Papers by Keyword: Bulk Metallic Glass (BMG)

Abstract: Nanoindentation, an advanced technique employed for characterizing materials, facilitates the precise determination of their hardness and Young's modulus by applying a specific, controlled force through an indenter, enabling highly localized deformation and measurement at nanometer scales. The nanoindentation gives us the view of the isotropic and anisotropic features of the materials by analyzing the zone beneath the indenter. The application of Bulk Metallic Glass (BMG) alloy, renowned for its unique combination of high strength, exceptional elasticity, and superior corrosion resistance, spans diverse industries including aerospace, biomedical, and consumer electronics. The study focuses on conducting nanoindentation analysis on the BMG alloy, aiming to characterize its deformation behavior. This involved utilizing Scanning Electron Microscopy (SEM) to discern deformation characteristics, followed by validation of the findings through simulations, ensuring robustness and reliability of the results. The modulus, determined to be 227GPa, provided insight into the material's structural rigidity, and the hardness 14.8GPa offered an indication of its resistance to localized plastic deformation. The results have been compared with the simulation results where the modulus was 242GPa and the hardness was 16.1GPa.

Abstract: Electrochemical corrosion of as-cast and annealed zirconium-based bulk metallic glass (BMG) Zr₄₈Cu₃₆Al₈Ag₈ in 0.1 M NaCl solution was investigated in this work. The as-cast specimen, in complete amorphous form, contained null percent of crystal phase (denoted as 0C); however, the annealed ones contained 11, 25, 50, 75 and 100 % crystal phase (denoted as 11C, 25C, 50C, 75C and 100C, respectively) determined by the annealing duration of 0C specimen at 471 °C. Through monitoring of open circuit potential (OCP), measurements of direct-current polarization resistance (PR), Tafel plot (TP), cyclic anodic potentiodynamic polarization (CAPD), and electrochemical impedance spectroscopy (EIS), we found that the corrosion behavior of the Zr₄₈Cu₃₆Al₈Ag₈ was detremined by the the crystal phase present in the specemns dominated by the annealing durations. The corrosion resistance decreased in the order: 25C > 11C > 0C > 50C > 75C > 100C. This result revealed that the corrosion resistance inclined to be better and reached a mxmium with increasing the percentgae of the crystal phase from 0 to 25%; however, it decreased with further increasing the crystal phase over 25%. A corrosion mechanism is proposed to rationalize the sequence of corrosion resistance. According to the mechanism, the remained free volume and residual strain energy are responsible for the specimens containing crystal phase less than 25% (i.e., 0C, 11C and 25C); whereas crystal defects such as grain boundaries governed the corrosion of those containing crystal phase more than 25 % (i.e., 50C, 75C and 100C).

Abstract: Researches and developments were carried out for obtaining of bulk metallic glass (BMG) from the Fe-Cr-Ni-Si-B system. The used processing methods were copper mold casting and melt spinning method. The resulted materials are in form of sheets with sizes of 69.7 x 64 x 3/1.5 mm and of strips with thickness less than 50 microns, which were obtained by varying the melt spin technological parameters. The both processing variants are not suitable for obtaining such of alloy in bulk metallic glass form. Adding of zirconium to this alloy produces bulk metallic glasses only for the melt spin products. The DSC analysis emphases that the zirconium modified alloy processed by melt spinning method exhibits a high glass forming ability (GFA).

Abstract: The Cu-Zr-Ag system is characterized by a miscibility gap. The liquid separates into Ag-rich and Cu-Zr rich liquids. Yttrium was added to the Cu-Zr-Ag and Cu-Zr-Ag-Al systems and its influence on liquid immiscibility was studied. This alloying element has been chosen to check the effect of the heat of mixing between silver and the given element. In the case of Ag-Y system it is highly negative (-29 kJ/mol). The liquid becomes immiscible in the Cu-Zr-Ag-Y system. To the effect of Y addition the quaternary liquid decomposed into Ag-Y rich and Cu-Zr rich liquids. The Y addition increased the field of miscibility gap. An amorphous/crystalline composite with 6 mm thickness has been successfully produced by liquid-liquid separation based on preliminary calculation of its composition. The matrix was Cu₃₈Zr₄₈Al₆Ag₈ and the crystalline phases were Ag-Y rich separate spherical droplets.

Abstract: Fe_68.16B_20.16Nd_7.68Nb₄ bulk metallic glass was annealed at 973 K for 15 min with or without external magnetic fields. The maximum energy product (BH)_max measured along the axial direction of a rod sample after annealed with a magnetic field parallel to the axis is 10.9 % higher than that annealed with a perpendicular field. The intrinsic coercivity _iH_c of the sample annealed with the parallel magnetic field reached 1014 kA/m. The induced magnetic anisotropy is attributed to the formation of preferred crystallographic orientation of ferromagnetic phases under the external magnetic field.

Abstract: By copper mold casting, a bulk Fe₆₃Co₇Nb₄Zr₆B₁₉Si₁ metallic glass was synthesized in the diameter of 2mm. The Fe-based amorphous alloy exhibits soft ferromagnetic characteristics with a saturation magnetization of 77Am²/kg and a saturated magnetostriction of 25.4×10^-6. The saturation magnetization is reduced while the coercive force is slightly lowered by annealing treatment below the crystallization temperature. The devitrification gives rise to a remarkable enhancement both in saturation magnetization and coercive force.

Abstract: The methodical expressions for the phonon frequencies of Zr57Ti5Cu20Ni8Al10 bulk metallic glass (BMG) both for longitudinal and transverse phonon modes are computed for the first time using Hubbard-Beeby (HB) approach and our well recognized model potential. The self-consistent phonon scheme given by Takeno-Goda, involving multiple scattering and phonon Eigen frequencies expressed in terms of many-body correlation functions of atoms as well as of interatomic potential in the solids, has been used to generate the collective modes in the Zr57Ti5Cu20Ni8Al10 BMG. In the present paper, the local field correction functions due to Hartree (H), Farid et al (F), Sarkar et al (S) and Hubbard Sham (HS) are used to examine the influence of screening effects on the vibrational properties. Further, from the long wavelength limit of phonon frequencies, various elastic constants have been calculated and are found to be in good agreement with experimental and other available data.

Abstract: In this paper, high resolution transmission electron microscopy (HRTEM) has been used to observe a Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 (at. %) bulk metallic glass (BMG) prepared from different methods, i.e. ion milling and electropolishing. The ion thinning brings out the white bulb pattern on the specimen surface and induces localized temperature increasing. The electropolishing does not influence microstructure of the amorphous phase. A new preparation technique of grinding method is introduced. For BMG, the electropolishing and grinding are the better method for TEM specimen preparation as compared with the ion thinning.

Abstract: Contrast ballistic tests were carried out on 93W alloy and W fiber reinforced Zr-based bulk metallic glass composite. The influence of penetrator material on micro-hardness around target crater was studied using microstructure observation and micro-hardness test. The results show that adiabatic shear band appears in both targets after severe plastic deformation of impact. The effect of composite on micro-hardness of target is greater than that of W alloy, and the thickness with high micro-hardness around target crater formed by composite penetrator is 2.5 times than that by W alloy penetrator.

Abstract: The effect of yield strength and elastic modulus of matrix on shear stress in two phases of composite reinforced with W fiber under pulse loading was simulated by ANSYS software. The results show that the effect of mechanical properties of matrix on composite should be taken into consideration in designing composite. The matrix with high yield strength and low elastic modulus can reduce the shear stress in W fiber, and is beneficial to keeping the integrity of W fiber during penetration, thus resulting in the improvement of penetration capacity.