• Journal of Magnetics
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• v.16 no.4
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• pp.431-434
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• 2011

The reduction of the Nb content in the $(Fe_{0.75}B_{0.20}Si_{0.05})_{96}Nb_4$ bulk metallic glass (BMG) has been studied. The glass-forming ability (GFA) is reduced by decreasing the Nb content, but it can be enhanced by replacing partially Fe by Co. Furthermore, the saturation magnetization of the $(Fe_{0.8}Co_{0.2})_{76}B_{18}Si_3Nb_3$ BMG is 1.35 T, being with 13% larger than that of the base alloy $(Fe_{0.75}B_{0.20}Si_{0.05})_{96}Nb_4$. $(Fe_{0.8}Co_{0.2})_{76}B_{18}Si_3Nb_3$ BMG exhibits slightly larger $B_{800}$ (the magnetic flux density at 800 A/m) and smaller core losses (20%-30%) compared with the commercial Fe-6.5 mass% Si steel.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.5
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• pp.104-109
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• 2011

Bulk metallic glasses (BMG) have been greatly improved by the advance of synthesis process during last three decades. It was also found that the Glass Forming Ability (GFA) strongly depends on the glass transition temperature. When the temperature approaches to a critical value, the crystals nucleation from the supercooled liquid can be suppressed so that bulk glass formation possible. Egami and others found that the local glass transition temperature depends on the volumetric strain of each atom and suggested the critical transition temperature. In this paper, we explore the strain dependency of local glass transition temperature using the atomic strain defined by the deformation tensor for the Voronoi polyhedra.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.335-335
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• 2013

최근 다기능 소재의 개발이 필요함에 따라 서로 상반되는 2가지 이상의 물성을 동시에 구현할 수 있는 소재의 개발이 요구되고 있다. 4 성분계 물질을 단일 타겟으로 제조함으로써 다수의 타겟을 이용하는 기존 PVD 방법의 복잡성과 재형성 등의 문제점을 해결하고 다기능성을 구현할 수 있는 코팅막을 제조할 수 있게 된다. 본 연구에서는 제조된 4 성분계 모물질을 UBM 최근 다기능 소재의 개발이 필요함에 따라 서로 상반되는 2가지 이상의 물성을 동시에 구현할 수 있는 소재의 개발이 요구되고 있다. 4 성분계 물질을 단일 타겟으로 제조함으로써 다수의 타겟을 이용하는 기존 PVD 방법의 복잡성과 재형성 등의 문제점을 해결하고 다기능성을 구현 할 수 있는 코팅막을 제조할 수 있게 된다. 본 연구에서는 제조된 4 성분계 모물질을 UBM 스퍼터링법을 이용하여 질화 공정을 도출하였고 질소 함량에 따른 물리적 특성 및 박막의 특성에 대해 연구하였다. BMG (Bulk Metallic Glass) 타겟을 이용하여 마그네트론 스퍼터링법으로 박막을 코팅하였다. 시편은 Si wafer, SUS 그리고 부식 특성 평가를 실시하기 위하여 냉연강판을 사용하였다. 시편은 아세톤, 알코올로 각각 10분간 초음파 세척한 후 진공장비에 장착하여 Ar 분위기에서 글로우 방전으로 청정을 30분간 실시하였다. 시편청정이 끝나면 ~$10^{-6}$ Torr까지 진공 배기를 실시하고 Ar 가스를 주입하여 2.5 mTorr로 진공도를 유지하여 스퍼터링으로 박막 코팅을 실시하였다. 스퍼터링 파워는 약 0.6 kW (2.0 A)으로 고정하였고 질소 유량은 0~10 SCCM으로 변화시켜 BMG 박막을 코팅하였다. 질소가 첨가된 BMG 박막에서는 시편의 색상이 노란빛으로 나타났으며 이것은 타겟의 조성 중 가장 많이 함유되어있는 Zr이 질화되어 색상의 변화가 일어난 것으로 판단된다. BMG 코팅을 위해서 진공용기로 주입한 질소의 유량이 소량인 경우에도 BMG 코팅층에 비교적 많은 양의 질소가 존재하였고 일정량 이상에서는 BMG 코팅층에 존재하는 질소의 양이 포화되는 현상을 보였다. 질소 유량 3, 4 SCCM의 BMG 코팅층에서 ZrN (111), ZrN (200) Peak이 관찰되었다. BMG 코팅층의 경도 측정결과 Bias 50 V 인가 시 ~22 Gpa로 경도가 가장 높았다. BMG 코팅층의 내부식 특성을 평가하기 위해 염수분무 시험을 실시하였고 ~$10{\mu}m$의 두께를 갖는 BMG 코팅층에서 염수분무 시작 후 48시간 만에 적청이 발생하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.107-108
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.199-202
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• 2004

In this present study, an attempt was made to determine the deformation mode of the Zr-Ti-Cu-Ni-Be bulk metallic glass by compression test over a wide range of temperatures and strain rates. From the results, empirical deformation map could be constructed including the boundaries of different deformation modes. Considering power dissipation map and instability map developed on the basis of the Dynamic Materials Model (DMM), the processing map for extrusion could also be constructed. In addition, the macroscopic formability of this BMG alloy has also been examined through the extrusion in laboratory scale within undercooled liquid state. From the results of macroscopic extrusion formability, both deformation map and processing map present good criteria to determine optimal forming conditions.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.43-48
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• 2009

