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In metallic glass composites (MGCs), the existence of crystalline phases causes the structures of amorphous matrix to become relatively heterogeneous near the crystalline phase, resulting in the difference of mechanical properties in micro- or nano-scale in amorphous matrix near crystalline/matrix interface. In this study, this difference was characterized by nanoindentation technology, and the pile-up height was quantitatively related to the activation volume of shear transformation zones (STZs). Molecular dynamics simulations were conducted to investigate the activation behaviors of STZs during nanoindentation process of amorphous matrix. The influences of crystalline phase on deformation behaviors of amorphous matrix near the interface in MGCs were analyzed in details. • For the interface area of MGCs, the hardnesses of interface, crystalline phase and amorphous matrix increase in turn. • The existence of crystalline phase will cause the gradient distribution of free volume away from the interface in amorphous matrix. • The relationship between the pile-up height of nanoindentation in amorphous matrix, the free volume content and the number of STZs is established. [ABSTRACT FROM AUTHOR]

The relative glass forming ability (GFA) of bulk amorphous Zr60Cu20Ni8Al7Hf3Ti2 (A1) and Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) alloys has been investigated by comparing the maximum thickness of amorphous region of wedge-shaped samples, as well as the evaluated critical cooling rates using differential thermal analysis (DTA). The results show that the maximum thickness of amorphous region of wedge-shaped samples are dm=2 mm for A1, dm=3.5 mm for Vit105, and the evaluated critical cooling rates are Rc=33.5 and 4.5 K/s for A1 and Vit105, respectively. It is suggested that the glass forming ability of A1 is smaller than that of well known Vit105 alloy, though A1 has the significant supercooled liquid region of over 140 K. Therefore, it is concluded that a large supercooled liquid region ΔTx does not necessarily mean good glass forming ability of an amorphous alloy. [Copyright &y& Elsevier]

In this study, the deformation behaviors of a Cu 47.5 Zr 48 Al 4 Nb 0.5 bulk metallic glass composite (BMGC) in the temperature ranging from 663 K to 763 K have been investigated using uniaxial tensile tests and high-energy X-ray diffraction. Within the supercooled liquid region (SLR), the studied BMGC exhibits superplasticity and the deformation of the studied BMGC basically involves two modes, i.e., homogeneous and inhomogeneous deformation. As the temperature increases in the SLR, the yield strength of the studied BMGC gradually decreases whereas the plastic strain increases, revealing that the amorphous phase plays a dominant role in the deformation. However, there is a significant increase in the yield strength above the crystallization temperature, which indicates that the deformation is mainly contributed by the crystalline phase. The results obtained in this manuscript provide a better understanding of the temperature dependence of deformation behaviors in BMGCs. [Display omitted] • The yield strength of the BMGC decreases with the increasing temperatures below T x. • The structural evolution of the BMGC was characterized using high energy X-ray diffraction (HE-XRD). • The amorphous phase leads the deformation behaviors of the BMGC below T x , otherwise the crystalline phase dominates. [ABSTRACT FROM AUTHOR]

A novel type of bi-constituent wire composite was obtained by combining melt-extracted Gd 50 Al 30 Co 20 and Gd 55 Al 20 Co 25 microwire components with Curie temperature ( T C ) of 86 K and 110 K, respectively. For a field change of 5 T, the wire composite possesses a table-like feature spanning a temperature interval of 30 K with value of ∼8.6 J kg −1  K −1 , and enhanced refrigerant capacity (RC) and relative cooling power (RCP) values of ∼680 J kg −1 and ∼863 J kg −1 , respectively. The experimental results agree well with those calculated by a simple bi-composition model, demonstrating the possibility of designing wire-based composites with desirable magnetocaloric effects (MCE) for active magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The structural evolution of CuZr-based metallic glass composite (MGC) near the crystalline/matrix interface is studied by in situ transmission electron microscope (TEM) tensile straining and molecular dynamics (MD) simulation. The crystalline phase is found to undergo plastic deformation before the amorphous phase, via recoverable martensite transformation, dislocation accumulation at the interface and local amorphization between grains. Fracture does not occur along the interphase interface, but within the crystalline phase at about half a micron from the interface and parallel to it, indicating a high strength of the interface and an elevated work hardening rate of the crystalline phase just next to the interface. MD simulations show that the amorphous phase is marginally metastable with respect to the stable B2 phase, while B19′ martensitic phase is metastable with a higher energy, thus explaining the easy mutual transformation between B2 and amorphous phase, and the rarer transformation product of B19' phase from B2 on straining. [Display omitted] [ABSTRACT FROM AUTHOR]

