• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.272-276
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• 2001

Multicomponent $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ bulk matallic glass alloy shows good bulk glass forming ability due to its high resistance to crystallization in the undercooled liquid state.1) In this study, DSC and X-ray diffractometry have been performed to confirm the amorphous structure of the master $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy. To investigate the mechanical properties and deformation behaviors of the bulk metallic $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy, a series of compression tests has been carried out at the temperatures ranging from $351^{\circ}C$ to $461^{\circ}C$ and at the various initial strain rates from $2{\times}10^{-4}s^{-1}\;to\;2{\times}10^{-2}s^{-1}$. There are two types of nominal stress-strain curves. The one shows linear stress-strain relationship meaning fracture at maximum stress, the other shows plastic deformation including steady-state flow. Also DSC analysis for the compressed specimens has been performed to investigate the change of thermal stability and crystallization behavior for the various test conditions.

• Transactions of Materials Processing
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• v.10 no.7
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• pp.565-572
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• 2001

It is well known that a multicomponent $Zr_{4l.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ bulk metallic glass alloy shows good bulk glass forming ability due to its high resistance to crystallization in the undercooled liquid state. DSC and XRD have been performed to confirm the amorphous structure of the master alloy. To investigate the mechanical properties and deformation behavior of the bulk metallic $Zr_{4l.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy, a series of compression tests has been carried out at the temperatures ranging from $351^{\circ}C$ to $461^{\circ}C$at the various initial strain rates from $2{\times}10^4s^1$ to $2{\times}10^2s^1$. Three types of nominal stress-strain curves have been identified such as linear stress-strain relationship meaning fracture at maximum stress, plastic deformation including stress overshoot and steady-state flow, plastic deformation without stress overshoot depending on the strain rate and test temperature. Also DSC analysis for the compressed specimens was carried out to investigate the change of structure, thermal stability and crystallization behavior for the various test conditions.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1145-1150
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• 2003

Zr-based bulk metallic glasses have a significant mechanical properties such as high strength and elastic strain limit, and a good processing ability due to the deformation behavior such as superplasticity under supercooled liquid region. Recently, many researches on the determination of optimum working condition in various bulk metallic glasses have been carried out. In this study, the deformation behavior and forming conditions of $Zr_{55}Cu_{30}Al_{10}Ni_{5}$ bulk metallic glass were investigated under three different strain rates and at various temperatures between 627K and 727K. The glass transition temperature, crystallization temperature and supercooled liquid region of $Zr_{55}Cu_{30}Al_{10}Ni_{5}$ bulk metallic glass are 680K, 762K and 82K, respectively.

• Journal of Powder Materials
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• v.9 no.6
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.930-936
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• 2011

In the present study, we show that the addition of Ag, an element having a positive enthalpy of mixing with Cu in the liquid state, enables the simultaneous enhancement of the glass forming ability and the plasticity in Cu-Zr-Ag bulk metallic glasses (BMGs). Rods of 4 mm diameter could be prepared with a fully amorphous structure and values of plastic strain up to 18% were measured under a compression mode for compositions around $Cu_{42.5}Zr_{47.5}Ag_{10}$. The possible role of Ag in the change of the atomic structure and the enhancement of the plastic strain in the ternary Cu-Zr-Ag BMGs is discussed based on analyses from transmission electron microscopy and EXAFS (extended X-ray absorption fine structure).

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.970-973
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• 2003

A new class of soluble PPV derivatives containing dimethyldodecylsilylphenyl unit as a pendant was synthesized by Gilch polymerization method. The resulting electroluminescent (EL) polymers showed good solubility, good film-forming ability onto the ITO substrate, and exhibited an amorphous morphology due to dimethyldodecylsilylphenyl branched group linked to the polymer backbone. The weight average molecular weights and polydispersities of the present EL polymers were in the range of 8.0-80.0 x $10^{4}$ and 2.67-7.80, respectively. The resulting EL polymers revealed a high thermal stability of up to $355-410^{\circ}C$. Their glass transition temperatures were in the range of $104-251^{\circ}C$. The emission colors could be tuned from green to orange-red colors by changing the MEH-PPV contents in copolymer systems. The turn-on voltages of the EL polymers were in the range of 1.8-4.0 V.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.169-178
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• 1998