In this study, Cu-based bulk metallic glass (BMG) coatings were deposited by atmospheric plasma spraying (APS) process with different process conditions (with- and without hydrogen gas). As adding the hydrogen gas, thermal energy in the plasma flame increased and induced difference in the melting state of the Cu-based BMG particles. The microstructure and mechanical properties of the coatings were analyzed using a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) and nano-indentation tester in the light of phase analysis. It was elucidated by the nano-indentation tests that un-melted region was a mainly amorphous phase which showed discrete plasticity observed as the flow serrations on the load.displacement (P - h) curves, and the curves of solidified region showed lower flow serrations as amorphous phase mingled with crystalline phase. Oxides produced during the spraying process had the highest hardness value among the phases and were well mixed with other phases resulted from the increase in melting degree.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.258-262
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• 2008

Micro forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). In this study, the micro forming property was studied, using Al5083 superplastic alloy with micro grain, suitable for the micro forming process and Zr-BMG amorphous with pseudo-superplastic phenomena in the supercooled liquid state. Micro forming experiments under stastic load status showed that distortion by slip and spin of the grain system and slip inside the grain was observed in the Al5083 superplastic alloy. In case of Zr-BMG, because there is no grain, the distribution of the forming property was similar to the load distribution between punch and metal.

• Journal of Korea Foundry Society
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• v.29 no.4
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• pp.181-186
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• 2009

The interrelationship between new parameter ${\sigma}$ and maximum diameter $D_{max}$ is elaborated and discussed in comparison with four other glass forming ability (GFA) parameters, i.e. (1) super-cooled liquid region ${\Delta}T_x (=T_x - T_g)$, (2) reduced glass transition temperature $T_{rg} (=T_g/T_l)$, (3) K parameter $K (=[T_x-T_g]/[T_l -T_x])$, and (4) gamma parameter ${\gamma}(=[T_x]/[T_l+T_g])$ in Ca-based bulk metallic glass (BMG) systems. The ${\sigma}$ parameter, defined as ${\Delta}T^*{\times}P^'$, has a far better correlation with $D_{max}$ than the GFA parameters suggested so far, clearly indicating that the liquid phase stability and atomic size mismatch dominantly affect the GFA of Ca-based BMGs. Thus, it can be understood that the GFA of BMGs can be properly described by considering structural aspects for glass formation as well as thermodynamic and kinetic aspects for glass formation.

• Journal of Korea Foundry Society
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• v.26 no.2
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• pp.77-84
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• 2006

The effect of alloy composition on the glass forming ability (GFA) of the Ca-rich Ca-Mg-Zn alloys has been investigated in $Ca_{65}Mg_{5+x}Zn_{30-x}$ and $Ca_{55+x}Mg_{15}Zn_{30-x}$ (x=0, 5, 10, 15, 20) alloys. In a wide composition range of 15-25% Zn and 10-20% Mg bulk metallic glass (BMG) samples with the diameter larger than 6 mm are fabricated by conventional copper mold casting method in air atmosphere. Among the alloys investigated, the $Ca_{65}Mg_{15}Zn_{20}$ alloy exhibits the highest GFA enabling to form BMG sample with the diameter of at least 15 mm. The crystalline phase formed during solidification of $Ca_{65}Mg_{15}Zn_{20}$ ($D_{max}=15\;mm$) could be identified as a mixture of $Ca_3Zn$ and $CaMg_2$ cause by the redistribution of the constituent elements on long-range scale. The compressive fracture strength and fracture elongation of the $Ca_{65}Mg_{15}Zn_{20}$ BMG are 602 MPa and 2.08% respectively. The ${\sigma}$ parameter which has been recently proposed for evaluating GFA exhibits better correlation with GFA of Ca-Mg-Zn alloys than other parameters suggested so far such as ${\Delta}T_x$, $T_{rg}$, K, ${\gamma}$, and ${\Delta}T^*$ parameters.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.118-121
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• 2007

Bulk metallic glass (BMG)/crystalline composites comprising a copper based BMG alloy and crystalline nickel were produced by means of eloctroless plating of nickel on $Cu_{54}Zr_{22}Ti_{18}Ni_6$ BMG powder and subsequent consolidation using spark plasma sintering. The plastic deformation behavior of BMG/crystalline composites was examined by uniaxial compression test at various temperatures in the supercooled liquid region (SLR) of the BMG alloy. The evolution of strain states during uniaxial compression was tackled by microstructure observations. Deformation temperature played an important role in the deformation behavior of BMG/crystalline composites, which was attributed to a strong temperature dependence of the flow stress of the BMG alloy in the SLR. BMG/crystalline composites deformed homogenously in the temperature range where the flow stress of the BMG alloy was close to that of crystalline nickel. In contrast, inhomogeneous deformation was observed in the temperature range where the flow stress of the BMG alloy largely differs from that of crystalline nickel.