properties of the composite can be obtained under loading. Moreover, all the elements contained in this composite are cheap and low cost, therefore, this composite can be priority considered for industrial applications. This work provides a way to counterbalance strain softening and the high ductility of metallic glasses, which could open up an opportunity to synthesize structural-application materials with advanced mechanical properties. References A highly processable metallic glass: Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5The elastic properties, elastic models and elastic perspectives of metallic glassesDamage tolerance at a priceCombinatorial development of bulk metallic glassesMechanical Behavior of Metallic Glasses: Microscopic Understanding of Strength and DuctilityAtomic-scale origin of shear band multiplication in heterogeneous metallic glassesLarge-sized Zr-based bulk-metallic-glass composite with enhanced tensile propertiesMicrostructure and mechanical properties of Ti48Zr18V12Cu5Be17 bulk metallic glass compositeNovel Mg46Li19Cu25Y10 multiphase composite containing amorphous and ductile phaseMicrostructure Controlled Shear Band Pattern Formation and Enhanced Plasticity of Bulk Metallic Glasses Containing in situ Formed Ductile Phase Dendrite DispersionsMetallic glass matrix compositesDesigning metallic glass matrix composites with high toughness and tensile ductilityBulk Metallic GlassesFracture toughness and crack-resistance curve behavior in metallic glass-matrix compositesMagneto-Caloric Response of a Gd 55 Co 25 Al 18 Sn 2 Bulk Metallic GlassDeformation-induced martensitic transformation in Cu–Zr–(Al,Ti) bulk metallic glass compositesShape Memory Bulk Metallic Glass CompositesMicrostructural heterogeneities governing the deformation of Cu47.5Zr47.5Al5 bulk metallic glass compositesFormation and Compression Behavior of Two-Phase Bulk Metallic Glasses with a Minor Addition of AluminumFabrication of porous NiTi shape memory alloy for hard tissue implants by combustion synthesisMechanical properties of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 ductile phase reinforced bulk metallic glass compositeNovel Ti-base nanostructure–dendrite composite with enhanced plasticityFormation of a bimodal eutectic structure in Ti–Fe–Sn alloys with enhanced plasticityDuctility of bulk metallic glass composites: Microstructural effectsContinuum Modeling of Bulk Metallic Glasses and CompositesTransformation-induced plasticity in bulk metallic glass composites evidenced by in-situ neutron diffraction
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