• Transactions of Materials Processing
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• v.13 no.8
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• pp.696-703
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• 2004

The purpose of this study is to examine the bulk/sheet forming characteristics of bulk amorphous alloys in the super cooled liquid state. Recently it is reported that amorphous alloys exhibit stress overshoot/undershoot and non-Newtonian behaviors even in the super cooled liquid state. The stress-strain curves with the temperature-dependences as well as strain-rate dependence of Newtonian/non-Newtonian viscosities of amorphous alloys are obtained based on the previous experimental works. Then, those curves are directly used in the thermo-mechanical finite element analyses. Upsetting and deep drawing of amorphous alloys are simulated to examine the effects of process parameters such as friction coefficient, forming speed and temperature. It could be concluded that the superior formability of an amorphous alloy can be obtained by taking the proper forming conditions.

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.759-772
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• 2009

Amorphous alloys, in addition to being promising materials for a variety of practical applications, provide an excellent test bed for evaluating our understanding of the underlying physics on deformation in amorphous solids. Like many amorphous materials, amorphous alloys can exhibit either homogeneous or inhomogeneous deformation depending on the stress level. The mode of deformation has a strong influence on whether the material behavior is classified as ductile or brittle. It was observed that the characteristics of these deformations are largely dependent on the atomic-scale structures of the alloys and determine the amount of the plastic deformation prior to failure. In this study, the structural features that control the homogeneous deformation of amorphous alloys are outlined on the basis on experiments and molecular dynamics simulations.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.276-280
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• 2009

The effect of the initial packing structure on the plasticity of amorphous alloys was investigated by tracing the structural evolution of the amorphous solid inside a shear band. According to the molecular dynamics simulations, the structural evolution of the amorphous solids inside the shear band was more abrupt in the alloy with a higher initial packing density. Such a difference in the structural evolution within the shear band observed from the amorphous alloys with different initial packing density is believed to cause different degrees of shear localization, providing an answer to the fundamental question of why amorphous alloys show different plasticity. We clarify the structural origin of the plasticity of bulk amorphous alloys by exploring the microstructural aspects in view of the structural disordering, disorder-induced softening, and shear localization using molecular dynamics simulations based on the recently developed MEAM (modified embedded atom method) potential.

• Journal of Welding and Joining
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• v.17 no.4
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• pp.26-31
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• 1999

An attempt was made in this study to investigate the brazing characteristics of Zr-Be binary amorphous alloys for the development of a new brazing filler metal for joining Zircaloy-4 nuclear fuel cladding tubes. This study was also aimed at the feasibility study of rapidly solidified amorphous alloys to substitute the conventional physical vapor-deposited(PVD) metallic beryllium. The $Zr_{1-x}Be_{x}$($0.3\leq$x$\leq0.5$) binary amorphous alloys were produced in the ribbon form by the melt-spinning method. It was confirmed by x-ray diffraction that the ribbons were amorphous. The amorphous. the amorphous alloys were used to join bearing pads on Zircaloy-4 nuclear fuel cladding tubes. Using Zr-Be amorphous alloys as filler metals, it was found that the reduction in the tube wall thickness caused by erosion was prevented. Especially, in the case of using $Zr_{0.65}Be_{0.35}$ and $Zr_{0.7}Be_{0.3}$ amorphousalloys, the smooth and spherical primary $\alpha$-Zr particles appeared in the brazed layer, which was the most desirable microstructure from the corrosion-resistance standpoint.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.2
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• pp.182-188
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• 2007

[ $Zr_{50}-Ni_{27}-Nb_{18}-Co_5$ ] amorphous alloys ribbon was prepared by a single-roller melt-spinning technique. In order to improve the hydrogen kinetics Pd-coating were carried out on each side of the amorphous ribbon. Pd prevents oxidation of Zr and catalyses the dissociation of molecular hydrogen to atomic hydrogen. In this work, the hydrogen embrittlement and surface properties on Zr-based amorphous alloys were investigated. The Zr-based amorphous alloys were characterized by X-ray diffractometry(XRD) and differential scanning calorimetry(DSC). The morphology of surface and roughness was observed by using scanning electron microscopy(SEM) and atomic force microscopy (AFM). A lattice parameter of both Pd and Zr-based amorphous alloy was increased after hydrogen permeation at 473 K. After hydrogen permeation at 473 K, some cracks were observed on the surface of Pd, which was the cause for the hydrogen embrittlement. The crystallization temperature of Zr-based amorphous alloy was decreased due to the permeated hydrogen.

