Jung Chan Bae

New Cu-Based Bulk Metallic Glasses with High Strength of 2000 MPa

New Cu-based bulk amorphous alloys exhibiting a large supercooled liquid region and good mechanical properties were formed in a quaternary Cu-Ni-Zr-Ti systems consisting of only metallic elements. The compositional range for the formation of the amorphous alloys that have high glass forming ability (GFA) (> 3 mm diameter) and large supercooled liquid region (> 50 K) is defined in the pseudo-ternary phase diagram Cu-Ni-(Zr, Ti). A bulk amorphous Cu54Ni6Zr22Ti18 alloy with the diameter of 6 mm can be prepared by copper mold casting. The Cu54Ni6Zr22Ti18 alloy shows glass transition temperature (Tg) of 712 K, crystallization temperature (Tx) of 769 K and supercooled liquid region (ΔTx) of 57 K. The Cu54Ni6Zr22Ti18 alloy exhibits high compressive fracture strength of about 2130 MPa with a plastic strain of about 1.5 %. The new Cu-based bulk amorphous alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material.

Effect of Powder Size of Mg-Zn-Y Alloy on the Consolidation

MgZn4.3Y0.7 alloy powders were prepared using an industrial scale gas atomizer, followed by warm extrusion. The powders were almost spherical in shape. The microstructure of powders as atomized and bars as extruded was examined as a function of initial powder size distribution using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscope (EDS) and X-ray Diffractometer (XRD). The grain sizes were decreased with extruding as well as decreasing the initial powder sizes. Both the ultimate strength and elongation were enhanced as the initial powder sizes were decreased.

Microstructures and mechanical properties of consolidated Mg-Zn-Y alloy

The microstructure and mechanical properties of the Mg97Zn1Y2 alloy prepared by spark plasma sintering of gas atomized powders have been investigated. After consolidation, precipitates were observed to form in the α-Mg solid solution matrix of the Mg97Zn1Y2 alloy. These precipitates consisted of Mg12YZn and Mg24Y5 phases. The density of the consolidated bulk Mg-Zn-Y alloy was 1.86 g/cm3. The ultimate tensile strength and elongation were dependent on the consolidation temperature, which were in the ranges of 280 to 293 MPa and 8.5 to 20.8 %, respectively.

Plasticity in Bulk Metallic Glass Composites Containing Dual Amorphous Phases

Bulk metallic glass (BMG) composites with dual amorphous phases were fabricated by spark plasma sintering of a mixture of Cu-based and Zr-based amorphous powders in their overlapped supercooled liquid region. The Zr-based amorphous phases are well distributed homogeneously in the Cu-based metallic glass matrix after consolidation. The BMG composite still remains as an amorphous structure after consolidation. The BMG composite with dual amorphous phases shows macroscopic plasticity after yielding, and the plastic strain increased to around 3.4% in the BMG composite containing 30 vol% Zr-based amorphous phase. The successful consolidation of BMG composite with enhanced plasticity was achieved by introducing a second amorphous phase in the metallic glass matrix.

Synthesis of Cu-Based Bulk Metallic Glass Matrix Composites by Warm Processing of Gas Atomized Powders

The bulk metallic glass matrix composite comprising Cu54Ni6Zr22Ti18 metallic glass powder and ductile brass powder was fabricated by the warm process. The warm process was carried out by spark plasma sintering, which led to the homogeneous distribution of both phases of brass and metallic glass without pores. The metallic glass matrix composite material exhibits the same crystallization behavior of the metallic glass powder. A compressive strength of 1.0 GPa with a plastic strain of 3 % was obtained in the present metallic glass composite. The composite with enhanced strength and ductility was successfully achieved by introducing a ductile phase in the hard bulk metallic glass.