The crystal phases precipitated in various compositions glass of CaO-$SiO_2-P_2O_5$ system, were identified by XRD. E composition (CaO 49.4, $SiO_2\;36.8,\;P_2O_5$ 8.8 wt%) glass in which both apatite(($Ca_{10}(PO_4)_6O$ and $\beta$-wollastonite($CaSiO_3$) crystals would precipitate by heating, was selected as an experimental composition to prepare the glass ceramics with high bending strength and good bioactivity to the living bone. Glass powders of E composition were unidirectionally crystallized at $1050^{\circ}$C in the temperature-gadient furnace and the resultant glass ceramics were characterized. Bending strength of the glass ceramics was also measured. To investigate the bond forming ability between the glass ceramics and living bone tissue, soaking test of glass ceramics in simulated body fluid was carried out. Densed glass ceramics composed of apatite and $\beta$-wollastonite crystal were prepared by unidirectional crystallization under the optimum conditions. (2 0 2) plane of $\beta$-wollastonite crystals tended to grow perpendicularly to the crystallization direction. Average bending strength of this glass ceramics was 186.9 MPa, higher than that of the glass ceramics prepared by isothermal (not directional) crystallization In soaking test, a thin layer of apatite crystallite was formed on surface of the glass ceramics in 3 days. Apatite crystals formed on the glass ceramics could be act a role to make the chemical bond between the glass ceramics and living bone tissue.

• Current Applied Physics
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• v.18 no.12
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• pp.1523-1527
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• 2018

The thermal stability, magnetic and magnetocaloric properties of $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) melts-pun ribbons were studied. The relatively high reduced glass transition temperature ($T_{x1}/T_m$ > 0.60) and low melting point ($T_m$) resulted in excellent glass forming ability (GFA). The Curie temperatures ($T_C$) of melt-spun amorphous ribbons $Gd_{55}Co_{35}M_{10}$ for M = Si, Zr and Nb were 166, 148 and 173 K, respectively. For a magnetic field change of 2 T, the values of maximum magnetic entropy change $(-{\Delta}S_M)^{max}$ for $Gd_{55}Co_{35}Si_{10}$, $Gd_{55}Co_{35}Zr_{10}$ and $Gd_{55}Co_{35}Nb_{10}$ were found to be 2.86, 4.28 and $4.05J\;kg^{-1}K^{-1}$, while the refrigeration capacity (RC) values were 154, 274 and $174J\;kg^{-1}$, respectively. The $RC_{FWHM}$ values of amorphous alloys $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) are comparable to or larger than that of $LaFe_{11.6}Si_{1.4}$ crystalline alloy. Large values of $(-{\Delta}S_M)^{max}$ and RC along with good thermal stability make $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) amorphous alloys be potential materials for magnetic cooling operating in a wide temperature range from 150 to 175 K, e.g., as part of a gas liquefaction process.

• Journal of Powder Materials
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• v.28 no.6
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• pp.483-490
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• 2021

A new Fe-Cr-Mo-B-C amorphous alloy is designed, which offers high mechanical strength, corrosion resistance as well as high glass-forming ability and its gas-atomized amorphous powder is deposited on an ASTM A213-T91 steel substrate using the high-velocity oxygen fuel (HVOF) process. The hybrid coating layer, consisting of nanocrystalline and amorphous phases, exhibits strong bonding features with the substrate, without revealing significant pore formation. By the coating process, it is possible to obtain a dense structure in which pores are hardly observed not only inside the coating layer but also at the interface between the coating layer and the substrate. The coating layer exhibits good adhesive strength as well as good wear resistance, making it suitable for coating layers for biomass applications.

• Journal of Powder Materials
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• v.9 no.6
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• pp.381-393
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• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.