Jason Shian-Ching Jang

Two-glassy-phase bulk metallic glass with remarkable plasticity

Using the computational-thermodynamic approach, the potential compositions of Zr–Cu–Ni–Al alloy system exhibiting the two-liquid miscibility phase equilibrium in the liquid temperature region have been identified. The resulting Zr base bulk metallic glasses show a microstructure of two microscaled glassy phases. The glass possesses a remarkable macroscopic plastic strain of 30% at room temperature. The gain of mechanical properties is attributed to the unique glassy structure correlated with the chemical inhomogeneity on the micron scale, the hard phases surrounded by the soft phases, leading extensive shear-band formation, interactions, and multiplication.

Flow serration and shear-band propagation in bulk metallic glasses

Flow serration in bulk metallic glasses (BMGs) was analyzed using high-sensitivity strain gauges. Based on the displacement-time profile for one serration, shear-band propagating speed was determined and found to be insensitive to the applied strain rates. The disappearance of serration at high strain rates is a result that the signal of displacement burst was overwhelmed by the applied strain rate. In comparison with the ductile Pd-based and brittle Mg-based BMGs, the ductility of BMGs appears to be closely related to the dynamics during shear-band propagation.

Enhanced mechanical performance of Mg metallic glass with porous Mo particles

We present a porous ductile Mo particles reinforced Mg-based metallic glass composite, exhibiting superior mechanical performance with up to 10% compressive strain and 1100MPa stress at room temperature. For a given amount of particles, the porous particles will generate more interfaces between the reinforcements and matrix and, thus, can confine lots of microsized compartments of the Mg based glassy phase within the porous particles. This promotes the deformation to distribute more uniformly across the specimens, improving the ductility. We suggest that porous ductile particles might preferably be used to toughen amorphous materials with stubborn brittleness.

Rapid screening of potential metallic glasses for biomedical applications

This paper presents a rapid screening process to select potential titanium and zirconium based metallic glasses (MGs) for bio-material applications. Electrochemical activity of 7 MGs including 6 bulk metallic glasses and 1 thin-film deposited MG in simulation body and human serum is first inspected. A low-voltage potential state test is also developed to simulate the cell membrane potential that the implant MGs will suffer. Results show that the MGs composed of Ti65Si15Ta10Zr10 and Ta57Zr23Cu12Ti8 exhibit excellent electrochemical stability in both simulation body fluid and human serum. In addition, the copper content in the MGs plays an important role on the electrochemical activity. MGs with the copper content higher than 17.5% show significant electrochemical responses. The cytotoxicity of the solid MG samples and the corrosion released ions are also evaluated by an in-vitro MTT test utilizing the murine bone marrow stem cells. Results indicate that all the solid MG samples show no acute cytotoxicity yet the corrosion released ions show significant toxicity for murine bone marrow stem cells. The rapid screening process developed in the present study suggests that the Ti65Si15Ta10Zr10 metallic glass has high potential for biomedical applications due to its good electrochemical stability and very low cytotoxicity.

Simulated body fluid electrochemical response of Zr-based metallic glasses with different degrees of crystallization.

The bio-electrochemical response in simulated body fluid of the Zr53Cu30Ni9Al8 metallic glasses with different degrees of partial crystallization was systematically examined and discussed. Through thermal annealing, the volume fractions of the crystalline phases are determined to be 0, 34, 63, and near 100%. Based on the bio-corrosion voltage and current, as well as the polarization resistance, it is concluded that the fully amorphous alloy exhibits the highest bio-electrochemical resistance. With an increasing degree of partial crystallization, the corrosion resistance becomes progressively degraded. The passive current reveals that the fully amorphous metallic glasses can form a more protective and denser passive film on the metallic glass surface. The formation of reactive nanocrystalline phases in the amorphous matrix would reduce the bio-corrosion resistance.