Hole Punching onto the Zr65Al10Ni10Cu15 BMG Sheet Fabricated by Squeeze Casting

Bulk metallic glass Zr65Al10Ni10Cu15 was fabricated in a sheet form with thickness 1.5 mm by a squeeze casting method. The structure of the as-cast Zr65Al10Ni10Cu15 sheet was confirmed to be fully amorphous. The sheet was punched into a blank under high hydrostatic pressure at room temperature. A round hole was created with a possible evidence for plastic-like deformation along the edge of rim. No visible cracks were observed around the hole. This result indicates that bulk metallic glasses, which are known to be very brittle at room temperature, can be deformed in a ductile mode under hydrostatic pressure condition. Hydrostatic pressure may suppress the formation and development of micro defects leading to ductile fracture

Microstructure and Formability of Different-Speeds Rolled AZ31 Mg Sheet

The aims of this study ares to investigate the microstructure evolution of AZ31 Mg alloys with normal rolling and different speeds rolling during hot rolling affects microstructure, texture and mechanical properties of AZ31 Mg alloy. In the microstructures of as-rolled both samples, twins are clearly apparent, small and recrystallized grains are visible along some grain boundary and twinned regions. The tensile strength and yield strength of DSR sample were slightly higher than that of NR sample. Also, in the case of the NR sample, tensile strength indicated different values to the rolling directions. From this result, NR sample compared to DSR sample strongly indicated to the plastic anisotropy tendency. Therefore, it is noted that DSR sample could be presented to the good formability, comparing to the NR sample. DSR samples deformed at 473K and 523K could be perfectly formed, indicating the potential application of the DSR process to improve formability of the Mg alloys at warm temperatures.

Microstructure and Mechanical Properties of Mg-Al-Ca Alloys with Yttrium Addition

The aims of this study are to investigate the effect of Y (yttrium) addition in the Mg-Al- Ca alloys on microstructure and mechanical properties. In additions, the alloys were solution treated in order to achieve a better understanding of the precipitation mechanisms. The as-cast microstructure of Mg-5Al-3Ca alloy and Mg-5Al-3Ca-xY alloys contains dendritic α-Mg matrix and eutectic intermetallic compound at grain boundary. The hardness values of Mg-Al-Ca alloy with Y additions were slightly increased than that of Mg-Al-Ca with no Y addition. It is because of reduction of α-Mg phase and presence of (Mg,Al)2Ca and Al-Y rich intermetallic phase at grain boundary and α-Mg matrix grains. Also, hardness value of yttrium (Y) containing alloys was increased with increasing Y contents. Compared to Mg-5Al-3Ca alloy, maximum strength and yield strength of the alloys with Y additions have slightly increased with increasing Y additions in the case of as-cast samples.

Characterization of Mg-Al Sheet Clad Materials Fabricated by Hot Rolling

AZ31 Mg / 5083 Al clad sheet was fabricated by the hot rolling method and its mechanical properties were investigated in this study. The tensile strength and yield strength of Mg- Al clad samples were slightly higher than that of AZ31 Mg sample, resulting in high strength 5083 Al alloy. Also, in the case of the AZ31 Mg sample, tensile strength indicated different values to the rolling directions. The thickness of interface layers between magnesium and aluminum materials increased with increasing rolling temperature. The thickness of interface layer was about 1.2 μm and 1.6 μm, respectively. The difference of thickness on the interface layer with variation of rolling temperature was attributed to promote the diffusion between magnesium and aluminum materials. The Vickers hardness of Mg-Al interface layer was around 125 Hv. The interface layer composed of hard inter-metallic phases which may act a increment of Vickers hardness depending upon its thickness.

Mechanical Properties and Biocompatibility of Porous Titanium Prepared by Powder Sintering

Porous Ti compacts were fabricated by spark plasma sintering (SPS) method and their Youngs modulus and biocompatibility were investigated in this study. Ti powders were made from commercially available pure Ti (grade 2) using the plasma rotating electrode process (PREP) in an Ar atmosphere. Porous Ti compacts for biomedical applications were successfully fabricated in the porosity range from 5.1 to 39.2 vol%. Youngs modulus of porous Ti compacts having porosity from 31 to 35 vol % is almost the same as that of human cortical bone. To investigate the biocompatibility of pure Ti, fibroblast-like L-929 and osteoblast-like MG-63 cells were cultured with the presence of the extract solution from pure Ti for 72 hours. The viabilities of cells cultured with the diluted extract solutions were almost the same compared to that of the control. Also, porous Ti compacts did not induce any morphologic damage of cells.