• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.114.2-114.2
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• 2007

• 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.

• Applied Microscopy
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• v.26 no.2
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• pp.235-241
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• 1996

Amophization and decomposition behaviour in $Mg_{62}Cu_{26}Y_{12}$ alloy prepared by melt spinning method and wedge type metal mold casting method have been investigated by a detailed transmission electron microscopy. Amorphous phase has formed in melt-spun ribbon. In the case of the wedge type specimen, however, the amorphous phase has formed only around the tip area within about 2 mm thickness. The remaining part of the wedge type specimen consists of crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$. The supercooling for crystallization behaviour of the amorphous $Mg_{62}Cu_{26}Y_{12}$ alloy, ${\Delta}T_x$ has been measured to be about 60 K. Such a large undercooling of the crystallization bahaviour enables formation of the amorphous phase in the $Mg_{62}Cu_{26}Y_{12}$ alloy under the cooling rate of $10^{2}K/s$. The amorphous $Mg_{62}Cu_{26}Y_{12}$ has decomposed into crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$ after heat treatment at $170^{\circ}C\;and\;250^{\circ}C$.

• Journal of Korea Foundry Society
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• v.32 no.4
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• pp.177-180
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• 2012

Ti-based bulk metallic glasses with high glass forming ability were developed through a systematic alloy design technique. The main alloy design strategy was the selection of alloying elements that may not be toxic in the human body. The $Ti_{45.0}Cu_{40.1}Zr_{12.7}Si_{2.2}$ alloy could be cast into an amorphous rod with the diameter of 3 mm by a suction casting technique using Cu mold. The compressive strength of the amorphous rod was measured as 1826 MPa. Since the Ti-based amorphous alloys consist of non-toxic elements, they can be widely used as bio-materials and eco-materials with unique and beneficial properties.

• Tribology and Lubricants
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• v.30 no.5
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• pp.295-302
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• 2014

The tribological behavior of an Fe-based bulk amorphous alloy while sliding against a AISI 304 disc is investigated using a unidirectional pin-on-disc type tribometer in dry and distilled water environments. The rod-shaped bulk pins are fabricated by suction casting. The crystallinities of the bulk amorphous alloys before and after the friction tests are determined by X-ray diffraction. The friction coefficient and specific wear rate of the amorphous pin in the water environment are found to be twice and thrice as much as in the dry environment at a low applied pressure, respectively. However, at a higher pressure, the friction coefficient and specific wear rate are 0.4 and 1.02 mg/(Nm/s), respectively, in the water environment. A microstructure analysis shows that the worn surface of the alloy is characterized by delamination from the smooth friction surface, and thus delamination is the main wear mechanism during the friction test in dry sliding environment. In contrast, brittle fracture morphologies are apparent on the friction surface formed in distilled water environment. For the sample tested at a lower sliding speed, the XPS data from the oxide layer are similar to those of the pure element with weak suboxide peaks. For higher sliding speeds, all the main sharp peaks representing the core level binding energies are shifted to the oxide region.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.50-55
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• 2007

The hydrogen sorption speeds of $Zr_{57}V_{36}Ti_7$ amorphous alloy and its crystallized alloys were evaluated at room temperature. $Zr_{57}V_{36}Ti_7$ amorphous alloy was prepared by ball milling. The hydrogen sorption rate of the partially crystallized alloy was higher than that of amorphous. The enhanced sorption rate of partially crystallized alloy was explained in terms of grain refinement that has been known to promote the diffusion into metallic bulk of the gases. The grain refinement could be obtained by crystallization of amorphous phase resulting in the observed increase in sorption property.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.113.1-113.1
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• 2007

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3315-3318
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• 2012

In this study, Fe-base alloy powder was prepared by gas atomizing method. Shape and crystal structure of the powder were investigated by FESEM, X-ray diffraction, and DSC. The powder was produced in a spherical shape, with a size of 45 ~ 90 ${\mu}m$. X-ray diffraction analysis revealed that the powder was fully amorphous, showing typical broad amorphous peak. From DSC analysis, Tg and Tx that are generally found in a bulk amorphous alloy were also observed in the alloy powder. Tg and Tx of the powder were $530^{\circ}C$ and $560^{\circ}C$, respectively. These results suggest us that the bulk amorphous alloy (BMG) powder prepared in this study is applicable to laser welding.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.139-142
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• 2005

Cu-Ni-Zr-Ti bulk amorphous thin strips were produced by multi-pass warm rolling of the amorphous powder at temperatures in the supercooled liquid region. Process variables for rolling of the bulk amorphous strips were properly controlled to prevent onset of crystallization and failure during rolling up to three passes. During rolling of the amorphous powder, both the deformation and densification took place and the newly developed surface on the deformed amorphous particles enhances the consolidation leading to an increase in the strength. The strain state during rolling was analyzed by FEM.