Papers by Keyword: Bulk Metallic Glass

Abstract: In the present study, Cu₆₀Zr₃₀Ti₁₀ metallic glass powders were prepared by mechanical alloying of pure Cu, Zr, and Ti powder mixtures. Cu₆₀Zr₃₀Ti₁₀ metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and transmission electron microscopy. The metallic glass powders were found to exhibit a supercooled liquid region before crystallization. Cu₆₀Zr₃₀Ti₁₀ bulk metallic glass were synthesized by vacuum hot pressing the as-milled Cu₆₀Zr₃₀Ti₁₀ metallic glass powders at 723 K in the pressure range of 0.72 ~ 1.20 GPa. Cu₆₀Zr₃₀Ti₁₀ BMG with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix was successfully prepared under applied pressures. It was found that the pressure could enhance the thermal stability and prolong the existence of amorphous phase inside Cu₆₀Zr₃₀Ti₁₀ powders.

Abstract: The theoretical study of dynamical variables: velocity autocorrelation function (VACF), power spectrum (PS) and mean square displacement (MSD) of Bi₅₀Zn₅₀ bulk metallic glass at T= 793K, 873K, 1023K and 1123K have been calculated based on the static harmonic well approximation. The effective interatomic potential for bulk metallic glass is computed using our established model potential with the exchange correlation functions due to Farid et al. It is observed that negative dip in velocity auto correlation function decreases as the temperature increases. In the power spectrum as temperature increases, the peak of power spectrum shifts toward lower ω. The obtained result of MSD concludes that the vibrating component in the atomic motion is decreases as increases the temperatures.

Abstract: Different elastic properties of Pd-based Pd₆₄Fe₁₆P₂₀ have been computed using two different forms of pseudopotential. Both the forms differ within the core region suggesting different degrees of orthogonalization and its r-dependence, while outside the core both preserves the Columbic nature. The only parameter, the core radius, separates these regions, and it is calculated using the realistic assumption based on the nearest neighbor distance. Further, five different forms of the local field correlated functions, namely, Hartree (H), Taylor (T), Ichimaru and Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are examined for better understanding regarding the screening effect on different elastic constants for Pd₆₄Fe₁₆P₂₀ bulk metallic glass. The calculated results for the various elastic moduli, Poisson's ratio, sound velocity and phonon dispersion curve are all found to be in general agreement with the available experimental data. This confirms the applicability of the model pseudopotential to bulk metallic systems.

Abstract: Metallic glasses have been expected to be used as structural materials since their high strength and high hardness. Unfortunately, their catastrophic brittle fracture behavior with poor plasticity becomes the major weakness for structural application. It has been recognized that the mechanism of plastic deformation in metallic glasses is through the formation of shear bands, which provide them with limited ductility. Laser shock peening (LSP) is an innovative surface treatment technique which can introduce deep compressive residual stress layer to materials for improving their mechanical behavior. In this work, a finite-element model has been developed to numerically simulate the pure bending process, LSP and subsequent bending process. An advanced constitutive equation was established based on the large deformation theory of nonlinear mechanics, the free volume model and the Coulomb-Mohr yield criterion. The model is able to capture the following results: (i) for a given bending deflection, the shear band spacing increases with increasing plate thickness; (ii) for a given plate thickness, the free volume increases with the bending deflection; (iii) for a given thickness and a given deflection, the shear bands increase under the effect of LSP.

Abstract: The state-of-the-art nano-diffraction technique available at the P06 beamline of the synchrotron radiation source PETRA III was used to observe the strain distribution induced within bulk metallic glass by nano-indentation. Bulk metallic glass (BMG) with nominal composition Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ at.% was prepared by conventional copper mold injection casting. Using the Berkovich indenter a series of indents forming a line was introduced on to the polished surface of the BMG sample. It has been shown that spatially resolved matrix scans with a nanometer sized beam (600 × 600 nm²) can identify positions of the indents and quantitatively describe the strain state after nano-indentation.

Abstract: The isothermal crystallization behavior of the Cu₄₂Zr₄₂Al₈Ag₈ bulk metallic glasse (BMG) was studied by the electrical resistance method. The increasing local activation energy means that the crystallization of the Cu₄₂Zr₄₂Al₈Ag₈ BMG becomes more and more difficult during the isothermal process. In the stage that the crystallized volume fraction falls into the range of 25–85%, the crystallization of the Cu₄₂Zr₄₂Al₈Ag₈ BMG is diffusion-controlled growth with a decreasing nucleation rate.

Abstract: Taking cup-shaped part (outer diameter D and wall thickness are chosen as 2.2 mm and 0.05 mm, respectively) as an example, the micro-back-extrusion forming process of a Zr₅₅Cu₃₀ Al₁₀Ni₅ bulk metallic glass (BMG) in its supercooled liquid region was studied by using finite-element analysis (FEM) and experiment. The effect of forming speed on the formability was analyzed based on the extrusion load, the rheological behavior of the material and the microstructure of the formed parts. It was found that while the forming speed is below than 4 μm/s, the extrusion load increases obviously with the increasing in forming speed, otherwise, the BMG will follow non-newtonian flow and the forming load is insensitive to the forming speed. The parts fabricated at 2 μm/s are obviously crystallized due to the long retention time of metallic glasses at high temperature, a higher forming speed is benefit to enhancing the formability if the BMG. On this basis, micro cup-shaped parts with only 0.05 mm in wall thickness are successfully extruded.

Abstract: Development of Fe-based bulk metallic glasses (BMG) with good mechanical and soft magnetic properties has become a major objective in the materials science field. Bulk metallic glasses present an interesting combination of properties. They exhibit very high strength (both in tension and compression), large elastic elongation limit, high hardness, excellent corrosion resistance, and good soft magnetic properties. These properties makes them suitable for many applications like high resistant control cables, pressure vessels, micro-components, pressure sensors, microgears for motors, magnetic cores for power supplies and hard fibers in composite materials. Multi-component Fe₆₀Co₁₄Ga₂P₁₀B₅Si₃Al₃C₃ bulk metallic glass was synthesized in rod form with a diameter of 1 mm by copper mould casting technique using raw industrial materials. The obtained alloy was analyzed by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) techniques, in order to determine the phase constituent, the thermal stability and the fracture surfaces of as-cast samples. The mechanical behaviour was investigated by microhardness and compression tests. The values recorded for hardness and fracture strength includes this alloy in the category of high resistant materials.

Abstract: Using the mixed powders containing gas-atomized powders of metallic glassy alloys (Cu₅₀Zr₄₅Al₅, Fe₇₃Si₇B₁₇Nb₃, Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5) blended with high-conductive Cu particulates, we produced bulk metallic glassy alloy composites with high strength and high electrical conductivity, as well as with enhanced plasticity and satisfying large size requirements by a spark plasma sintering process. In this paper we present and review our research results on the fabrication and properties of the bulk glassy alloy composites by the spark plasma sintering process.

Abstract: It was reported that micrometer-sized ductile crystalline phases can improve the ductility of Zr-based bulk metallic glasses. The present authors reported the synthesis of bulk metallic glass composites by a process combining cooling slope casting and suction casting for Zr_66.4Nb_6.4Cu_10.5Ni_8.7Al₈ alloys. This study aims to investigate basics of Zr-based metallic glass matrix composites with semisolid structure. As a result, it was found that the Zr-based metallic glass matrix composites with very uniform semisolid structure can be produced by heat treatment process at semisolid region. Moreover, it was found that experimental results can be explained by the pseudo-binary phase diagram.