Bulk metallic glass composites (BMGCs) reinforced with a B2-CuZr phase exhibit improved ductility. However, the relationship between the macroscopic plastic deformation of BMGCs and the microscopic strain evolution is still poorly understood. Here, we investigated the strain-field evolution of a Cu 44.3 Zr 48 Al 4 Nb 3.7 (at%) BMGC by using an in-situ digital image correlation technique during tensile deformation. The strain-field evolution in the composite containing B2-CuZr particles was analysed and compared to that in a Cu 47 Zr 48 Al 4 Nb 1 BMG. We found that a high degree of shear strain heterogeneity played a key role in the macroscale plastic deformation, which was attributed to the intrinsic structural heterogeneities. These findings have implications for the development of BMGCs with excellent tensile properties. [ABSTRACT FROM AUTHOR]

Abstract: New bulk metallic glasses are produced by substituting a few atomic percentages of iron with yttrium in the Fe45−x Cr16Mo16C18B5Y x (x =0, 1, 2, 3) alloy systems. The study shows that the optimum yttrium content in the alloy for the best glass-forming ability is 2at.%, and with this composition fully amorphous as-cast samples with a size of 6mm in diameter can be produced by the copper mold casting. The mechanism for the effect of yttrium addition on the glass-forming ability of the Fe45−x Cr16Mo16C18B5Y x (x =0, 1, 2, 3) alloys is discussed according to the effect of yttrium content in the alloy on the characteristic temperature values as measured by using DTA in this study. Furthermore, the compression tests of the bulk amorphous samples of Fe43Cr16Mo16C18B5Y2 alloy show that the room temperature compressive strength of the amorphous alloy is approximately 1824MPa. [Copyright &y& Elsevier]

• The cooling induced structural evolution of CuZr-based BMGC is in-situ studied. • The hydrostatic pressure exerts a crucial role on the martensitic transformation of B2 CuZr phase. • The thermodynamics mechanism of the phase transformation of CuZr phase is clarified. [Display omitted] In - situ high-energy X-ray diffraction and molecular dynamic simulation were employed to study the structural evolution of a B2 phase reinforced CuZr-based bulk metallic glass composite in different structural states during cryogenic treatment between 300 K and 100 K. No phase transformation occurs in the as-cast sample during cryogenic treatment, while the pre-strained sample undergoes martensitic transformation and reverse martensitic transformation. The ambient temperature, uniaxial stress, and hydrostatic pressure on the B2 CuZr phase are closely related to the phase transformation behavior of the CuZr phase in the pre-strained composite sample. Molecular dynamic simulation confirms the experimental results. The findings in this work will help to clarify the mechanism of the martensitic transformation in the B2 CuZr phase, and finely tune the structure and mechanical behaviors of CuZr-based bulk metallic glass composites. [ABSTRACT FROM AUTHOR]