Direct-write, Well-aligned Chitosan-Poly(ethylene oxide) Nanofibers Deposited via Near-field Electrospinning

A continuous near-field electrospinning (NFES) process has been demonstrated to be able to achieve direct-write and well-aligned chitosan/poly(ethylene oxide) nanofibers. The ability to precisely control and deposit chitosan-based nanofibers in a direct-write manner is favorable in manipulating cells attachment and proliferation at a preferred position. Experimental results show that fiber diameters can be reliably controlled in the range of 265–1255 nm by adjusting various operating parameters of the NFES processes. These prescribed patterns of nanofibers exceed tens of centimeters long and complex configurations such as grid arrays and arc shapes are assembled at specified separations as small as 5 μm. FTIR analysis reveals that NFES nanofibers have a similar morphology and composition as conventional electrospinning counterpart and constitute all components formerly present in the polymer solution. The versatile functionality to fabricate chitosan-based nanofibers with controllable size and directional alignment as well as highly ordered and customized patterns may represent an ideal candidate of a functional biomaterial and in tissue-engineering scaffolds that are predominantly representative of extracellular matrix (ECM).

Mechanical and thermal behaviors of nitrogen-doped Zr-Cu-Al-Ag-Ta––An alternative class of thin film metallic glass

Super-plasticity and nano-scale surface roughness make thin film metallic glass (TFMG) a candidate for master mold of micro/nano imprint technique. Meanwhile, better mechanical properties of TFMG undoubtedly expand the life time of master mold. In this study, nitrogen is doped into Zr-based TFMG to exhibit the hardness higher than 10 GPa. Different from elements used to be doped into metallic glass, the role of nitrogen atoms plays in metallic glass is distinct and vital owing to its strong electronegativity. From the correlation of thermal and mechanical behavior, the role and effect of nitrogen in Ta-Zr-Cu-Al-Ag TFMG is discussed and proposed.

The effect of boron on the microstructure and mechanical behavior of an Ni–19Si–3Nb based alloy

Abstract The mechanical properties of Ni–19Si–3Nb– x B alloys were investigated by microhardness and tensile tests. X-ray diffraction, high-temperature differential thermal analysis, and scanning electron microscopy were conducted to characterize the microstructure change by the additions of boron for these alloys. The results reveal that there are three phases, α(fcc) phase, β(L1 2 ) phase, and the Nb-rich precipitates in the as-cast Ni–19Si–3Nb alloys. The strengthening effect of this alloy is suggested to be due to the lattice expansion of the β phase matrix by the addition of Nb and the hardening by the hard Nb-rich precipitates on the β matrix. Additionally, the addition of boron element does not appeal to affect their phase content and thermal analysis results. But, the fracture behavior of the Ni–19Si–3Nb alloys significantly change from brittle mode to ductile mode with increasing boron doping. The relationship between the effect of boron doping, the microstructure change, and the fracture mode on the Ni–19Si–3Nb based alloys are discussed in this paper.

Microstructure evolution of mechanical alloyed Ni—24 at% Si

Nickel and silicon powders, of average composition Ni3Si, were mechanical alloyed in a high energy ball mill. The severe plastic deformation produced by mechanical milling induced transformations with increasing milling time as follows: mixture of elemental Ni and Si powder → f.c.c. solid solution → nanocrystalline f.c.c. The structural evolution with milling time was followed by X-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Complete f.c.c. solid solution occurred at a milling time of 4 h and the saturated ΔH (by DSC) peak in the range of estimated enthalpy even after 24 h milling. The similarity of the mechanism of structural development by mechanical alloying of the Ni76Si24 powder mixture, and by mechanical milling of Ni76Si24 compound was also investigated in this study.

Imprinting of Metallic Glasses: A Simple Approach to Making Durable Terahertz High-Pass Filters

An imprint process of Pd-based metallic glass is used to create a high-aspect-ratio two-dimensional wire array structure for filtering terahertz (THz) radiation. By the simplified imprinting process, a 10×10 straight wire array with a wire height of ~320 µm and a diameter of 100.6 µm is produced. The negligibly small expansion of ~0.3% confirms the excellent thermal imprinting property of metallic glass. The periodic wire array is shown to act as a high-pass filter in the THz range, and the transmission property measurement reveals a turn-on frequency of 0.4 THz, suggesting the promising approach and material for robust high-pass filters.