• Proceedings of the Korean Magnestics Society Conference
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• 2005.12a
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• pp.7-7
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• 2005

• Journal of Magnetics
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• v.3 no.3
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• pp.78-81
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• 1998

Large magneto crystalline anisotropy energy and demagnetization energy of rare earth-transition metal (RF-TM) alloys play roles of bottlenecks towards their commercial applications for giant magnetostrictive and blue wavelength magneto optical recording materials, respectively. To solve the above problems, boron is added into amorphous RE-TM alloys to produce its electron transferring. The boron added amorphous RE-TM alloys show novel magnetic and magneto-optical properties as follows; 1) an amorphous $(Sm_{33}Fe_{76})$97B3 alloy obtains the magnetostriction of$ -550{times}10^{-6}$ at 400 Oe compared with saturation magnetostriction of$ -60{\times}10^{-6}$ in conventional Ni based alloys, 2) an amorphous$ (Nd_{33}Fe_{67})_{95}B_5$ alloy increases effective magnetic anisotropy to$ -0.5{\times}10^{-6} ergs/cm^3 from -3.5{\times}10^6 ergs/cm^3$ without boron, which correspond to the polar Kerr rotation angles of 0.52$^{\circ}$and 0.33$^{\circ}$, respectively. These results attribute to selective 2p-3d electron orbits exchange coupling (SEC).

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.671-675
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• 2016

In this study, the glass-forming ability and mechanical properties of newly developed Fe-Mn-Cr-Mo-B-C-P-Si-Al bulk amorphous alloys were investigated, and metalloid elements such as B, C, and P were found to have a strong influence on the properties of the Fe-based amorphous alloys. When the total metalloid content (B, C, and P) is less than 5 %, only the crystal phase is formed, but the addition of more than 10 % metalloid elements enhances the glass forming ability. In particular, the alloys with 10 % metalloid content exhibit the best combination of very high compressive strength (~2.8 GPa) and superior fracture elongation (~30 %) because they consist of crystal/amorphous composite phases.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.320-326
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• 1999

In rapidly solidified $Al_{92-x}Nd_8$(Cu,Ag)x ($0{\leq}X{\leq}10at%$) alloys, amorphous single phases were obtained in the ranges of $Oat%{\leq}X{\leq}4at%$ for Al-Nd-Cu system and $Oat%{\leq}X{\leq}6at%$ for Al-Nd-Ag system, respectively. Mesoscopic structures consisted of amorphous and crystalline phases were formed above solute ranges. It was founded that the mesoscopic structures were also formed near 1st exothermic peak on DSC curve by aging in amorphous single phase alloys. For example, amorphous $Al_{92-x}Nd_8$(Cu,Ag)x (X=2.4at%) alloys containing nanoscale Al particles and compounds, i.e., mesoscopic structure, exhibited higher tensile fracture strength(${\sigma}_f$) than those of amorphous single phase alloys with the same composition. The ${\sigma}_f$ showed a maximum value in the $V_f$ ranges of 10~15%. The reason is presumed that the nanoscale precipitates which have higher mechanical strength compared with the amorphous phase with the same composition act as an effective resistance to shear deformation of the amorphous matrix.

• Applied Microscopy
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• v.46 no.1
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• pp.32-36
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• 2016

The Cu-based bulk glassy alloys in Cu-Zr-Ti-Ni systems were prepared by means of copper mold casting. The Cu-based bulk glassy alloys samples were tested by X-ray diffractomer (XRD), differential scanning calorimeter, scanning electron microscopy (SEM), Instron testing machine and Vickers hardness instruments. The result indicated that the prepared Cu-Zr-Ti-Ni alloys were bulk glassy alloys. The temperature interval of supercooled liquid region (${\Delta}T_x$) was about 45.48 to 70.98 K for the Cu-Zr-Ti-Ni alloy. The Vickers hardness was up to 565 HV for the $Cu_{50}Zr_{25}Ti_{15}Ni_{10}$ bulk glassy alloy. The $Cu_{50}Zr_{25}Ti_{15}Ni_{10}$ bulk glassy alloys were annealed in order to obtain nanocrystals. The results showed that the Vickers hardness was raise up to 630 HV from 565 HV. As shown in XRD results, the amorphous alloys changed to nanocrystals, which were $Cu_8Zr_3$, $Cu_3Ti_2$ and CuZr, improved the hardness. The SEM analysis showed that the compression fractured morphology of amorphous alloys was brittle fracture, and the fracture morphology after annealing was ductile fracture. This proved that annealing of amorphous to nanocrystals can improve the plasticity and toughness of amorphous alloys.