In this work, deformation behaviors of a CuZrAlNb bulk metallic glass composite (BMGC) with different volume fractions of the crystalline phase were characterized using in-situ tensile tests in an optical microscope. For the studied composite, it was found that the volume fraction of the crystalline phase plays a significant role in shear band types. Shear bands which are not restrained by the crystalline phase, disappeared with increasing the crystallization volume fraction. There exists a critical volume fraction (~ 29.63 %) of the crystalline phase determining deformation behaviors of the studied composite. Beyond the critical value, this composite exhibits the homogeneous plastic deformation. Otherwise, the deformation of the BMGC is affected by shear bands which are not restrained by the crystalline phase, resulting in a decrease in the plasticity of the BMGC. Besides, the crystalline phase with a large-size bears more strain than that with a small-size in BMGCs, thereby improving their mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, the effect of cryogenic testing temperatures on the deformation behavior of a CuZr-based bulk metallic glass composite (BMGC) has been investigated using in situ high energy X-ray diffraction. The yield strength and work-hardenability of the studied BMGC show an increasing trend from 298 K to 153 K. A higher yield strength at a lower temperature can be attributed to the larger difference in the volume shrinkage between the crystalline phase and the amorphous matrix. The increasing martensitic transformation degree of the crystalline phase from 298 K to 153 K results in the enhanced work-hardenability. These results lead to a better understanding of the temperature dependence of phase-transformation induced plasticity in CuZr-based BMGCs. ga1 • The yield strength of the BMGC shows an increasing trend from 298 K to 153 K. • The increase of the work-hardenability is attributed to martensitic transformation. • Martensitic transformation degree is higher at a lower temperature. [ABSTRACT FROM AUTHOR]

In this work, a long-term room-temperature aging treatment of the order of years is applied to a B2 phase-reinforced CuZr-based bulk metallic glass composite (BMGC). Presumably governed by residual stress, B19' CuZr martensitic phase gradually precipitates in the crystals after such long-term aging, while structural relaxation takes place in the glassy matrix, which finally induces precipitation of Cu 10 Zr 7 nanocrystals. Tensile tests prove that these time-dependent structural changes have a measurable effect on deformation behaviors of BMGC. The findings are helpful for understanding the thermodynamic stability and the kinetics of structural evolution of metastable alloys and have useful implications for tailoring the structure and mechanical behavior of BMGCs. Image 1 • Natural aging induces structure evolution in CuZr-based bulk metallic glass composite. • Structure stabilization occurs in both the B2 CuZr phase and the amorphous phase. • Hydrostatic pressure plays a crucial role in the structural transformation of phases. [ABSTRACT FROM AUTHOR]

• B2 CuZr phase under high stress transforms to martensite as the temperature decreases. • Molecular dynamics verifies the martensitic transformation of B2 CuZr phase. • Hydrostatic pressure plays a crucial role in phase transformation of B2 CuZr phase. In this work, the cryogenic-temperature-induced structural evolution of B2 CuZr phase-reinforced Cu 48 Zr 47.2 Al 4 Nb 0.8 bulk metallic glass composite (BMGC) is in - situ studied under tensile stress. During the cooling process from 280 K down to 80 K, the B2 CuZr phase in the nearly yielding BMGC undergoes the martensitic transformation, whereas the composite sample retains its structure at lower stress. Molecular dynamics results confirm the structural changes of the B2 CuZr phase during the cooling process. The findings will be helpful for fine tailoring the structure of CuZr-based BMGCs and thus widening their applications. [ABSTRACT FROM AUTHOR]

To understand the shear banding evolution and the effect of individual shear band on deformation mechanisms of bulk metallic glass composites (BMGCs), tensile tests of CuZrAlNb BMGCs have been in situ studied. It is found that the type and sequence of shear bands are independent of volume fraction of crystalline phase. All the types of shear bands can be considered as shear bands controlled by stress affected zones (SAZs) at crystal/matrix interface and those far away from SAZs. Based on the analysis of elastic energy dissipation, the shear bands far away from SAZs play a dominant role in the deformation stability. For current BMGCs, the propagation of shear bands far away from SAZs can be delayed by reducing the average elastic energy dissipation. High Young's modulus and volume fraction of crystalline phase are effective for decreasing the average elastic energy stored in shear bands. It is expected that the obtained results can offer better understanding of deformation mechanism in bulk metallic glass composites, which should be beneficial to design bulk metallic glass composites with improved mechanical performances. Image 1 • The type and sequence of shear bands are independent of crystalline phase contents. • All types of shear bands can be classified into two categories. • The plasticity is related to the average elastic energy dissipation in shear bands. • Elastic energy can be reduced by tuning Young's modulus and stress affected zones. [ABSTRACT FROM AUTHOR]