Large-sized Zr-based bulk-metallic-glass composite with enhanced tensile properties
Graphical abstract
Highlights
► We successfully produce the large-sized Zr-based BMG composite with 11 mm diameter. ► The composite with 6 mm diameter of the gauge section exhibits 6% tensile plasticity. ► The deformation process and work-hardening behavior of the composite are clarified. ► The precipitated β-Zr particles with different length scales are obtained using SSPS. ► The tensile plasticity is enhanced significantly by increasing the size of the β-Zr.
Introduction
Bulk metallic glasses (BMGs) draw much attention due to their excellent mechanical properties including high hardness, elastic limit and strength [1]. However the room temperature brittleness has significantly limited their application as an engineering material [2]. To answer this challenge, Johnson and his coworkers [3], [4] developed an in situ fine dendrite-reinforced BMG matrix composite which exhibits about 7% compression plasticity. This opens a new way to develop BMG composites. Since then, a series of in situ BMG matrix composites have been developed, including the Zr- [5], [6], [7], [8], [9], [10], Ti- [11], [12], [13], Cu- [14], Pd- [15], La- [16], Fe- [17] and Mg-based [18] BMGs composites. Chen's group also got a great progress in the development of BMG composites [7], [8]. They found that the morphology and size of the precipitated crystals have a strong effect on the plasticity of the BMG composites and firstly used isothermal treatment in the liquid/solid two-phase regions to tailor the microstructure of the BMG composite. The plasticity of the composite (the composition is the same as [3], [4]) with coarse and spherical β-Zr particles was significantly enhanced to 12% [8]. In 2008, Johnson et al. produced some BMG composites in which the coarse β-Zr phase dendrites embeds in the glass matrix, and the plasticity reached ∼10% at room temperature [9]. Hereafter, several BMG composites with large tensile ductility have been obtained [10], [11], [12], [13]. However, the tensile samples are fairly small (the diameters of the gauge section of these tensile samples were ≤3 mm) in previous works [4], [9], [10], [11], [12], [13], [16]. From the technological point of view, large sized BMG is especially important for engineering applications.
In this study, large-sized in-situ Zr-based BMG composite with 11 mm diameter was fabricated using the semi-solid progressive solidification (SSPS) method and its mechanical properties were investigated by tensile testing. We systematically studied microstructure evolution with isothermal temperature and holding time, and its effects on the mechanical properties. Moreover, the tensile deformation micromechanism was studied based on the analysis of microscopic images of the deformed samples and nanoindentation. The objective of this work is to inspire more work on the design of new BMG composites with superior mechanical properties.
Section snippets
Experimental
Ingots of the nominal composition (at.%) Zr60Ti14.67Nb5.33Cu5.56Ni4.44Be10 were prepared by arc-melting a mixture of Zr, Ti, Nb, Cu, Ni and Be with purity higher than 99.9 wt% under a Ti-gettered argon atmosphere. The ingots were cast into rods and then placed into graphite crucibles. The alloys were remelted at 1623 K for 10 min, and then the temperature was dropped to the liquid/solid two-phase field for different time to coarsen in-situ precipitated β-Zr particles. Subsequently, to eliminate
Microstructure and tensile properties of the large-sized in-situ BMG composite
Fig. 1(a) shows the XRD pattern of the Zr60Ti14.67Nb5.33Cu5.56Ni4.44Be10 BMG composite with 11 mm diameter which was held at 1173 K for 40 min and then progressively solidified at 4.0 mm/s withdrawal velocity. Only three sharp diffraction peaks are superimposed on a broad scattering hump characteristic of an amorphous phase. These diffraction peaks are corresponding to the body-centered cubic (bcc) β-Zr solid solution. DSC curves obtained from the composite clearly show both the glass
Conclusions
In summary, the large-sized Zr-based BMG composite is fabricated by directly-solidified SSPS. The tensile properties, microstructure evolution and deformation process of the composites have been studied systematically. The main results are summarized as follows:
- 1.
Using the SSPS, we successfully produce the Zr-based BMG composite with 11 mm diameter. The excellent plasticity (∼6%) is shown in this composite with 6 mm diameter of the gauge section, which is the largest tensile sample in the BMG
Acknowledgements
This work was supported by the National Natural Sciences Foundation of China (Grant No. 50871054), the National Basic Research Program of China (Grant No. 2011CB605504), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20093219110035). C.T. Liu was supported by an internal funding from the City University of Hong Kong. The authors are grateful to Prof. Ian Baker (Dartmouth College, U.S.A.) for careful proofreading.
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