Improving plasticity and toughness of Cu-Zr-Y-Al bulk metallic glasses via compositional tuning towards the CuZr
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In this work, we propose a simple approach for designing plastic bulk metallic glasses (BMGs) by exploiting the ductility of intermetallic compounds involved in the BMGforming system. Its validity was examined by investigating a series of quaternary CuZr-Y-Al alloys along the composition tie-line between Cu42Zr44.4Y3.6Al10 (Y1) and the B2 CuZr phase, expressed as (Cu0.5Zr0.5)x(M)100-x (M = Zr0.15Y0.225Al0.625, 84x93). When tuning the composition towards the CuZr, the glass-forming ability of alloys is dramatically degraded, showing a reduction of critical diameter Dc for BMG formation from 16 mm at x = 84 (Y1) to 2 mm at x = 93. As the composition of BMGs shifts to the CuZr terminal, the shear modulus m of the BMGs decreases, whereas the Poisson’s ratio n increases. With respect to the Y1 BMG, compressive plasticity and toughness of the Y2 BMG (x = 92, Dc = 4 mm) with a higher concentration of the CuZr are improved, which is consistent with its lower m and higher n values. I. INTRODUCTION
Bulk metallic glasses (BMGs) exhibit many attractive properties such as high strength, high-specific strength, excellent corrosion and wear resistance, and near-net-shape processibility. However, the lack of macroscopic plasticity before failure under loading for the monolithic BMGs has been a critical issue to limit their application. It has recently been revealed that, in a given BMG-forming alloy system, mechanical properties of as-cast BMGs are evidently compositiondependent.1–4 Therefore, it is promising to improve the intrinsic plastic deformability of BMGs through composition tuning starting from the currently available BMG-forming alloys. On the other hand, it has been proven that the intrinsic ductility of BMGs correlates with their elastic properties including the shear modulus (m), Poisson’s ratio (n), or equivalently a ratio (m/B) of the m to the bulk modulus (B).5–8 In other words, these parameters can be used as the indicators for alloy design because they directly correlate with the structural configuration of BMGs that determines the energy barrier of shear events during deformation.9,10 Furthermore, it was empirically suggested that the elastic properties of BMGs can be predicted from the properties of the constituent elements,11 as a guideline for the selection of compositions to promote plasticity. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0031 J. Mater. Res., Vol. 25, No. 2, Feb 2010
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From the structural perspective, the intrinsic ductility of BMGs correlates with their atomic scale structure, asymmetry of short-range ordered clusters and their fraction.4 However, characterization and visualization of metallic glass structure remains a challenging and tedious task even for computer simulation. It is well known that, in the sense of energy levels, the global ground state of the easy glass-forming alloy is crystalline phases, at least containing an intermetallic compound, in the majority of cases. Theref
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