• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1804-1809
• /
• 2003

The purpose of this study is to clarify the bulk/sheet forming characteristics of bulk amorphous alloys in the supercooled liquid state. The temperature dependences of Newtonian viscosities of amorphous materials are obtained based on the previous experimental works. Finite element analyses for compression forming and sheet deep drawing of amorphous materials are performed. Effects of friction coefficients and temperature are examined and formability of amorphous material is explained in detail.

• Transactions of Materials Processing
• /
• v.13 no.2
• /
• pp.168-173
• /
• 2004

Microforming can be a good application for bulk metallic glasses. It is important to simulate the deformation behaviour of the bulk metallic glasses in a supercooled liquid region for manufacturing micromachine parts. For these purposes, a correct constitutive model which can reproduce viscosity results is essential for good predicting capability. In this paper, we studied deformation behaviour of the bulk metallic glasses using the finite element method in conjunction with the fictive stress constitutive model which can describe non-Newtonian as well as Newtonian behaviour. A combination of kinetic equation which describes the mechanical response of the bulk metallic glasses at a given temperature and evolution equations fur internal variables provide the constitutive equation of the fictive stress model. The internal variables are associated with fictive stress and relation time. The model has a modular structure and can be adjusted to describe a particular type of microforming process. Implementation of the model into the MARC software has shown its versatility and good predictive capability.

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

• Transactions of Materials Processing
• /
• v.16 no.4 s.94
• /
• pp.309-312
• /
• 2007

Deformation behavior of $Zr_{55}Cu_{30}Al_{10}Ni_5$(at. %) bulk metallic glass(BMG) fabricated by suction casting method has been investigated at elevated temperatures in this study. The BMG was first verified to have an amorphous structure with the analysis of X-ray diffraction(XRD) and differential scanning calorimetry(DSC) data. A series of compression tests has consequently been performed in the region of supercooled liquid temperature to investigate the behavior of high temperature deformation. A transition from Newtonian to non-Newtonian flow appeared to take place depending upon both the strain rate and test temperature. A processing map based on a dynamic materials model has been constructed to estimate a feasible forming condition for this BMG alloy.

• Journal of Powder Materials
• /
• v.14 no.6
• /
• pp.399-404
• /
• 2007

The Cu-based bulk metallic glass (BMG) composite was fabricated by spark plasma sintering (SPS) using of gas-atomized metallic glass powders and ductile brass powders. No defect such as pores and cavities was observed at the interface between the brass powder and the metallic glass matrix, suggesting that the SPS process caused a severe viscous flow of the metallic glass and brass phases in the supercooled liquid region, resulting in a full densification. The BMG composites shows some macroscopic plasticity after yielding, although the levels of strength decreased.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1057-1058
• /
• 2006

The preparation of $Ti_{50}Cu_{28}Ni_{15}Sn_7$ metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/$Ti_{50}Cu_{28}Ni_{15}Sn_7$ metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.950-951
• /
• 2006

[ $Mg_{55}Y_{15}Cu_{30}$ ] metallic glass powders were prepared by the mechanical alloying of pure Mg, Y, and Cu after 10 h of milling. The thermal stability of these $Mg_{55}Y_{15}Cu_{30}$ amorphous powders was investigated using the differential scanning calorimeter (DSC). $T_g$, $T_x$, and ${\Delta}T_x$ are 442 K, 478 K, and 36 K, respectively. The as-milled $Mg_{55}Y_{15}Cu_{30}$ powders were then consolidated by vacuum hot pressing into disk compacts with a diameter and thickness of 10 mm and 1 mm, respectively. This yielded bulk $Mg_{55}Y_{15}Cu_{30}$ metallic glass with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix. The pressure applied during consolidation can enhance thermal stability and prolong the existence of amorphous phase within $Mg_{55}Y_{15}Cu_{30}$ powders.

• Journal of Powder Materials
• /
• v.14 no.3 s.62
• /
• pp.197-201
• /
• 2007

Bulk metallic glass (BMG) composite was fabricated by consolidation of milled metallic glass composite powders. The metallic glass composite powder was synthesized by a controlled milling process using the Cu-based metallic glass powder blended with 30 vol% Zr-based metallic glass powders. The milled composite powders showed a layered structure with three metallic phases, which is formed as a result of mechanical milling. By spark plasma sintering of milled metallic glass powders in the supercooled liquid region, a fully dense BMG composite was successfully synthesized.

• Journal of the Korean Ceramic Society
• /
• v.27 no.5
• /
• pp.677-683
• /
• 1990

Melt-textured growth of the YBa2Cu3O7-x phase from a supercooled melt created locally aligned, barshaped grains of the orthorhombic 1-2-3 phase. Based on all the observed phenomena, the gross mechanism of the melt-textrued growth of YBa2Cu3O7-x on the (100) plane of MgO was delineated by three basic patterns of reactions. These are : (ⅰ) formation of the aligned 1-2-3 phase and the Y-rich 2-1-1 phase at the bulk region away from the (100) plane of MgO ; (ⅱ) formation of the Cu-richprecipitates at the interfacial region by the selective interface-induced precipitation of the liquid phase ; (ⅲ) condensation reaction of the entrapped Cu-rich vapor with Mg atoms during the initial stage of rapid cooling from 130$0^{\circ}C$ to 98$0^{\circ}C$.

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