Haein Choi-Yim

Synthesis and characterization of particulate reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass composites

The Zr[sub 57]Nb[sub 5]Al[sub 10]Cu[sub 15.4]Ni[sub 12.6] bulk metallic glass forming liquid is reinforced with WC, SiC, W, or Ta particles. Structure, microstructure and thermal stability of the composites are studied by X-ray diffraction, optical microscopy and differential scanning calorimetry. The metallic glass matrix remains amorphous after adding up to 20 vol.% of particles. The reactions at the interfaces between the matrix and the different reinforcing materials are investigated with scanning electron microscopy, transmission electron microscopy and electron microprobe. The mechanical properties of the composites are studied in compression and tension. The influence of the introduced particles on the thermal stability of the matrix as well as on the mechanical properties is discussed.

Ni-based bulk metallic glass formation in the Ni-Nb-Sn and Ni-Nb-Sn-X (X=B, Fe, Cu) alloy systems

Refractory Ni-based bulk metallic glasses are formed in the three-component Ni–Nb–Sn system near a ternary eutectic composition located within the three-phase field bounded by the three intermetallics Ni3Nb, Ni6Nb7 (μ-phase), and Ni2NbSn (BiF3-type). Bulk amorphous alloys of composition Ni60Nb40−xSnx with 3<x<9 were prepared by injection-casting the molten alloys into copper models. X-ray diffraction and differential scanning calorimetry studies show the cast strips to be fully amorphous up to thicknesses from 0.5 to 3 mm as x is varied. Maximum glass-forming ability (GFA) observed when x is between 6 and 7. These refractory bulk amorphous alloys exhibit high glass transition temperatures 881<Tg<895 K, a large, stable, undercooled liquid region with ΔT=Tx−Tg, at ∼40–60 K, very high Vickers hardness (VH∼1000–1280 Kg/mm2), and estimated yield strengths in the range of 3 to 3.8 GPa. The effects of small quaternary additions of B and Fe on the GFA of the ternary alloys are also reported.

Mechanical properties of Zr 57 Nb 5 Al 10 Cu 15.4 Ni 12.6 metallic glass matrix particulate composites

To increase the toughness of a metallic glass with the nominal composition Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), it was used as the matrix in particulate composites reinforced with W, WC, Ta, and SiC. The composites were tested in compression and tension experiments. Compressive strain to failure increased by more than 300% compared with the unreinforced Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), and energy to break of the tensile samples increased by more than 50%. The increase in toughness came from the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area. There was direct evidence of viscous flow of the metallic glass matrix within the confines of the shear bands.

Processing, microstructure and properties of ductile metal particulate reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass composites

The Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass forming liquid is reinforced with up to 50 Volume-percent (% Vf) Ta, Nb, or Mo particles. An extensive reaction layer of varying composition formed in the metallic–glass matrix surrounding the particles. A characterization based on X-ray diffraction, differential scanning calorimeter, electron microprobe, and scanning electron microscopy is presented. The composites were tested in compression and tension. Compressive strain-to-failure increased by up to a factor of 12 compared to the unreinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass. The increase in compressive strain-to-failure is due to the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area.

The effect of silicon on the glass forming ability of the Cu47Ti34Zr11Ni8 bulk metallic glass forming alloy during processing of composites

Composites of the Cu47Ti34Zr11Ni8 bulk metallic glass, reinforced with up to 30 vol % SiC particles are synthesized and characterized. Results based on x-ray diffraction, optical microscopy, scanning Auger microscopy, and differential scanning calorimetry (DSC) are presented. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the Cu47Ti34Zr11Ni8 matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4 mm for Cu–Ti–Zr–Ni alloys to 7 mm for Cu–Ti–Zr–Ni–Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy are affected significantly by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt.

Processing of carbon-fiber-reinforced Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass composites

Carbon-fiber-reinforced bulk metallic glass composites are produced by infiltrating liquid Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 into carbon fiber bundles with diameter of the individual fiber of 5 μm. Reactive wetting occurs by the formation of a ZrC layer around the fibers. This results in a composite with a homogeneous fiber distribution. The volume fraction of the fibers is about 50% and the density of the composite amounts to 4.0 g/cm3.

Quasistatic and dynamic deformation of tungsten reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass matrix composites

Quasistatic and dynamic deformation behavior of composites of Zr57Nb5Al10Cu15.4Ni12.6 metallic glass reinforced with tungsten is studied. The plastic deformation of the metallic glass was increased under quasistatic compression in composites. Localized shear band failure of these composites results in self-sharpening behavior during ballistic impact.

Microstructures and mechanical properties of tungsten wire/particle reinforced Zr57Nb5Al10Cu15.4Ni12.6 metallic glass matrix composites

Tungsten wire or particle reinforced metallic glass matrix composites are produced by infiltrating liquid Zr57Nb5Al10Cu15.4Ni12.6 (Vit106) into tungsten reinforcements at 1150 and at 1425 K. X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy are carried out to characterize the composite. The matrix of the composite processed at 1150 K is mostly amorphous, with some embedded crystals. During processing, tungsten dissolves in the glass-forming melt and upon quenching precipitates over a relatively narrow zone near the interface between the tungsten and matrix. In the composites processed at 1425 K, tungsten dissolves in the melt and diffuses through the liquid medium, and then reprecipitates upon quenching. The faster kinetics at this high temperature results in a uniform distribution of the crystals throughout the matrix. Mechanical properties of the differently processed composites containing wires and particles are compared and discussed. The composites exhibit a plastic strain failure of up to 16% without sacrificing the high-failure strength, which is comparable to monolithic Vit106.

Processing, microstructure and properties of bulk metallic glass composites

A Zr-Nb-Cu-Ni-Al bulk metallic glass was reinforced with up to 80 volume-percent (% Vf) continuous fibers, short fibers or particles. Characterization based on X-ray diffraction, differential scanning calorimetry, electron microprobe and scanning electron microscopy is presented. The metallic glass matrix remains amorphous after adding reinforcements. Reactions at the matrix/reinforcement interfaces were examined using transmission electron microscopy. A narrow band of crystalline particles typically forms adjacent to the reinforcement. The composites were tested in compression. Compressive strain-to-failure increased by up to factor of 12 compared to the unreinforced bulk metallic glass. The increase in compressive strain-to-failure is due to the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area.

Formation of Refractory Ni-Based Bulk Metallic Glass in the Ni-Nb-Sn and Ni-Nb-Sn-X (X= Fe, B, Cu, Ta) Alloy Systems

Novel refractory Ni-based bulk metallic glasses are formed in the 3-component Ni-Nb-Sn system near a ternary eutectic composition located within the 3-phase field bounded by the three intermetallics Ni3Nb, Ni6Nb7 (μ-phase), and Ni2NbSn (BiF3-type). Bulk amorphous alloys of composition Ni60Nb40-xSnx with 3<x<9 were prepared by injection casting the molten alloys into copper molds. X-ray diffraction and DSC studies show the cast strips to be fully amorphous up to thicknesses from 0.5 to 3mm as x is varied. Maximum Glass Forming Ability (GFA) observed near x = 6-7. These refractory bulk amorphous alloys exhibit high glass transition temperatures 881< Tg < 895 K, a large stable undercooled liquid region with ∆T = Tx-Tg ~ 40-60 K, very high Vickers hardness (V.H.~ 1000-1280 Kg/mm 2 ) and estimated yield strengths in the range 3-3.8 GPa. The effects of small quaternary additions of B, Fe, and Ta on the GFA of the ternary alloys are also reported.